capbtabboxtable[][] [a]T. Wach

# Joint H.E.S.S. and Fermi-LAT analysis of the region around PSR J1813-1749

A. M. W. Mitchell  V. Joshi  S. Funk  on behalf of the H.E.S.S. Collaboration

###### Abstract

HESS J1813-178 is one of the brightest sources detected during the first HESS
Galactic Plane survey. The compact source, also detected by MAGIC, is believed
to be a pulsar wind nebula powered by one of the most powerful pulsars known
in the Galaxy, PSR J1813-1749 with a spin-down luminosity of
$\dot{\mathrm{E}}=5.6\cdot 10^{37}\,\mathrm{erg}\,\mathrm{s}^{-1}$. With its
extreme physical properties, as well as the pulsar’s young age of 5.6 kyrs,
the $\gamma$-rays detected in this region allow us to study the evolution of a
highly atypical system. Previous studies of the region in the GeV energy range
show emission extended beyond the size of the compact H.E.S.S. source. Using
the archival H.E.S.S. data with improved background methods, we perform a
detailed morphological and spectral analysis of the region. Additionally to
the compact, bright emission component, we find significantly extended
emission, whose position is coincident with HESS J1813-178. We reanalyse the
region in GeV and derive a joint-model in order to find a continuous
description of the emission in the region from GeV to TeV. Using the results
derived in this analysis, as well as X-ray and radio data of the region, we
perform multi-wavelength spectral modeling. Possible hadronic or leptonic
origins of the $\gamma$-ray emission are investigated, and the diffusion
parameters necessary to explain the extended emission are examined.

##  1 Introduction

The Imaging Atmospheric Cherenkov Telescope (IACT) Array H.E.S.S. has highly
contributed to our knowledge of the $\gamma$-ray sky, by identifying many
previously unknown sources during their surveys of the galactic plane (HGPS)
conducted in 2006 [3] and 2018 [12]. One of these sources is HESS J1813$-$178,
a single-component compact source, centered at $\text{R.A.}=(273.40\pm
0.005)^{\circ}$, $\text{Dec}=-(17.84\pm 0.005)^{\circ}$ with an extension of
$\sigma=(0.036\pm 0.006)^{\circ}$. Compact counterparts to this high energy
$\gamma$-ray emission have been observed in X-ray with INTEGRAL [19] and XMM-
Newton [11] and in radio with the VLA [7]. Additionally, faint extended
emission enclosing the bright compact emission has been detected during the
HGPS in 2006. This detection however could not be established as significant
[3].

The detection of the shell-type Supernova Remnant (SNR) G12.82–0.02 [7], and
the very young and energetic pulsar PSR J1813$-$1749, with a characteristic
age of $5600\,$years and a spin-down luminosity of $\dot{\text{E}}=5.6\times
10^{37}\,\text{erg}\text{s}^{-1}$ [8], both positionally coincident with the
detected TeV emission, result in two different scenarios for the origin of the
$\gamma$-ray emission. Several studies showed that it is more likely that the
compact $\gamma$-ray emission observed in the TeV range is a result of Inverse
Compton (IC) scattering of electrons from the pulsar with photons of the ISM
[11, 10]

An analysis of the region in the GeV energy range, utilising data taken with
the _Fermi_ -LAT satellite, showed emission that is positionally coincident
with PSR J1813$-$1749, but extended $(0.6\pm 0.06)^{\circ}$ [6]. They
concluded that the origin of the TeV and GeV emission should be considered
separately, and found that the origin of the $\gamma$-ray emission in the GeV
energy range is most likely Cosmic Rays (CRs) accelerated at the shock fronts
of the SNR. An additional hadronic scenario could be CRs accelerated at the
shock fronts of the young stellar cluster Cl J1813$-$178, located in close
proximity to the pulsar as projected along the line of sight [16]. Due to the
mismatch in observed emission extension, and the very different interpretation
of the data acquired in different energies, the origin of the emission in the
region around PSR J1813$-$1749 could not be firmly established yet.

