-
F Aharonian,
A G Akhperjanian,
U Barres,
De Almeida,
A R Bazer-Bachi,
B Behera,
M Beilicke,
W Benbow,
K Bernï Ohr,
C Boisson, [......],
C Venter,
J P Vialle,
P Vincent,
M Vivier,
H J Völk,
F Volpe,
S J Wagner,
M Ward,
A A Zdziarski,
A Zech
[show abstract]
[hide abstract]
ABSTRACT: We report on the first completely simultaneous observation of a gamma-ray burst (GRB) using an array of Imaging Atmospheric Cherenkov Telescopes, which is sensitive to photons in the very high energy (VHE) γ -ray range (100 GeV). On 2006 June 2, the Swift Burst Alert Telescope (BAT) registered an unusually soft γ -ray burst (GRB 060602B). The burst position was under observation using the High Energy Stereoscopic System (HESS) at the time the burst occurred. Data were taken before, during, and after the burst. A total of 5 hr of observations were obtained during the night of 2006 June 2–3, and five additional hours were obtained over the next three nights. No VHE γ -ray signal was found during the period covered by the HESS observations. The 99% confidence level flux upper limit (> 1 TeV) for the prompt phase (9 s) of GRB 060602B is 2.9 × 10 −9 erg cm −2 s −1 . Due to the very soft BAT spectrum of the burst compared with other Swift GRBs and its proximity to the Galactic center, the burst is likely associated with a Galactic X-ray burster, although the possibility of it being a cosmological GRB cannot be ruled out. We discuss the implications of our flux limits in the context of these two bursting scenarios.
The Astrophysical Journal. 08/2015; 690:1068-1073.
-
H. E. S. S. Collaboration,
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
S. Balenderan,
A. Balzer,
A. Barnacka,
Y. Becherini, [......],
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
D. Wouters,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin
[show abstract]
[hide abstract]
ABSTRACT: The quasar PKS 1510-089 (z=0.361) was observed with the H.E.S.S. array of
imaging atmospheric Cherenkov telescopes during high states in the optical and
GeV bands, to search for very high energy (VHE, defined as E >= 0.1 TeV)
emission. VHE \gamma-rays were detected with a statistical significance of 9.2
standard deviations in 15.8 hours of H.E.S.S. data taken during March and April
2009. A VHE integral flux of I(0.15 TeV < E < 1.0 TeV) = (1.0 +- 0.2 (stat) +-
0.2 (sys) x 10^{-11} cm^{-2}s^{-1} is measured. The best-fit power law to the
VHE data has a photon index of \Gamma=5.4 +- 0.7 (stat) +- 0.3 (sys). The GeV
and optical light curves show pronounced variability during the period of
H.E.S.S. observations. However, there is insufficient evidence to claim
statistically significant variability in the VHE data. Because of its
relatively high redshift, the VHE flux from PKS 1510-089 should suffer
considerable attenuation in the intergalactic space due to the extragalactic
background light (EBL). Hence, the measured \gamma-ray spectrum is used to
derive upper limits on the opacity due to EBL, which are found to be comparable
with the previously derived limits from relatively-nearby BL Lac objects.
Unlike typical VHE-detected blazars where the broadband spectrum is dominated
by non-thermal radiation at all wavelengths, the quasar PKS 1510-089 has a
bright thermal component in the optical to UV frequency band. Among all VHE
detected blazars, PKS 1510-089 has the most luminous broad line region (BLR).
The detection of VHE emission from this quasar indicates a low level of
\gamma-\gamma absorption on the internal optical to UV photon field.
Astronomy and Astrophysics 04/2013; · 4.59 Impact Factor
-
H.E.S.S.~Collaboration,
A Abramowski,
F Acero, F Aharonian,
A ~G Akhperjanian,
G Anton,
S Balenderan,
A Balzer,
A Barnacka,
Y Becherini, [......],
M Ward,
R White,
A Wierzcholska,
P Willmann,
D Wouters,
M Zacharias,
A Zajczyk,
A ~A Zdziarski,
A Zech,
H -S Zechlin
åp. 03/2013; 551:A94.
