Swift observations of a new outburst of the SFXT IGR 16418-4532

ATel #5398; H. A. Krimm (CRESST/GSFC/USRA), V. Mangano (PSU), P. Romano (INAF-IASFPA), B. Sbarufatti (PSU), P. A. Evans (U Leicester), J. A. Kennea (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), P. Esposito (INAF-IASFMI), N. Gehrels (GSFC), S. Vercellone (INAF-IASFPA)
on 18 Sep 2013; 13:33 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

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The Swift Burst Alert Telescope (BAT) triggered on a new outburst from the Supergiant Fast X-ray Transient (SFXT) IGR 16418-4532 on 2013 September 17 at 14:41:17 UT (image trigger=571067). Swift had a delayed slew to the target, so that the narrow field instruments started observing about 5261 s after the trigger and observations continued until T+6411 sec.

Using the BAT data set from T-239 to T+903 sec from the recent telemetry downlink, we report that the time-averaged spectrum from T+0 to T+448 s is best-fit by a simple power-law model with a photon index of 3.05+/-0.43. The fluence in the 15-150 keV band is (7.0+/-1.4)E-7 erg/cm2. All the quoted errors are at the 90% confidence level. The source was in the BAT field of view from approximately T-80 sec to T+530 sec.

The Swift/XRT light curve reached a count rate of about 0.5 counts/s in a late flare from ~T+5900 to T+6300 s. The XRT/PC spectrum (T0+5211 to 6319 s, integration 1108 s) can be fit with an absorbed power law, with a photon index of 1.1 (+1.9, -1.2), and an absorbing column density of NH=0.94 (+0.7, -0.5)E+23 cm-2. The mean observed (unabsorbed) flux is about 1.7E-11 (3.3E-11) erg/cm2/s (0.3-10 keV).

Previously, Swift observed bright flares from this source on 2011 February 17 (Romano et al., 2012, MNRAS, 419, 2695), 3 June 2012 (Romano et al., 2012, ATel #4148) and 2 April 2013 (Romano et al., 2012, ATel #4939). The historical light curve from the BAT hard X-ray transient monitor (Krimm et al., 2013, ApJS, in press, arXiv:1309.0755; 15-50 keV) can be found at http://swift.gsfc.nasa.gov/docs/swift/results/transients/weak/IGRJ16418-4532/ .

Swift/BAT Transient Monitor light curves for IGR J16418-4532