We present a reanalysis of the TeV data in the region around HESS J1813$-$178,
using improved background rejection and event reconstruction. We also present
a new analysis of the _Fermi_ -LAT data, with increased exposure compared to
the previous work, and perform a joint-likelihood minimisation of the GeV and
TeV data simultaneously.

##  2 H.E.S.S. Data Analysis and Results

H.E.S.S. data is taken in $\sim 28\,$min observation intervals referred to as
runs. We select the runs for this analysis based on requiring that all four
telescopes must participate, and the pointing position of the telescopes,
which must be less than $2^{\circ}$ offset from the position of HESS
J1813$-$178 derived in the previous analysis. Additionally, standard data
quality cuts [2] are applied and the energy threshold of the analysis is set
to $0.4\,$TeV. Applying these quality cuts results in a dataset with
$31\,$hours of livetime, taken between 2004 and 2012. We then analyse the data
using the open-source Python package gammapy, version 0.18.2 [9].

The first galactic plane survey [3] was evaluated using the Ring background
method. This method estimates the background from source-free regions at equal
distance from the source. The results acquired from this background method
depend on a correct estimation of the source extension and is highly sensitive
to point-like sources, but not suitable for faint or very extended sources and
problematic for sources without a defined edge, like pulsar wind nebulae. In
order to increase the sensitivity towards large extended sources, we use a
template-based approach to describe the background. This template is generated
from a large set of source-free regions, following the scheme in [17].

Figure 1 shows the significance map of the region around HESS J1813$-$178 with
a correlation radius of $0.4^{\circ}$.

Figure 1: Significance map of the region around PSR J1813$-$1749 as seen by
H.E.S.S. before removal of emission using source models. The galactic plane is
indicated by the white dotted line, $3\,\sigma$ and $5\,\sigma$ contours are
shown in pink. The best-fit source model for HESS J1809$-$193 derived in [14]
is shown by the black dashed line and the best-fit model for the emission
around PSR J1813$-$1749 derived in this study.

The position of the galactic plane is indicated by the white dotted line. We
also show $3\,\sigma$ and $5\,\sigma$ contours of the emission, as well as the
position of PSR J1813$-$1749 and PSR J1809$-$1917, a nearby pulsar enclosed by
the TeV source HESS J1809$-$193\. In this analysis, the emission of the
neighbouring source HESS J1809$-$193 is removed by adding a two-component
model, following the description derived in a recent analysis of this region
[14].

We observe a compact bright emission centered around the pulsar, as well as a
fainter, extended emission in the region around the pulsar. We account for the
emission around PSR J1813$-$1749 by adding a Gaussian source model with an
extension of $\sigma=0.056^{\circ}\pm 0.003^{\circ}$. The best-fit results
derived for this source model agree within the error with the previously
results for HESS J1813$-$178 [3]. Hereafter, we will refer to this emission
component as component A. After the removal of this component by modeling the
emission, we observe a remaining large-scale $\gamma$-ray emission component.
We find that this emission can be best described by an asymmetric Gaussian
model, aligned along the galactic plane. We will refer to this source model as
component B. The best-fit values for the two source models used to account for
the emission around PSR J1813$-$1749, as well as the source models used to
account for the emission in the vicinity of PSR J1809$-$1917, are indicated by
the black dashed lines in figure 1.

##  3 _Fermi_ -LAT Data Analysis and Results

In a previous analysis of the _Fermi_ -LAT data of the region around PSR
J1813$-$1749 using the standard LAT analysis software Fermitools, extended
emission has been discovered [6]. This source, referred to as 4FGL
J1813$-$1737e, is positionally coincident with PSR J1813$-$1749 and HESS
J1813$-$178, but with an extension of $0.6^{\circ}$, no connection could be
made with the TeV emission. We reanalyse the data using gammapy, version
0.18.2, which enables us to optimise the morphology and spectrum of a source
model simultaneously.