-
H.E.S.S.~Collaboration,
A Abramowski,
F Acero, F Aharonian,
A ~G Akhperjanian,
G Anton,
S Balenderan,
A Balzer,
A Barnacka,
Y Becherini, [......],
S ~J Wagner,
M Ward,
R White,
A Wierzcholska,
D Wouters,
M Zacharias,
A Zajczyk,
A ~A Zdziarski,
A Zech,
H -S ~G Zechlin
åp. 03/2013; 551:A26.
-
H.E.S.S.~Collaboration,
A Abramowski,
F Acero, F Aharonian,
A ~G Akhperjanian,
G Anton,
S Balenderan,
A Balzer,
A Barnacka,
Y Becherini, [......],
M Ward,
R White,
A Wierzcholska,
P Willmann,
D Wouters,
M Zacharias,
A Zajczyk,
A ~A Zdziarski,
A Zech,
H -S Zechlin
åp. 03/2013; 551:A94.
-
H.E.S.S.~Collaboration,
A Abramowski,
F Acero, F Aharonian,
A ~G Akhperjanian,
G Anton,
S Balenderan,
A Balzer,
A Barnacka,
Y Becherini, [......],
S ~J Wagner,
M Ward,
R White,
A Wierzcholska,
D Wouters,
M Zacharias,
A Zajczyk,
A ~A Zdziarski,
A Zech,
H -S ~G Zechlin
åp. 03/2013; 551:A26.
-
H.E.S.S.~Collaboration,
A Abramowski,
F Acero, F Aharonian,
A ~G Akhperjanian,
G Anton,
S Balenderan,
A Balzer,
A Barnacka,
Y Becherini, [......],
S ~J Wagner,
M Ward,
R White,
A Wierzcholska,
D Wouters,
M Zacharias,
A Zajczyk,
A ~A Zdziarski,
A Zech,
H -S Zechlin
åp. 02/2013; 550:A4.
-
H.E.S.S.~Collaboration,
A Abramowski,
F Acero, F Aharonian,
A ~G Akhperjanian,
G Anton,
S Balenderan,
A Balzer,
A Barnacka,
Y Becherini, [......],
S ~J Wagner,
M Ward,
R White,
A Wierzcholska,
D Wouters,
M Zacharias,
A Zajczyk,
A ~A Zdziarski,
A Zech,
H -S Zechlin
åp. 02/2013; 550:A4.
-
A Abramowski,
F Acero, F Aharonian,
A ~G Akhperjanian,
G Anton,
S Balenderan,
A Balzer,
A Barnacka,
Y Becherini,
J Becker Tjus, [......],
S ~J Wagner,
M Ward,
R White,
A Wierzcholska,
D Wouters,
M Zacharias,
A Zajczyk,
A ~A Zdziarski,
A Zech,
H -S Zechlin
Physical Review Letters 01/2013; 110(4):041301. · 7.37 Impact Factor
-
A Abramowski,
F Acero, F Aharonian,
A ~G Akhperjanian,
G Anton,
S Balenderan,
A Balzer,
A Barnacka,
Y Becherini,
J Becker Tjus, [......],
S ~J Wagner,
M Ward,
R White,
A Wierzcholska,
D Wouters,
M Zacharias,
A Zajczyk,
A ~A Zdziarski,
A Zech,
H -S Zechlin
Physical Review Letters 01/2013; 110(4):041301. · 7.37 Impact Factor
-
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
S. Balenderan,
A. Balzer,
A. Barnacka,
Y. Becherini,
J. Becker Tjus, [......],
M. deNaurois,
D. Nedbal,
N. Nguyen,
J. Niemiec,
S. J. Nolan,
S. Ohm,
E. deOñ aWilhelmi,
B. Opitz,
M. Ostrowski,
I. Oya
-
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
S. Balenderan,
A. Balzer,
A. Barnacka,
Y. Becherini,
J. Becker Tjus, [......],
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
D. Wouters,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin
[show abstract]
[hide abstract]
