EDP Sciences
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Volume 370, Number 2, May I 2001
Page(s) 468 - 478
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20010239

A&A 370, 468-478 (2001)
DOI: 10.1051/0004-6361:20010239

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

D. F. Torres1, G. E. Romero1, J. A. Combi1, P. Benaglia1, H. Andernach2 and B. Punsly3

1  Instituto Argentino de Radioastronomía, C.C.5, (1894) Villa Elisa, Buenos Aires, Argentina
2  Depto. de Astronomía, Univ. Guanajuato, Apartado Postal 144, Guanajuato, CP 36000, GTO, Mexico
3  4014 Emerald Street No. 116, Torrance, CA 90503, USA

(Received 4 August 2000 / Accepted 26 January 2001)

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.

Key words: gamma-rays: observations -- gamma-rays: theory -- ISM: supernova remnants -- black holes physics

Offprint request: D. F. Torres, dtorres@venus.fisica.unlp.edu.ar

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