[ Previous | Next ]
ATEL # 1174; L. Sidoli (INAF-IASF Milano), P. Romano (Univ Bicocca&INAF-OABrera), S. Mereghetti (INAF-IASF Milano), M. Del Santo(INAF-IASF Roma)
on 9 Aug 2007; 12:56 UT
Password Certification: Lara Sidoli (email@example.com)
Subjects: Binaries, Transients
We are performing a monitoring with Swift/XRT of the Very Faint X-ray Transient (VFXT) XMMUJ174716.1-281048 (ATel #147 and Sidoli et al., 2006, A&A 456, 287) which is undergoing an accretion phase since 2003 (Del Santo et al., 2007, A&A 468, L17; ATel #1078, #1136). To date, this is the first VFXT displaying a ``quasi persistent" behaviour.
Swift/XRT observed the source four times: on 13 and 17 May 2007 (results reported by Degenaar et al. 2007 (ATel #1136)), on 3 July 2007 (16:19:21 to 19:14:52 UT; net exposure Texp=1148 s) and on 8 August 2007 (03:27:56 to 18:00:58; Texp=1991 s). We report here the results from the two latest observations.
The source is detected with a 0.2-10 keV count rate of (3.56+\-0.71)E-02 counts/s (3 July 2007) and (1.50+/-0.35)E-02 counts/s (8 Aug 2007), which translates into a 2-10 keV flux, corrected for the absorption, of (5.3+/-1.0)E-12 erg/cm2/s and (2.2+/-0.5)E-12 erg/cm2/s (1sigma errors), assuming a power law model with a photon index of 2.25, absorbed by a column density of 9E22 cm-2.
A comparison of these values with the previous measurements since 2003 reveals a complex lightcurve, apparently not compatible with a simply linear decay. We will continue to monitor the source flux in the next months with Swift/XRT.
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.