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A new bright flare during the last (long) outburst from the Supergiant Fast X-ray Transient IGR J16479-4514

ATel #1929; V. La Parola, P. Romano (INAF-IASF Palermo), L. Sidoli (INAF-IASF Milano), P. A Evans (U. Leicester), J. A. Kennea (PSU), G. Cusumano, V. Mangano, S. Vercellone (INAF-IASF Palermo), H. K. Krimm (CRESST/GSFC/USRA), D. N. Burrows (PSU), N. Gehrels (GSFC)
on 9 Feb 2009; 16:18 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Pat Romano (romano@ifc.inaf.it)

Subjects: X-ray, Binary, Transient

The Supergiant Fast X-ray Transient IGR J16479-4514 has undergone a new bright flare on 2009 February 8 at ~20:30 UT, which reached a count rate of 5 counts/s. This is interestingly part of the same outburst which triggered the BAT on January 29 at 06:33:07 UT (ATel #1920) at a rate of 150 mCrab.

Swift/XRT has been monitoring the source flux since January 29, with several daily observations. The XRT light curve shows a large variability, with the source being almost always detected with a rate ranging from about 3E-2 to 5 counts/s, thus demonstrating that the source is still active since January 29.

The XRT spectrum, fitted with an absorbed powerlaw model, yields a photon index of 1.0 (-0.5,+0.6) and an absorbing column density of 6.3 (-2.0,+2.7)E+22 cm-2. The observed (unabsorbed) 0.3-10 keV flux is 2.1E-10 (3.4E-10) erg/cm2/s. These results are consistent with the ones derived for the previous outburst which occurred on March 19, 2008 (i.e. 315 days ago), recorded by Swift (ATel#1435; Romano et al. 2008, ApJ, 680, L137) and with the previous flare of this outburst event (ATel#1920).

These results demonstrate that in IGR J16479-4514 bright flares spaced by a few days are part of the same outburst phase. This could be the case also of other SFXTs were flaring activity spaced by several days have been observed (e.g. IGR17544-2619, ATel #1697) and could indicate a long outburst, instead of separate and frequent shorter outbursts.

Further Swift observations are ongoing.