# Speed and Acceleration of CMEs Associated with Sustained Gamma-Ray Emission
Events Observed by Fermi/LAT

Pertti Mäkelä The Catholic University of America
620 Michigan Ave., N.E.
Washington, DC 20064, USA  NASA Goddard Space Flight Center
8800 Greenbelt Road
Greenbelt, MD 20771, USA  Nat Gopalswamy  NASA Goddard Space Flight Center
8800 Greenbelt Road
Greenbelt, MD 20771, USA  Sachiko Akiyama  The Catholic University of America
620 Michigan Ave., N.E.
Washington, DC 20064, USA  NASA Goddard Space Flight Center
8800 Greenbelt Road
Greenbelt, MD 20771, USA  Hong Xie  The Catholic University of America
620 Michigan Ave., N.E.
Washington, DC 20064, USA  NASA Goddard Space Flight Center
8800 Greenbelt Road
Greenbelt, MD 20771, USA  Seiji Yashiro  The Catholic University of America
620 Michigan Ave., N.E.
Washington, DC 20064, USA  NASA Goddard Space Flight Center
8800 Greenbelt Road
Greenbelt, MD 20771, USA

###### Abstract

The sustained gamma-ray emission (SGRE) from the Sun is a prolonged
enhancement of $>$100 MeV gamma-ray emission that extends beyond the flare
impulsive phase. The origin of the $>$300 MeV protons resulting in SGRE is
debated, both flares and shocks driven by coronal mass ejections (CMEs) being
the suggested sites of proton acceleration. We compared the near-Sun
acceleration and space speed of CMEs with ’Prompt’ and ’Delayed’ (SGRE) gamma-
ray components (Ajello et al., 2021). We found that ’Delayed’-component-
associated CMEs have higher initial acceleration and space speed than ’Prompt-
only’-component-associated CMEs. We selected halo CMEs (HCMEs) associated with
type II radio bursts (shock-driving HCMEs) and compared the average
acceleration and space speed between HCME populations with or without SGRE
events, major solar energetic particle (SEP) events, metric, or decameter-
hectometric (DH) type II radio bursts. We found that the SGRE-producing HCMEs
associated with a DH type II radio burst and/or a major SEP event have higher
space speeds and especially initial accelerations than those without an SGRE
event. We estimated the radial distance and speed of the CME-driven shocks at
the end time of the 2012 January 23 and March 07 SGRE events using white-light
images of STEREO Heliospheric Imagers and radio dynamic spectra of Wind WAVES.
The shocks were at the radial distances of 0.6–0.8 au and their speeds were
high enough ($\approx$975 km s-1 and $\approx$750 km s-1, respectively) for
high-energy particle acceleration. Therefore, we conclude that our findings
support the CME-driven shock as the source of $>$300 MeV protons.

Solar gamma-ray emission (1490) — Solar coronal mass ejection shocks (1997) —
Solar energetic particles (1517)

##  1 Introduction

The sustained gamma-ray emission (SGRE) from the Sun is a prolonged
enhancement of $>$100 MeV gamma-ray emission that extends beyond the flare
impulsive phase. SGRE typically lasts for several hours, extending well beyond
the end of the associated soft X-ray flare emission. The first SGRE event at
energies above 100 MeV was detected on 1991 June 15 by the Gamma-1 telescope
on board the Gamma spacecraft and it lasted at least 2.16 hours (Akimov et
al., 1991). Similar observation of a long-duration $>$50 MeV gamma-ray
emission was reported by Kanbach et al. (1993) during the 1991 June 11 flare.
The $>$100 MeV SGRE is produced by $>$300 MeV protons precipitating from the
solar corona into the solar chromosphere, where their interactions with the
dense plasma layers create pions, which then decay into the observed $>$100
MeV gamma-rays (e.g., Murphy et al., 1987). The dominant source of $>$100 MeV
gamma-rays is neutral pion decay (e.g., Kafexhiu et al., 2018; Gopalswamy,
2020). Forrest et al. (1985) first reported a clear detection of $>$40 MeV
gamma-rays that require pion production during the extended phase of the 1982
June 3 gamma-ray flare. SGRE events were originally called long duration
gamma-ray flares (LDGRFs; e.g., Ryan, 2000). Nowadays they are also known as
late-phase $>$100 MeV gamma-ray emission (LPGRE; e.g., Share et al., 2018)
events. A review of gamma-ray observations analogous to Gamma-1 measurements
by Ryan (2000) listed 13 LDGRFs between 1982–1991. A few more early events
have been discovered from observations by non-dedicated gamma-ray telescopes
(Kuznetsov et al., 2014). Most recently, observations by the Large Area
Telescope (LAT, Atwood et al., 2009) on board the Fermi satellite have shown
that SGRE events are relatively common (Ackermann et al., 2014, 2017; Ajello
et al., 2014, 2021; Pesce-Rollins et al., 2015; Share et al., 2018; Allafort,
2018). The $>$100 MeV SGRE event on 2012 March 7 was observed to last over 20
hours (e.g., Gopalswamy et al., 2018; Share et al., 2018).

The origin of the $>$300 MeV protons producing SGRE is still debated. Murphy
et al. (1987) studied the 1982 June 03 event and suggested a two-phase
particle acceleration scenario, where a short-duration impulsive-phase
acceleration is followed by a second acceleration phase, probably due protons
accelerated by coronal shocks and resulting in SGREs (see also, Ramaty et al.,
1987). Ryan & Lee (1991) investigated the same 1983 June 03 gamma-ray flare
and found a good agreement between their model of turbulent solar flare loops
and the observed gamma-ray light-curves, including the extended emission
phase, which their model explained to be due to delayed protons diffusing both
in momentum space and spatially in the flare loops. The flare loop scenario
requires that flare-accelerated protons must remain trapped and/or be
continuously re-accelerated in the coronal loops long after the X-ray flare
itself has ended. However, trapping of high-energy protons in coronal loops
for several hours requires force-free loops (Lau et al., 1993) with a
sufficiently low density and turbulence level (Ryan, 2000). As an alternative
to particle trapping in the coronal loops, Kocharov et al. (1994) suggested a
continuous stochastic acceleration due to additional pulses of energy that
could explain gamma-ray observations during the extended phase of the 1991
June 15 LDGRF (see also, Akimov et al., 1991, 1996).

Gamma-ray-line observations of the behind-the-limb flare on 1989 September 29
were interpreted to require a spatially extended gamma-ray source and hence to
suggest shocks driven by fast and wide coronal mass ejections (CMEs) as a
likely source of the gamma-ray-emission producing particles (e.g., Cliver et
al., 1993; Vestrand & Forrest, 1993). Recent LAT observations of SGRE events
during eruptions occurring behind the solar limb, have confirmed that an
extended source of gamma-rays must exist at the Sun (e.g., Pesce-Rollins et
al., 2015; Plotnikov et al., 2017). The CME-driven shock naturally extends
over large regions of solar surface allowing the shock-accelerated protons to
have access to areas far from the behind-the-limb eruption site. Gopalswamy et
al. (2020) forward modelled the CME flux rope and the surrounding shock in the
2014 September 1 behind-the-limb event and found that the Fermi/LAT SGRE
source was located far from the flare site - in the space between the flux
rope and shock confirming the extended nature of the emission. Hudson (2018)
suggested another scenario where closed magnetic loops extended up to the
height of several solar radii will capture high-energy protons that might be
accelerated by a CME shock and subsequently the loops retract and enable
sufficiently large number of $>$300 MeV protons to interact with the solar
atmosphere.

Recently, de Nolfo et al. (2019) compared the estimated fluxes of gamma-ray
producing particles precipitating into the solar atmosphere with the fluxes of
SEPs escaping into interplanetary space and did not find significant
correlation. They suggested that the lack of correlation rules out the CME-
driven shock as a common source of both fluxes. However, Gopalswamy et al.
(2021b) pointed out that the correlation is high when systematic effects are
corrected differently. Kouloumvakos et al. (2020) compared the SGRE time
profile observed during the ground level enhancement (GLE) on 2017 September
10 with the time profiles of simulated shock parameters and found a good match
between them, supporting the CME shock as a common source of SGRE-producing
protons at the Sun and GLE protons at 1 au. Winter et al. (2018) studied
properties of flares and CMEs with and without SGREs. They found that SGRE
events are associated with intense X-class flares but only one-third of the
X-class solar flares Fermi/LAT observed have an SGRE event. They also note
that fast and wide CMEs are associated with SGRE events. Therefore, their
results on the flare and CME associations favor CME-driven shock as the source
of $>$300 MeV protons.

Additional support for the CME-shock scenario is provided by the correlation
of the SGRE durations with the durations and the end frequencies of type II
radio bursts (Gopalswamy et al., 2018, 2019). Figure 1 shows two examples of
concurrent SGRE events and type II radio bursts during SGRE event in January
and March 2012. Although type II radio bursts are produced by CME-shock
accelerated electrons, they indicate the presence of a strong shock that could
also accelerate protons to high energies. Therefore, the correlations suggest
that CME-driven shocks could be the source of both the electrons resulting in
the decameter-hectometric (DH) type II radio bursts and the $>$300 MeV protons
generating the SGRE events. Pesce-Rollins et al. (2022) investigated the EUV
wave connection to the behind-the-limb (BTL) flare at S20E140 on 2021 July 17.
They found that the time when the EUV wave crosses the limb onto the visible
disk and the onset of the LAT $>$100 MeV flux enhancement are concurrent. They
also found a coupling between the peak times of the time derivative of the EUV
wave intensity profile observed at 193 Å and the $>$100 MeV gamma-ray flux
suggesting that the EUV wave and the acceleration of the SGRE-producing
protons are connected. They found the correlation to be valid in three other
Fermi/LAT BTL flares. Pesce-Rollins et al. (2022) conclude that the
correlation between the derivative of the EUV wave intensity and gamma-ray
flux and the near-simultaneous appearance of a complex type II radio burst
indicate that radio, EUV and gamma-ray emissions share the same source (CME-
shock) although the emissions originate at different heights in the corona.

Back-precipitation of shock-accelerated protons have been studied using
numerical simulations but results so far have not been accordant with one
another. Hutchinson et al. (2022) modelled particle precipitation including
enhanced turbulence and found scattering to increase back-precipitation but
even that being the case the fraction of protons able to precipitate down to
the radial distance of 1 R☉ relative to the injected back-propagating protons
is less than 1%. The precipitation fraction decreases as a function of the
radial distance of the CME shock. Therefore, they conclude that the CME-driven
shocks cannot provide a sufficient flux of $>$300 MeV protons to explain the
SGRE events. Opposite conclusions in support of a CME-shock as the source of
the gamma-ray-producing protons have been obtained by Jin et al. (2018) who
studied the Fermi behind-the-limb flare on 2014 September 1. Their simulations
of the CME-driven shock indicated that the quasi-perpendicular part of the
shock had a magnetic connection to the gamma-ray source at the front-side of
the Sun and the shock compression ratio increase matched the increase in the
observed gamma-ray emission. Afanasiev et al. (2018) simulated proton
acceleration in the CME-driven shocks during the 2012 January 23 and May 17
SGRE events. The 2012 May 17 SGRE event was also observed as a GLE by neutron
monitors. They concluded that proton acceleration by coronal shocks and
diffusive downstream particle transport could explain the SGRE events.
However, the authors of the above-mentioned studies suggest that more
elaborated MHD models for the particle transport back to the Sun is required
because the complex structure of the magnetic fields near the Sun, which the
current simulation efforts cannot fully replicate. The lack of direct
observations of the precipitating protons close to the Sun leaves the question
whether they can propagate back to the solar atmosphere deep enough open.

