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Swift/XRT imaging of XTE J1812-182 (=XMMU J181227.8-181234?)

ATEL # 1696; M.A.P. Torres (CfA), D. Steeghs (Warwick/CfA), J. A. Kennea (PSU), J. Homan (MIT) and J. M. Miller (Michigan)
on 4 Sep 2008; 13:21 UT
Password Certification: Manuel Torres (

Subjects: X-ray, Black Holes, Neutron Stars, Transients

We report on target of opportunity observations of XTE J1812-182 taken by Swift/XRT starting on 2008-09-03 13:12 UT and performed in Photon Counting (PC) and Window Timing (WT) modes for 257 and 387 seconds, respectively.

PC mode data were taken to ensure an accurate localization of this transient and determine whether this source is a new transient or renewed activity from XMMU J181227.8-181234 (Markwardt, Pereira & Swank 2008, ATEL #1685). Analysis of the data reveals a single bright (2.0 cts/s) point source at R.A. (J2000) = 18:12:28.37, Dec(J2000) = -18:12:36.0, with an estimated uncertainty of 3.7 arcseconds radius (90% confidence). These coordinates lie 8.3 arcseconds away from the position of XMMU J181227.8-181234 reported in Cackett, Wijnands & Remillard,2006,MNRAS,369,1965.

The WT mode observation with 4.1 cts/s provided data free of pile-up. As in Cackett et al, (2008), the X-ray spectrum can be described by 1) an absorbed power-law model with N_H = (11.3 +/- 1.0)e22 cm^-2 and a photon index of 2.2 +/- 0.2 (reduced chi**2 = 0.96) and by 2) an absorbed multi-color disk blackbody model with N_H = (9.0 +/- 0.7)e22 cm^-2 and kT_in = 2.3 +/- 0.2 keV (reduced chi**2 = 0.95). Uncertainties are at the 68% level confidence. From the above fits we derive an unabsorved 0.5 - 10 keV flux of (1.1-2.3)e-09 ergs/cm^2/s (range depending on the model used). The above fit parameters and flux are in line with those reported for XMMU J181227.8-181234 during the 2003 discovery outburst.

We therefore conclude that the X-ray source detected by RXTE is likely due to renewed activity of XMMU J181227.8-181234.

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