Figure 2: Significance map of the region containing 4FGL J1813$-$1737e as seen
by _Fermi_ -LAT. Additional emission in the field of view attributed to other
astrophysical sources has been removed using their description in the 4FGL
source catalogue. $3\,\sigma$ and $5\,\sigma$ contours of the residual
emission in the field of view are overlaid in pink. The best-fit model is for
4FGL J1813$-$1737e is indicated by the black dashed line

For this study, data from the beginning of the _Fermi_ -LAT mission in August
2008 until October 2021 is used. We use the most recent IRFs from Pass 8
version 3 — P8R3_SOURCE_V2 [4], and the corresponding background models
iso_P8R3_SOURCE_V3_v1.txt, gll_iem_v07.fits. Other sources in the $6^{\circ}$
Region-of-Interest (ROI) are accounted for by using source models from the
12-year 4FGL source catalogue [1]. We allow a maximum zenith angle of
$90^{\circ}$ for all events to avoid the inclusion of secondary $\gamma$-rays
from the Earth’s horizon, and use a bin size of $0.025^{\circ}$, as well as 8
energy bins per decade with logarithmic spacing. In order to avoid a large
point-spread function we adopt an energy threshold of $1\,$GeV up to $1\,$TeV.

Figure 2 shows the significance map of the region around PSR J1813$-$1749, as
seen by _Fermi_ -LAT. The emission from all sources in the ROI, except 4FGL
J1813$-$1737e, has been accounted for by the respective source model in the
4FGL catalog. We again overlay the galactic plane as a white dotted line, the
position of PSR J1813$-$1749, as well as $3\,\sigma$ and $5\,\sigma$ contours
of the emission. Similarly to previous analyses of the region [6, 20], we
observe extended emission around the pulsar PSR J1813$-$1749, positionally
coincident with HESS J1813$-$178\. In contrast to the previous studies, using
a disk model to describe the emission, we find that the emission can be
described best by an asymmetric Gaussian model, with an extension of
$0.38^{\circ}$, and an alignment along the galactic plane. The best-fit
morphology of this model is indicated by the black dashed lines in figure 2.

This emission is positionally coincident with the results derived in the
H.E.S.S. data for component B, though less extended. The addition of a second,
compact component, coincident with component A in the H.E.S.S. data, improves
the description of the region, but cannot be established at a $5\,\sigma$
level and is therefore omitted for this study.

##  4 Energy-dependent behaviour of the emission

On account of the positional coincidence between the detected $\gamma$-ray
emission and the pulsar PSR J1813$-$1749, a leptonic origin of the emission is
plausible. Previous studies of such systems have shown an energy-dependent
morphology caused by electron diffusion and cooling [18, 15, 13].

Energy band | Energy [GeV]
---|---
1 | $1.0\,-\,2.0$
2 | $2.0\,-\,4.0$
3 | $4.0\,-\,7.5$
4 | $7.5\,-\,18$
5 | $18\,-\,58$
6 | $58\,-\,1.0\times 10^{3}$
1-2 H1 | $(0.4\,-\,1.3)\times 10^{3}$
H2 | $(1.3\,-\,5.7)\times 10^{3}$
H3 | $(5.7\,-\,100)\times 10^{3}$
Table 1: Energy bands used to test for energy-dependent morphology. Fermi
bands are shown as 1- 6 and HESS bands as H1-H3

Figure 3: The distance between the centre of the best-fit model and the
position of PSR J1813$-$1749 is estimated in each energy bin and plotted
against the extension of the semi-major axis.

To test for an energy-dependent morphology in the emission observed in this
study the datasets are divided into six logarithmically spaced energy bins for
the _Fermi_ -LAT data, as well as three energy bins for the H.E.S.S. data.
This binning was chosen based on the available statistics for each dataset.
The best-fit models described above are then fitted in each energy bin
respectively and the distance of the centre of the best-fit component to the
position of PSR J1813$-$1749 is computed and compared to the extension of the
semi-major axis in the respective energy bin. These results are shown in
Figure 4.