The initial acceleration and speed of the CME in part control the formation
height and strength of the shock, which in turn affect particle acceleration
efficiency of the shock. Therefore, the CME acceleration and speed provide a
proxy for the effectiveness of high-energy particle acceleration in the CME-
driven shocks. Gopalswamy et al. (2022) studied SGRE association with on-disk
CMEs producing major SEP events and HCMEs with sky-speeds $\geq$1800 km s-1
during cycle 24. They investigated the initial acceleration and space speed of
the CMEs, which they defined to be the instantaneous peak space speed and
acceleration obtained from forward fitting of the graduated cylindrical shell
(GCS) flux rope model (Thernisien et al., 2009; Thernisien, 2011) to the EUV
and coronagraph images of the CMEs. They found that the peak space speed and
peak initial acceleration of the SGRE-producing CME are 2516 km s-1 and 3.87
km s-2, respectively. Gopalswamy et al. (2022) suggest that the close
connection they found between CME kinematics and the SGRE events give support
to the CME-shock scenario.

In addition to SEP events, type II radio burst are related to particle
acceleration by CME-driven shocks. In this report we estimate the initial
acceleration and space speed of the CMEs associated with the Fermi/LAT solar
flares (FLSFs) during solar cycle 24 listed by Ajello et al. (2021). In order
to evaluate the feasibility of the CME-driven shocks in producing SGRE events,
we compare average initial acceleration and space speed of CME populations
associated with SGRE and SEP events and type II radio bursts. We use space
speeds obtained by applying geometrical correction to close-to-the-limb CMEs
or by applying the model by Xie et al. (2004) to HCMEs. Initial acceleration
is estimated by assuming that the CME obtains its estimated space speed during
the interval extending from the onset time to the peak time of the associated
soft X-ray flare (Gopalswamy et al., 2012; Mäkelä et al., 2015). In addition,
we estimate the radial distance and the space speed of shocks at the end time
of the two longest-duration SGRE events on 2012 January 23 and March 07.

##  2 Data

In the analysis we use the catalog published by Ajello et al. (2021) that
contains 45 FLSFs with $>$30 MeV gamma-ray emission in the period 2010
January–2018 January. We do not repeat here all the details of the event data
analysis, which are given in Ajello et al. (2021). We briefly describe their
categorization method of FLSFs. Ajello et al. (2021) characterized the light
curves of the FLSFs based on the associated hard X-ray (HXR) observations made
by the Fermi Gamma-ray Burst Monitor (GBM, Meegan et al., 2009). If the early
evolution of the gamma-ray emission was synchronous with the Fermi/GBM HXR
evolution, the flare was deemed to have an impulsive ’Prompt’ component
lasting $\lesssim$10 minutes. If the flare had a second phase of gamma-ray
emission without a corresponding HXR evolution, the flare was deemed to have a
gradual ’Delayed’ component that could last up to $\approx$20 hours. Ajello et
al. (2021) found that a total of 39 out of the 45 FLSFs had detectable level
of $>$100 MeV emission. One should note that Fermi/LAT does not observe the
Sun continuously, the average LAT measurement interval lasts about 30 minutes
(Ajello et al., 2021). Of those 45 FLSFs, they classified 6 flares as ’Prompt
only’ and 4 flares as ’Delayed only’. In 10 flares both the ’Prompt’ and
’Delayed’ emission were detected by LAT and 6 flares were detected with LAT
Low Energy (LLE) analysis only.

The existence of the DH type II radio bursts is based on Wind spacecraft’s
radio and plasma wave instrument (WAVES, Bougeret et al., 1995) observations
(https://cdaw.gsfc.nasa.gov/CME_list/radio/waves_type2.html), STEREO/WAVES
instrument (Bougeret et al., 2008) observations, and on the analysis by
Gopalswamy et al. (2018, 2019). The metric type II radio burst and soft X-ray
flare observations are obtained from the NOAA Solar and Geophysical Event
Reports. We adjusted the NOAA-reported flare onset times in some events after
inspecting concurrent EUV images and soft X-ray curves of the solar eruption.
The CME data near the Sun is provided by the Large Angle and Spectrometric
Coronagraph (LASCO, Brueckner et al., 1995) on the Solar and Heliospheric
Observatory (SOHO, Domingo et al., 1995) spacecraft. The CME data is collected
from the SOHO/LASCO CME Catalogs
(https://cdaw.gsfc.nasa.gov/CME_list/index.html,
https://cdaw.gsfc.nasa.gov/CME_list/halo/halo.html). SEP event data are from
the Major SEP Event list (https://cdaw.gsfc.nasa.gov/CME_list/sepe/) and from
the GOES-equivalent $>$10 MeV intensities calculated using data provided by
the High Energy Telescope (HET; von Rosenvinge et al., 2008) onboard STEREO.
For the shock distance estimation at the end of the SGRE event, we used white-
light images of the Sun Earth Connection Coronal and Heliospheric
Investigation (SECCHI, Howard et al., 2008) Heliospheric Imagers (HIs, Eyles
et al., 2009) onboard the Solar Terrestrial Relations Observatory (STEREO,
Driesman et al., 2008) spacecraft. The HI images were provided by the STEREO
Archive maintained by the UK Solar System Data Centre
(https://www.ukssdc.ac.uk/solar/stereo/data.html). To identify the associated
CMEs, we inspected the CME catalogues provided by the Heliospheric
Cataloguing, Analysis and Techniques Service (HELCATS, https://www.helcats-
fp7.eu/).

##  3 Estimation Method of the CME Initial Acceleration

The initial acceleration of the CME near the Sun is difficult to measure
because the cadence of white-light coronagraphs is limited. In our study we
follower the method previously used by Gopalswamy et al. (2012) and Mäkelä et
al. (2015). We assume that the CME accelerates from rest to its final maximum
speed, which it reaches at the peak time of the associated soft X-ray flare.
Zhang & Dere (2006) have shown that the main acceleration phase of the CME
coincides with the impulsive phase of the associated X-ray flare. Therefore,
we calculate the initial acceleration a of the CME with a formula:
$a=V_{Space}/(t_{FlarePeak}-t_{FlareOnset})$, where $V_{Space}$ is the
estimated space speed of the CME and $t_{FlarePeak}$ and $t_{FlareOnset}$ are
the flare peak and onset times, respectively. The space speed of halo CMEs
(HCMEs) has been estimated by using a cone model for HCMEs (Xie et al., 2004)
and the space speeds are listed in the SOHO/LASCO HALO CME catalog
(https://cdaw.gsfc.nasa.gov/CME_list/halo/halo.html). For non-HCMEs, the space
speed, $V_{Space}$, is calculated from the measured CME speed on the sky
plane, $V_{Sky}$, by using a geometrical correction $V_{Sky}/\cos{\theta}$,
where $\theta$ is the angle the CME propagation direction makes away from the
sky plane. The angle $\theta$ depends on the longitude of the flare location.
To avoid unrealistically large corrections, we have included in the analysis
only non-HCMEs for which $\theta$ is $\leq$30∘ as seen either from the SOHO or
STEREO spacecraft. The method calculates an average over the acceleration
phase of the CME. The peak initial acceleration of the CME can be higher than
obtained average initial acceleration as was shown by Gopalswamy et al.
(2021b).

In general, we know that the CME speed profiles near the Sun vary from event
to event and CME speed is an important parameter governing particle
acceleration efficiency of the CME-driven shocks. Gopalswamy et al. (2016,
2017) showed that CMEs associated with major SEP events have a hierarchical
relationship between the initial acceleration and speed of the CME and the SEP
fluence spectral indices (see also, Mäkelä et al., 2019): CMEs associated with
filament eruptions have low initial speeds and acceleration and produce the
softest SEP spectra at 1 au, while the CMEs with highest initial speed and
acceleration have the hardest SEP spectra. The CMEs with an intermediate speed
and acceleration result in moderately hard SEP spectra at 1 au. Therefore,
initial acceleration and speed provide a proxy for the effectiveness of high-
energy particle acceleration in the CME-driven shocks.

###  3.1 Initial Acceleration and Space Speed of CMEs Associated with LAT
Gamma-ray Flares

In our analysis we use the on-disk gamma-ray events listed in Ajello et al.
(2021). Their list contains 45 gamma-ray flares during cycle 24. Ajello et al.
(2021) categorized the flares based on whether ’Prompt’ or ’Delayed’ component
(SGRE event) of gamma-ray emission was detected. In the 6 events of the 45
events, only ’Prompt’ (impulsive) emission was detected, 4 events had no
detected ’Prompt’ emission at all, 10 events have both ’Prompt’ and ’Delayed’
emission and the remaining 25 had ’Delayed’ emission, but the presence of
’Prompt’ emission could not be excluded because of LAT was not pointing to the
Sun at the appropriate time. 32 of the flares were associated with a HCME, 10
were associated with non-HCMEs, and 3 had no associated CME. Based on our own
estimations, we changed the CME of the 2014 September 10 flare to the 08:00 UT
HCME. We have excluded the 3 back sided flares, the 3 flares without a CME and
the 2017 September 06 X2.2 flare for which we could not estimate the space
speed of the CME at 09:48 UT, because there is no suitable side-view either
from SOHO or STEREO-A.

Table 1 list the total number and the average value of the initial
acceleration and space speed of CMEs in different categories. First, we
divided the CMEs into two main categories: those associated with flares
showing only a ’Prompt’ component, labelled as ’Prompt Only’ and those with a
’Delayed’ component, labelled ’All Delayed’ in Table 1. The ’Prompt Only’
flares are impulsive gamma-ray flares and the ’All Delayed’ ones are SGRE
events. Clearly, the impulsive gamma-ray flares are associated with
significantly slower CMEs (775 km s-1) than flares with an SGRE event (1708 km
s-1). The difference in the initial acceleration is not as clear, but again
the CMEs with SGRE events show a larger initial acceleration than those
without an SGRE event. From SEP event comparisons by Gopalswamy et al. (2016;
see also Mäkelä et al. 2019) we know that higher acceleration and speed
indicate that the CME-driven shock produces harder energy spectra, i.e., more
likely to have $>$300 MeV protons. Similar high initial acceleration and fast
speed characteristics are shared by CMEs associated with GLEs, which are
guaranteed to have $>$300 MeV protons.

Then we divided the ’All Delayed’ CMEs into three subcategories: the ’Prompt
Delayed’ CMEs are associated with gamma-ray flares having both emission
components, the ’No-Prompt Delayed’ CMEs do not have a detectable ’Prompt’
component and the ’Delayed’ CMEs have a ’Delayed’ component but the existence
of the ’Prompt’ component is uncertain because of the lack of LAT observations
during the impulsive phase of the flare. Differences are now less significant
(the sample sizes also become small), but the ’Prompt Delayed’ CMEs appear to
have the highest average initial acceleration and space speed and the ’No-
prompt Delayed’ the lowest ones among the three groups. Most likely the CMEs
without associated ’Prompt’ gamma-ray component are more slowly accelerating
CMEs but are still able to produce $>$300 MeV protons as their space speed
becomes high enough in the later phase. Again, similar slower initial
acceleration but high later-phase speed has been detected for CMEs producing
major SEP events (Gopalswamy et al., 2016). Table 4 in Appendix lists the data
for events included in calculations of Table 1.

