677 research outputs found
Determination of the Night Sky Background around the Crab pulsar using its optical pulsation
The poor angular resolution of imaging gamma-ray telescopes is offset by the
large reflector areas of next generation telescopes such as MAGIC (17~m
diameter), which makes the study of optical emission associated with some
gamma-ray sources feasible. Furthermore, the extremely fast time response of
photomultipliers (PMs) makes them ideal detectors for fast (subsecond) optical
transients and periodic sources like pulsars. The optical pulse of the Crab
pulsar was detected with the HEGRA CT1 central pixel using a modified PM,
similar to the future MAGIC camera PMs. The purpose of these periodic
observations was to determine the light of the night sky (LONS) for the
galactic anticenter Crab region.Our results are between 2.5 and 3 times larger
than the previously measured LONS (outside the galactic plane), as expected
since the Crab pulsar is in the galactic plane, which implies a slightly higher
energy threshold for Crab observations, if the higher value of CT1 measured
LONS rate for galactic sources is used.Comment: 19 pages, 6 figures, accepted by Astroparticle Physic
Application of an analysis method based on a semi-analytical shower model to the first H.E.S.S. telescope
Application of an analysis method based on a semi-analytical shower model to the first H.E.S.S. telescope
H.E.S.S. observations of galaxy clusters
Clusters of galaxies, the largest gravitationally bound objects in the
universe, are expected to contain a significant population of hadronic and
leptonic cosmic rays. Potential sources for these particles are merger and
accretion shocks, starburst driven galactic winds and radio galaxies.
Furthermore, since galaxy clusters confine cosmic ray protons up to energies of
at least 1 PeV for a time longer than the Hubble time they act as storehouses
and accumulate all the hadronic particles which are accelerated within them.
Consequently clusters of galaxies are potential sources of VHE (> 100 GeV)
gamma rays. Motivated by these considerations, promising galaxy clusters are
observed with the H.E.S.S. experiment as part of an ongoing campaign. Here,
upper limits for the VHE gamma ray emission for the Abell 496 and Coma cluster
systems are reported.Comment: Contribution to the 30th ICRC, Merida Mexico, July 200
New AGNs discovered by H.E.S.S
During the last year, six new Active Galactic Nuclei (AGN) have been
discovered and studied by H.E.S.S. at Very High Energies (VHE). Some of these
recent discoveries have been made thanks to new enhanced analysis methods and
are presented at this conference for the first time. The three blazars 1ES
0414+009, SHBL J001355.9-185406 and 1RXS J101015.9-311909 have been targeted
for observation due to their high levels of radio and X-ray fluxes, while the
Fermi/LAT catalogue of bright sources triggered the observation of PKS 0447-439
and AP Librae. Additionally, the BL Lac 1ES 1312-423 was discovered in the
field-of-view (FoV) of Centaurus A thanks to the large exposure dedicated by
H.E.S.S. to this particularly interesting source. The newly-discovered sources
are presented here and in three companion presentations at this conference.Comment: 8 pages, 3 figures, proceeding from the 25th Texas Symposium on
Relativistic Astrophysics (Heidelberg, Germany, 2010
Extreme Blazars Studied with Fermi-LAT and Suzaku: 1ES 0347-121 and Blazar Candidate HESS J1943+213
We report on our study of high-energy properties of two peculiar TeV
emitters: the "extreme blazar" 1ES 0347-121 and the "extreme blazar candidate"
HESS J1943+213 located near the Galactic Plane. Both objects are characterized
by quiescent synchrotron emission with flat spectra extending up to the hard
X-ray range, and both were reported to be missing GeV counterparts in the
Fermi-LAT 2-year Source Catalog. We analyze a 4.5 year accumulation of the
Fermi-LAT data, resulting in the detection of 1ES 0347-121 in the GeV band, as
well as in improved upper limits for HESS J1943+213. We also present the
analysis results of newly acquired Suzaku data for HESS J1943+213. The X-ray
spectrum is well represented by a single power law extending up to 25 keV with
photon index 2.00+/-0.02 and a moderate absorption in excess of the Galactic
value, in agreement with previous X-ray observations. No short-term X-ray
variability was found over the 80 ks duration of the Suzaku exposure. Under the
blazar hypothesis, we modeled the spectral energy distributions of 1ES 0347-121
and HESS J1943+213, and derived constraints on the intergalactic magnetic field
strength and source energetics. We conclude that although the classification of
HESS J1943+213 has not yet been determined, the blazar hypothesis remains the
most plausible option, since in particular the broad-band spectra of the two
analyzed sources along with the source model parameters closely resemble each
other, and the newly available WISE and UKIDSS data for HESS J1943+213 are
consistent with the presence of an elliptical host at the distance of
approximately ~600 Mpc.Comment: 10 pages, 7 figures, 3 tables. Accepted by Ap
Observations of the Crab Nebula with H.E.S.S. Phase II
The High Energy Stereoscopic System (H.E.S.S.) phase I instrument was an
array of four mirror area Imaging Atmospheric Cherenkov
Telescopes (IACTs) that has very successfully mapped the sky at photon energies
above GeV. Recently, a telescope was added to
the centre of the existing array, which can be operated either in standalone
mode or jointly with the four smaller telescopes. The large telescope lowers
the energy threshold for gamma-ray observations to several tens of GeV, making
the array sensitive at energies where the Fermi-LAT instrument runs out of
statistics. At the same time, the new telescope makes the H.E.S.S. phase II
instrument. This is the first hybrid IACT array, as it operates telescopes of
different size (and hence different trigger rates) and different field of view.
In this contribution we present results of H.E.S.S. phase II observations of
the Crab Nebula, compare them to earlier observations, and evaluate the
performance of the new instrument with Monte Carlo simulations.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
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