Swift reports a recent brightening of XTE J1543-568

ATel #4008; H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), W. Baumgartner (CRESST/GSFC/UMBC), J. Cummings (CRESST/GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. B. Markwardt (GSFC), D. Palmer (LANL), T. Sakamoto (CRESTT/GSFC/UMBC), G. Skinner (CRESST/GSFC/UMD), M. Stamatikos (OSU/GSFC), J. Tueller (GSFC), T. Ukwatta (GSFC/MSU)
on 29 Mar 2012; 15:32 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

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The Swift/BAT hard X-ray transient monitor has recorded a recent flux increase from the transient X-ray pulsar and likely Be binary system XTE J1543-568. In the 15-50 keV band, the source was first detected in an 8-day integration covering 2012 March 9-16 (MJD 55995-56002) with a rate of 0.0016 +/- 0.0003 ct/s/cm2. The peak day in the light curve was 2012 March 22 when the rate was 0.0043 +/- 0.001 ct/s/cm2 (~20 mCrab). The rate has subsequently declined to an undetectable level in the BAT: 1-sigma upper limit of 0.00075 ct/s/cm2 on 2012 March 28.

A target of opportunity observation with Swift was performed beginning 2012 Mar 22 at 16:49:59 for a total of 3172 seconds in photon counting mode. A bright source was found at the location (J2000):

RA = 236.02169 (15:44:05.21)
dec = -56.76194 (-56:45:43.0)
with an estimated error of 2.1 arcsec (90% confidence)

This is the best measured position of XTE J1543-568 and is within the error circle of the position reported by BeppoSAX (in’t Zand, Corbet & Marshall, 2001, ApJ 553, L165).

There is a source in the 2MASS all sky catalog within the XRT error circle. This is 2MASS 15440515-5645425 at the location RA=236.021468, dec=-56.761826. The catalog magnitudes are J=14.315 +/- 0.050, H=13.344 +/- 0.043, K=12.780 +/- 0.040. We tentatively identify this star as the optical counterpart of XTE J1543-568.

The simultaneous UVOT U-band image shows no source within the XRT error circle as would be expected with the high absorption. However, two other nearby bright stars found in the USNO A2.0 catalog are clearly seen.

The spectrum was fitted with an absorbed power-law model with the parameters:

NH 2.08 +/- 0.53 X 10^22 cm^-2
Photon index 0.76 +/- 0.27
Flux (0.3-10 keV)(Observed) 1.025 +/- 0.10 X 10^-10 erg/cm2/s
Flux (0.3-10 keV)(Unabsorbed) 1.284 +/- 0.10 X 10^-10 erg/cm2/s
C-stat (dof) 359.05 (440)

The flux is fainter by a factor of >2 than what was seen when the source was discovered in 2000 (in’t Zand, Corbet & Marshall, 2001, ApJ 553, L165).

The estimated galactic absorption is 1.33 x 10^22 cm-2 (Kalberla et al. 2005). All XRT analysis is from the web-based analysis process of Evans et al. (2009, MNRAS, 2009, 397, 1177).

BAT Transient Monitor light curve for XTE J1543-568