A variability analysis of low-latitude unidentified gamma-ray sources

• Published in: Astronomy and astrophysics (Berlin) 2001-05, Vol.370 (2), p.468-478
• Main Authors: Torres, D. F., Romero, G. E., Combi, J. A., Benaglia, P., Andernach, H., Punsly, B.
• Format: Article
• Language: English
• Subjects: black holes physics; gamma-rays: observations; gamma-rays: theory; ISM: supernova remnants
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20010239

We present a study of 40 low-latitude unidentified 3EG gamma-ray sources which were found to be not positionally coincident with any known class of potential gamma-ray emitters in the Galaxy (Romero et al. 1999). We have performed a variability analysis which reveals that many of these 40 sources are variable. These sources have, in addition, a steep mean value of the gamma-ray spectral index, $< \Gamma> = 2.41 \pm 0.2$, which, combined with the high level of variability, seems to rule out a pulsar origin. The positional coincidences with uncatalogued candidates to supernova remnants were also studied. Only 7 sources in the sample are spatially coincident with these candidates, a result that is shown to be consistent with the expected level of pure chance association. A complementary search for weak radio counterparts was also conducted and the results are presented as an extensive table containing all significant point-like radio sources within the 40 EGRET fields. We argue that in order to produce the high variability, steep gamma-ray spectra, and absence of strong radio counterparts observed in some of the gamma-ray sources of our sample, a new class of objects should be postulated, and we analyze a viable candidate.