On the distribution of EGRET unidentified sources in the Galactic plane

Abstract

Abstract. 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.

Broad-band electromagnetic radiation from microquasars interacting with ISM

“…While the search of such objects in TeV gamma-rays will constitute an important part of the future surveys of the galactic plane by forthcoming ground-based instruments, it is possible that some such objects are already detected by EGRET. In fact, statistical studies of the unidentified EGRET sources in the galactic plane point to a possible link with high density regions in the inner spiral arms ( [7]). It is likely that the low latitude EGRET sources are grouped in two subpopulations; one formed by variable sources with possible association with MQs ( [8]), and another subpopulation consisting of persistent objects ( [9]).…”

High Energy Emission from Microquasars

“…While recent follow-ups suggest that some of the previously unidentified sources may be young pulsars (Halpern et al 2001;D'Amico et al 2001;Torres et al 2001), the spatial distribution seems more consistent with that of molecular clouds (e.g. Bhattacharya et al 2003), and the follow-up of LS 5039 as the counterpart of a previously unidentified EGRET source suggests that at least some fraction of these sources may be X-ray binaries.…”

A microquasar model applied to unidentified gamma-ray sources

“…This SNR, yet not part of the Green's Catalog, was not a member of the sample in the systematic study of molecular material by Torres et al (2003), although the source variability argues against a physical association with the SNR shock. Association with the SNR would imply a lower energy requirement to explain the observed EGRET flux, although with such a distance the source would not be associated with the Carina arm, as most of the EGRET sources in the galactic plane seem to be (Bhattacharya et al 2003). Also, there is a strong flat spectrum radio source within the error box of this source which has been proposed to be a blazar (Halpern et al 2003;Sowards-Emmerd et al 2003 assigned to the blazar J1826+0149 an association probability of 60−80%).…”