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تسجيل مستخدم جديدSearch for >= 400 GeV gamma-rays from the SNR Cas A
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The recent detection of a hard X-ray component in the supernova remnant Cassiopeia A is interpreted as synchrotron emission from electrons accelerated to energies up to 40 TeV (Allen et al., 1997). It is therefore tempting to consider TeV gamma-ray emission from this object through : i) bremsstrahlung and inverse Compton radiation from electrons and/or ii) pi0 production from an associated high energy cosmic ray component hitting surrounding material. Cas A was observed by the CAT imaging Cherenkov telescope during the observing season Aug-Nov 1998. An upper limit to the integral flux above 400 GeV of 0.74x10^-11 gamma.cm^-2.s^-1 is derived. This result is used to constrain shock-acceleration models for production of VHE gamma-rays in SNRs.
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The shell type SNR RXJ1713.7-3946 is a new SNR discovered by the ROSAT all sky survey. Recently, strong non-thermal X-ray emission from the northwest part of the remnant was detected by the ASCA satellite. This synchrotron X-ray emission strongly sug
gests the existence of electrons with energies up to hundreds of TeV in the remnant. This SNR is, therefore, a good candidate TeV gamma ray source, due to the Inverse Compton scattering of the Cosmic Microwave Background Radiation by the shock accelerated ultra-relativistic electrons, as seen in SN1006. In this paper, we report a preliminary result of TeV gamma-ray observations of the SNR RXJ1713.7-3946 by the CANGAROO 3.8m telescope at Woomera, South Australia.
This paper reports the first discovery of TeV gamma-ray emission from a supernova remnant made with the CANGAROO 3.8 m Telescope. TeV gamma rays were detected at the sky position and extension coincident with the north-east (NE) rim of shell-type Sup
ernova remnant (SNR) SN1006 (Type Ia). SN1006 has been a most likely candidate for an extended TeV Gamma-ray source, since the clear synchrotron X-ray emission from the rims was recently observed by ASCA (Koyama et al. 1995), which is a strong evidence of the existence of very high energy electrons up to hundreds of TeV in the SNR. The observed TeV gamma-ray flux was $(2.4pm 0.5(statistical) pm 0.7(systematic)) times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($ge 3.0pm 0.9$ TeV) and $ (4.6pm 0.6 pm 1.4) times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($ge 1.7pm 0.5$ TeV) from the 1996 and 1997 observations, respectively. Also we set an upper limit on the TeV gamma-ray emission from the SW rim, estimated to be $ 1.1 times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($ge 1.7pm 0.5$ TeV, 95% CL) in the 1997 data. The TeV gamma rays can be attributed to the 2.7 K cosmic background photons up-scattered by electrons of energies up to about 10$^{14}$ eV by the inverse Compton (IC) process. The observed flux of the TeV gamma rays, together with that of the non-thermal X-rays, gives firm constraints on the acceleration process in the SNR shell; a magnetic field of $6.5pm2$ $mu$G is inferred from both the synchrotron X-rays and inverse Compton TeV gamma-rays, which gives entirely consistent mechanisms that electrons of energies up to 10$^{14}$ eV are produced via the shock acceleration in SN1006.
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R W28, for its associated system of dense molecular clouds, provides an excellent opportunity to test this hypothesis. We present the AGILE/GRID observations of SNR W28, and compare them with observations at other wavelengths (TeV and 12CO J=1-->0 molecular line emission). The gamma-ray flux detected by AGILE from the dominant source associated with W28 is (14 +- 5) 10^-8 ph cm^-2 s^-1 for E > 400 MeV. This source is positionally well correlated with the TeV emission observed by the HESS telescope. The local variations of the GeV to TeV flux ratio suggest a difference between the CR spectra of the north-west and south molecular cloud complexes. A model based on a hadronic-induced interaction and diffusion with two molecular clouds at different distances from the W28 shell can explain both the morphological and spectral features observed by AGILE in the MeV-GeV energy range and by the HESS telescope in the TeV energy range. The combined set of AGILE and H.E.S.S. data strongly support a hadronic model for the gamma-ray production in W28.
Observations have been made, using the University of Durham Mark 6 gamma ray telescope, of the very high energy gamma ray emission from a number of active galactic nuclei visible from the Southern hemisphere. Limits are presented to the VHE gamma ray
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