Discovery of a Transient ULX in M83
ATel #3092; R. Soria (UCL), K. S. Long (STScI), L. Bianchi (JHU), W. P. Blair (JHU), P. Ghavamian (STScI), K. D. Kuntz (JHU), P. P. Plucinsky (CfA), P. F. Winkler (Middlebury College)
on 29 Dec 2010; 21:10 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Howard E. Bond (bond@stsci.edu)
Subjects: Optical, X-ray, Transient
We report our discovery of a transient ultraluminous X-ray source in the inner disk of the spiral galaxy M83 (d = 4.5 Mpc). Our recent Chandra/ACIS observations of this galaxy (60 ks on 2010 December 23 and 100 ks on 2010 December 25) show a bright point-like source about 1 arcmin (1.3 kpc) to the east of the nucleus, at R.A.(J2000) = 13h 37m 05.143s and Dec.(J2000) = -29d 52m 06.9s (0.5 arcsec uncertainty). Its spectrum is well fitted by a single power law with photon index Gamma = 1.71 +/- 0.03, and low absorption (intrinsic NH ~ 10^{20} cm^{-2} in addition to a line-of-sight column of ~5 x 10^{20} cm^{-2}). The unabsorbed 0.3-8 keV flux is ~1.3 x 10^{-12} erg cm^{-2} s^{-1}, corresponding to a luminosity ~3 x 10^{39} erg s^{-1}. No spectral or luminosity changes are found between the Dec 23 and 25 observations. In the previous Chandra/ACIS observation on 2000 April 29, no sources are detected at the same position down to a limit of ~5 x 10^{36} erg s^{-1}. We do not find any optical counterparts in our Magellan images from 2009 April or in the HST/WFC3 images obtained in 2009 August, down to V ~ 26 mag, corresponding to an absolute brightness MV ~ -2 mag; for this ULX, the donor is clearly not an OB star. We encourage follow-up multi-band observations of the field.
