CXOU J004233.2+411742: A new X-ray transient in the M 31 globular cluster Bol 112
ATel #4164; F. Hofmann, M. Henze, W. Pietsch, F. Haberl, J. Greiner (Max-Planck-Institut fuer extraterrestrische Physik, MPE)
on 12 Jun 2012; 13:40 UT
Credential Certification: Martin Henze (mhenze@mpe.mpg.de)
Subjects: X-ray, Transient
We report the discovery of a new X-ray transient (CXOU J004233.2+411742) in a Chandra HRC-I observation of the Andromeda Galaxy starting 2012-06-01.90 UT (ObsID 13281). The position of the source is RA = 00h42m33.26s Dec = +41d17'42.7" (± 0.5 arcsec, J2000). The source is also detected in a quasi simultaneous Swift X-ray telescope (XRT) observation starting 2012-06-01.77 UT (ObsID 00035336053).In a Swift XRT observation starting 2012-06-09.26 UT (ObsID 00035336054), one week later, the source had increased its luminosity by a factor of ~10. We derived 3σ upper limits for the last observations of Chandra HRC-I and Swift XRT 80 and 8 days before the first detection, respectively. This indicates that the source brightened by a factor of at least 130. No source was reported for this position in earlier Chandra and XMM-Newton observations. The table below gives observation details, count rates and luminosities.
In the second Swift observation we detected about 50 photons extending to 5 keV, that clearly indicate a hard spectrum. Absorption corrected luminosities in the 0.2-10 keV band have been calculated using a foreground column density of
NH = 6.6 × 1020 cm-2, assuming a power law spectrum with a photon index of 1.7 and a distance of 780 kpc to M 31.
The position of the transient coincides within the errors with the globular cluster (GC) Bol 112 from the Revised Bologna Catalog of M 31 globular clusters (Galleti et. al. 2004, A&A, 416, 917). The relatively hard spectrum and the correlation with a GC indicate a low mass X-ray binary nature.
This source correlates with the ROSAT HRI source 1RXH J004241.8+411535 (ROSAT Team, 2000), which was detected with a 0.2-10 keV band luminosity of 0.77 ± 0.31 × 1037 erg/s in July 1994 (ObsID US600474H.N1) with a positional error of 9". If the ROSAT detection indeed is the same source, CXOU J004233.2+411742 might be a recurrent transient detected by ROSAT at the beginning or end of a previous outburst 18 years ago.
Telescope/ ObsID Exposure MJD Count rate Luminosity
Instrument [ks] [d] [10-3 ct/s] [1037 erg/s]
Chandra HRC-I 13280 19.3 55999.21 < 0.5 < 0.1
Chandra HRC-I 13281 18.9 56079.90 6.5 ± 0.6 1.4 ± 0.1
Swift XRT 00035336052 4.2 56071.62 < 6.4 < 2.0
Swift XRT 00035336053 4.0 56079.77 4.1 ± 1.3 1.5 ± 0.5
Swift XRT 00035336054 2.0 56087.26 36.0 ± 5.0 13.3 ± 1.8
We would like to thank the Swift Team for making these observations possible, in particular N. Gehrels, the duty scientists as well as the science planners.