ABSTRACT: Vela X is a region of extended radio emission in the western part of the Vela constellation: one of the nearest pulsar wind nebulae (PWNe), and associated with the energetic Vela pulsar (PSR B0833-45). Extended very-high-energy (VHE) $\gamma$-ray emission (HESS J0835-455}) was discovered using the H.E.S.S. experiment in 2004. The VHE $\gamma$-ray emission was found to be coincident with a region of X-ray emission discovered with ${\it ROSAT}$ above 1.5 keV (the so-called \textit{Vela X cocoon}): a filamentary structure extending southwest from the pulsar to the centre of Vela X. A deeper observation of the entire Vela X nebula region, also including larger offsets from the cocoon, has been performed with H.E.S.S. This re-observation was carried out in order to probe the extent of the non-thermal emission from the Vela X region at TeV energies and to investigate its spectral properties. In order to increase the sensitivity to the faint $\gamma$-ray emission from the very extended Vela X region, a multivariate analysis method combining three complementary reconstruction techniques of Cherenkov-shower images is applied for the selection of $\gamma$-ray events. The analysis is performed with the On/Off background method, which estimates the background from separate observations pointing away from Vela X; towards regions free of $\gamma$-ray sources but with comparable observation conditions. The $\gamma$-ray surface brightness over the large Vela X region reveals that the detection of non-thermal VHE $\gamma$-ray emission from the PWN HESS J0835-455 is statistically significant over a region of radius 1.2$^{\circ}$ around the position $\alpha$ = 08h 35m 00s,
$\delta$ = -45$^{\circ}$ 36' 00'' (J2000).
Astronomy and Astrophysics 12/2012; 548:38. · 4.59 Impact Factor
-
HESS Collaboration,
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
S. Balenderan,
A. Balzer,
A. Barnacka,
Y. Becherini, [......],
M. Vorster,
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin
[show abstract]
[hide abstract]
ABSTRACT: We present the significant detection of the first extragalactic pulsar wind
nebula (PWN) detected in gamma rays, N157B, located in the large Magellanic
Cloud (LMC). Pulsars with high spin-down luminosity are found to power
energised nebulae that emit gamma rays up to energies of several tens of TeV.
N157B is associated with PSRJ0537-6910, which is the pulsar with the highest
known spin-down luminosity. The High Energy Stereoscopic System telescope array
observed this nebula on a yearly basis from 2004 to 2009 with a dead-time
corrected exposure of 46 h. The gamma-ray spectrum between 600 GeV and 12 TeV
is well-described by a pure power-law with a photon index of 2.8 \pm 0.2(stat)
\pm 0.3(syst) and a normalisation at 1 TeV of (8.2 \pm 0.8(stat) \pm 2.5(syst))
\times 10^-13 cm^-2s^-1TeV^-1. A leptonic multi-wavelength model shows that an
energy of about 4 \times 10^49erg is stored in electrons and positrons. The
apparent efficiency, which is the ratio of the TeV gamma-ray luminosity to the
pulsar's spindown luminosity, 0.08% \pm 0.01%, is comparable to those of PWNe
found in the Milky Way. The detection of a PWN at such a large distance is
possible due to the pulsar's favourable spin-down luminosity and a bright
infrared photon-field serving as an inverse-Compton-scattering target for
accelerated leptons. By applying a calorimetric technique to these
observations, the pulsar's birth period is estimated to be shorter than 10 ms.
