We report the discovery of faint very high energy (VHE; E > 100 GeV) g-ray emission from the radio galaxy Centaurus A in observations performed with the High Energy Stereoscopic System (H.E.S.S.) ...experiment, an imaging atmospheric Cherenkov telescope array consisting of four telescopes located in Namibia. Centaurus A has been observed for more than 120 hr. A signal with a statistical significance of 5.0s is detected from the region including the radio core and the inner kpc jets. The integral flux above an energy threshold of ~250 GeV is measured to be 0.8% of the flux of the Crab Nebula (apparent luminosity: L(>250 GeV) 2.6 X 1039 erg s-1, adopting a distance of 3.8 Mpc). The spectrum can be described by a power law with a photon index of 2.7 ± 0.5stat ± 0.2sys. No significant flux variability is detected in the data set. However, the low flux only allows detection of variability on the timescale of days to flux increments above a factor of ~15-20 (3s and 4s, respectively). The discovery of VHE g-ray emission from Centaurus A reveals particle acceleration in the source to >TeV energies and, together with M 87, establishes radio galaxies as a class of VHE emitters.
The Outer Tracker detector of the HERA-B experiment—Part I: Detector Albrecht, H.; Bauer, Th.S.; Beck, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2005, Volume:
555, Issue:
1
Journal Article
Peer reviewed
Open access
The HERA-B Outer Tracker is a large system of planar drift chambers with about 113
000 read-out channels. Its inner part has been designed to be exposed to a particle flux of up to
2
×
10
5
cm
-
2
s
...-
1
, thus coping with conditions similar to those expected for future hadron collider experiments. Thirteen superlayers, each consisting of two individual chambers, have been assembled and installed in the experiment. The stereo layers inside each chamber are composed of honeycomb drift tube modules with 5 and
10
mm
diameter cells. Chamber aging is prevented by coating the cathode foils with thin layers of copper and gold, together with a proper drift gas choice. Longitudinal wire segmentation is used to limit the occupancy in the most irradiated detector regions to about 20%. The production of 978 modules was distributed among six different laboratories and took 15 months. For all materials in the fiducial region of the detector good compromises of stability versus thickness were found. A closed-loop gas system supplies the Ar/CF
4/CO
2 gas mixture to all chambers. The successful operation of the HERA-B Outer Tracker shows that a large tracker can be efficiently built and safely operated under huge radiation load at a hadron collider.
In this paper we describe the operation and performance of the HERA-B Outer Tracker, a 112
674 channel system of planar drift tube layers. The performance of the HERA-B Outer Tracker system ...fullfilled all requirements for stable and efficient operation in a hadronic environment, thus confirming the adequacy of the honeycomb drift tube technology and of the front-end readout system. The detector was stably operated with a gas gain of
3
×
10
4
in an
Ar
/
CF
4
/
CO
2
(65:35:5) gas mixture, yielding a good efficiency for triggering and track reconstruction, larger than 95% for tracks with momenta above
5
GeV
/
c
. The hit resolution of the drift cells was 300–
320
μ
m
and the relative momentum resolution can be described as:
σ
(
p
)
/
p
%
=
(
1.61
±
0.02
)
+
(
0.0051
±
0.0006
)
·
p
GeV
/
c
. At the end of the HERA-B running no aging effects in the Outer Tracker cells were observed.
Observations with imaging atmospheric Cherenkov telescopes (IACTs) have enhanced our knowledge of nearby supernova (SN) remnants with ages younger than 500 years by establishing Cassiopeia A and the ...remnant of Tycho's SN as very-high-energy (VHE) gamma-ray sources. The remnant of Kepler's SN, which is the product of the most recent naked-eye supernova in our Galaxy, is comparable in age to the other two, but is significantly more distant. If the gamma-ray luminosities of the remnants of Tycho's and Kepler's SNe are similar, then the latter is expected to be one of the faintest gamma-ray sources within reach of the current generation IACT arrays. Here we report evidence at a statistical level of 4.6 sigma for a VHE signal from the remnant of Kepler's SN based on deep observations by the High Energy Stereoscopic System (H.E.S.S.) with an exposure of 152 hours. The measured integral flux above an energy of 226 GeV is ~0.3% of the flux of the Crab Nebula. The spectral energy distribution (SED) reveals a gamma-ray emitting component connecting the VHE emission observed with H.E.S.S. to the emission observed at GeV energies with Fermi-LAT. The overall SED is similar to that of the remnant of Tycho's SN, possibly indicating the same non-thermal emission processes acting in both these young remnants of thermonuclear SNe.
Aims: The BL Lac object RGB J0152+017 (z=0.080) was predicted to be a very high-energy (VHE; > 100 GeV) gamma-ray source, due to its high X-ray and radio fluxes. Our aim is to understand the ...radiative processes by investigating the observed emission and its production mechanism using the High Energy Stereoscopic System (H.E.S.S.) experiment. Methods: We report recent observations of the BL Lac source RGB J0152+017 made in late October and November 2007 with the H.E.S.S. array consisting of four imaging atmospheric Cherenkov telescopes. Contemporaneous observations were made in X-rays by the Swift and RXTE satellites, in the optical band with the ATOM telescope, and in the radio band with the Nancay Radio Telescope. Results: A signal of 173 gamma-ray photons corresponding to a statistical significance of 6.6 sigma was found in the data. The energy spectrum of the source can be described by a powerlaw with a spectral index of 2.95+/-0.36stat+/-0.20syst. The integral flux above 300 GeV corresponds to ~2% of the flux of the Crab nebula. The source spectral energy distribution (SED) can be described using a two-component non-thermal synchrotron self-Compton (SSC) leptonic model, except in the optical band, which is dominated by a thermal host galaxy component. The parameters that are found are very close to those found in similar SSC studies in TeV blazars. Conclusions: RGB J0152+017 is discovered as a source of VHE gamma-rays by H.E.S.S. The location of its synchrotron peak, as derived from the SED in Swift data, allows clearly classification it as a high-frequency-peaked BL Lac (HBL).
SS 433 is a microquasar, a stellar binary system with collimated relativistic jets. We observed SS 433 in gamma rays using the High Energy Stereoscopic System (H.E.S.S.), finding an energy-dependent ...shift in the apparent position of the gamma-ray emission of the parsec-scale jets. These observations trace the energetic electron population and indicate the gamma rays are produced by inverse-Compton scattering. Modelling of the energy-dependent gamma-ray morphology constrains the location of particle acceleration and requires an abrupt deceleration of the jet flow. We infer the presence of shocks on either side of the binary system at distances of 25 to 30 parsecs and conclude that self-collimation of the precessing jets forms the shocks, which then efficiently accelerate electrons.
PDF