Table 1: Initial acceleration and space speed of CMEs associated with LAT gamma-ray flares  Quantity |  | Main Types |  | Subtypes of ’All Delayed’
---|---|---|---|---
|  | Prompt Only | All Delayed |  | Delayed | Prompt Delayed | No-Prompt Delayed
(1) |  | (2) | (3) |  | (4) | (5) | (6)
Count |  | 6 | 32 |  | 18 | 8 | 4
Mean Acceleration (km s-2) |  | 1.37 | 1.75 |  | 1.73 | 1.87 | 1.62
Mean Space Speed (km s-1) |  | 775 | 1708 |  | 1745 | 1753 | 1663

##  4 Comparison with HCMEs Associated with Type II Radio Bursts and Major SEP
Events

Because the ’All Delayed’ gamma-ray flares are mainly associated with HCMEs,
we compare their initial acceleration and space speed with HCMEs associated
with type II radio bursts and major SEP events. Major SEP events are defined
as those with the peak proton flux in the GOES $>$10 MeV integral channel
above 10 particles cm-2 s-1 sr-1. Since SEPs are charged particles, they
spiral along the interplanetary magnetic field lines as they propagate away
from the acceleration source. Therefore, at Earth we can detect mostly SEP
events originating from eruptions occurring in the western hemisphere of the
Sun. Some very intense eruptions from the eastern limb can produce particle
events at Earth but in that case only at the lower energies.

In general, DH type II radio bursts are well correlated with major SEP events
(Gopalswamy et al., 2002, 2019; Cliver et al., 2004). Both radio and gamma-ray
emissions can be detected from all on-disk eruptions because electromagnetic
emission can propagate away from the Sun without being significantly affected
by coronal or interplanetary medium. Type II solar radio bursts occur at the
fundamental and second harmonic of local plasma frequency that depends on the
electron density at the upstream of the CME shock. Because the electron number
density decreases as a function of the radial distance, the plasma frequency
decreases away from the Sun and higher frequency emissions originating from a
lower height can propagate freely outwards. Therefore, the type II burst can
be identified in the radio dynamic spectra as an intensity feature slowly
drifting towards lower frequencies at the rate that depends on the shock speed
and the density scale height of the ambient medium.

Table 2: Initial acceleration and space speed of cycle-24 HCMEs with metric type II radio bursts  HCME Category |  | ’Delayed’ Component (SGRE Event) |  | No ’Delayed’ Component
---|---|---|---|---
|  | Count | Mean Acceleration | Mean Space Speed |  | Count | Mean Acceleration | Mean Space Speed
|  |  | (km s-2) | (km s-1) |  |  | (km s-2) | (km s-1)
(1) |  | (2) | (3) | (4) |  | (5) | (6) | (7)
DH Type II |  | 23 | 1.85 | 1869 |  | 37 | 1.09 | 1211
No DH Type II |  | 1 | Too low statistics |  | 26 | 1.11 | 959
SEP Event |  | 17 | 1.83 | 2004 |  | 13 | 1.15 | 1499
SEP Event (w/STEREO) |  | 21 | 1.70 | 1858 |  | 18 | 1.07 | 1396
No SEP Event |  | 7 | 1.81 | 1360 |  | 50 | 1.09 | 1006
No SEP Event (w/STEREO) |  | 3 | 2.68 | 1524 |  | 45 | 1.11 | 992

In Table 2 we have divided the 87 cycle-24 HCMEs with metric type II radio
emission into CMEs with and without a ’Delayed’ gamma-ray component. The
existence of the metric type II radio burst indicates that a shock forms
early, making these HCMEs good candidates for SGRE production. We investigated
how many of the metric type II-associated HCMEs are with and without a DH type
II radio burst or a major SEP event. We selected major SEP events as they are
intense events and could have enhancements of $>$300 MeV protons, which are
unlikely to be present in the inherently low-intensity SEP events. Because
observer’s connection to the SEP source affects the possibility to detect
SEPs, the group without a major SEP event could still contain events that were
able to accelerate particles, especially the poorly connected eastern
hemisphere events could have produced high-energy particles that were not
detected. We account for this possibility by using GOES $>$10 MeV equivalent
STEREO intensities to identify major SEP events observed by STEREO. The STEREO
$>$10 MeV flux is estimated using data from the STEREO/HET (von Rosenvinge et
al., 2008), which covers the energy ranges of 13–100 MeV. The flux is
estimated by fitting a power law to HET data points and integrating the flux
in the 10–150 MeV range (see Gopalswamy et al., 2016). In Tables 2 and 3, we
have separated the two SEP event sets and marked the one containing both GOES
and STEREO events as ”(w/STEREO)”, although in Table 3 the statistics for the
SGRE events are mostly too low. One should note that STEREO spacecraft drift
around the Sun, so their magnetic connection to the Sun changes continuously.
In addition, STEREO-A observations have significant data gaps during solar
conjunction period during 2014–2015 and contact to STEREO-B was lost on
October 1, 2014. We surveyed also STEREO/WAVES data for additional DH type II
radio bursts but we found only one on 03 August 2011. The STEREO-A data showed
a short-duration, slanted feature in the 10–14 MHz frequency range starting at
13:38 UT, which we added to our DH type II burst list. All other STEREO/WAVES
DH type II bursts were accompanied with a Wind/WAVES DH type II burst, so we
study STEREO and Wind DH type II bursts together. The most western event of
the 7 SGRE events without a major GOES SEP event occurred at the heliographic
longitude W18 and 4 of the 7 SGRE events occurred less than 30$\arcdeg$ from
the eastern limb. The two bottom rows of Table 2 are difficult to interpret,
but we have added them mainly for completeness. Results show that all HCMEs
associated with an SGRE event have similar average initial acceleration values
(1.70–1.85 km s-2) with the exception of the group without a GOES or STEREO
SEP event, which contains only three events and the average initial
acceleration (2.68 km s-2) is very high, possibly indicating missed major SEP
event identification. The range is considerably higher than those of HCMEs
without an SGRE event (1.07–1.15 km s-2). The SGRE and SEP-associated HCMEs
have the highest average space speed, whereas two groups of HCMEs, SGRE-
associated HCMEs without an SEP event and SEP-associated HCMEs without an SGRE
event, seem to have similar speeds. However, the average initial accelerations
of SGRE-associated HCMEs without a major SEP event are higher (even when we
ignore the group without a GOES or STEREO SEP event that has only 3 events in
total) than those of without SGRE event but with a major SEP event. The DH
type II-associated HCMEs without an SGRE event have only slightly lower
average space speed (1211 km s-1), but we know that DH type II bursts are
associated with SEP events and this mixed population includes 12 HCMEs with an
SEP event, which have high space speeds. If we exclude these 12 SEP-associated
events, then the average space speed of the remaining 25 events decreases down
to 1064 km s-1. Clearly, the existence of $>$300 MeV protons is connected to a
high initial acceleration and speed of the associated HCME. The HCMEs without
an SEP and SGRE event have the lowest average speed (992 km s-2). Therefore,
the SGRE-associated HCMEs conform to the hierarchy between the initial
acceleration and speed of the CME and the fluence spectral index as described
by Gopalswamy et al. (2016). Especially the high initial acceleration seems to
be crucial for SGRE production.

The average accelerations and speeds of the 20 cycle-24 HCMEs associate with
only a DH type II radio burst are shown in Table 3. HCMEs are mostly without
SGRE events (only 4 SGRE events) or major SEP events (only 6 SEP events if
STEREO observations are included, two of which have also an SGRE event).
Therefore, statistics for SGRE events are low, but the average space speed of
SGRE events without an SEP event ($\approx$1579 km s-1) is below the space
speed of the SGRE events with an SEP event ($\approx$2004 km s-1;
$\approx$1858 km s-1 if STEREO observations are included) in Table 2. None of
the three eruptions without an major SEP event detected by GOES were
magnetically well-connected to Earth, so they probably accelerated high-energy
particles efficiently but particles didn’t reach Earth. One of them, the 10
June 2014 HCME with a solar source at S17E82, actually had a major SEP event
observed by STEREO-B, which was located at the heliographic longitude E164.
The 05 March 2012 HCME had a solar source at N17E52, but the GOES-equivalent
$>$10 MeV intensities observed by STEREO-B at longitude E117 were already
elevated above 100 pfu due to a preceding HCME on 04 March that was not
associated with an SGRE event. At the onset of the 10 March 2012 HCME launched
from N17W24, the $>$10 MeV intensities were elevated above 10 pfu at all three
spacecraft. In fact, the March 5 and 10 events are the first and last events
in a cluster of 4 SGRE events accompanied by high level of SEP flux
(Gopalswamy et al., 2019). So, it is quite possible that the two March 2012
events also accelerated particles. The average initial acceleration value is
lower than respective value for SGRE events with SEP events in Table 2, but
this is expected because CMEs associated with only a DH type II radio burst
accelerate slowly and the shock forms later. This probably explains the lower
average space speed near the Sun. The initial acceleration and average space
speed of HCMEs without an SGRE event and an SEP event are lower or similar,
respectively, to the respective values in Table 2. Table 5 in Appendix lists
the data for events included in calculations of Tables 2 and 3.

Table 3: Initial acceleration and space speed of cycle-24 HCMEs with DH type II radio bursts only  HCME Category |  | ’Delayed’ Component (SGRE Event) |  | No ’Delayed’ Component
---|---|---|---|---
|  | Count | Mean Acceleration | Mean Space Speed |  | Count | Mean Acceleration | Mean Space Speed
|  |  | (km s-2) | (km s-1) |  |  | (km s-2) | (km s-1)
(1) |  | (2) | (3) | (4) |  | (5) | (6) | (7)
SEP Event |  | 1 | Too low statistics |  | 3 | 0.46 | 1263
SEP Event (w/STEREO) |  | 2 | Too low statistics |  | 4 | 0.38 | 1265
No SEP Event |  | 3 | 1.00 | 1579 |  | 13 | 0.44 | 1164
No SEP Event (w/STEREO) |  | 2 | Too low statistics |  | 12 | 0.47 | 1155

##  5 Radial Distance of the Shock at the End of the SGRE Events

We selected two SGRE events, the 2012 January 23 and March 07 events, with the
longest duration of the associated type II radio burst (Gopalswamy et al.
2019) and for which the STEREO observations provided sideview white-light
images of the HCMEs.

The 2012 January 23 04:00 UT HCME produced a DH type II burst with a duration
about 25.0$\pm$9.6 hr, while the estimated duration of the SGRE event was
15.4$\pm$0.8 hr. The SGRE ended around 19:25 UT. The estimated space speed was
2511 km s-1, and the interplanetary shock arrived at the SOHO spacecraft at
14:33 UT on January 24. The eruption was associated with a M8.7 X-ray flare
starting at 03:38 UT at the heliographic location of N28W21. The STEREO-A and
STEREO-B longitudes were W108 and E114, respectively. The eruption produced a
major SEP event at Earth with a GOES $>$10 MeV peak proton flux 6310 cm-2 s-1
sr-1. The 2012 January 23 eruption close to the Sun has been studied
extensively because the eruption involved two flux ropes that merged below the
radial distance of 15 R☉ (e.g. Cheng et al., 2013; Joshi et al., 2013; Li &
Zhang, 2013).