Due to the low statistics in the H.E.S.S. dataset, as well as the low
statistics in the high energy regime of the _Fermi_ -LAT dataset, this study
is subject to large uncertainties for the respective measurements. The derived
extensions are compatible within the errors, we do not find a significant
indication of an energy-dependent morphology. However, the extension in the
last energy bin of the _Fermi_ -LAT data is compatible with the extension
derived in the first energy bin of the H.E.S.S. data, suggesting that the
emission from 4FGL J1813$-$1737e can be connected to the extended emission
observed in the H.E.S.S. dataset.

##  5 Joint-Modeling

The discovery of extended emission in the H.E.S.S. data enables a continuous
description of the region around PSR J1813$-$1749, while the search for
energy-dependent morphology showed that component B and the extended emission
observed in the _Fermi_ -LAT data show a comparable extension. To investigate
this result, we perform a joint analysis. To describe the emission observed by
_Fermi_ -LAT and H.E.S.S. we add a symmetric model, as well as an asymmetric
model to both datasets. The likelihood minimisation is then performed on both
datasets at the same time, while the IRFs for each dataset are taken into
account.

This minimisation returns a compact component, centred at a best-fit position
of $\text{R.A.}=(273.40\pm 0.003)^{\circ}$, $\text{Dec}=(-17.832\pm
0.003)^{\circ}$ with an extension of $\sigma=(0.056\pm 0.003)^{\circ}$. Based
on the shape of the SED derived in the analysis of the respective datasets, we
use a logarithmic parabola spectral model as spectral model. The estimated
best-fit spectral index is $\Gamma=2.05\pm 0.03$, with a curvature
$\beta=0.06\pm 0.001$ and a flux normalization at $1\,$TeV of $(3.16\pm
0.13)\times 10^{-12}\,\text{cm}^{-2}\text{s}^{-1}\text{TeV}^{-1}$.

For the second component, we find a best-fit position of
$\text{R.A.}=(273.39\pm 0.03)^{\circ}$, $\text{Dec}=(-17.504\pm 0.04)^{\circ}$
with an extension of $\sigma=(0.54\pm 0.03)^{\circ}$. This model is
asymmetric, with an eccentricity of $e=0.73\pm 0.04$ and a position angle of
$\varphi=(213.76\pm 7.22)^{\circ}$. We again used a logarithmic parabola model
with a spectral index of $\Gamma=2.17\pm 0.03$, a curvature of $\beta=0.04\pm
0.001$, and a flux normalisation at $1\,$TeV of $(6.47\pm 0.43)\times
10^{-12}\,\text{cm}^{-2}\text{s}^{-1}\text{TeV}^{-1}$.

The spectrum and the spectral energy distribution (SED) for both components
can be seen in Figure 4. Additionally, the broadband sensitivity of _Fermi_
-LAT for sources located in the galactic plane and 12 years of data taking is
overlaid [5]. Most of the predicted emission from component A is below the
detectable flux for the LAT, explaining why the emission could not be observed
in the analysis of the _Fermi_ -LAT data. After removing the emission from
components A and B using the best-fit parameters derived in this joint
analysis, no emission remains in the H.E.S.S. data. The addition of component
A to the _Fermi_ -LAT dataset does not overestimate the emission in the region
and the significance map is reasonably flat, indicating that this two-
component source model is a good description of the region in the GeV and the
TeV data.

Figure 4: Spectrum and SED for component A and component B derived from a
joint-fit to both datasets. The broadband sensitivity of the _Fermi_ -LAT is
indicated by the purple line [5].

##  6 Conclusion and Outlook

In previous studies, the emission from HESS J1813$-$178 and 4FGL J1813$-$1737e
could not be connected, despite their positional coincidence, because of
disagreements in the extension measurements. Due to these disagreements, all
attempts to draw conclusions on the physical origin of the emission have used
either the SED derived in the analysis of the GeV data, or the TeV data
separately. As a consequence, the TeV source HESS J1813$-$178 remains to be a
source with an unknown origin.

