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A new outburst of the SFXT IGR J08408-4503 observed by Swift

ATel #2520; P. Romano (INAF-IASF Palermo), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), C. B. Markwardt (GSFC/UMD), D. N. Burrows (PSU), M. M. Chester (PSU), G. Cusumano (INAF-IASF Palermo), P. Esposito (INAF-IASF Milano), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), V. La Parola (INAF-IASF Palermo), S. Vercellone (INAF-IASF Palermo), N. Gehrels (GSFC)
on 29 Mar 2010; 11:23 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Pat Romano (romano@ifc.inaf.it)

Subjects: X-ray, Gamma Ray, Request for Observations, Binary, Transient

Referred to by ATel #: 3586, 5190

The Swift Burst Alert Telescope (BAT) triggered on a new outburst from the Supergiant Fast X-ray Transient (SFXT) IGR J08408-4503 on 2010 March 28 at 15:53:38 UT (image trigger=417420). Swift did not execute an immediate slew, because of an Earth-limb constraint.

Using the BAT data from T-220 to T+280 s, the emission starts at ~T-120 and ends at ~T+120 s. The peak emission occurs at ~T+10 s at about 0.09 counts/cm2/s. The partial coding was 92%. The time-averaged spectrum from T-96.8 to T+118.6 s is best fit by a power law with an exponential cutoff. This fit gives a photon index of 0.27 +/- 1.78, and Epeak of 28.4 +/- 11.6 keV (chi squared 69.7 for 56 d.o.f.). The 1-s peak flux measured from T+13.04 s in the 15-150 keV band is 0.4 +/- 0.1 ph/cm2/s. A fit to a simple power law gives a photon index of 2.40 +/- 0.29 (chi squared 76.1 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.

The XRT began observing the field at 16:48:29.2 UT, 3290.9 seconds after the BAT trigger, for two orbits. At that time, the source count rate was ~ 0.1 counts/s. The spectrum (PC mode data, T+3298 to 10460 s) can be fitted with an absorbed power-law with a photon index of 1.2+/-0.4 and an absorbing column density of NH=[9 (+6,-4)]E21 cm-2. The average 2-10 keV unabsorbed flux is ~9E-12 erg/cm2/s.

Previously, Swift observed flares from this source on 2006 October 4 (Gotz et al. 2007,ApJ,655,L101; Romano et al. 2009,MNRAS,392,45), 2008 July 05 (Romano et al. 2009,MNRAS,392,45), 2008 September 21 (Sidoli et al. 2009,MNRAS,397,1528), and 2009 August 28 (ATel #2178). The historical light curve from the BAT hard X-ray transient monitor (Krimm et al, 2006, ATel #904; 15-50 keV) can be found at http://swift.gsfc.nasa.gov/docs/swift/results/transients/weak/IGRJ08408-4503 .

We would like to thank the Swift Team for making these observations possible, in particular the duty scientists as well as the science planners.