Variable unidentified gamma-ray sources near the Galactic plane (original) (raw)
Related papers
Unidentified 3EG gamma-ray sources at low galactic latitude
1999
We present a study on the possible association of unidentified γ-ray sources in the Third EGRET (3EG) catalog with different types of galactic objects such as Wolf-Rayet and Of stars, supernova remnants (SNRs), and OB associations (considered as pulsar tracers). We have made use of numerical simulations of galactic populations of γ-ray point sources in order to determine the statistical significance of the positional coincidences. New constraints on pure chance association are presented for SNRs and OB associations. There is overwhelming statistical support for the hypothesis that some SNRs are γray sources (we obtain probabilities of pure chance association < 10 −5 ). OB star associations present higher, but still negligible probabilities (< 10 −3 ). It is also shown that although massive stars present just marginally significant correlation with 3EG sources, there is a posteriori support for at least three candidates.
Unidentified 3EG gamma-ray sources at low galactic latitudes
We present a study on the possible association of unidentified -ray sources in the Third EGRET (3EG) catalog with different types of galactic objects such as Wolf-Rayet and Of stars, supernova remnants (SNRs), and OB associations (considered as pulsar tracers). We have made use of numerical simulations of galactic populations of -ray point sources in order to determine the statistical significance of the positional coincidences. New constraints on pure chance association are presented for SNRs and OB associations. There is overwhelming statistical support for the hypothesis that some SNRs are - ray sources (we obtain probabilities of pure chance association < 10−5).OBstar associations present higher, but still negligible probabilities (< 10−3). It is also shown that although massive stars present just marginally significant correlation with 3EG sources, there is a posteriori support for at least three candidates.
On the distribution of EGRET unidentified sources in the Galactic plane
Astronomy and Astrophysics, 2003
It has been suggested that young pulsars, with ages less than a million years, are possible counterparts of some of the Galactic unidentified gamma-ray sources detected by the EGRET instrument on-board the Compton Gamma Ray Observatory. In this work, we compare different aspects of the EGRET unidentified (EUI) source distribution in the Galactic plane with those of the pulsar distribution. An EUI source Log N-Log S analysis is presented and compared with the Galactic radio pulsar Log N-Log S distribution. A number of systematic effects that could introduce errors to the EGRET Log N-Log S relation are discussed. A two-point angular correlation analysis of the EUI sources and Galactic pulsars is performed. We find that the global distribution properties of the plane EUI sources do not follow those of the young pulsar population. We conclude that even though a fraction of the EUI sources may have young pulsar counterparts, the majority of them follow a distribution that is similar to the molecular cloud distribution in nearby spiral arms.
A revised catalogue of EGRET sfgamma{\sf \gamma}sfgamma-ray sources
Astronomy & Astrophysics, 2008
Aims. We present a catalog of point γ-ray sources detected by the EGRET detector on the Compton Gamma Ray Observatory. We used the entire γ-ray dataset of reprocessed photons at energies above 100 MeV and new Galactic interstellar emission models based on CO, HI, dark gas, and interstellar radiation field data. Two different assumptions are used to describe the cosmic-ray distribution in the Galaxy to analyse the systematic uncertainties in source detection and characterization. Methods. We applied a 2-dimensional maximum-likelihood detection method similar to that used to analyze the 3rd EGRET catalogue. Results. The revised catalogue lists 188 sources, 14 of which are marked as confused, in contrast to the 271 entries of the 3rd EGRET (3EG) catalogue. We do not detect 107 sources discovered previously because additional structure is present in the interstellar background. The vast majority of them were unidentified and marked as possibly extended or confused in the 3EG catalogue. In particular, we do not confirm most of the 3EG sources associated with the local clouds of the Gould Belt. Alternatively, we found 30 new sources that have no 3EG counterpart. The new error circles for the confirmed 3EG sources largely overlap the previous ones, but several counterparts of particular interest discussed before, such as Sgr A*, radiogalaxies, and several microquasars are now found outside the error circles. We cross-correlated the source positions with a large number of radio pulsars, pulsar wind nebulae, supernova remnants, OB associations, blazars and flat radiosources and we found a surprising large number of sources (87) at all latitudes that have no counterpart among the potential γ-ray emitters.
