386 research outputs found
Constraining leptonic emission scenarios for the PeVatron candidate HESS J1702-420 with deep XMM-Newton observations
The unidentified TeV source HESS J1702-420 has recently been proposed as a
new hadronic PeVatron candidate, based on the discovery of a small-scale
emission sub-region with extremely hard gamma-ray spectrum up to 100 TeV (named
HESS J1702-420A). Given the difficulty to discriminate between a hadronic or
leptonic origin of the TeV emission, based on the H.E.S.S. measurement alone,
we opted for a multi-wavelength approach. A deep X-ray observation was carried
out using the XMM-Newton satellite, with the goal of probing a possible
association with a hidden leptonic accelerator. No evidence of a clear
counterpart for HESS J1702-420A was found in the X-ray data. After excluding an
association with all nearby X-ray point sources, we derived strict upper limits
on the diffuse X-ray emission and average magnetic field in the HESS J1702-420A
region. We additionally report the serendipitous discovery of a new extended
X-ray source, whose association with HESS J1702-420A is not obvious but cannot
be ruled out either. A set of scripts dedicated to the multi-wavelength
modeling of X-ray and gamma-ray data, based on Gammapy, Naima and Xspec, was
developed in the context of this work and is made publicly available along with
this paper.Comment: Accepted for publication in Astronomy & Astrophysics, 13 pages, 11
figures, 3 table
Cherenkov Telescope Array Data Management
Very High Energy gamma-ray astronomy with the Cherenkov Telescope Array (CTA)
is evolving towards the model of a public observatory. Handling, processing and
archiving the large amount of data generated by the CTA instruments and
delivering scientific products are some of the challenges in designing the CTA
Data Management. The participation of scientists from within CTA Consortium and
from the greater worldwide scientific community necessitates a sophisticated
scientific analysis system capable of providing unified and efficient user
access to data, software and computing resources. Data Management is designed
to respond to three main issues: (i) the treatment and flow of data from remote
telescopes; (ii) "big-data" archiving and processing; (iii) and open data
access. In this communication the overall technical design of the CTA Data
Management, current major developments and prototypes are presented.Comment: 8 pages, 2 figures, In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
Calcium-dependent dephosphorylation of the histone chaperone DAXX regulates H3.3 loading and transcription upon neuronal activation.
Activity-dependent modifications of chromatin are believed to contribute to dramatic changes in neuronal circuitry. The mechanisms underlying these modifications are not fully understood. The histone variant H3.3 is incorporated in a replication-independent manner into different regions of the genome, including gene regulatory elements. It is presently unknown whether H3.3 deposition is involved in neuronal activity-dependent events. Here, we analyze the role of the histone chaperone DAXX in the regulation of H3.3 incorporation at activity-dependent gene loci. DAXX is found to be associated with regulatory regions of selected activity-regulated genes, where it promotes H3.3 loading upon membrane depolarization. DAXX loss not only affects H3.3 deposition but also impairs transcriptional induction of these genes. Calcineurin-mediated dephosphorylation of DAXX is a key molecular switch controlling its function upon neuronal activation. Overall, these findings implicate the H3.3 chaperone DAXX in the regulation of activity-dependent events, thus revealing a new mechanism underlying epigenetic modifications in neurons
Observation of an extended VHE gamma-ray emission from MSH 15-52 with CANGAROO-III
We have observed the supernova remnant MSH 15-52 (G320.4-1.2), which contains
the gamma-ray pulsar PSR B1509-58, using the CANGAROO-III imaging atmospheric
Cherenkov telescope array from April to June in 2006. We detected gamma rays
above 810 GeV at the 7 sigma level during a total effective exposure of 48.4
hours. We obtained a differential gamma-ray flux at 2.35 TeV of
(7.9+/-1.5_{stat}+/-1.7_{sys}) \times 10^{-13} cm^{-2}s^{-1}TeV^{-1} with a
photon index of 2.21+/-0.39_{stat}+/-0.40_{sys}, which is compatible with that
of the H.E.S.S. observation in 2004. The morphology shows extended emission
compared to our Point Spread Function. We consider the plausible origin of the
high energy emission based on a multi-wavelength spectral analysis and
energetics arguments.Comment: 9 pages, 9 figures, Accepted in Ap
Discovery of the Binary Pulsar PSR B1259-63 in Very-High-Energy Gamma Rays around Periastron with H.E.S.S
We report the discovery of very-high-energy (VHE) gamma-ray emission of the
binary system PSR B1259-63/SS 2883 of a radio pulsar orbiting a massive,
luminous Be star in a highly eccentric orbit. The observations around the 2004
periastron passage of the pulsar were performed with the four 13 m Cherenkov
telescopes of the H.E.S.S. experiment, recently installed in Namibia and in
full operation since December 2003. Between February and June 2004, a gamma-ray
signal from the binary system was detected with a total significance above 13
sigma. The flux was found to vary significantly on timescales of days which
makes PSR B1259-63 the first variable galactic source of VHE gamma-rays
observed so far. Strong emission signals were observed in pre- and
post-periastron phases with a flux minimum around periastron, followed by a
gradual flux decrease in the months after. The measured time-averaged energy
spectrum above a mean threshold energy of 380 GeV can be fitted by a simple
power law F_0(E/1 TeV)^-Gamma with a photon index Gamma =
2.7+-0.2_stat+-0.2_sys and flux normalisation F_0 = (1.3+-0.1_stat+-0.3_sys)
10^-12 TeV^-1 cm^-2 s^-1. This detection of VHE gamma-rays provides unambiguous
evidence for particle acceleration to multi-TeV energies in the binary system.
In combination with coeval observations of the X-ray synchrotron emission by
the RXTE and INTEGRAL instruments, and assuming the VHE gamma-ray emission to
be produced by the inverse Compton mechanism, the magnetic field strength can
be directly estimated to be of the order of 1 G.Comment: 10 pages, 8 figures, accepted in Astronomy and Astrophysics on 2 June
2005, replace: document unchanged, replaced author field in astro-ph entry -
authors are all members of the H.E.S.S. collaboration and three additional
authors (99+3, see document
Detection of the BL Lac object 1ES1426+428 in the Very High Energy gamma-ray band by the CAT Telescope from 1998-2000
The BL Lac Object 1ES 1426+428, at a red-shift of z=0.129, has been monitored
by the CAT telescope from February 1998 to June 2000. The accumulation of 26
hours of observations shows a gamma-ray signal of 321 events above 250 GeV at
5.2 standard deviations, determined using data analysis cuts adapted to a weak,
steep-spectrum source. The source emission has an average flux of Phi_diff(400
GeV) = 6.73 +/- 1.27stat +/- 1.45syst x 10^-11 /cm^-2/s/TeV, and a very steep
spectrum, with a differential spectral index of gamma = -3.60 +/- 0.57 which
can be refined to gamma = -3.66 +/- 0.41 using a higher flux data subset. If,
as expected from its broad-band properties, the Very High Energy emission is
hard at the source, these observations support a strong absorption effect of
gamma-rays by the Intergalactic Infrared field.Comment: 4 pages, 3 figures, accepted for publication in A&A Letter
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
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&
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