11,350 research outputs found
HESS J1825-137: A pulsar wind nebula associated with PSR B1823-13?
HESS J1825-137 was detected with a significance of 8.1 in the
Galactic Plane survey conducted with the H.E.S.S. instrument in 2004. Both HESS
J1825-137 and the X-ray pulsar wind nebula G18.0--0.7 (associated with the
Vela-like pulsar PSR B1823-13) are offset south of the pulsar, which may be the
result of the SNR expanding into an inhomogeneous medium. The TeV size ( pc, for a distance of 4 kpc) is times larger than the X-ray size,
which may be the result of propagation effects as a result of the longer
lifetime of TeV emitting electrons, compared to the relatively short lifetime
of keV synchrotron emitting electrons. The TeV photon spectral index of can also be related to the extended PWN X-ray synchrotron photon index of
, if this spectrum is dominated by synchrotron cooling. The
anomalously large size of the pulsar wind nebula can be explained if the pulsar
was born with a relatively large initial spindown power and braking index
, provided that the SNR expanded into the hot ISM with relatively low
density ( cm).Comment: 4 pages, 4 figures, to appear in the Proc. of the 29th International
Cosmic Ray Conference, OG Sessio
The GeV-TeV Connection in Galactic gamma-ray sources
Recent observations with atmospheric Cherenkov telescope systems such as
H.E.S.S. and MAGIC have revealed a large number of new sources of
very-high-energy (VHE) gamma-rays from 100 GeV - 100 TeV, mostly concentrated
along the Galactic plane. At lower energies (100 MeV - 10 GeV) the
satellite-based instrument EGRET revealed a population of sources clustering
along the Galactic Plane. Given their adjacent energy bands a systematic
correlation study between the two source catalogues seems appropriate. Here,
the populations of Galactic sources in both energy domains are characterised on
observational as well as on phenomenological grounds. Surprisingly few common
sources are found in terms of positional coincidence and spectral consistency.
These common sources and their potential counterparts and emission mechanisms
will be discussed in detail. In cases of detection only in one energy band, for
the first time consistent upper limits in the other energy band have been
derived. The EGRET upper limits are rather unconstraining due to the
sensitivity mismatch to current VHE instruments. The VHE upper limits put
strong constraints on simple power-law extrapolation of several of the EGRET
spectra and thus strongly suggest cutoffs in the unexplored energy range from
10 GeV - 100 GeV. Physical reasons for the existence of cutoffs and for
differences in the source population at GeV and TeV energies will be discussed.
Finally, predictions will be derived for common GeV - TeV sources for the
upcoming GLAST mission bridging for the first time the energy gap between
current GeV and TeV instruments.Comment: (1) Kavli Institute for Particle Astrophysics and Cosmology (KIPAC),
Stanford, USA (2) Stanford University, W.W. Hansen Experimental Physics Lab
(HEPL) and KIPAC, Stanford, USA (3) ICREA & Institut de Ciencies de l'Espai
(IEEC-CSIC) Campus UAB, Fac. de Ciencies, Barcelona, Spain. (4) School of
Physics and Astronomy, University of Leeds, UK. Paper Submitted to Ap
A future very-high-energy view of our Galaxy
The survey of the inner Galaxy with H.E.S.S. was remarkably successful in
detecting a wide range of new very-high-energy gamma-ray sources. New TeV
gamma-ray emitting source classes were established, although several of the
sources remain unidentified, and progress has been made in understanding
particle acceleration in astrophysical sources. In this work, we constructed a
model of a population of such very-high-energy gamma-ray emitters and
normalised the flux and size distribution of this population model to the
H.E.S.S.-discovered sources. Extrapolating that population of objects to lower
flux levels we investigate what a future array of imaging atmospheric
telescopes (IACTs) such as AGIS or CTA might detect in a survey of the Inner
Galaxy with an order of magnitude improvement in sensitivity. The sheer number
of sources detected together with the improved resolving power will likely
result in a huge improvement in our understanding of the populations of
galactic gamma-ray sources. A deep survey of the inner Milky Way would also
support studies of the interstellar diffuse gamma-ray emission in regions of
high cosmic-ray density. In the final section of this paper we investigate the
science potential for the Galactic Centre region for studying energy-dependent
diffusion with such a future array.Comment: Proceeding of "Heidelberg International Symposium on High Energy
Gamma-Ray Astronomy", held in Heidelberg, 7-11 July 2008, submitted to AIP
Conference Proceedings. 4 pages, 4 figure
Monitoring of Grandes Jorasses hanging glacier (Aosta Valley, Italy):improving monitoring techniques for glaciers instability
Fermi Detection of the Pulsar Wind Nebula HESS J1640-465
We present observations of HESS J1640-465 with the Fermi-LAT. The source is
detected with high confidence as an emitter of high-energy gamma-rays. The
spectrum lacks any evidence for the characteristic cutoff associated with
emission from pulsars, indicating that the emission arises primarily from the
pulsar wind nebula. Broadband modeling implies an evolved nebula with a low
magnetic field resulting in a high gamma-ray to X-ray flux ratio. The Fermi
emission exceeds predictions of the broadband model, and has a steeper
spectrum, possibly resulting from a distinct excess of low energy electrons
similar to what is inferred for both the Vela X and Crab pulsar wind nebulae.Comment: 6 pages, 5 figures, accepted for publication in Ap
Comparison of Fermi-LAT and CTA in the region between 10-100 GeV
The past decade has seen a dramatic improvement in the quality of data
available at both high (HE: 100 MeV to 100 GeV) and very high (VHE: 100 GeV to
100 TeV) gamma-ray energies. With three years of data from the Fermi Large Area
Telescope (LAT) and deep pointed observations with arrays of Cherenkov
telescope, continuous spectral coverage from 100 MeV to TeV exists for
the first time for the brightest gamma-ray sources. The Fermi-LAT is likely to
continue for several years, resulting in significant improvements in high
energy sensitivity. On the same timescale, the Cherenkov Telescope Array (CTA)
will be constructed providing unprecedented VHE capabilities. The optimisation
of CTA must take into account competition and complementarity with Fermi, in
particularly in the overlapping energy range 10100 GeV. Here we compare the
performance of Fermi-LAT and the current baseline CTA design for steady and
transient, point-like and extended sources.Comment: Accepted for Publication in Astroparticle Physic
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