The second HCME at 00:24 UT on 2012 March 07 was associated with an SGRE event
that had even longer duration, about 21.3$\pm$1.6 hr (Ajello et al., 2014;
Gopalswamy et al., 2018). The 2012 March 07 SGRE had a slightly longer
estimated duration of about 21 hr but the SGRE durations cannot be measured
accurately because LAT does not observe the Sun continuously. The SGRE end
time was 21:40 UT. The estimated duration of the DH type was 27.9$\pm$6.8 hr.
The LASCO space speed of the HCME was 3146 km s-1 and it was associated with a
X5.4 X-ray flare at 00:02 UT from N17E27. A second X1.3-class flare started
about an hour later at 01:05 UT. The associated HCME at 01:30 UT had a
slightly slower space speed of 2160 km s-1. The STEREO-A and STEREO-B
longitudes were W109 and E118, respectively. The SOHO shock arrival time was
at 10:53 UT on March 08. The GOES $>$10 MeV peak proton flux was 6530 cm-2 s-1
sr-1. The onset of the HCME has been studied by Chintzoglou et al. (2015) and
the heliopsheric propagation by Patsourakos et al. (2016) and Soni et al.
(2023).

Figure 1: Data points of Fermi/LAT $>$100 MeV gamma-ray flux overplot on
Wind/WAVES radio dynamic spectra for the 2012 January 23 and March 07 SGRE
events. The LAT data points are connected by straight lines to guide the eye.
The estimated end times of the SGRE events and type II radio bursts are marked
by long and short vertical lines.

###  5.1 Distance Estimation

We estimated the radial distance and the space speed of the shock by forward
fitting a spheroidal shock model to white-light images of STEREO/HIs (Eyles et
al., 2009) around the end time of the SGRE event. For shock fitting, we used
IDL programs in the Solar Corona Ray-Tracing Software package developed to
forward modeling of structures of the solar corona (e.g., Thernisien et al.,
2009, https://soho.nascom.nasa.gov/solarsoft/stereo/secchi/idl/scraytrace/).

The fitting of the spheroidal shock model to HI observations is shown in
Figure 2. The propagation direction of the shock is difficult to estimate, our
estimates were N25W05 for the 2012 January 23 CME and N34E27 for the 2012
March 07 CME. For the 2012 January 23 HCME we obtained the radial distance
r=121 R☉, and the space speed 975 km s-1. In the case of the 2012 March 07
HCME the estimated radial r=140 R☉, and the space speed 750 km s-1. The
obtained speeds are reasonably high for a strong CME-driven shock to exist.

We compared these results with radial distances estimated using Wind/WAVES
observations of the type II radio burst. First, we measured the mid-frequency
of type II emission lane at the time the CME leading edge was around 20 R☉,
because type II emissions are often very complex and overlapped by more
intense type III emission during the early phase of the eruption, which makes
radio measurements at frequencies corresponding the shock distances close to
the Sun difficult. From the frequency formula
$f_{plasma}=9.0\times\sqrt{N\times n(r)}$, where the radial distance $r$ is in
units of R☉ and frequency $f$ in kHz, we calculated the multiplier $N$ for the
Leblanc density model $n(r)$ (Leblanc et al., 1998). The measurement time was
obtained by extrapolating the CME height-time profiles obtained by forward
fitting a flux rope model to LASCO and SECCHI/COR images to a radial distance
20 R☉.

We then estimated the radial distance at the SGRE end time from the mid-
frequency of the type II emission lane: For the 2012 January 23 HCME we
obtained the multiplier $N=4.51$, which then gave for the mid-frequency $f=83$
kHz the radial distance of $r=132$ R☉. For the 2012 March 07 HCME the
respective values were $N=9.07$, $f=90$ kHz and $r=173$ R☉. The distances
estimated from the radio bursts data are 9% and 24% larger than those
estimated from the STEREO/HI images. The STEREO/HI height-time measurements
are complicated because the actual shape, location, and propagation direction
of the shock ahead of the CME body are difficult to discern from the white-
light images. The CME structure in white-light is also transparent, so we may
confuse structures (e.g., Scott et al., 2019) and brightness depends on local
density and Thomson-scattering geometry (Howard & Tappin, 2009; Xiong et al.,
2013). On the other hand, type II radio emissions are sporadic and depend on
local density at the radio source, which the general density model cannot
capture. We also assume that the location of the radio source is at the shock
nose (e.g., Mäkelä et al., 2018) and the type II emission in interplanetary
space occurs at the fundamental of the plasma frequency (Lengyel-Frey et al.,
1985).

Figure 2: Spheroidal shock fits (red lines) on to the STEREO/HI images of the
2012 January 23 CME (top row) and the 2012 March 07 CME (bottom row).

##  6 Discussion

In the first part of our analysis, we showed that the near-Sun kinematics of
the CMEs correlate with the properties of the gamma-ray emission observed by
Fermi/LAT. The population of the CMEs (total of 8 CMEs) that were associated
with a gamma-ray event whose light-curve indicated both ’Prompt’ and ’Delayed’
emission component, as defined by Ajello et al. (2021), had the highest
average initial acceleration (1.87 km s-2) and fastest average space speed
(1753 km s-1). The mixed ’Delayed’ category, where the existence of the
’Prompt’ component is uncertain due to the lack of LAT measurements around the
flare onset, has a similar average space speed (1745 km s-1) but somewhat
lower initial acceleration (1.73 km s-2). The lowest average values (1.37 km
s-2 and 775 km s-1, respectively) had the population of CMEs (total of 6 CMEs)
associated with gamma-ray flares showing a ’Prompt’ emission component only,
i.e., there were no SGRE emissions detected by LAT. The speeds correspond well
with those obtained by Winter et al. (2018) who studied CME properties for
X-class flares with and without gamma-ray emission. They found a median CME
linear speed of 768 km s-1 for X-class flares without gamma-ray emission. If
Fermi detected gamma-rays during the X-class flare, the median speed of the
associated CMEs was 1828 km s-1. CMEs associated with SGRE events had the
highest median speed of 2125 km s-1. The definition of SGRE in their study was
that the $>$100 MeV gamma-ray duration is $\gtrsim\sim 2$ hr. Ajello et al.
(2021) definition used here is based on details of hard X-ray and gamma-ray
light-curves, which probably explains why Winter et al. (2018) SGRE events
were associated with faster CMEs.

In addition, we divided cycle 24 on-disk HCMEs associated with type II radio
bursts into groups with and without (a) SGRE events, (b) DH type II bursts,
and (c) major SEP events observed. For SEP events we analyzed major events
observed by GOES only and the second group of major SEP events observed by
GOES or STEREO spacecraft. Our statistical analysis show that all metric type
II-associated HCMEs with an SGRE event have considerably higher initial
acceleration and also space speed if an major SEP event was also detected than
those of metric type II-associated HCMEs without an SGRE event. The average
space speeds of the SGRE-associated HCMEs without an SEP event and the non-
SGRE-associated HCMEs with an major SEP event were similar. The analysis of
the HCMEs associated with only DH type II emission shows that the three SGRE-
producing HCMEs without an SEP event observed by GOES spacecraft have higher
space speed than any studied population of HCMEs not associated with an SGRE
event. However, one of those three HCMEs had an major SEP event observed by
STEREO-B and the other two had elevated backgrounds at leat at the best
connected spacecraft, so all three events could have accelerated protons.
Whereas the avergae initial acceleration is slightly lower than those of the
metric type II-associated HCMEs without an SGRE event, but clearly higher than
those of the DH type II-associated HCMEs without an SGRE event. The lower
value is expected because CMEs associated with only a DH type II radio burst
accelerate slowly and the shock forms later. This result resembles the
kinematic hierarchy of CMEs with major SEP events, where rare, slowly
accelerating but eventually fast CMEs associated with filament eruptions
outside active regions can produce large SEP events at 1 au. In the case
filament eruptions, we know that the resulting energy spectrum is soft, but
the general idea that occasionally the initial acceleration of the CME is
slower, but acceleration continues long enough so that a sufficiently strong
shock forms later at higher altitudes is comparable. In general, our results
are similar to those reported by Gopalswamy et al. (2022). The SGRE-associated
HCMEs seem to conform to the hierarchy between the initial acceleration and
speed of the CME and the fluence spectral index as described by Gopalswamy et
al. (2016). Clearly, the existence of $>$300 MeV protons is connected to a
high initial acceleration and speed of the associated HCME. Therefore, our
results suggest that CME-driven shocks are the likely source for the $>$300
MeV protons required to produce SGREs at the Sun.

The mirror effect near the Sun limits the number of protons that can penetrate
deep enough, i.e., particles with a pitch angle $\alpha$ in the sheath region
cannot penetrate a near-Sun region if $\mu=\cos{\alpha}$ is larger than the
critical value $\mu_{c}$:

$\left|\mu\right|\geq\mu_{c}\equiv\sqrt{1-\frac{B_{sheath}}{B_{\odot}}}.$ (1)

Because the foot points of the field lines crossing the shock nose could be
connected to areas outside the source active region where the average magnetic
field strength $B_{\sun}$ is considerably lower than in active regions, the
mirror ratio $B_{sheath}/B_{\sun}$ increases and the width of the loss cone
$\alpha_{c}=\cos^{-1}{\mu_{c}}=\sin^{-1}{\sqrt{B_{sheath}/B_{\sun}}}$ becomes
larger. Because the CME flux ropes have a pile-up region in front of them, the
magnetic field within the sheath could be significantly larger than the
ambient field, which will further lower the mirror ratio. Therefore, more
protons can precipitate deep into solar atmosphere. As mentioned earlier,
enhanced turbulence increases scattering into the loss cone, which in turn
increases the number of precipitating particles at the foot points. The level
of the turbulence and its time evolution along the flux-rope-wrapping field
lines and in the atmospheric layers close to the Sun are difficult to
estimate. For example, EUV waves associated with large solar eruptions and
propagating long distances over the solar surface clearly indicate that
coronal shocks and CME lateral expansion affect the solar atmosphere far from
the eruption site, most likely resulting in large volumes of enhanced
turbulence around the source active region.