Low-Latitude Gamma-Ray Sources: Correlations and Variability
Astrophysics and Space Science Library, 2001
A review of the main characteristics of low-latitude sources in the third EGRET catalog is presented. There are 75 unidentified gamma-ray sources detected by EGRET at |b| < 10 •. About a half of these sources are spatially correlated with potential galactic gamma-ray emitters such as supernova remnants, OB associations and early-type stars with very strong stellar winds. The other half is formed by sources without positional correlation with known galactic objects capable to generate a gamma ray flux significant enough as to be detected by EGRET. A variability analysis shows that this second group of sources contains several objects with high levels of gamma-ray variability. These variable sources resemble very much the AGNs detected by EGRET, but without their typical strong radio emission. To establish the nature of these sources is one of the most urgent problems of high-energy astrophysics.
Gamma-ray sources at high latitudes (Extragalactic gamma-ray sources)
arXiv (Cornell University), 2003
This chapter provides a review of γ-ray sources lying at high Galactic latitudes. Their statistical properties and variability status, as well as studies involving cross correlations with lower frequency catalogs and multiwavelength observations, are summarized. The case for active galactic nuclei is analyzed with special emphasis, since they represent the largest population of high energy sources known to date. Other potential γ-ray emitters (including nearby starburst galaxies, normal galaxies, molecular clouds in the Galactic halo, galaxy clusters, and radio galaxies) that may appear in the next generation of γ-ray catalogs and, perhaps, that might have been already observed by EGRET as unidentified detections, are also discussed.
Space Science Reviews, 1983
The Einstein X-ray Imaging Instruments have been used to explore, down to an unprecedented sensitivity, the X-ray behavior of 7 high-energy 7-ray sources discovered by the COS-B satellite. 32 low latitude (Ib] < 5 ~ IPC fields, mosaic-arranged to cover the few-square-degrees COS-B error circles, yielded 30 soft X-ray sources, the fluxes of which range from ~ 1/100 to few UFU, and no diffuse features. While the density of ~ 1 source/IPC field is consistent with the value found at higher latitudes, the percentage of 'stellar' identifications among these low-latitude sources is significantly higher than in non-galactic-biased samples. Unfortunately, the positional accuracy achieved with the IPC does not allow astronomical identification in the absence of obvious counterpart(s). However, after the exploratory coverage, the IPC data were used, when possible, to point out potentially interesting targets for the HRI instrument capable of an accuracy of ~ 3 arc sec. Due to the misfortunes which occurred to the Einstein satellite, this time-consuming process was feasible only in two cases: within the error circle of 2CG 135 + 01, the radio variable star LS161.303 was pinpointed by the HRI, while the HRI exposure of the brightest X-ray source discovered in 2CG 195 + 04 (Geminga) positioned a source in an empty POSS field. The latter case will be presented and the nature of the X-and V(?)-ray source briefly discussed.
On the Nature of the Variable Gamma-Ray Sources at Low Galactic Latitudes
Astrophysics and Space Science, 2005
Population studies of EGRET gamma-ray sources indicate that there is a distinctive population of bright sources at low galactic latitudes. The sources have a distribution consistent with that of young galactic objects, with a concentration toward the inner spiral arms. There is a subgroup that displays strong variability with timescales from days to months. Following an earlier suggestion by Kaufman Bernadó et al. (2002), we explore the possibility that these sources could be highmass microquasars. Detailed models for the gamma-ray emission that include inverse Compton interactions of electrons in the relativistic jets and photons from all local fields (stellar UV photons, synchrotron photons, soft X-ray photons from the accretion disk, and hard X-ray photons from a corona) are presented. We conclude that microquasars are excellent candidates for the parent population of the subgroup of variable low-latitude EGRET sources.