Chandra detects new outburst for M31 ULX XMMU J004243.6+412519
ATel #6405; R. Barnard (CfA), M. R. Garcia (CfA) and S. S. Murray (Johns Hopkins)
on 19 Aug 2014; 21:30 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Robin Barnard (rbarnard@cfa.harvard.edu)
Subjects: X-ray, Binary, Black Hole, Transient
The M31 X-ray transient XMMU J004243.6+412519 was first discovered by Henze et al (2012, Atel#3890); 6 days after first detection, its apparent 0.3-10 keV luminosity exceeded 10^39 erg/s, and Henze et al. (2012b, Atel #3921) classified this system as the second ultra-luminous X-ray source to be found in M31. In Barnard et al. (2013, ApJ 772, 126) we reported our discovery of an optical counterpart with ~B band magnitude 25.97 +/-0.03 in a HST ACS/WFC observation soon after outburst, fading to >28 ~6 months later, indicating a low mass donor (the optical emission during outburst is dominated by reprocessed X-rays).
In our 2014 August 18 Chandra ACIS observation, XMMU J0042.6+412519 (hereafter referred to as ULX2) yielded 249 photons, with 98.8% source contribution. Ignoring bad data and data below 0.3 keV yielded 214 photons, with 99.5% source contribution. The spectrum was soft, well described by a 0.37+/-0.04 keV disk blackbody absorbed by a column density equivalent to 3.37 E+21 H atom cm^-2 (fixed to the value observed in our serendipitous 120 ks XMM-Newton observation, Barnard et al 2013). The 0.3--10 keV luminosity was 1.22+/-0.14 E+38 erg/s.
In the most recent Chandra ACIS observation, on 2014 July 22, the 0.3-10 keV luminosity of ULX2 was ~5E+37 erg/s, suggesting that the X-ray output is increasing. We encourage further observation of this object
