450 research outputs found
Phase-resolved Crab pulsar measurements from 25 to 400 GeV with the MAGIC telescopes
We report on observations of the Crab pulsar with the MAGIC telescopes. Our
data were taken in both monoscopic (> 25GeV) and stereoscopic (> 50GeV)
observation modes. Two peaks were detected with both modes and phase-resolved
energy spectra were calculated. By comparing with Fermi- LAT measurements, we
find that the energy spectrum of the Crab pulsar does not follow a power law
with an exponential cutoff, but has an additional hard component, extending up
to at least 400 GeV. This suggests that the emission above 25 GeV is not
dominated by curvature radiation, as suggested in the standard scenarios of the
OG and SG models.Comment: 4 pages, 2 figures, Proc. TAUP 2011, submitted for publication in
JCP
A major electronics upgrade for the H.E.S.S. Cherenkov telescopes 1-4
The High Energy Stereoscopic System (H.E.S.S.) is an array of imaging
atmospheric Cherenkov telescopes (IACTs) located in the Khomas Highland in
Namibia. It consists of four 12-m telescopes (CT1-4), which started operations
in 2003, and a 28-m diameter one (CT5), which was brought online in 2012. It is
the only IACT system featuring telescopes of different sizes, which provides
sensitivity for gamma rays across a very wide energy range, from ~30 GeV up to
~100 TeV. Since the camera electronics of CT1-4 are much older than the one of
CT5, an upgrade is being carried out; first deployment was in 2015, full
operation is planned for 2016. The goals of this upgrade are threefold:
reducing the dead time of the cameras, improving the overall performance of the
array and reducing the system failure rate related to aging. Upon completion,
the upgrade will assure the continuous operation of H.E.S.S. at its full
sensitivity until and possibly beyond the advent of CTA. In the design of the
new components, several CTA concepts and technologies were used and are thus
being evaluated in the field: The upgraded read-out electronics is based on the
NECTAR readout chips; the new camera front- and back-end control subsystems are
based on an FPGA and an embedded ARM computer; the communication between
subsystems is based on standard Ethernet technologies. These hardware solutions
offer good performance, robustness and flexibility. The design of the new
cameras is reported here.Comment: Proceedings of the 34th International Cosmic Ray Conference, 30 July-
6 August, 2015, The Hague, The Netherland
MAGIC Upper Limits for two Milagro-detected, Bright Fermi Sources in the Region of SNR G65.1+0.6
We report on the observation of the region around supernova remnant G65.1+0.6
with the stand-alone MAGIC-I telescope. This region hosts the two bright GeV
gamma-ray sources 1FGL J1954.3+2836 and 1FGL J1958.6+2845. They are identified
as GeV pulsars and both have a possible counterpart detected at about 35 TeV by
the Milagro observatory. MAGIC collected 25.5 hours of good quality data, and
found no significant emission in the range around 1 TeV. We therefore report
differential flux upper limits, assuming the emission to be point-like (<0.1
deg) or within a radius of 0.3 deg. In the point-like scenario, the flux limits
around 1 TeV are at the level of 3 % and 2 % of the Crab Nebula flux, for the
two sources respectively. This implies that the Milagro emission is either
extended over a much larger area than our point spread function, or it must be
peaked at energies beyond 1 TeV, resulting in a photon index harder than 2.2 in
the TeV band.Comment: 8 pages, 3 figures, 1 tabl
Simultaneous multi-frequency observation of the unknown redshift blazar PG 1553+113 in March-April 2008
The blazar PG 1553+113 is a well known TeV gamma-ray emitter. In this paper,
we determine its spectral energy distribution using simultaneous
multi-frequency data in order to study its emission processes. An extensive
campaign was carried out between March and April 2008, where optical, X-ray,
high-energy (HE) gamma-ray, and very-high-energy (VHE) gamma-ray data were
obtained with the KVA, Abastumani, REM, RossiXTE/ASM, AGILE and MAGIC
telescopes, respectively. This is the first simultaneous broad-band (i.e.,
HE+VHE) gamma-ray observation, though AGILE did not detect the source. We
combine data to derive source's spectral energy distribution and interpret its
double peaked shape within the framework of a synchrotron self compton modelComment: 5 pages, 2 figures, publishe
Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3
Context. Recently, the high-energy (HE, 0.1-100 GeV) -ray emission
from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered
to be modulated with a 10.3-day period, making it the first extra-galactic
-ray binary.
Aims. This work aims at the detection of very-high-energy (VHE, >100 GeV)
-ray emission and the search for modulation of the VHE signal with the
orbital period of the binary system.
Methods. LMC P3 has been observed with the High Energy Stereoscopic System
(H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has
been folded with the known orbital period of the system in order to test for
variability of the emission. Energy spectra are obtained for the orbit-averaged
data set, and for the orbital phase bin around the VHE maximum.
