Search for counterparts of newly discovered INTEGRAL/IBIS sources
ATel #4166; R. Landi, L. Bassani, N. Masetti (INAF - IASF Bologna), A. Bazzano, P. Ubertini (INAF - IAPS Rome), A. J. Bird, M. Goossens (University of Southampton)
on 12 Jun 2012; 15:45 UT
Credential Certification: Raffaella Landi (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Request for Observations
With respect to the recent INTEGRAL/IBIS 9-year Galactic Hard X-ray Survey (Krivonos et al.
2012, arXiv:1205.3941), we used archival Swift/XRT data to find
likely counterparts for two hard X-ray sources newly detected by INTEGRAL:
SWIFT J0958.0-4208 and IGR J22534+6243.
This source is also reported in the Swift/BAT 58-month catalogue
Within the hard X-ray positional error circles we find a ROSAT bright source
XRT pointed at the region surrounding SWIFT J0958.0-4208 for a total exposure of ~21.3 ks.
There are two X-ray objects within the IBIS/BAT error circles:
Source #1: This is the brightest of the two detections and the closest to the
ROSAT source, although the relative positional uncertainties do not intersect.
It is seen at 31 and 23 sigma confidence level (c.l.) in the 0.3-10 keV energy range and above 3 keV,
The XRT position is RA(J2000) = 09h 57m 50.66s and Dec(J2000) = -42d 08m 37.5s (3.6 arcsec
uncertainty, at 90% c.l.). There are three USNO-B1.0 objects falling within the XRT positional
uncertainty and one
2MASS source (2MASS J09575064-4208355), with magnitudes J ~15.4, H ~14.9, and K ~14.9.
The X-ray data are well modelled using a black body component (kT ~0.1 keV) and a power law having a
flat (Gamma ~0.77) spectrum (NH(Gal) = 1.65 x 1021 cm-2). The observed
2-10 keV flux is ~4.7 x 10-12 erg cm-2 s-1.
Source #2: This second source is detected at 10.4 and 4.8 sigma c.l. in the 0.3-10 keV
energy range and above 3 keV, respectively. It is located at
RA(J2000) = 09h 57m 40.71s and Dec(J2000) = -42d 08m 44.6s (4.0 arcsec uncertainty, at 90% c.l.).
Within the XRT positional error, we find a USNO-B1.0 source (USNO-B1.0 0478-0250012) with magnitudes
B ~19.7 and R ~17.6-19.3.
The X-ray spectrum is fitted with a power law (NH(Gal) = 1.66 x 1021
cm-2) having photon index Gamma
~1.5 and an observed 2-10 keV flux of ~2.8 x 10-13 erg cm-2 s-1.
Although source #1 is probably the more likely counterpart to SWIFT J0958.0-4208,
we cannot exclude at this stage contamination from the second object.
In this case, there is an X-ray source compatible with the 90% IBIS error circle, serendipitously detected
during the Swift/XRT pointing of the gamma ray burst GRB060421. It has coordinates
RA(J2000) = 22h 53m 55.23s and Dec(J2000) = +62d 43m 38.0s (3.5 arcsec uncertainty, at 90% c.l.), and
at 45 and 35 sigma c.l. in the 0.3-10 keV energy range and above 3 keV, respectively. It is associated
with the ROSAT faint source 1RXS J225352.8+624354, which is still unidentified.
Within the XRT positional uncertainty we find a
USNO-B1 object (USNO-B1 1527-0428738) having magnitudes R ~13 and B~ 15.5, which is also listed
in the 2MASS catalogue (2MASS J22535512+6243368), with magnitudes J ~11.6, H ~11.0, and K ~10.5.
The X-ray spectrum is well modelled with an absorbed (NH(Gal) = 8.96 x 1021
cm-2, NH(intr) ~1.1 x 1022 cm-2) power law
(Gamma ~1.4) having an observed 2-10 keV flux of ~3.4 x 10-12 erg cm-2
Given the location of both sources on the Galactic plane, their X-ray spectral properties,
and the lack of any evident radio counterparts we favour a Galactic nature for both objects.
We acknowledge the use of public data from the Swift data archive.