Astronomy and Astrophysics 09/2012; 545:2. · 4.59 Impact Factor
-
HESS Collaboration,
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
S. Balenderan,
A. Balzer,
A. Barnacka,
Y. Becherini, [......],
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin,
M. O. Ali
[show abstract]
[hide abstract]
ABSTRACT: In some galaxy clusters powerful AGN have blown bubbles with cluster scale extent into the ambient medium. The main pressure support of these bubbles is not known to date, but cosmic rays are a viable possibility. For such a scenario copious gamma-ray emission is expected as a tracer of cosmic rays from
these systems. Hydra A, the closest galaxy cluster hosting a cluster scale AGN outburst, located at a redshift of 0.0538, is investigated for being a gamma-ray emitter with the High Energy Stereoscopic System (H.E.S.S.) array and the Fermi Large Area Telescope (Fermi-LAT). Data obtained in 20.2 hours of
dedicated H.E.S.S. observations and 38 months of Fermi-LAT data, gathered by its usual all-sky scanning mode, have been analyzed to search for a gamma-ray signal. No signal has been found in either data set. Upper limits on the gamma-ray flux are derived and are compared to models. These are the first limits on gamma-ray emission ever presented for galaxy clusters hosting cluster scale AGN outbursts. The non-detection of Hydra A in gamma-rays has important implications on the particle populations and physical conditions inside the bubbles in this system. For the case of bubbles mainly supported by hadronic cosmic rays, the most favorable scenario, that involves full mixing between cosmic rays and embedding medium, can be excluded. However, hadronic cosmic rays still remain a viable pressure support agent to sustain the bubbles against the thermal pressure of the ambient medium. The largest population of highly-energetic electrons which are relevant for inverse-Compton gamma-ray production is found in the youngest inner lobes of Hydra A. The limit on the inverse-Compton gamma-ray flux excludes a magnetic field below half of the equipartition value of 16 muG in the inner lobes.
Astronomy and Astrophysics 08/2012; 545:103. · 4.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The evidence of a line-like spectral feature at 130 GeV recently reported
from some parts of the galactic plane poses serious challenges for any
interpretation of this surprise discovery. It is generally believed that the
unusually narrow profile of the spectral line cannot be explained by
conventional processes in astrophysical objects, and, if real, is likely to be
associated with Dark Matter. In this paper we argue that cold ultrarelativistic
pulsar winds can be alternative sources of very narrow gamma-ray lines. We
demonstrate that Comptonization of a cold ultrarelativistic electron-positron
pulsar wind in the deep Klein-Nishina regime can readily provide very narrow
distinct gamma-ray line features. To verify this prediction, we produced photon
count maps based on the Fermi LAT data in the energy interval 100 to 140 GeV.
We confirm earlier reports of the presence of marginal gamma-ray line-like
signals from three regions of the galactic plane. Although the maps show some
structure inside these regions, unfortunately the limited photon statistics do
not allow any firm conclusion in this regard. The confirmation of 130 GeV line
emission by low-energy threshold atmospheric Cherenkov telescope systems, in
particular by the new 27 m diameter dish of the H.E.S.S. array, would be
crucial for resolving the spatial structure of the reported hotspots, and thus
for distinguishing between the Dark Matter and Pulsar origins of the `Fermi
Lines'.
07/2012;
-
H. E. S. S. Collaboration,
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
A. Balzer,
A. Barnacka,
Y. Becherini,
J. Becker, [......],
M. Vorster,
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin
[show abstract]
[hide abstract]
ABSTRACT: Very-high-energy (VHE; E >100 GeV) and high-energy (HE; 100 MeV < E < 100 GeV) data from \gamma-ray observations performed with the H.E.S.S. telescope array and the Fermi-LAT instrument, respectively, are analysed in order to investigate the non-thermal processes in the starburst galaxy NGC 253. The VHE
\gamma-ray data can be described by a power law in energy with differential photon index \Gamma=2.14 \pm 0.18_stat \pm 0.30_sys and differential flux normalisation at 1 TeV of F_0 = (9.6 \pm 1.5_stat (+5.7,-2.9)_sys) x 10^{-14} TeV^{-1} cm^{-2} s^{-1}. A power-law fit to the differential HE \gamma-ray
spectrum reveals a photon index of \Gamma=2.24 \pm 0.14_stat \pm 0.03_sys and an integral flux between 200 MeV and 200 GeV of F(0.2-200 GeV) = (4.9 \pm 1.0_stat \pm 0.3_sys) x 10^{-9} cm^{-2} s^{-1}. No evidence for a spectral break or turnover is found over the dynamic range of both the LAT instrument
and the H.E.S.S. experiment: a combined fit of a power law to the HE and VHE \gamma-ray data results in a differential photon index \Gamma=2.34 \pm 0.03 with a p-value of 30%. The \gamma-ray observations indicate that at least about 20% of the energy of the cosmic rays capable of producing hadronic interactions is channeled into pion production. The smooth alignment between the spectra in
the HE and VHE \gamma-ray domain suggests that the same transport processes dominate in the entire energy range. Advection is most likely responsible for charged particle removal from the starburst nucleus from GeV to multiple TeV energies. In a hadronic scenario for the \gamma-ray production, the single
overall power-law spectrum observed would therefore correspond to the mean energy spectrum produced by the ensemble of cosmic-ray sources in the starburst region.