We reanalyse the region using an improved background model for the analysis of
the TeV data, and increased exposure in the GeV data. We find that the
emission in the H.E.S.S. data can be well described by a two-component model.
The first component, a compact Gaussian component with an extension of
$0.06^{\circ}$, referred to as component A in this analysis, can be connected
to HESS J1813$-$178\. The detection of a second, extended component in this
study makes it possible, for the first time, to connect the emission from 4FGL
J1813$-$1737e to the emission observed in the TeV range and, therefore find a
continuous description of the region around PSR J1813$-$1749 over five decades
of energy. Utilising these new results, we will be able to further investigate
the physical origin of the emission.

The observed emission is coincident with the pulsar PSR J1813$-$1749, but also
with the SNR G12.82$-$0.02 and the stellar cluster Cl 1813$-$178\. Therefore
the emission could be caused by electrons escaping the confines of the pulsar
and forming a pulsar wind nebula, which we would then observe as HESS
J1813$-$178\. Some of these electrons further escape into the ISM, forming the
halo-like structure observed as 4FGL J1813$-$1737e and component B. Another
possibility is that the observed $\gamma$-ray emission is caused by protons
from the cosmic ray sea. These protons are accelerated at the shock fronts of
the SNR or the stellar cluster. producing $\gamma$-rays through the
interaction with photons from molecular clouds in the region. A forthcoming
publication will examine these possible emission scenarios in depth and
further investigate possible evolution scenarios of the system around PSR
J1813$-$1749.

##  7 Acknowledgments

This work is supported by the Deutsche Forschungsgemeinschaft (DFG, German
Research Foundation) – Project Number 452934793.

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## Full Authors List: H.E.S.S. Collaboration

