Swift and INTEGRAL observations of activity in XTEJ1739-302/IGRJ17391-3021
ATel #1961; P. Romano (INAF-IASF Palermo), L. Sidoli (INAF-IASF Milano), H. A. Krimm (CRESST/GSFC/USRA), G. Cusumano (INAF-IASF Palermo), E. Kuulkers (ESA/ESAC, Spain; on behalf of the Galactic bulge monitoring team), S. Vercellone (INAF-IASF Palermo), D. N. Burrows (PSU), N. Gehrels (GSFC), J. A. Kennea (PSU), V. La Parola, V. Mangano (INAF-IASF Palermo)
on 11 Mar 2009; 15:07 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, Transient
Referred to by ATel #: 3182
On 2009 March 10 at 18:39:55.43 UT, the Swift Burst Alert Telescope (BAT)
triggered on the supergiant fast X-ray transient
XTE J1739-302/IGRJ17391-3021 (trigger=346069).
Swift did not slew to the source at once, so no NFI data were collected immediately.
Since this was an image trigger, the Swift/BAT light curve does not show any significant structure.
The rate remained roughly constant during the 1600 s observation when the source
was in the field of view (18:18:35 - 18:45:15 UT).
The average rate for the observation was 0.0195 +/- 0.0025 counts/s/cm2 (15-50 keV),
which corresponds to 85 mCrab.
The rate increased somewhat to ~100 mCrab toward the end of the observation
(the trigger interval).
Using the Swift/BAT data set from T-239 to T+963 sec from the recent telemetry downlink,
we find that the time-averaged spectrum (T+0.0 to T+320.0 s) is best fit by a simple
power-law model with a photon index of 3.02 +- 0.75.
The fluence in the 15-150 keV band is 3.6 +- 1.4 x 10^-07 erg/cm2.
All the quoted errors are at the 90% confidence level.
The Swift/XRT light curve obtained between 2009-03-10 20:07:35
and 2009-03-10T21:35:54 (1.9ks net exposure) shows a mean count rate of
0.4-1 counts/s. The mean XRT/PC spectrum (T+5257s to T+10538s since the
trigger) can be fit with an absorbed powerlaw with a photon index
of Gamma=1.2+-0.4 and an absorbing column density of NH=(4+-1)E+22
cm-2 (chi^2_red=0.95 for 25 dof). The mean flux is 8E-11 erg/cm2/s (unabsorbed,
2-10 keV), which translates into a luminosity of 7E+34 erg/s (assuming
the optical counterpart distance of 2.7 kpc, Rahoui et al. 2008, A&A, 484, 801).
More observations were performed on 2009-03-11 05:52:47 to 07:19:57
(1.9ks net exposure), and the XRT count rate was down to (1.9 +/- 0.4)E-02
counts/s (4.8 sigma detection).
INTEGRAL observations taken on 2009-02-21 09:56 - 13:38,
2009-02-25 13:21 - 17:02, 2009-03-09 11:16 - 14:57 did not reveal the source
with a typical 3 sigma upper limit of about 6 mCrab (18-40 keV) per observation.
A 4.5 sigma detection was obtained during observations taken on 2009-03-03
11:42 - 15:24, at with an average flux of 7+/-1.5 mCrab (18-40 keV).
The previous outbursts that triggered Swift/BAT occurred on 2008 Aug 13 (ATel #1659)
and 2008 Apr 8 (ATel #1466).
Further Swift observations are being carried out. We encourage multifrequency observations.