The end of the long outburst of the very faint X-ray transient XMMU J174716.1-281048
ATel #7293; Melania Del Santo, Patrizia Romano (INAF/IASF-Palermo, Italy), Lara Sidoli (INAF/IASF-Milano)
on 26 Mar 2015; 09:41 UT
Credential Certification: Melania Del Santo (melania@ifc.inaf.it)
The very faint X-ray transient (VFXT) XMMU J174716.1-281048 was discovered in 2003 by XMM-Newton (ATel #147 and Sidoli et al., 2006, A&A 456, 287) and it was unveiled as an accreting neutron star after the discovery of a type-I burst with INTEGRAL (ATel #970; #972; Del Santo et al., 2007, A&A 468, L17).
The burst properties allowed us to derive a burst recurrence time t_rec=3Ã(alpha/40) yrs (where alpha is typically in the range 40-100, Strohmayer & Bildsten, 2006).
We proposed that the source was undergoing an accretion episode lasting several years, and we suggested that XMMU J174716.1-281048 could be defined as the first "quasi-persistent" VFXT (Del Santo et al. 2007, A&A, 468, L17).
We have been regularly monitoring this long-lived outburst since 2007 (ATel #3471; #2624; #2050; #1496; #1174),
with one Swift/XRT observation per year (http://www.ifc.inaf.it/~romano/ATels/XMMUJ174716.1_281048_xrt.html) until 2012 (ATel #4099).
New Swift/XRT observations were obtained during 2015 between 2015-02-17 04:37:48 UT and 2015-03-17 21:16:56 UT for a total exposure of 11 ks.
The source was not detected with a 3 sigma upper limit of 5.7E-03 ct/s (0.2-10 keV). This translates into a 2-10 keV flux (corrected for the absorption) of 6E-13 ergs/cm2/s and a luminosity at 8 kpc (ATel #1207) of 7E+33 erg/s, which indicates that the source is back to quiescence.
Additional data were retrieved from the Swift archive for a set of observations performed in March 2014, for a total of 1.7 ks.
For these data we obtain a 3 sigma upper limit on the flux of 3E-12 erg/cm2/s (2-10 keV), or a luminosity of 2.3E+34 erg/s.
Given the relatively short exposure, we cannot therefore conclude whether in 2014 the source was fainter than the previous
observations or already in quiescence.
We can however conclude that XMMU J174716.1-281048 is now back to quiescence after a long outburst.
Based on the fact that the last observation of the source being in quiescence was done in 2001 with Chandra (Del Santo et al. 2007), we can put a lower limit to the outburst duration of 11 years (latest detection in ATel #4099), and an upper limit to 14 years.
We would like to thank the Swift Team for making these observations possible, the duty scientists as well as the science planners.