Results. VHE -ray emission is detected with a statistical
significance of 6.4 . The data clearly show variability which is
phase-locked to the orbital period of the system. Periodicity cannot be deduced
from the H.E.S.S. data set alone. The orbit-averaged luminosity in the
TeV energy range is erg/s. A luminosity of erg/s is reached during 20% of the orbit. HE and VHE
-ray emissions are anti-correlated. LMC P3 is the most luminous
-ray binary known so far.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&
Lateral Distribution of Muons in IceCube Cosmic Ray Events
In cosmic ray air showers, the muon lateral separation from the center of the
shower is a measure of the transverse momentum that the muon parent acquired in
the cosmic ray interaction. IceCube has observed cosmic ray interactions that
produce muons laterally separated by up to 400 m from the shower core, a factor
of 6 larger distance than previous measurements. These muons originate in high
pT (> 2 GeV/c) interactions from the incident cosmic ray, or high-energy
secondary interactions. The separation distribution shows a transition to a
power law at large values, indicating the presence of a hard pT component that
can be described by perturbative quantum chromodynamics. However, the rates and
the zenith angle distributions of these events are not well reproduced with the
cosmic ray models tested here, even those that include charm interactions. This
discrepancy may be explained by a larger fraction of kaons and charmed
particles than is currently incorporated in the simulations
Detailed spectral and morphological analysis of the shell type SNR RCW 86
Aims: We aim for an understanding of the morphological and spectral
properties of the supernova remnant RCW~86 and for insights into the production
mechanism leading to the RCW~86 very high-energy gamma-ray emission. Methods:
We analyzed High Energy Spectroscopic System data that had increased
sensitivity compared to the observations presented in the RCW~86 H.E.S.S.
discovery publication. Studies of the morphological correlation between the
0.5-1~keV X-ray band, the 2-5~keV X-ray band, radio, and gamma-ray emissions
have been performed as well as broadband modeling of the spectral energy
distribution with two different emission models. Results:We present the first
conclusive evidence that the TeV gamma-ray emission region is shell-like based
on our morphological studies. The comparison with 2-5~keV X-ray data reveals a
correlation with the 0.4-50~TeV gamma-ray emission.The spectrum of RCW~86 is
best described by a power law with an exponential cutoff at TeV and a spectral index of ~. A static
leptonic one-zone model adequately describes the measured spectral energy
distribution of RCW~86, with the resultant total kinetic energy of the
electrons above 1 GeV being equivalent to 0.1\% of the initial kinetic
energy of a Type I a supernova explosion. When using a hadronic model, a
magnetic field of ~100G is needed to represent the measured data.
Although this is comparable to formerly published estimates, a standard
E spectrum for the proton distribution cannot describe the gamma-ray
data. Instead, a spectral index of ~1.7 would be required, which
implies that ~erg has been transferred into
high-energy protons with the effective density cm^-3. This
is about 10\% of the kinetic energy of a typical Type Ia supernova under the
assumption of a density of 1~cm^-3.Comment: accepted for publication by A&
Characterizing the gamma-ray long-term variability of PKS 2155-304 with H.E.S.S. and Fermi-LAT
Studying the temporal variability of BL Lac objects at the highest energies
provides unique insights into the extreme physical processes occurring in
relativistic jets and in the vicinity of super-massive black holes. To this
end, the long-term variability of the BL Lac object PKS 2155-304 is analyzed in
the high (HE, 100 MeV 200 GeV)
gamma-ray domain. Over the course of ~9 yr of H.E.S.S observations the VHE
light curve in the quiescent state is consistent with a log-normal behavior.
The VHE variability in this state is well described by flicker noise
(power-spectral-density index {\ss}_VHE = 1.10 +0.10 -0.13) on time scales
larger than one day. An analysis of 5.5 yr of HE Fermi LAT data gives
consistent results ({\ss}_HE = 1.20 +0.21 -0.23, on time scales larger than 10
days) compatible with the VHE findings. The HE and VHE power spectral densities
show a scale invariance across the probed time ranges. A direct linear
correlation between the VHE and HE fluxes could neither be excluded nor firmly
established. These long-term-variability properties are discussed and compared
to the red noise behavior ({\ss} ~ 2) seen on shorter time scales during
VHE-flaring states. The difference in power spectral noise behavior at VHE
energies during quiescent and flaring states provides evidence that these
states are influenced by different physical processes, while the compatibility
of the HE and VHE long-term results is suggestive of a common physical link as
it might be introduced by an underlying jet-disk connection.Comment: 11 pages, 16 figure
The exceptionally powerful TeV gamma-ray emitters in the Large Magellanic Cloud
The Large Magellanic Cloud, a satellite galaxy of the Milky Way, has been
observed with the High Energy Stereoscopic System (H.E.S.S.) above an energy of
100 billion electron volts for a deep exposure of 210 hours. Three sources of
different types were detected: the pulsar wind nebula of the most energetic
pulsar known N 157B, the radio-loud supernova remnant N 132D and the largest
non-thermal X-ray shell - the superbubble 30 Dor C. The unique object SN 1987A
is, surprisingly, not detected, which constrains the theoretical framework of
particle acceleration in very young supernova remnants. These detections reveal
the most energetic tip of a gamma-ray source population in an external galaxy,
and provide via 30 Dor C the unambiguous detection of gamma-ray emission from a
superbubble.Comment: Published in Science Magazine (Jan. 23, 2015). This ArXiv version has
the supplementary online material incorporated as an appendix to the main
pape
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