It should be noted that fast CME shocks are the only sites for which we have
clear corroborating observational evidence for acceleration of $>$300 MeV
protons over extended times long after the end of the solar flare. Winter et
al. (2018) studied the properties of the soft X-ray flares, CMEs and SEP
events associated with SGRE events. They found that SGRE events are not
produced by the brightest, most intense X-ray flares. In their reverse study,
they found that during the period from 2011 March to 2015 June 45 X-class soft
X-ray flares were detected, but only 15 of those were associated with a SGRE
event. Similarly, their study showed that SGRE events are associated with fast
CMEs and the SGRE duration increases as the CME speed increases. The reverse
study of the fast HCMEs with speeds above 1500 km s-1 found only four HCMEs
without a reported gamma-ray event. Two of the four HCMEs, the 2011 September
22 10:48 UT and 2012 July 19 05:24 UT halos, had concurrent Fermi/LAT
observations. In both events, the LAT spectra showed slight increases that
were not significant enough to be characterized as detection. In the study of
related SEP events observed by GOES, Winter et al. (2018) list only the 2011
March 07 SGRE event as a magnetically well-connected to GOES and without a
significant background increase due to a preceding event but did not show any
increase in the GOES $>$300 MeV flux. Gopalswamy et al. (2019) suggest that
the lack of high-energy protons is due to a poor latitudinal magnetic
connection of the shock nose to Earth because the flare occurred at the
heliographic latitude of N31 and the northern polar region of the Sun is
tilted away from Earth in March. Similarly, Gopalswamy et al. (2021a) showed
that soft energy spectrum observed by GOES during the 2014 January 7 SGRE
event was due to poor magnetic connectivity of the shock nose to an Earth
observer. The final conclusion of Winter et al. (2018) is that their results
favor the CME-shock as the source of the SGRE-producing protons.

The $>$300 MeV protons are accelerated near the nose of the CME-driven shock
(e.g., Gopalswamy et al., 2013, 2014; Gopalswamy & Mäkelä, 2014), with a
possible exception of the earliest phase of the eruption, where the fast
lateral expansion of the shock could result in efficient particle acceleration
away from the nose region. Some fraction of the shock-accelerated protons
escapes into the IP space and are detected as an SEP event, but others
propagate along the magnetic field lines deep down into the solar atmosphere
and generate SGRE. In addition, the magnetic field lines that are pushed ahead
of the CME body maintain a continuous connection between the shock and the
solar atmosphere. Therefore, if the shock can accelerate protons to energies
$>$300 MeV, protons will have a propagation path back to the Sun and can
generate SGREs. The key aspect of the CME-shock model is that the magnetic
field lines protons travel along sunwards cross the shock front into the
sheath region behind the shock, wrap around the CME flux rope and connect back
to the Sun in areas outside the foot points of the CME flux rope and possibly
also areas outside the source active region. Therefore, the locations of the
foot points are widely separated providing a natural explanation for the
spatially extended source of gamma-ray emission.

We estimated the radial distance the CME-driven shock at the end time of the
SGRE event for the 2012 January 23 and 2012 March 07 SGRE events. These events
were associated with the two longest duration type II radio bursts. We
estimated the shock radial distance by forward fitting a spheroidal shock
model to STEREO/HI white-light images of the CME and obtained for the 2012
January 23 SGRE event the shock radial distance $r=121$ R☉ and for the 2012
March 07 SGRE event $r=140$ R☉. In addition, we used the frequency of the type
II radio burst obtained from the radio dynamic spectra of Wind/WAVES together
with a radial density model to get another estimate for the shock radial
distance. The obtained distances from radio measurement were slightly longer,
for the 2012 January 23 SGRE event $r=132$ R☉, and for the 2012 March 07 SGRE
event $r=173$ R☉.

Patsourakos et al. (2016) estimated the speed of the 2012 March 07 CME using
the standard aerodynamic drag-force model approach, where the CME travelled
through quiet or perturbed solar wind (SW). Based on their results (their
Figure 8), the estimated speed of the CME at 22 UT for the quiet SW model was
$\approx$740 km s-1 and for the perturbed SW model $\approx$820 km s-1. The
perturbed SW model matches better the CME arrival time and speed at the Wind
spacecraft. Therefore, our estimated CME speed of 750 km s-1 seems to be
slightly below the one obtained from the perturbed SW model. Recently, Soni et
al. (2023) studied the arrival signatures of the 2012 March 07 CME at several
heliospheric locations. They report that Venus Express detected the arrival of
the CME ejecta at 13:28 UT, when Venus was at the radial distance of 154 R☉.
Therefore, the radial distance estimated from the forward fitting of the
spheroidal shock model, r=140 R☉, is clearly too low and most likely the
radial distance obtained from radio observations, r=173 R☉, is closer to the
actual distance. The model fitting to images of the 2012 March 07 CME was
difficult because the CME structure was very faint in the STEREO-B images (see
Figure 2c). Therefore, the sensitivity of the imaging system may not be high
enough to detect the shock in front of the CME.

The estimation of the radial distance of the shock at the end time of the SGRE
event is quite complicated. The location and the shape of the shock front is
difficult to discern from white-light images of the CME (e.g., Odstrcil &
Pizzo, 2009; Scott et al., 2019). CMEs are transparent structures and
intensity of Thomson scattering depends on viewing angle relative to the
structure. The location of type II radio source on the shock front is also
difficult to measure. Imaging radio instrument operate at the higher
frequencies, which correspond to heights of couple solar radius above the
solar surface. Direction finding and triangulation can be used to locate the
interplanetary type II radio sources at lower frequencies. However, scattering
of radio waves and low intensity of type II emission limit the accuracy of the
direction-finding measurements.

The CME-driven shock in both events reached SOHO spacecraft (2012 January 24
14:33 UT and 2012 March 08 10:53 UT respectively) and when shocks passed 1 au
about 30 minutes later, GOES spacecraft observed a clear increase around the
shock time visible in Figure 3. Both events had particle flux increase in the
GOES 350–429 MeV channels indicating that the CME-driven shock did accelerate
$>$300 MeV protons. In both cases the 1-au enhancement continued beyond the
end times of the SGRE events, estimated to be at 2012 January 23 19:25 UT and
2012 March 07 21:40 UT, respectively. During the March 07 event, the particle
increase was detectable at even higher energies, up to the 510–700 MeV energy
range. The event integrated fluence spectrum of 2012 January 23 event provided
by PAMELA indicate that SEP flux at 1 au extended above 300 MeV (Bruno et al.,
2018). Therefore, the CME-driven shock clearly must accelerate $>$300 MeV
protons far away from the Sun, providing support for the CME-shock as the
source of the SGRE-producing protons.

Figure 3: GOES-13 measurements of the SEP events associated with the 2012
January 23 (a) and 2012 March 07 CMEs and SGRE events. Both events show
enhanced intensity in the 350–420 MeV channel (blue). The March 07 event has a
clear flux increase in the higher-energy 510–700 MeV channel (brown). The
estimated SGRE end times at 2012 January 23 19:25 UT and March 07 21:40 UT are
marked by dashed lines and the SOHO shock times at 2012 January 24 14:33 UT
and March 08 10:53 UT by dash-dot lines.

The 2012 March 07 SGRE event was very bright that the location of the $>$100
MeV gamma-ray emission source could be estimated over several time intervals
over a period of about 10 hours (Ajello et al., 2014, 2021). The emission
centroid seemed to move away from the flare site across the solar towards
west. Ajello et al. (2021) studied two other, bright SGRE flares on 2014
February 25 and 2017 September 10. The gamma-ray intensity of the 2014
February flare was weaker, so they could determine the location of the
emission centroid only during two intervals over three hours. The September
2017 flare was brighter, and the location was determined in three intervals
over 7 hours, but the flare occurred over the western limb of the Sun making
the detection of possible source movement difficult. In both events the
centroid remained consistent with the AR location. Therefore, the movement of
the SGRE source during the 2012 March 07 event supports CME-shock scenario,
whereas the detection of a possible source movement in the 2014 February 25
and 2017 September 10 events is complicated because of the weaker gamma-ray
intensity or unfavorable location of the flare.

##  7 Conclusions

We compared acceleration and speed of CMEs associated with gamma-ray flares
with ’Prompt’ and/or ’Delayed’ (SGRE event) component as defined by Ajello et
al. (2021). In addition, we divided the on-disk HCMEs associated with type II
radio bursts into groups with or without SGRE events, SEP events, metric or DH
type II radio bursts and compared the average acceleration and speed between
the HCME groups. We showed that the CMEs associated with the ’Delayed’ gamma-
ray component and the metric type II-producing HCMEs associated with SGRE
events together with a DH type II radio burst and/or a major SEP events have
higher initial acceleration and space speed than the CMEs associated with the
’Prompt-only’ gamma-ray component or the SEP- or type II-associated HCMEs
without SGRE. The only exception was the space speed of metric type II
-associated HCMEs with an major SEP event but without an SGRE event that had
similar average space speeds as the SGRE-associated HCMEs without an major SEP
event. Similar high initial acceleration and fast speed characteristics are
shared by CMEs associated with GLEs, which are guaranteed to have $>$300 MeV
protons. The SGRE-associated CMEs also conform to the hierarchy between the
initial acceleration and speed of the CME and the fluence spectral index as
described by Gopalswamy et al. (2016). Therefore, our findings support the
CME-driven shock as the source of $>$300 MeV protons producing SGRE events.

We estimated the radial distance the CME-driven shock at the end time of the
SGRE event with the long-duration type II radio bursts on 2012 January 23 and
2012 March 07 using STEREO/HI white-light images of the CME and radio dynamic
spectra of Wind/WAVES. The shock radial distances for 2012 January 23 SGRE
event were r=121 R☉ and r=132 R☉, and for the 2012 March 07 SGRE event r=140
R☉ and r=173 R☉, respectively. The distances derived from white-light and
radio observations are reasonably consistent, indicating that the radio source
is near the shock nose as assumed. The distances are also consistently longer
that the estimated shock height $\approx$70 R☉ for the shorter-duration 2014
February 25 SGRE event Gopalswamy et al. (2019) (Gopalswamy et al. 2019).
Because the shock location is not visible in the white-light images, the
radial distance estimated from forward fitting of the spheroidal shock model
are probably underestimations. At the end time of the SGRE event, the shock
speeds were still high enough (975 km s-1 and 750 km s-1) for high-energy
particle acceleration. Therefore, we conclude that strong CME-driven shocks
accelerate $>$300 MeV protons up to the radial distances of 0.6–0.8 au.

We thank the Fermi/LAT, GOES, SOHO/LASCO, STEREO/SECCHI, Wind/WAVES, and
HELCATS teams for providing the data. PM and SA were partially supported by
NSF grant AGS-2043131. NG was supported by NASA’s STEREO project and the
Living With a Star program. HX was partially supported by NSF grant
AGS-2228967.

##  Appendix A CMEs and X-ray Flares Associated with On-disk Fermi/LAT Solar
Flares

Table 4 contains data for the CME and X-ray flare data used in Table 2. The
first column gives the first observation date and time of the CME followed by
the measured sky-plane speed and the projection-corrected space speed in the
second and third columns. The fourth column lists the estimated initial
acceleration of the CME. The columns 5–7 list the location in heliographic
coordinates, the onset and peak times of the GOES soft X-ray flare. The last
column lists the gamma-ray components detected by Fermi/LAT taken from Ajello
et al. (2021).

