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Decreased flux of the new X-ray source XMMSL1 J171900.4-353217 detected by Swift-XRT

ATEL # 2656; M. Armas Padilla, N. Degenaar, Y. Yang, A. Patruno, R. Wijnands (University of Amsterdam)
on 2 Jun 2010; 15:18 UT
Password Certification: Rudy Wijnands (

Subjects: X-ray, Binaries, Black Holes, Neutron Stars, Transients
Referred to by ATEL #: 2722

Following the recent discovery of XMMSL1 J171900.4-353217 [ATel #2607] and its subsequent detections with RXTE-PCA between March 5 and April 15 [ATel #2615] and with Swift-XRT on May 11 [ATel #2627], we report on a new Swift-XRT observation of 1 ks carried out on 2010 May 31. The source was clearly detected in the photon-counting mode with a count rate (0.5-10 keV) of 0.07 counts/s.

The source spectrum can be described by an absorbed powerlaw model with a photon index of 2.3+/-0.7, where the hydrogen column has been fixed to the value obtained for a previous Swift-XRT observation (3.4E22 cm-2; ATel#2627). The resulting absorbed 2-10 keV flux is 5.5E-12 ergs cm-2 s-1 and the unabsorbed 2-10 keV flux is 7.7E-12 ergs cm-2 s-1. The corresponding X-ray luminosity assuming a distance of 8 kpc is Lx~5.9E34 ergs s-1.

The flux has decreased nearly one order of magnitude with respect to the previous Swift-XRT observation [ATel #2627], which suggests that the source may be a transient system which is returning back to quiescence. However, it is still possible that XMMSL1 J171900.4-353217 is a persistent X-ray source which is highly variable (more than 1 magnitude variability).

Further Swift-XRT observations are scheduled to monitor the behavior of the source.

We thank the Swift team for making these observations possible.

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R. E. Rutledge , Editor
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