Swift observes a new outburst from the Supergiant Fast X-ray Transient XTEJ1739-302/IGRJ17391-3021
ATel #1466; P. Romano (INAF-IASF Palermo), L. Sidoli (INAF-IASF Milano), V. Mangano (INAF-IASF Palermo), H. A. Krimm (CRESST/GSFC/USRA), S. Barthelmy (GSFC), D. N. Burrows (PSU), G. Cusumano (INAF-IASF Palermo), N. Gehrels (GSFC), J. A. Kennea(PSU), A. Paizis (INAF-IASF Milano), J. Tueller (GSFC), S. Vercellone (INAF-IASF Milano)
on 9 Apr 2008; 15:16 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Pat Romano (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Request for Observations, Binary, Transient
A new outburst from the source XTEJ1739-302/IGRJ17391-3021
(Smith et al. 1998, ApJ 501, L101),
the prototype of the class of the Supergiant Fast X-ray Transients
(SFXT; Smith et al. 2005 ApJ, 638, 974; Negueruela et al. 2006 ApJ, 638, 982),
was observed by the Swift Burst Alert Telescope (BAT) on 2008-04-08 at 21:28:15
Swift immediately slewed to the target, so that the narrow-field instruments
began observing the field 387 s after the BAT trigger.
Using the BAT data set from T-119 to T+950 s from the recent telemetry downlink,
we obtained a nearly constant mask-weighted light curve at the level of
0.25 counts/cm2/s in the 15-150 keV band. The partial coding was 100%.
We extracted two time-averaged spectra in the time intervals form
T+0 s to T+341 s (before the slew to the target) and from T+373 s to T+850 s
(after the slew, simultaneous with XRT observation).
Both spectra can be fit with simple power law models with photon
indices of 2.7 +/- 0.5 and 3.0 +/- 0.6, consistent with a constant slope.
The 15-150 keV fluxes in the given time intervals are 1.8E-9 and
1.2E-9 ergs/cm2/s, respectively.
The Swift/XRT light curve shows two distinct flares
of decreasing intensity;
during the first one, which was caught in its descending part,
the source reached ~10 counts/s;
the second flare is roughly half as bright as the first one
(< 4 counts/s).
The Swift/XRT data consist of the initial WT data,
and subsequent PC data, when the source was fainter.
The XRT spectrum from WT data (393-468s since the trigger)
can be fit with an absorbed powerlaw with
a photon index of 1.29(-0.58,+0.67)
and an absorbing column density of NH=(11-3+4)E+22 cm-2
(chi2_red=1.253 for 21 dof).
The peak of the flare reached 1.7E-9 erg/cm2/s (unabsorbed, 2-10 keV),
which translates into a luminosity of 1.4E+36 erg/s (assuming the optical
counterpart distance of 2.7 kpc, Rahoui et al. 2008, arXiV 0802.1770).
The fainter X-ray emission (PC data, 565-6649s since the BAT trigger)
resulted in a photon index of 1.27(-0.73,+0.92), NH=(10-4+6)E+22 cm-2
(chi2_red=1.252 for 14 dof)
and an unabsorbed flux of 4.3E-10 erg/cm2/s (2-10 keV).
In the past, several bright flares have been observed from this SFXT,
mainly with RXTE (Smith et al. 2005 ApJ, 638, 974)
and INTEGRAL (Sguera et al. 2005 A&A, 444, 221;
Sguera et al. 2006 ApJ, 646, 452; Walter et al., 2007, A&A, 476, 335).
The last outburst was observed with the IBIS/ISGRI instrument on-board
INTEGRAL, about 403 days ago, on March 2, 2007 (Turler, et al., 2007 ATel#1019).
In the BAT hard X-ray transient monitor (15-50 keV), this source has
shown six past episodes of emission above 150 mcrab and 3.0 sigma
significance including an onboard trigger on June 18, 2007.
The IGR J17391-3021 light curve from the BAT monitor can be found at http://swift.gsfc.nasa.gov/docs/swift/results/transients/weak/IGRJ17391-3021/
We would like to thank the Swift Team for making these observations possible,
in particular the duty scientists as well as the science planners.
BAT Transient Monitor page: IGRJ17391-3021/