Table 4: CME and X-ray flare data for Fermi/LAT solar flares

CME | Sky Speed | Space Speed | Acc | Location | Flare Onset | Flare Peak | Gamma-ray Components
---|---|---|---|---|---|---|---
(UT) | (km -1) | (km s-1) | (km s-2) | (UT) | (UT) | (UT) |
2010/06/12 01:31 | 620 | 674 | 0.42 | N23W43 | 2010/06/12 00:30 | 2010/06/12 00:57 | LLE-Prompt
2011/03/07 20:00 | 2125 | 2223 | 1.28 | N30W48 | 2011/03/07 19:43 | 2011/03/07 20:12 | Delayed
2011/06/07 06:49 | 1255 | 1321 | 0.88 | S21W54 | 2011/06/07 06:16 | 2011/06/07 06:41 | Delayed
2011/08/04 04:12 | 1315 | 1477 | 1.54 | N19W36 | 2011/08/04 03:41 | 2011/08/04 03:57 | Delayed
2011/08/09 08:12 | 1610 | 1640 | 1.61 | N17W69 | 2011/08/09 07:48 | 2011/08/09 08:05 | Prompt Short-Delayed
2011/09/06 23:05 | 575 | 830 | 1.73 | N14W18 | 2011/09/06 22:12 | 2011/09/06 22:20 | LLE-Prompt Short-Delayed
2011/09/07 23:05 | 710 | 735 | 2.04 | N14W28 | 2011/09/07 22:32 | 2011/09/07 22:38 | Delayed
2011/09/24 09:48 | 1936 | 2235 | 1.96 | N12E60 | 2011/09/24 09:21 | 2011/09/24 09:40 | LLE-Prompt Short-Delayed
2012/01/23 04:00 | 2175 | 2511 | 1.99 | N28W21 | 2012/01/23 03:38 | 2012/01/23 03:59 | Delayed
2012/01/27 18:27 | 2508 | 2541 | 0.71 | N27W78 | 2012/01/27 17:37 | 2012/01/27 18:37 | Delayed
2012/03/05 04:00 | 1531 | 1627 | 0.52 | N17E52 | 2012/03/05 03:17 | 2012/03/05 04:09 | Delayed
2012/03/07 00:24 | 2684 | 3146 | 2.38 | N17E27 | 2012/03/07 00:02 | 2012/03/07 00:24 | Delayed
2012/03/09 04:26 | 950 | 1229 | 0.66 | N15W03 | 2012/03/09 03:22 | 2012/03/09 03:53 | No-Prompt Delayed
2012/03/10 18:00 | 1296 | 1638 | 0.94 | N17W24 | 2012/03/10 17:15 | 2012/03/10 17:44 | Delayed
2012/05/17 01:48 | 1582 | 1596 | 1.21 | N11W76 | 2012/05/17 01:25 | 2012/05/17 01:47 | Delayed
2012/06/03 18:12 | 772 | 786 | 1.87 | N16E38 | 2012/06/03 17:48 | 2012/06/03 17:55 | LLE-Prompt Short-Delayed
2012/07/06 23:24 | 1828 | 1907 | 4.54 | S13W59 | 2012/07/06 23:01 | 2012/07/06 23:08 | Delayed
2012/08/06 05:12 | 198 | 199 | 0.66 | S14E84 | 2012/08/06 04:33 | 2012/08/06 04:38 | LLE-Prompt
2012/11/13 02:24 | 980 | 1002 | 2.78 | S25E46 | 2012/11/13 01:58 | 2012/11/13 02:04 | Prompt
2013/04/11 07:24 | 861 | 1369 | 1.09 | N09E12 | 2013/04/11 06:55 | 2013/04/11 07:16 | No-Prompt Short-Delayed
2013/05/13 02:00 | 1270 | 1270 | 0.88 | N11E90 | 2013/05/13 01:53 | 2013/05/13 02:17 | Delayed
2013/05/13 16:07 | 1850 | 1852 | 1.82 | N11E85 | 2013/05/13 15:48 | 2013/05/13 16:05 | Delayed
2013/05/14 01:25 | 2625 | 2645 | 4.01 | N08E77 | 2013/05/14 01:00 | 2013/05/14 01:11 | No-Prompt Delayed
2013/05/15 01:48 | 1366 | 1408 | 0.71 | N12E64 | 2013/05/15 01:15 | 2013/05/15 01:48 | No-Prompt Delayed
2013/10/25 08:12 | 587 | 599 | 1.25 | S08E73 | 2013/10/25 07:53 | 2013/10/25 08:01 | Delayed
2013/10/28 02:24 | 695 | 726 | 0.55 | N04W66 | 2013/10/28 01:41 | 2013/10/28 02:03 | LLE-Prompt
2013/10/28 04:48 | 1201 | 1270 | 2.35 | N08W71 | 2013/10/28 04:32 | 2013/10/28 04:41 | LLE-Prompt
2013/10/28 15:36 | 812 | 1098 | 2.29 | S06E28 | 2013/10/28 15:07 | 2013/10/28 15:15 | Delayed
2013/10/28 21:25 | 771 | 777 | 1.44 | N07W83 | 2013/10/28 20:48 | 2013/10/28 20:57 | LLE-Prompt
2014/01/07 18:24 | 1830 | 2246 | 1.34 | S15W11 | 2014/01/07 18:04 | 2014/01/07 18:32 | Delayed
2014/02/25 01:25 | 2147 | 2153 | 3.59 | S12E82 | 2014/02/25 00:39 | 2014/02/25 00:49 | LLE-Prompt Delayed
2014/06/10 13:30 | 1469 | 1473 | 1.53 | S17E82 | 2014/06/10 12:36 | 2014/06/10 12:52 | LLE-Prompt Delayed
2014/06/11 09:24 | 829 | 915 | 2.18 | S18E65 | 2014/06/11 08:59 | 2014/06/11 09:06 | Short-Delayed
2014/09/10 18:00 | 1267 | 1652 | 1.15 | N14E02 | 2014/09/10 17:21 | 2014/09/10 17:45 | Short-Delayed
2015/06/21 02:36 | 1366 | 1740 | 0.97 | N12E16 | 2015/06/21 02:06 | 2015/06/21 02:36 | Prompt Delayed
2015/06/25 08:36 | 1627 | 1805 | 2.15 | N09W42 | 2015/06/25 08:02 | 2015/06/25 08:16 | Delayed
2017/09/06 12:24 | 1571 | 1819 | 3.37 | S08W33 | 2017/09/06 11:53 | 2017/09/06 12:02 | Delayed
2017/09/10 16:00 | 3163 | 3163 | 1.70 | S09W92 | 2017/09/10 15:35 | 2017/09/10 16:06 | Prompt Delayed

Note. — Gamma-ray Components are taken from Ajello et al. (2021).

##  Appendix B Cycle 24 HCMEs with Type II Radio Bursts and on-disk X-ray
Flares

Table 5 contains data for the cycle-24 HCME and X-ray flares used in Tables 2
and 3. The columns 1–7 are the same as in Table 4. Columns 8–9 list the onset
times of the reported metric and DH type II radio bursts. The DH type II onset
times are listed for Wind/WAVES, except on 03 August 2011, when only
STEREO-A/WAVES detected a DH type II burst. The column 10 indicates on which
spacecraft the WAVES instruments could detect a DH type II radio burst
(W=Wind, A=STEREO-A, B=STEREO-B, ’-’=no report). The columns 11–12 mark if the
event had a major SEP event (G=GOES, A=STEREO-A, B=STEREO-B, ’-’=data gap) and
an SGRE event (’Delayed’ component detected), respectively.

