Exposing the symbiosis of 3A 1954+319

Abstract

Symbiotic X-ray Binaries (SyXB) are a rare class (∼8 known members) of Low Mass X-ray Binaries (LMXB), in which a compact object accretes material from an evolved M-type giant companion. The SyXB and accreting pulsar 3A 1954+319 is further exceptional since it has the longest pulse period known for an X-ray binary. It undergoes rapid changes, which we found span a range of 5.0– 5.8 h over the interval 2005–2012 monitored with SwiftBAT, probably an indication of the expected strong interaction with the dense M-giant wind. We present an analysis of a Chandra observation performed on 2010, December 26, and an RXTE observation performed on 2011, January 10–11. The Swift-BAT context shows that during both observations the source was in a state of comparatively stable and low hard X-ray flux. We discuss the broad band “baseline” spectrum and compare it to the two earlier X-ray broad band studies described in the literature. Strong flaring activity on timescales of hundreds to thousands of seconds is observed and studied in the light of a possible accretion shock interpretation.