The Astrophysical Journal 05/2012; 757:158. · 6.02 Impact Factor
-
HESS Collaboration,
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
A. Balzer,
A. Barnacka,
Y. Becherini,
J. Becker, [......],
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin,
T. Montmerle
[show abstract]
[hide abstract]
ABSTRACT: The massive binary system Eta Carinae and the surrounding HII complex, the Carina Nebula, are potential particle acceleration sites from which very-high-energy (VHE; E > 100 GeV) \gamma-ray emission could be expected. This paper presents data collected during VHE \gamma-ray observations with the H.E.S.S. telescope array from 2004 to 2010, which cover a full orbit of Eta Carinae. In the 33.1-hour data set no hint of significant \gamma-ray emission from Eta Carinae has been found and an upper limit on the \gamma-ray flux of 7.7 x 10-13 ph cm-2 s-1 (99% confidence level) is derived above the energy
threshold of 470 GeV. Together with the detection of high-energy (HE; 0.1 GeV >
E > 100 GeV) \gamma-ray emission by the Fermi-LAT up to 100 GeV, and assuming a continuation of the average HE spectral index into the VHE domain, these results imply a cut-off in the \gamma-ray spectrum between the HE and VHE \gamma-ray range. This could be caused either by a cut-off in the accelerated
particle distribution or by severe \gamma-\gamma\ absorption losses in the wind collision region. Furthermore, the search for extended \gamma-ray emission from the Carina Nebula resulted in an upper limit on the \gamma-ray flux of 4.2 x 10-12 ph cm-2 s-1 (99% confidence level). The derived upper limit of ~23 on the cosmic-ray enhancement factor is compared with results found for the old-age
mixed-morphology supernova remnant W 28.
Monthly Notices of the Royal Astronomical Society 04/2012; 424:128. · 4.90 Impact Factor
-
HESS Collaboration,
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
A. Balzer,
A. Barnacka,
Y. Becherini,
J. Becker, [......],
M. Vorster,
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin
[show abstract]
[hide abstract]
ABSTRACT: 1RXS J101015.9-311909 is a galaxy located at a redshift of z=0.14 hosting an active nucleus belonging to the class of bright BL Lac objects. Observations at high (HE, E > 100 MeV) and very high (VHE, E > 100 GeV) energies provide insights into the origin of very energetic particles present in such sources
and the radiation processes at work. We report on results from VHE observations performed between 2006-10 with H.E.S.S. H.E.S.S. data have been analysed with enhanced analysis methods, making the detection of faint sources more significant. VHE emission at a position coincident with 1RXS J101015.9-311909 is detected with H.E.S.S. for the first time. In a total good-quality livetime of about 49 h, we measure 263 excess counts, corresponding to a significance of 7.1\sigma. The photon spectrum above 0.2 TeV can be described by a power-law with a photon index of \Gamma\ = 3.08\pm0.42_{stat}\pm0.20_{sys}. The integral flux above 0.2 TeV is about 0.8% of the flux of the Crab nebula and shows no
significant variability over the time reported. In addition, public Fermi/LAT data are analysed to search for high energy emission from the source. The Fermi/LAT HE emission is significant at 8.3\sigma\ in the chosen 25-month dataset. UV and X-ray contemporaneous observations with the Swift satellite in May 2007 are also reported, together with optical observations performed with the ATOM telescope located at the H.E.S.S. site. Swift observations reveal an absorbed X-ray flux of F_{0.3-7 keV} = 1.04^{+0.04}_{-0.05} \times 10^{-11} erg.cm^{-2}.s^{-1} in the 0.3-7 keV range. Finally, all the available data are used to study the source's multi-wavelength properties. The SED can be reproduced using a simple one-zone SSC model with emission from a region with a Doppler factor of 30 and a magnetic field between 0.025 and 0.16 G. These parameters are similar to those obtained for other sources of this type.