Table 5: Cycle 24 HCMEs with type II radio bursts

HCME | Sky Speed | Space Speed | Acc | Location | Flare Onset | Flare Peak | m-Type II | DH-Type II | WAVES S/C | SEP | SGRE
---|---|---|---|---|---|---|---|---|---|---|---
(UT) | (km $s^{-1}$) | (km s-1) | (km s-2) |  | (UT) | (UT) | (UT) | (UT) |  | G/A/B |
2010/08/01 13:42 | 850 | 1030 | 0.34 | N20E36 | 2010/08/01 07:36 | 2010/08/01 08:26 | $\cdots$ | 2010/08/01 09:20 | W/A/B | 0/-/0 | 0
2010/08/07 18:36 | 871 | 1102 | 0.63 | N11E34 | 2010/08/07 17:55 | 2010/08/07 18:24 | 2010/08/07 18:08 | 2010/08/07 18:35 | W/A/B | 0/0/1 | 0
2010/08/14 10:12 | 1205 | 1280 | 0.51 | N17W52 | 2010/08/14 09:23 | 2010/08/14 10:05 | 2010/08/14 09:52 | $\cdots$ | -/-/- | 1/0/0 | 0
2011/02/14 18:24 | 326 | 544 | 1.51 | S20W04 | 2011/02/14 17:20 | 2011/02/14 17:26 | 2011/02/14 17:28 | $\cdots$ | -/-/- | 0/0/0 | 0
2011/02/15 02:24 | 669 | 960 | 1.33 | S20W10 | 2011/02/15 01:44 | 2011/02/15 01:56 | 2011/02/15 01:52 | 2011/02/15 02:10 | W/A/B | 0/0/1 | 0
2011/03/07 20:00 | 2125 | 2223 | 1.28 | N30W48 | 2011/03/07 19:43 | 2011/03/07 20:12 | 2011/03/07 19:54 | 2011/03/07 20:00 | W/A/- | 1/1/0 | 1
2011/06/02 08:12 | 976 | 1147 | 0.64 | S19E25 | 2011/06/02 07:16 | 2011/06/02 07:46 | $\cdots$ | 2011/06/02 08:00 | W/A/B | 0/0/0 | 0
2011/06/07 06:49 | 1255 | 1321 | 0.88 | S21W54 | 2011/06/07 06:16 | 2011/06/07 06:41 | 2011/06/07 06:25 | 2011/06/07 06:45 | W/A/B | 1/0/0 | 1
2011/06/21 03:16 | 719 | 882 | 0.12 | N16W08 | 2011/06/21 01:22 | 2011/06/21 03:25 | $\cdots$ | 2011/06/21 03:07 | W/-/- | 0/0/0 | 0
2011/08/03 14:00 | 610 | 785 | 0.37 | N16W30 | 2011/08/03 13:13 | 2011/08/03 13:48 | 2011/08/03 13:35 | 2011/08/03 13:38 | -/A/- | 0/0/0 | 0
2011/08/04 04:12 | 1315 | 1477 | 1.54 | N19W36 | 2011/08/04 03:41 | 2011/08/04 03:57 | 2011/08/04 03:54 | 2011/08/04 04:15 | W/A/B | 1/0/0 | 1
2011/08/09 08:12 | 1610 | 1640 | 1.61 | N17W69 | 2011/08/09 07:48 | 2011/08/09 08:05 | 2011/08/09 08:01 | 2011/08/09 08:20 | W/-/- | 1/0/0 | 1
2011/09/06 02:24 | 782 | 1232 | 1.37 | N14W07 | 2011/09/06 01:35 | 2011/09/06 01:50 | 2011/09/06 01:46 | 2011/09/06 02:00 | W/-/- | 0/0/0 | 0
2011/09/06 23:05 | 575 | 830 | 1.73 | N14W18 | 2011/09/06 22:12 | 2011/09/06 22:20 | 2011/09/06 22:19 | 2011/09/06 22:30 | W/A/- | 0/0/0 | 1
2011/09/22 10:48 | 1905 | 1905 | 0.99 | N09E89 | 2011/09/22 10:29 | 2011/09/22 11:01 | 2011/09/22 10:39 | 2011/09/22 11:05 | W/-/B | 1/1/1 | 0
2011/09/24 12:48 | 1915 | 2018 | 0.58 | N10E56 | 2011/09/24 12:22 | 2011/09/24 13:20 | $\cdots$ | 2011/09/24 12:50 | W/-/B | 0/0/0 | 0
2011/09/24 19:36 | 972 | 1076 | 1.49 | N12E42 | 2011/09/24 19:09 | 2011/09/24 19:21 | 2011/09/24 19:14 | $\cdots$ | -/-/- | 0/0/1 | 0
2011/11/09 13:36 | 907 | 1012 | 0.54 | N24E35 | 2011/11/09 13:04 | 2011/11/09 13:35 | 2011/11/09 13:11 | 2011/11/09 13:30 | W/-/B | 0/0/0 | 0
2011/11/26 07:12 | 933 | 1001 | 0.60 | N17W49 | 2011/11/26 06:42 | 2011/11/26 07:10 | $\cdots$ | 2011/11/26 07:15 | W/A/- | 1/1/0 | 0
2012/01/19 14:36 | 1120 | 1269 | 0.15 | N32E22 | 2012/01/19 13:44 | 2012/01/19 16:05 | $\cdots$ | 2012/01/19 15:00 | W/A/B | 0/0/1 | 0
2012/01/23 04:00 | 2175 | 2511 | 1.99 | N28W21 | 2012/01/23 03:38 | 2012/01/23 03:59 | 2012/01/23 03:43 | 2012/01/23 04:00 | W/A/- | 1/1/1 | 1
2012/01/27 18:27 | 2508 | 2541 | 0.71 | N27W78 | 2012/01/27 17:37 | 2012/01/27 18:37 | 2012/01/27 18:10 | 2012/01/27 18:30 | W/A/B | 1/1/0 | 1
2012/03/05 04:00 | 1531 | 1627 | 0.52 | N17E52 | 2012/03/05 03:17 | 2012/03/05 04:09 | $\cdots$ | 2012/03/05 04:00 | W/A/B | 0/0/0 | 1
2012/03/07 00:24 | 2684 | 3146 | 2.38 | N17E27 | 2012/03/07 00:02 | 2012/03/07 00:24 | 2012/03/07 00:17 | 2012/03/07 01:00 | W/A/B | 1/0/1 | 1
2012/03/07 01:30 | 1825 | 2160 | 4.00 | N15E26 | 2012/03/07 01:05 | 2012/03/07 01:14 | 2012/03/07 01:09 | $\cdots$ | -/-/- | 0/0/0 | 0
2012/03/09 04:26 | 950 | 1229 | 0.66 | N15W03 | 2012/03/09 03:22 | 2012/03/09 03:53 | 2012/03/09 03:43 | 2012/03/09 04:10 | W/-/- | 0/1/0 | 1
2012/03/10 18:00 | 1296 | 1638 | 0.94 | N17W24 | 2012/03/10 17:15 | 2012/03/10 17:44 | $\cdots$ | 2012/03/10 17:55 | W/A/- | 0/0/0 | 1
2012/03/13 17:36 | 1884 | 1931 | 0.89 | N17W66 | 2012/03/13 17:05 | 2012/03/13 17:41 | 2012/03/13 17:15 | 2012/03/13 17:35 | W/A/- | 1/0/0 | 0
2012/04/05 21:25 | 828 | 1065 | 0.66 | N18W29 | 2012/04/05 20:43 | 2012/04/05 21:10 | 2012/04/05 21:08 | $\cdots$ | -/-/- | 0/0/0 | 0
2012/04/09 12:36 | 921 | 945 | 0.38 | N20W65 | 2012/04/09 12:02 | 2012/04/09 12:44 | 2012/04/09 12:28 | 2012/04/09 12:20 | W/A/- | 0/0/0 | 0
2012/04/23 18:24 | 528 | 769 | 0.99 | N14W17 | 2012/04/23 17:38 | 2012/04/23 17:51 | 2012/04/23 17:42 | $\cdots$ | -/-/- | 0/0/0 | 0
2012/05/17 01:48 | 1582 | 1596 | 1.21 | N11W76 | 2012/05/17 01:25 | 2012/05/17 01:47 | 2012/05/17 01:31 | 2012/05/17 01:40 | W/A/- | 1/0/0 | 1
2012/07/04 17:24 | 662 | 830 | 2.31 | N14W34 | 2012/07/04 16:33 | 2012/07/04 16:39 | 2012/07/04 16:42 | 2012/07/04 17:00 | W/-/- | 0/0/0 | 0
2012/07/06 23:24 | 1828 | 1907 | 4.54 | S13W59 | 2012/07/06 23:01 | 2012/07/06 23:08 | 2012/07/06 23:09 | 2012/07/06 23:10 | W/A/- | 1/0/0 | 1
2012/07/12 16:48 | 885 | 1405 | 0.51 | S15W01 | 2012/07/12 16:03 | 2012/07/12 16:49 | 2012/07/12 16:25 | 2012/07/12 16:45 | W/-/- | 1/0/1 | 0
2012/07/19 05:24 | 1631 | 1631 | 0.37 | S13W88 | 2012/07/19 04:45 | 2012/07/19 05:58 | 2012/07/19 05:24 | 2012/07/19 05:30 | W/-/- | 1/0/0 | 0
2012/07/28 21:12 | 420 | 463 | 0.64 | S25E54 | 2012/07/28 20:44 | 2012/07/28 20:56 | 2012/07/28 20:52 | $\cdots$ | -/-/- | 0/0/0 | 0
2012/07/31 11:24 | 567 | 605 | 0.23 | N19E59 | 2012/07/31 10:46 | 2012/07/31 11:30 | 2012/07/31 11:04 | $\cdots$ | -/-/- | 0/0/0 | 0
2012/08/13 13:25 | 435 | 705 | 1.68 | N22W03 | 2012/08/13 12:33 | 2012/08/13 12:40 | 2012/08/13 12:41 | $\cdots$ | -/-/- | 0/0/0 | 0
2012/08/31 20:00 | 1442 | 1495 | 0.35 | S19E50 | 2012/08/31 19:32 | 2012/08/31 20:43 | 2012/08/31 19:42 | 2012/08/31 20:00 | W/A/- | 1/0/1 | 0
2012/09/28 00:12 | 947 | 1093 | 0.87 | N09W31 | 2012/09/27 23:36 | 2012/09/27 23:57 | 2012/09/27 23:44 | 2012/09/27 23:55 | W/A/- | 1/0/1 | 0
2012/11/08 02:36 | 855 | 855 | 0.95 | N13E89 | 2012/11/08 02:08 | 2012/11/08 02:23 | 2012/11/08 02:21 | $\cdots$ | -/-/- | 0/0/0 | 0
2012/11/21 16:00 | 529 | 942 | 0.79 | N05E05 | 2012/11/21 15:10 | 2012/11/21 15:30 | 2012/11/21 15:33 | $\cdots$ | -/-/- | 0/0/0 | 0
2013/03/15 07:12 | 1063 | 1366 | 0.39 | N11E12 | 2013/03/15 06:00 | 2013/03/15 06:58 | $\cdots$ | 2013/03/15 07:00 | W/-/- | 1/0/0 | 0
2013/04/11 07:24 | 861 | 1369 | 1.09 | N09E12 | 2013/04/11 06:55 | 2013/04/11 07:16 | 2013/04/11 07:02 | 2013/04/11 07:10 | W/-/B | 1/0/1 | 1
2013/05/13 02:00 | 1270 | 1270 | 0.88 | N11E90 | 2013/05/13 01:53 | 2013/05/13 02:17 | 2013/05/13 02:10 | 2013/05/13 02:20 | W/-/B | 0/0/1 | 1
2013/05/13 16:07 | 1850 | 1852 | 1.82 | N11E85 | 2013/05/13 15:48 | 2013/05/13 16:05 | 2013/05/13 15:57 | 2013/05/13 16:15 | W/A/B | 0/0/1 | 1
2013/05/14 01:25 | 2625 | 2645 | 4.01 | N08E77 | 2013/05/14 01:00 | 2013/05/14 01:11 | 2013/05/14 01:07 | 2013/05/14 01:16 | W/A/B | 0/0/0 | 1
2013/05/15 01:48 | 1366 | 1408 | 0.71 | N12E64 | 2013/05/15 01:15 | 2013/05/15 01:48 | 2013/05/15 01:37 | 2013/05/15 01:49 | W/-/- | 1/0/0 | 1
2013/05/17 09:12 | 1345 | 1412 | 1.68 | N12E57 | 2013/05/17 08:43 | 2013/05/17 08:57 | 2013/05/17 08:50 | $\cdots$ | -/-/- | 0/0/0 | 0
2013/05/22 13:25 | 1466 | 1491 | 0.71 | N15W70 | 2013/05/22 12:57 | 2013/05/22 13:32 | 2013/05/22 12:59 | 2013/05/22 13:10 | W/A/B | 1/1/0 | 0
2013/06/28 02:00 | 1037 | 1254 | 0.91 | S18W19 | 2013/06/28 01:36 | 2013/06/28 01:59 | $\cdots$ | 2013/06/28 01:53 | W/-/- | 0/0/0 | 0
2013/08/17 19:12 | 1202 | 1418 | 0.54 | S05W30 | 2013/08/17 18:49 | 2013/08/17 19:33 | 2013/08/17 18:56 | 2013/08/17 20:25 | W/-/- | 0/0/0 | 0
