RXTE/PCA observations reveal fast-transient nature of IGR J17191-2821
ATel #1022; J. H. Swank (NASA/GSFC), C. B. Markwardt (CRESST/U. Md./NASA/GSFC), M. Klein-Wolt (Amsterdam), and R. Wijnands (Amsterdam)
on 7 Mar 2007; 17:57 UT
Credential Certification: Jean Swank (firstname.lastname@example.org)
Subjects: X-ray, Transient
On March 3 at 14:31 UTC, the RXTE/PCA had a scan of the Galactic bulge
which detected a new source, at a position which is consistent with it
being IGR J17191-2821, at an intensity of 10+-1 mCrab (2-10 keV).
INTEGRAL's IBIS/IGRI discovered IGR J17191-2821 (Turler et al. 2007, Atel
#1021) in an average over the interval March 2, 13:22 to March 4,
05:21 UTC, which included the time or the RXTE scan. However a
follow-up RXTE observation on March 6, 14:45 - 15:26 UTC, found a flux of no
more than 0.5 mCrab. This flux can be fit with a power law of photon
index 2.4+-0.5 or a bremsstrahlung spectrum with kT=5+-2 keV, with
little absorption, and is approximately the estimated flux from that
position in the Galactic bulge before the source was
identified. Therefore it could be due to unresolved emission; the
source may have decayed below this level. No significant oscillations
or noise which are characteristic of accreting sources were detected
in this flux.
In a bulge scan at March 7, 09:06 UTC, the source was not detected,
with a 3 sigma upper limit of 1.2 mCrab, confirming the decay of the
transient. The scans since their beginning on February 5, 1999 were
reanalyzed for contributions from a source at the position of IGR
J17191-2821. No flares brighter than 2 mCrab were seen. These non-detections
during the bulge scans spanning 8 years show that
this source is relatively infrequently active.
So far we know only that this source was active during a maximum of
1.7 d, with a hard spectrum. The source might be binary with a compact
object and a high mass companion. Although a low-mass companion cannot
be excluded, it then had a very short outburst and an unusually
hard spectrum. A stellar flare from
a near-by star or an outburst from a magnetar cannot be ruled out.