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Optical Constraints on an X-ray Transient Source in M31

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, , Citation Benjamin F. Williams et al 2005 ApJ 631 832 DOI 10.1086/432597

0004-637X/631/2/832

Abstract

We have detected a transient X-ray source in the M31 bulge through a continuing monitoring campaign with the Chandra ACIS-I camera. The source was detected at R.A. = 00h42m33fs428 ± 0farcs11, decl. = +41°17'03farcs37 ± 0farcs11 in only a single observation taken 2004 May 23. Fortuitous optical HST ACS imaging of the transient location prior to the X-ray outburst, along with follow-up HST ACS imaging during and after the outburst, reveals no transient optical source brighter than B(equivalent) = 25.5. The location of the source and its X-ray properties suggest that it is a low-mass X-ray binary (LMXB). Assuming the transient is similar to many Galactic X-ray novae, the X-ray luminosity of (3.9 ± 0.4) × 1037 ergs s-1 and the upper limit on the optical luminosity provide a prediction of ≤1.6 days for the orbital period of the binary system.

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10.1086/432597