Optical study of the Geminga candidate field

Creators: Djorgovski, S.; Kulkarni, Shrinivas R.

Abstract

We have observed the field of the x-ray source IE 0630 + 178, proposed as a probable counterpart of the γ-ray source 2CG 195+04 (Geminga). Deep CCD images of the field show two very faint optical sources within the x-ray error circle, as well as the 21 mag star (hereafter referred to as the G candidate) proposed earlier as the possible optical counterpart. The G candidate does not have a proper motion greater than 0.15 arcsec yr^(-1). The spectrum of this object shows no strong emission or absorption features. We conclude that the G candidate is most probably a distant G dwarf or a nearby, cool, white dwarf. We believe that one of the fainter objects within the x-ray circle is more likely to be the true counterpart of the x-ray source, and possibly of the γ-ray source as well. This result is consistent with the interpretation of Geminga as a nearby neutron star, if all the γ rays are generated by some nonthermal mechanism. Deep Hα images do not reveal presence of any emission-line nebulosity (e.g., a supernova remnant).

Additional Information

© 1986 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received 26 July 1985; revised 6 September 1985. Based in part on research done at Lick Observatory, University of California. We are indebted to Dr. J. Halpem for communicating positions of the field stars for our proper-motion study, and to Dr. H. Sol for communicating the offsets of the G' candidate. We also thank Drs. J. Halpem, J. Grindlay, G. Bignami, P. Caraveo, and J. Stocke for interesting discussions and communication of prepublication data. This paper benefited from a constructive refereeing by Dr. J. Halpem. Dr. H. Spinrad made generous contributions of observing time at Lick. The solar spectrum used for the comparison in Table I was kindly communicated by Dr. D. Schleicher. We acknowledge the valuable and competent help of the staff of Lick Observatory, and in particular R. Stone, K. Baker, W. Earthman, J. Morey, B. Alcott, and C. Clark. This work was supported in part by NSF Grant No. AST84-16863, and a University of California Regents Fellowship to S.D.

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Published - 1986AJ_____91___90D.pdf

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