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تسجيل مستخدم جديدThe VERITAS Survey of the Cygnus Region of the Galactic Plane
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Amanda Weinstein
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The Cygnus region of the Galactic plane contains many known supernova remnants, pulsars, X-ray and GeV gamma-ray emitters which make it a prime candidate for a Very High Energy (VHE) gamma-ray survey in the Northern Hemisphere. The VERITAS observatory, an array of four atmospheric Cherenkov telescopes located at the base of Mt. Hopkins in southern Arizona, USA, has carried out an extensive survey of the Cygnus region between 67 and 82 degrees in galactic longitude and between -1 and 4 degrees in galactic latitude. The survey, comprising more than 140 hours of observations, reaches an average VHE flux sensitivity of better than 4% of the Crab Nebula at energies above 200 GeV. Here we report on the preliminary results from this survey.
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The VERITAS IACT observatory has carried out an extensive survey of the Cygnus region between 67 and 82 degrees in galactic longitude and between -1 and 4 degrees in galactic latitude. This region is a natural choice for a Very High Energy (VHE) gamm
a-ray survey in the Northern Hemisphere, as it contains a substantial number of potential VHE gamma-ray emitters such as supernova remnants, pulsar wind nebulae, high-mass X-ray binaries, and massive star clusters, in addition to a few previously detected VHE gamma-ray sources. It is also home to a number of GeV gamma-ray sources, including no less than four new high-significance sources detected in the first six months of Fermi data. The VERITAS survey, comprising more than 140 hours of observations, reaches an average VHE point-source flux sensitivity of better than 4% of the Crab Nebula flux at energies above 200 GeV. Here we report on preliminary results from this survey, including two source detections, and discuss the prospects for further studies that would exploit the joint coverage provided by VERITAS and Fermi data in this region.
The Galactic center is an interesting region for high-energy (0.1-100 GeV) and very-high-energy (E > 100 GeV) gamma-ray observations. Potential sources of GeV/TeV gamma-ray emission have been suggested, e.g., the accretion of matter onto the supermas
sive black hole, cosmic rays from a nearby supernova remnant (e.g. SgrA East), particle acceleration in a plerion, or the annihilation of dark matter particles. The Galactic center has been detected by EGRET and by Fermi/LAT in the MeV/GeV energy band. At TeV energies, the Galactic center was detected with moderate significance by the CANGAROO and Whipple 10 m telescopes and with high significance by H.E.S.S., MAGIC, and VERITAS. We present the results from three years of VERITAS observations conducted at large zenith angles resulting in a detection of the Galactic center on the level of 18 standard deviations at energies above ~2.5TeV. The energy spectrum is derived and is found to be compatible with hadronic, leptonic and hybrid emission models discussed in the literature. Future, more detailed measurements of the high-energy cutoff and better constraints on the high-energy flux variability will help to refine and/or disentangle the individual models.
The Galactic Center has long been a region of interest for high-energy and very-high-energy observations. Many potential sources of GeV/TeV gamma-ray emission have been suggested, e.g., the accretion of matter onto the black hole, cosmic rays from a
nearby supernova remnant, or the annihilation of dark matter particles. The Galactic Center has been detected at MeV/GeV energies by EGRET and recently by Fermi/LAT. At GeV/TeV energies, the Galactic Center was detected by different ground-based Cherenkov telescopes such as CANGAROO, Whipple 10m, H.E.S.S., and MAGIC. We present the results from 15 hrs of VERITAS observations conducted at large zenith angles, resulting in a >10 standard deviation detection and confirmation of the high-energy spectrum observed by H.E.S.S. The combined Fermi/VERITAS results are compared to astrophysical models.
We report the results of an optical campaign carried out by the XMM-Newton Survey Science Centre with the specific goal of identifying the brightest X-ray sources in the XMM-Newton Galactic Plane Survey of Hands et al. (2004). In addition to photomet
ric and spectroscopic observations obtained at the ESO-VLT and ESO-3.6m, we used cross-correlations with the 2XMMi, USNO-B1.0, 2MASS and GLIMPSE catalogues to progress the identification process. Active coronae account for 16 of the 30 identified X-ray sources. Many of the identified hard X-ray sources are associated with massive stars emitting at intermediate X-ray luminosities of 10^32-34 erg/s. Among these are a very absorbed likely hyper-luminous star with X-ray/optical spectra and luminosities comparable with those of eta Carina, a new X-ray selected WN8 Wolf-Rayet star, a new Be/X-ray star belonging to the growing class of Gamma-Cas analogs and a possible supergiant X-ray binary of the kind discovered recently by INTEGRAL. One of the sources, XGPS-25 has a counterpart which exhibits HeII 4686 and Bowen CIII-NIII emission lines suggesting a quiescent or X-ray shielded Low Mass X-ray Binary, although its properties might also be consistent with a rare kind of cataclysmic variable (CV). We also report the discovery of three new CVs, one of which is a likely magnetic system. The soft (0.4-2.0 keV) band LogN-LogS curve is completely dominated by active stars in the flux range of 1x10^-13 to 1x10^-14 erg/cm2/s. In total, we are able to identify a large fraction of the hard (2-10 keV) X-ray sources in the flux range of 1x10^-12 to 1x10^-13 erg/cm2/s with Galactic objects at a rate consistent with that expected for the Galactic contribution only. (abridged)
The study of $gamma$-ray emission from galactic sources such as supernova remnants (SNR) may provide key insights into their potential role as accelerators of cosmic rays up to the knee ($sim 10^{15}$ eV). The VERITAS Observatory is sensitive to gala
ctic and extragalactic $gamma$-ray sources in the 100 GeV to 30 TeV energy range. We report here on VERITAS observations of the vicinity of the cocoon of freshly accelerated cosmic rays reported by Fermi, which lies between potential accelerators in the Cygnus OB2 association and the $gamma$-Cygni SNR. A particular focus is placed on the source VER J2019 +407 in $gamma$-Cygni.
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