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Swift observations of an outburst of the SFXT AX J1845.0-0433/IGR J18450-0435

ATEL # 2102; P. Romano (INAF-IASF Palermo), S. Barthelmy (GSFC), R. Margutti (Univ Bicocca&OAB), C. Guidorzi (U. Ferrara), L. Sidoli (INAF-IASF Milano), J.A. Kennea (PSU), V. La Parola (INAF-IASF Palermo), D.N. Burrows (PSU), P. Esposito (INAF-IASF Milano), P.A. Evans (U. Leicester), H.A. Krimm (CRESST/GSFC/USRA), N. Gehrels (GSFC), S. Vercellone (INAF-IASF Palermo)
on 28 Jun 2009; 18:33 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Pat Romano (

Subjects: X-ray, Gamma Ray, Request for Observations, Binaries, Transients

Swift has observed a new outburst from the Supergiant Fast X-ray Transient AX J1845.0-0433/IGR J18450-0435. The Swift Burst Alert Telescope (BAT) triggered on it on 2009 June 28 at 08:06:03 UT (image trigger=355911). Swift slewed to the target, so that the XRT began observing the field at about 795 seconds after the BAT trigger.

Using the BAT data set from T-239 to T+963 s from the recent telemetry downlink, we find that the time-averaged spectrum from T+8.4 to T+790.7 s is best fit by a simple power-law model with a photon index of 2.41 +/- 0.34 (90% cl.). The fluence in the 15-150 keV band is (1.1 +/- 0.2)E-06 erg/cm2.

The Swift/XRT data (WT mode, 795-806 s since the trigger; PC mode, 808-829 s) show a decaying light curve with an initial count rate of 2 counts/s. The PC spectrum only contains 23 photons, so only an estimate of the observed flux (in the 0.3-10 keV energy band) can be derived, at ~3E-10 erg/cm2/s.

Previously, Swift caught a flare from this source on 2005 November 4. 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

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R. E. Rutledge , Editor
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