Astronomy and Astrophysics 04/2012; 542:94. · 4.59 Impact Factor
-
HESS Collaboration,
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
A. Balzer,
A. Barnacka,
U. Barres de Almeida,
Y. Becherini, [......],
M. Vorster,
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin
[show abstract]
[hide abstract]
ABSTRACT: The observational coverage with HESS of the Carina region in VHE gamma-rays benefits from deep exposure (40 h) of the neighboring open cluster Westerlund 2. The observations have revealed a new extended region of VHE gamma-ray emission. The new VHE source HESS J1018-589 shows a bright, point-like emission region positionally coincident with SNR G284.3-1.8 and 1FGL J1018.6 - 5856 and
a diffuse extension towards the direction of PSR J1016-5857. A soft Gamma=2.7+-0.5 photon index, with a differential flux at 1TeV of N0=(4.2+-1.1)10^-13 TeV^-1 cm^-2 s^-1 is found for the point-like source, whereas the total emission region including the diffuse emission region is well fit by a power-law function with spectral index Gamma=2.9+-0.4 and differential flux at 1TeV of N0=(6.8+-1.6) 10^-13 TeV^-1 cm^-2 s^-1. This H.E.S.S. detection motivated follow-up X-ray observations with the XMM-Newton satellite to
investigate the origin of the VHE emission. The analysis of the XMM-Newton data resulted in the discovery of a bright, non-thermal point-like source (XMMU J101855.4-58564) with a photon index of Gamma=1.65+-0.08 in the center of SNRG284.3-1.8, and a thermal, extended emission region coincident with its bright northern filament. The characteristics of this thermal emission are used to estimate the plasma density in the region as n~0.5 cm^-3(2.9kpc/d)^2. The position of XMMUJ101855.4-58564 is compatible with the position reported by the Fermi-LAT collaboration for the binary system 1FGL J1018.6-5856 and the variable Swift XRT source identified with it. The new X-ray data are used
alongside archival multi-wavelength data to investigate the relationship between the VHE gamma-ray emission from HESSJ1018-589 and the various potential counterparts in the Carina arm region.
Astronomy and Astrophysics 03/2012; 541:5. · 4.59 Impact Factor
-
HESS Collaboration,
A. Abramowski,
F. Acero, F. Aharonian,
A. G. Akhperjanian,
G. Anton,
A. Balzer,
A. Barnacka,
U. Barres de Almeida,
Y. Becherini, [......],
M. Vorster,
S. J. Wagner,
M. Ward,
R. White,
A. Wierzcholska,
M. Zacharias,
A. Zajczyk,
A. A. Zdziarski,
A. Zech,
H. -S. Zechlin
[show abstract]
[hide abstract]
ABSTRACT: The Fornax galaxy cluster was observed with the High Energy Stereoscopic System (H.E.S.S.) for a total live time of 14.5 hours, searching for very-high-energy (VHE, E>100 GeV) gamma-rays from dark matter (DM) annihilation. No significant signal was found in searches for point-like and extended emissions. Using several models of the DM density distribution, upper limits on the DM velocity-weighted annihilation cross-section as a function of the DM particle mass are derived. Constraints are derived for different DM particle models, such as those arising from Kaluza-Klein and supersymmetric models. Various annihilation final states are considered. Possible enhancements of the DM annihilation gamma-ray flux, due to DM substructures of the DM host halo, or from the Sommerfeld effect, are studied. Additional gamma-ray contributions from internal bremsstrahlung and inverse Compton radiation are also discussed. For a DM particle mass of 1 TeV, the exclusion limits at 95% of confidence level reach values of ~10^-23cm^3s^-1, depending on the DM particle model and halo properties. Additional contribution from DM substructures can improve the upper limits on <\sigma v> by more than two orders of magnitude. At masses around 4.5 TeV, the enhancement by substructures and the Sommerfeld resonance effect results in a velocity-weighted annihilation cross-section upper limit at the level of <\sigma v> ~ 10^-26cm^3s^-1.
The Astrophysical Journal 02/2012; 750:123. · 6.02 Impact Factor