2013/08/30 02:48 | 949 | 1031 | 0.31 | N15E46 | 2013/08/30 01:51 | 2013/08/30 02:46 | 2013/08/30 02:12 | 2013/08/30 02:34 | W/-/- | 0/0/0 | 0
2013/09/29 22:12 | 1179 | 1370 | 0.21 | N17W29 | 2013/09/29 21:43 | 2013/09/29 23:31 | 2013/09/29 21:53 | 2013/09/29 21:53 | W/A/B | 1/0/0 | 0
2013/10/22 21:48 | 459 | 1070 | 3.57 | N04W01 | 2013/10/22 21:15 | 2013/10/22 21:20 | 2013/10/22 21:21 | 2013/10/22 21:33 | W/-/- | 0/0/0 | 0
2013/10/24 01:25 | 399 | 766 | 1.42 | S10E08 | 2013/10/24 00:21 | 2013/10/24 00:30 | 2013/10/24 00:31 | $\cdots$ | -/-/- | 0/0/0 | 0
2013/10/25 08:12 | 587 | 599 | 1.25 | S08E73 | 2013/10/25 07:53 | 2013/10/25 08:01 | 2013/10/25 07:59 | $\cdots$ | -/-/- | 0/0/1 | 1
2013/10/25 15:12 | 1081 | 1103 | 1.53 | S06E69 | 2013/10/25 14:51 | 2013/10/25 15:03 | 2013/10/25 14:58 | 2013/10/25 15:08 | W/-/B | 0/0/0 | 0
2013/10/28 02:24 | 695 | 726 | 0.55 | N04W66 | 2013/10/28 01:41 | 2013/10/28 02:03 | 2013/10/28 02:00 | $\cdots$ | -/-/- | 0/0/0 | 0
2013/10/28 15:36 | 812 | 1098 | 2.29 | S06E28 | 2013/10/28 15:07 | 2013/10/28 15:15 | 2013/10/28 15:10 | 2013/10/28 15:24 | W/-/- | 0/0/0 | 1
2013/10/29 22:00 | 1001 | 1001 | 1.39 | N05W89 | 2013/10/29 21:42 | 2013/10/29 21:54 | 2013/10/29 21:48 | $\cdots$ | -/-/- | 0/0/0 | 0
2013/11/19 10:36 | 740 | 761 | 1.06 | S14W70 | 2013/11/19 10:14 | 2013/11/19 10:26 | 2013/11/19 10:24 | 2013/11/19 10:39 | W/-/- | 0/0/0 | 0
2013/12/07 07:36 | 1085 | 1165 | 1.62 | S16W49 | 2013/12/07 07:17 | 2013/12/07 07:29 | 2013/12/07 07:27 | 2013/12/07 07:43 | W/-/- | 0/0/0 | 0
2014/01/07 18:24 | 1830 | 2246 | 1.34 | S15W11 | 2014/01/07 18:04 | 2014/01/07 18:32 | 2014/01/07 18:17 | 2014/01/07 18:33 | W/A/B | 1/1/1 | 1
2014/01/20 22:00 | 721 | 750 | 0.18 | S07E67 | 2014/01/20 21:39 | 2014/01/20 22:49 | $\cdots$ | 2014/01/20 22:24 | W/-/- | 0/0/0 | 0
2014/02/20 08:00 | 948 | 960 | 0.53 | S15W73 | 2014/02/20 07:26 | 2014/02/20 07:56 | 2014/02/20 07:45 | 2014/02/20 08:05 | W/-/- | 1/0/0 | 0
2014/02/25 01:25 | 2147 | 2153 | 3.59 | S12E82 | 2014/02/25 00:39 | 2014/02/25 00:49 | 2014/02/25 00:56 | 2014/02/25 00:56 | W/A/B | 1/1/1 | 1
2014/03/20 04:36 | 740 | 921 | 1.10 | S14E35 | 2014/03/20 03:42 | 2014/03/20 03:56 | 2014/03/20 03:52 | $\cdots$ | -/-/- | 0/0/0 | 0
2014/03/29 18:12 | 528 | 679 | 0.87 | N11W32 | 2014/03/29 17:35 | 2014/03/29 17:48 | 2014/03/29 17:53 | 2014/03/29 17:59 | W/-/- | 0/0/0 | 0
2014/04/02 13:36 | 1471 | 1564 | 0.55 | N11E53 | 2014/04/02 13:18 | 2014/04/02 14:05 | 2014/04/02 13:23 | 2014/04/02 13:42 | W/-/B | 0/0/1 | 0
2014/04/18 13:25 | 1203 | 1359 | 0.71 | S20W34 | 2014/04/18 12:31 | 2014/04/18 13:03 | 2014/04/18 12:55 | 2014/04/18 13:05 | W/-/- | 1/0/0 | 0
2014/06/10 13:30 | 1469 | 1473 | 1.53 | S17E82 | 2014/06/10 12:36 | 2014/06/10 12:52 | $\cdots$ | 2014/06/10 12:58 | W/-/B | 0/0/1 | 1
2014/07/08 16:36 | 773 | 841 | 1.00 | N12E56 | 2014/07/08 16:06 | 2014/07/08 16:20 | 2014/07/08 16:14 | $\cdots$ | -/-/- | 0/-/0 | 0
2014/08/01 18:36 | 789 | 1256 | 1.16 | S10E11 | 2014/08/01 17:55 | 2014/08/01 18:13 | 2014/08/01 18:18 | 2014/08/01 18:58 | W/-/- | 0/0/0 | 0
2014/08/22 11:12 | 600 | 993 | 1.18 | N12E01 | 2014/08/22 10:13 | 2014/08/22 10:27 | $\cdots$ | 2014/08/22 10:37 | W/-/- | 0/-/0 | 0
2014/08/24 12:36 | 551 | 569 | 0.56 | S07E75 | 2014/08/24 12:00 | 2014/08/24 12:17 | 2014/08/24 12:14 | $\cdots$ | -/-/- | 0/-/0 | 0
2014/08/25 15:36 | 555 | 697 | 0.46 | N05W36 | 2014/08/25 14:46 | 2014/08/25 15:11 | 2014/08/25 15:08 | 2014/08/25 15:20 | W/-/- | 0/-/0 | 0
2014/09/09 00:06 | 920 | 1080 | 0.33 | N12E29 | 2014/09/08 23:34 | 2014/09/09 00:29 | $\cdots$ | 2014/09/09 00:05 | W/-/- | 0/0/0 | 0
2014/09/10 18:00 | 1267 | 1652 | 1.15 | N14E02 | 2014/09/10 17:21 | 2014/09/10 17:45 | $\cdots$ | 2014/09/10 17:45 | W/-/- | 1/-/0 | 1
2014/12/17 05:00 | 587 | 855 | 0.46 | S20E09 | 2014/12/17 04:20 | 2014/12/17 04:51 | 2014/12/17 04:44 | 2014/12/17 05:00 | W/-/- | 0/-/- | 0
2014/12/19 01:04 | 1195 | 1513 | 1.48 | S11E15 | 2014/12/18 21:41 | 2014/12/18 21:58 | 2014/12/18 22:22 | 2014/12/18 22:31 | W/-/- | 0/-/- | 0
2014/12/21 12:12 | 669 | 906 | 0.28 | S14W25 | 2014/12/21 11:24 | 2014/12/21 12:17 | $\cdots$ | 2014/12/21 12:05 | W/-/- | 0/-/- | 0
2015/02/09 23:24 | 1106 | 1148 | 0.53 | N12E61 | 2015/02/09 22:59 | 2015/02/09 23:35 | 2015/02/09 23:14 | $\cdots$ | -/-/- | 0/-/- | 0
2015/03/07 22:12 | 1261 | 1304 | 0.59 | S19E74 | 2015/03/07 21:45 | 2015/03/07 22:22 | 2015/03/07 21:57 | $\cdots$ | -/-/- | 0/-/- | 0
2015/03/10 00:00 | 995 | 1081 | 0.75 | S18E45 | 2015/03/09 23:29 | 2015/03/09 23:53 | 2015/03/10 00:05 | 2015/03/10 00:10 | W/-/- | 0/-/- | 0
2015/03/10 03:36 | 1040 | 1156 | 3.85 | S15E40 | 2015/03/10 03:19 | 2015/03/10 03:24 | 2015/03/10 03:28 | $\cdots$ | -/-/- | 0/-/- | 0
2015/03/15 01:48 | 719 | 932 | 0.27 | S22W25 | 2015/03/15 01:15 | 2015/03/15 02:13 | 2015/03/15 01:27 | $\cdots$ | -/-/- | 0/-/- | 0
2015/04/23 09:36 | 857 | 864 | 0.29 | N12W89 | 2015/04/23 09:18 | 2015/04/23 10:07 | 2015/04/23 09:22 | $\cdots$ | -/-/- | 0/-/- | 0
2015/05/05 22:24 | 715 | 721 | 2.00 | N15E79 | 2015/05/05 22:05 | 2015/05/05 22:11 | 2015/05/05 22:12 | 2015/05/05 22:24 | W/-/- | 0/-/- | 0
2015/05/13 18:48 | 438 | 730 | 1.35 | N13W16 | 2015/05/13 18:09 | 2015/05/13 18:18 | 2015/05/13 18:21 | $\cdots$ | -/-/- | 0/-/- | 0
2015/06/18 17:24 | 1305 | 1398 | 0.35 | N15E50 | 2015/06/18 16:30 | 2015/06/18 17:36 | $\cdots$ | 2015/06/18 17:42 | W/-/- | 0/-/- | 0
2015/06/21 02:36 | 1366 | 1740 | 0.97 | N12E16 | 2015/06/21 02:06 | 2015/06/21 02:36 | 2015/06/21 02:24 | 2015/06/21 02:33 | W/-/- | 1/-/- | 1
2015/06/22 18:36 | 1209 | 1573 | 0.60 | N12W08 | 2015/06/22 17:39 | 2015/06/22 18:23 | 2015/06/22 18:05 | 2015/06/22 18:20 | W/-/- | 0/-/- | 0
2015/06/25 08:36 | 1627 | 1805 | 2.15 | N09W42 | 2015/06/25 08:02 | 2015/06/25 08:16 | 2015/06/25 08:16 | 2015/06/25 08:35 | W/-/- | 1/-/- | 1
2015/08/22 07:12 | 547 | 817 | 1.36 | S15E20 | 2015/08/22 06:39 | 2015/08/22 06:49 | 2015/08/22 06:50 | 2015/08/22 07:07 | W/-/- | 0/-/- | 0
2015/09/20 18:12 | 1239 | 1458 | 0.78 | S22W50 | 2015/09/20 17:32 | 2015/09/20 18:03 | 2015/09/20 18:16 | 2015/09/20 18:23 | W/-/- | 0/-/- | 0
2015/11/04 14:48 | 578 | 987 | 0.01 | N09W04 | 2015/11/04 14:08 | 2015/11/05 13:31 | 2015/11/04 13:43 | 2015/11/04 14:07 | W/-/- | 0/-/- | 0
2015/12/16 09:36 | 579 | 937 | 0.43 | S13W04 | 2015/12/16 08:27 | 2015/12/16 09:03 | $\cdots$ | 2015/12/16 08:45 | W/-/- | 0/-/- | 0
2015/12/28 12:12 | 1212 | 1471 | 0.29 | S23W11 | 2015/12/28 11:20 | 2015/12/28 12:45 | $\cdots$ | 2015/12/28 11:50 | W/-/- | 0/-/- | 0
2016/01/01 23:24 | 1730 | 1734 | 2.22 | S25W82 | 2016/01/01 23:58 | 2016/01/02 00:11 | 2016/01/01 23:21 | 2016/01/02 00:55 | W/A/- | 1/0/- | 0
2016/02/11 21:17 | 719 | 1174 | 0.43 | N11W07 | 2016/02/11 20:18 | 2016/02/11 21:03 | 2016/02/11 20:35 | $\cdots$ | -/-/- | 0/0/- | 0
2017/04/18 19:48 | 926 | 932 | 0.32 | N14E77 | 2017/04/18 19:21 | 2017/04/18 20:10 | 2017/04/18 19:49 | $\cdots$ | -/-/- | 0/1/- | 0
2017/07/14 01:25 | 1200 | 1422 | 0.38 | S06W29 | 2017/07/14 01:07 | 2017/07/14 02:09 | $\cdots$ | 2017/07/14 01:18 | W/-/- | 1/0/- | 0
2017/09/04 20:36 | 1418 | 1831 | 6.10 | S10W12 | 2017/09/04 20:28 | 2017/09/04 20:33 | 2017/09/04 20:42 | 2017/09/04 20:27 | W/-/- | 1/0/- | 0
2017/09/06 12:24 | 1571 | 1819 | 3.37 | S08W33 | 2017/09/06 11:53 | 2017/09/06 12:02 | 2017/09/06 12:02 | 2017/09/06 12:05 | W/A/- | 1/0/- | 1
2017/09/10 16:00 | 3163 | 3163 | 1.70 | S09W92 | 2017/09/10 15:35 | 2017/09/10 16:06 | 2017/09/10 16:08 | 2017/09/10 16:02 | W/A/- | 1/1/- | 1

Note. — The SEP column gives major SEP events observed by GOES and the SGRE
column gamma-ray flares with a ’Delayed’ component observed by Fermi/LAT
(Ajello et al., 2021)

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