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Swift observes another outburst from the Supergiant Fast X-ray Transient XTEJ1739-302/IGRJ17391-3021

ATEL # 1659; P. Romano (INAF-IASF Palermo), C. Guidorzi (INAF-OAB), L. Sidoli (INAF-IASF Milano), J.A. Kennea(PSU), P.A. Evans (U. Leicester), S. Vercellone (INAF-IASF Milano), V. Mangano (INAF-IASF Palermo), D.N. Burrows (PSU), G. Cusumano (INAF-IASF Palermo), H.A. Krimm (CRESST/GSFC/USRA), N. Gehrels (GSFC)
on 14 Aug 2008; 14:47 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Pat Romano (

Subjects: X-ray, Gamma Ray, Binaries, Transients

XTEJ1739-302/IGRJ17391-3021 (Smith et al. 1998, ApJ 501, L101), triggered Swift/BAT twice in the past 24 hours, on 2008-08-13 23:49:17 UT and 2008-08-14 00:12:53 UT.

The Swift/BAT time-averaged spectrum from T-61.8 to T+648.9 s is best fit by a power law with an exponential cutoff with a photon index of 0.35+-1.78, and Epeak of 21.9+-13.6 keV (chi^2=57.9 for 56 d.o.f.). The 1-s peak flux for this model, measured from T-59.83 s in the 15-150 keV band, is 0.4+-0.3 ph/cm2/s. A fit with a simple power law yields a photon index of 2.73+-0.26 (chi^2=65.49 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.

The Swift/XRT light curve shows one bright flare that reached about 40 counts/s. The mean XRT/WT spectrum (T+397 to T+2390s since the trigger) can be fit with an absorbed powerlaw with a photon index of Gamma=1.26+-0.06 and an absorbing column density of NH=(5.5+-0.2)E+22 cm-2 (chi^2_red=1.3 for 644 dof). The mean flux is 3E-9 erg/cm2/s (unabsorbed, 2-10 keV), which translates into a luminosity of 2.5E+36 erg/s (assuming the optical counterpart distance of 2.7 kpc, Rahoui et al. 2008, arXiV 0802.1770). At the peak (T+1384 to T+1454 since the trigger) the spectrum could be fit with a simple absorbed power law with Gamma=1.15+-0.20 and NH=(3.6+-0.6)E22 (chi^2_red=1.08 for 81 dof). The flux reached 3.7E-9 erg/cm2/s (luminosity of 3.0E+36 erg/s).

The best UVOT-enhanced XRT position is: RA(J2000)=264.79863, Dec(J2000)=30.34351 (or RA=17 39 11.67, Dec=+30 20 36.6), with an estimated uncertainty of 3.1 arcsec.

The previous outburst that triggered Swift/BAT occurred on 2008 Apr 8 (Romano et al 2008; ATel #1466), and showed consistent X-ray spectral properties.

Further Swift observations are underway and we encourage multifrequency observations.

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R. E. Rutledge , Editor
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