RXTE PCA Detection of a New Outburst of XTE J1728-295 (probably IGR J17285-2922)
ATel #2823; Craig B. Markwardt (NASA/GSFC), Jean H. Swank (NASA/GSFC)
on 31 Aug 2010; 04:38 UT
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Subjects: X-ray, Gamma Ray, Request for Observations, Binary, Black Hole, Transient
We report the detection of a new outburst of a source designated XTE
J1728-295 in the RXTE PCA scans, which is probably the same as IGR
J17285-2922. This source was first detected in August-October 2003 with
PCA scans of the galactic center region, and is speculated to be a black
hole candidate (Barlow et al. 2005, A&A, 437, L27).
In PCA scans on 2010-08-28 near 09:35 UTC, the source rose to a flux of
6.5 mCrab (2-10 keV). Observations in the previous ~2 weeks set upper
limits of ~1 mCrab (95%). The detection on 2010-08-28 signals a new
outburst of the source. The peak flux in the previous outburst was also
about 6-7 mCrab.
The best fit RXTE PCA position is based on the PCA scans themselves,
which yielded a position of R.A. = 262.157, Decl. = -29.520 (J2000),
with a position error of approximately 5-10 arcmin. This position is
consistent with a transient detected by INTEGRAL, IGR J17285-2922, which
was detected by a Galactic Center Deep Exposure during a similar time
window (Sep/Oct 2003; Barlow et al. 2005). INTEGRAL did not detect
another nearby source during that time, so XTE J1728-295 and
IGR J17285-2922 are very likely to be the same source.
We do not yet have PCA pointed observations of the source during this
outburst. In the previous outburst, the PCA spectrum of the source
during pointed observations on 2003-08-11 and 2003-08-22 were consistent
with a steep power law model with photon index 3.6-3.8 and no detectable
interstellar absorption, and 2-10 keV flux of ~1e-10 erg/s/cm2. A line
was detectable at ~6.7 keV and equivalent width ~1000 eV, which may be
due to contamination in the PCA field of view. The source later became
detectable by INTEGRAL (approx. 2003-09-25 to 2003-10-10) with a much
harder photon index of ~2.1 (Barlow et al. 2005), but still consistent
with PCA scan count rates.
No strong variability such as pulsations was detected in PCA pointed
observations in August 2003. Similar to Barlow et al. (2005), we
speculate that this source is a black hole binary system, which exhibits
the commonly known soft and hard states at different times. Further
observations at other wavelengths are encouraged.