F. Aharonian1,2,3, F. Ait Benkhali4, A. Alkan5, J. Aschersleben6, H. Ashkar7,
M. Backes8,9, A. Baktash10, V. Barbosa Martins11, A. Barnacka12, J. Barnard13,
R. Batzofin14, Y. Becherini15,16, G. Beck17, D. Berge11,18, K. Bernlöhr2, B.
Bi19, M. Böttcher9, C. Boisson20, J. Bolmont21, M. de Bony de Lavergne5, J.
Borowska18, M. Bouyahiaoui2, F. Bradascio5, M. Breuhaus2, R. Brose1, A.
Brown22, F. Brun5, B. Bruno23, T. Bulik24, C. Burger-Scheidlin1, T. Bylund5,
F. Cangemi21, S. Caroff25, S. Casanova26, R. Cecil10, J. Celic23, M.
Cerruti15, P. Chambery27, T. Chand9, S. Chandra9, A. Chen17, J. Chibueze9, O.
Chibueze9, T. Collins28, G. Cotter22, P. Cristofari20, J. Damascene
Mbarubucyeye11, I.D. Davids8, J. Davies22, L. de Jonge9, J. Devin29, A.
Djannati-Ataï15, J. Djuvsland2, A. Dmytriiev9, V. Doroshenko19, L. Dreyer9, L.
Du Plessis9, K. Egberts14, S. Einecke28, J.-P. Ernenwein30, S. Fegan7, K.
Feijen15, G. Fichet de Clairfontaine20, G. Fontaine7, F. Lott8, M. Füßling11,
S. Funk23, S. Gabici15, Y.A. Gallant29, S. Ghafourizadeh4, G. Giavitto11, L.
Giunti15,5, D. Glawion23, J.F. Glicenstein5, J. Glombitza23, P. Goswami15, G.
Grolleron21, M.-H. Grondin27, L. Haerer2, S. Hattingh9, M. Haupt11, G.
Hermann2, J.A. Hinton2, W. Hofmann2, T. L. Holch11, M. Holler31, D. Horns10,
Zhiqiu Huang2, A. Jaitly11, M. Jamrozy12, F. Jankowsky4, A. Jardin-Blicq27, V.
Joshi23, I. Jung-Richardt23, E. Kasai8, K. Katarzyński32, H. Katjaita8, D.
Khangulyan33, R. Khatoon9, B. Khélifi15, S. Klepser11, W. Kluźniak34, Nu.
Komin17, R. Konno11, K. Kosack5, D. Kostunin11, A. Kundu9, G. Lamanna25, R.G.
Lang23, S. Le Stum30, V. Lefranc5, F. Leitl23, A. Lemière15, M. Lemoine-
Goumard27, J.-P. Lenain21, F. Leuschner19, A. Luashvili20, I. Lypova4, J.
Mackey1, D. Malyshev19, D. Malyshev23, V. Marandon5, A. Marcowith29, P.
Marinos28, G. Martí-Devesa31, R. Marx4, G. Maurin25, A. Mehta11, P.J.
Meintjes13, M. Meyer10, A. Mitchell23, R. Moderski34, L. Mohrmann2, A.
Montanari4, C. Moore35, E. Moulin5, T. Murach11, K. Nakashima23, M. de
Naurois7, H. Ndiyavala8,9, J. Niemiec26, A. Priyana Noel12, P. O’Brien35, S.
Ohm11, L. Olivera-Nieto2, E. de Ona Wilhelmi11, M. Ostrowski12, E. Oukacha15,
S. Panny31, M. Panter2, R.D. Parsons18, U. Pensec21, G. Peron15, S. Pita15, V.
Poireau25, D.A. Prokhorov36, H. Prokoph11, G. Pühlhofer19, M. Punch15, A.
Quirrenbach4, M. Regeard15, P. Reichherzer5, A. Reimer31, O. Reimer31, I.
Reis5, Q. Remy2, H. Ren2, M. Renaud29, B. Reville2, F. Rieger2, G.
Roellinghoff23, E. Rol36, G. Rowell28, B. Rudak34, H. Rueda Ricarte5, E. Ruiz-
Velasco2, K. Sabri29, V. Sahakian37, S. Sailer2, H. Salzmann19, D.A.
Sanchez25, A. Santangelo19, M. Sasaki23, J. Schäfer23, F. Schüssler5, H.M.
Schutte9, M. Senniappan16, J.N.S. Shapopi8, S. Shilunga8, K. Shiningayamwe8,
H. Sol20, H. Spackman22, A. Specovius23, S. Spencer23, Ł. Stawarz12, R.
Steenkamp8, C. Stegmann14,11, S. Steinmassl2, C. Steppa14, K. Streil23, I.
Sushch9, H. Suzuki38, T. Takahashi39, T. Tanaka38, T. Tavernier5, A.M.
Taylor11, R. Terrier15, A. Thakur28, J. H.E. Thiersen9, C. Thorpe-Morgan19, M.
Tluczykont10, M. Tsirou11, N. Tsuji40, R. Tuffs2, Y. Uchiyama33, M. Ullmo5, T.
Unbehaun23, P. van der Merwe9, C. van Eldik23, B. van Soelen13, G.
Vasileiadis29, M. Vecchi6, J. Veh23, C. Venter9, J. Vink36, H.J. Völk2, N.
Vogel23, T. Wach23, S.J. Wagner4, F. Werner2, R. White2, A. Wierzcholska26, Yu
Wun Wong23, H. Yassin9, M. Zacharias4,9, D. Zargaryan1, A.A. Zdziarski34, A.
Zech20, S.J. Zhu11, A. Zmija23, S. Zouari15 and N. Żywucka9.

1Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2,
Ireland 2Max-Planck-Institut für Kernphysik, P.O. Box 103980, D 69029
Heidelberg, Germany 3Yerevan State University, 1 Alek Manukyan St, Yerevan
0025, Armenia 4Landessternwarte, Universität Heidelberg, Königstuhl, D 69117
Heidelberg, Germany 5IRFU, CEA, Université Paris-Saclay, F-91191 Gif-sur-
Yvette, France 6Kapteyn Astronomical Institute, University of Groningen,
Landleven 12, 9747 AD Groningen, The Netherlands 7Laboratoire Leprince-
Ringuet, École Polytechnique, CNRS, Institut Polytechnique de Paris, F-91128
Palaiseau, France 8University of Namibia, Department of Physics, Private Bag
13301, Windhoek 10005, Namibia 9Centre for Space Research, North-West
University, Potchefstroom 2520, South Africa 10Universität Hamburg, Institut
für Experimentalphysik, Luruper Chaussee 149, D 22761 Hamburg, Germany
11Deutsches Elektronen-Synchrotron DESY, Platanenallee 6, 15738 Zeuthen,
Germany 12Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171,
30-244 Kraków, Poland 13Department of Physics, University of the Free State,
PO Box 339, Bloemfontein 9300, South Africa 14Institut für Physik und
Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, D 14476
Potsdam, Germany 15Université de Paris, CNRS, Astroparticule et Cosmologie,
F-75013 Paris, France 16Department of Physics and Electrical Engineering,
Linnaeus University, 351 95 Växjö, Sweden 17School of Physics, University of
the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg, 2050 South
Africa 18Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, D
12489 Berlin, Germany 19Institut für Astronomie und Astrophysik, Universität
Tübingen, Sand 1, D 72076 Tübingen, Germany 20Laboratoire Univers et Théories,
Observatoire de Paris, Université PSL, CNRS, Université Paris Cité, 5 Pl.
Jules Janssen, 92190 Meudon, France 21Sorbonne Université, Université Paris
Diderot, Sorbonne Paris Cité, CNRS/IN2P3, Laboratoire de Physique Nucléaire et
de Hautes Energies, LPNHE, 4 Place Jussieu, F-75252 Paris, France 22University
of Oxford, Department of Physics, Denys Wilkinson Building, Keble Road, Oxford
OX1 3RH, UK 23Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen
Centre for Astroparticle Physics, Nikolaus-Fiebiger-Str. 2, 91058 Erlangen,
Germany 24Astronomical Observatory, The University of Warsaw, Al. Ujazdowskie
4, 00-478 Warsaw, Poland 25Université Savoie Mont Blanc, CNRS, Laboratoire
d’Annecy de Physique des Particules - IN2P3, 74000 Annecy, France 26Instytut
Fizyki Ja̧drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
27Université Bordeaux, CNRS, LP2I Bordeaux, UMR 5797, F-33170 Gradignan,
France 28School of Physical Sciences, University of Adelaide, Adelaide 5005,
Australia 29Laboratoire Univers et Particules de Montpellier, Université
Montpellier, CNRS/IN2P3, CC 72, Place Eugène Bataillon, F-34095 Montpellier
Cedex 5, France 30Aix Marseille Université, CNRS/IN2P3, CPPM, Marseille,
France 31Universität Innsbruck, Institut für Astro- und Teilchenphysik,
Technikerstraße 25, 6020 Innsbruck, Austria 32Institute of Astronomy, Faculty
of Physics, Astronomy and Informatics, Nicolaus Copernicus University,
Grudziadzka 5, 87-100 Torun, Poland 33Department of Physics, Rikkyo
University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
34Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul.
Bartycka 18, 00-716 Warsaw, Poland 35Department of Physics and Astronomy, The
University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom
36GRAPPA, Anton Pannekoek Institute for Astronomy, University of Amsterdam,
Science Park 904, 1098 XH Amsterdam, The Netherlands 37Yerevan Physics
Institute, 2 Alikhanian Brothers St., 0036 Yerevan, Armenia 38Department of
Physics, Konan University, 8-9-1 Okamoto, Higashinada, Kobe, Hyogo 658-8501,
Japan 39Kavli Institute for the Physics and Mathematics of the Universe (WPI),
The University of Tokyo Institutes for Advanced Study (UTIAS), The University
of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa, Chiba, 277-8583, Japan 40RIKEN, 2-1
Hirosawa, Wako, Saitama 351-0198, Japan