Swift/XRT follow-up observations of unidentified INTEGRAL sources (2)
ATel #3272; R. Landi, L. Bassani, N. Masetti (INAF/IASF Bologna), A. Bazzano (INAF/IASF Rome), A. J. Bird (University of Southampton)
on 11 Apr 2011; 15:24 UT
Credential Certification: Raffaella Landi (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Request for Observations
Referred to by ATel #: 3933
We report the results of X-ray follow-up observations performed with Swift/XRT of 3 unidentified
INTEGRAL sources listed in the INTEGRAL all sky survey (Krivonos et al. 2010, A&A, 523, 61).
Within the IBIS error circle, XRT does not detect any X-ray source above 3 sigma confidence level (c.l.);
the upper limit on the 0.2-12 keV flux is 0.8 x 10-12 erg cm-2 s-1.
However, inside the INTEGRAL positional uncertainty there is an XMM Slew Survey source (XMMSL1
J182155.0-134719) with a 0.2-12 keV flux of 8 x 10-12 erg cm-2 s-1.
This source is located at R.A.(J2000) = 18h 21m 55.06s and Dec.(J2000) =
+13d 47m 18.6s (10.2 arcsec uncertainty). The XMM detection coincides with a 2MASS object (2MASS
18215463-1347232) having magnitudes J ~14.3, H ~12.3 and K ~11.5 and no detection in optical. The
comparison between the XMM Slew and XRT fluxes indicates that this
possible counterpart to the INTEGRAL source is highly variable.
The XRT image only covers part of the IBIS error circle but still provides the detection of a hard
variable source (6.5 sigma c.l. in the 0.3-10 keV energy band and above 3 keV) during XRT pointings.
This object is located at R.A.(J2000) = 16h 33m 29.88s and Dec.(J2000) = -47d 33m 33.1s (4.2 arcsec
uncertainty). Within the XRT positional uncertainty we find a 2MASS object (2MASS 16332956-4733327) with
magnitudes J ~15.3, H ~11.7 and K ~10.0, which is also reported in the GLIMPSE catalogue (around
8.8 magnitude at both 3.6 and 4.5 micron).
The X-ray data are well described by an absorbed
(NH ~3 x 1022 cm-2) power law (Gamma fixed at 1.8) with a 2-10 keV
flux of 1.6 x 10-12 erg cm-2 s-1.
This source has also been reported as a JEM-X object (Westergaard et al 2006, ATel #967) and is
listed as transient in the SWIFT 22 month catalogue (Tueller et al. 2010, ApJS, 186, 378). Inside
the IBIS and JEM-X error circles, we find an X-ray source detected at 79 sigma c.l. in the 0.3-10
keV and 72 sigma c.l. above 3 keV. It is located at R.A.(J2000) = 20h 37m 05.51s and Dec.(J2000) =
+41d 50m 05.7s (3.5 arcsec uncertainty). Within the XRT positional uncertainty we find a 2MASS
object (2MASS 20370560+4150051) detected with magnitudes J ~16.2, H ~13.5 and K ~12.1.
A good fit to the average X-ray spectrum is provided by an absorbed (NH ~3 x 1022
power law (Gamma ~0.8) plus an iron line at 6.7 keV with an EW ~550 eV.
Comparison between XRT observations indicates variability in the source flux by a factor of ~1.5 over a
period of a year.
The authors acknowledge the use of public data from the Swift data archive.