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ATEL # 2731; R. Landi, E. Maiorano (INAF/IASF Bologna), M. Fiocchi, A. Bazzano (INAF/IASF Rome), A. J. Bird (Univ. Southampton), N. Gehrels (NASA/GSFC), D. N. Burrows (PSU)
on 12 Jul 2010; 14:54 UT
Password Certification: Raffaella Landi (firstname.lastname@example.org)
Subjects: Radio, X-ray, Gamma Ray, Request for Observations
We report on results of X-ray follow-up observations obtained with Swift/XRT of two unidentified INTEGRAL sources listed in the 4th IBIS Survey Catalogue (Bird et al. 2010, ApJS, 186, 1): IGR J05255-0711 and IGR J16413-4046.
XRT pointed at the source region on 2010, April 27 and May 01 for a total exposure of 6.9 ks. Three sources compatible with the IBIS error circle were detected by XRT, and are shown as crosses over-laid on an NVSS image of the field (XRT sources are #1, #2 and #3 in the figure).
Source #1: this source, located at RA(J2000) = 05h 25m 12.4s and Dec(J2000) = -07d 09m 28.0s (6 arcsec uncertainty), is detected at 2.8 sigma c.l. in 0.3-10 keV band and disappears above 3 keV. This object has a moderately bright radio counterpart (NVSS J052513-070935) with a 20 cm flux of 185.43 mJy. No optical or infrared counterpart is found for this object. Unfortunately, because of the low statistical quality of the X-ray data, we can only infer a 2-10 keV flux of 6.7 x 10-14 erg cm-2 s-1, assuming a simple power law model with the photon index fixed at 1.8.
Source #2: its location (RA(J2000) = 05h 25m 09.83s and Dec(J2000) = -07d 07m 48.38s, 4.6 arcsec uncertainty) is outside the 90% error box, but compatible with the 99% IBIS uncertainty. It is detected at 7 sigma c.l. in 0.3-10 keV and it is still visible at E > 3 keV with a 2.5 sigma c.l.. Also this objects has a moderately bright radio counterpart (NVSS J052509-070746) with a 20 cm flux of 177.22 mJy. Within the XRT uncertainty, we find a USNO-A2.0 counterpart having magnitude R ~ 18.9; this source is not listed in the 2MASS catalogue. The X-ray spectroscopy indicates a steep power law spectrum (Gamma ~2.2) and a 2-10 keV flux of 1.6 x 10-13 erg cm-2 s-1.
Source #3: the source is located at RA(J2000) = 05h 25m 32.80s and Dec(J2000) = -07d 13m 06.2s (6 arcsec uncertainty) and is detected at 2.5 sigma c.l. in 0.3-10 keV, disappearing above 3 keV. No counterparts are found at radio, infrared and optical wavelengths.
These information, along with the fact that the IBIS source is detected only during a revolution (n. 478) and hence indicating a variable nature for this object, suggest that the hard XRT source could be the possible X-ray counterpart.
Further deeper X-ray observations are encouraged in order to investigate the real nature of this source.
XRT pointed at the source region on 2010, June 14 for 1.4 ks. Within the IBIS error circle, we find a hard (3-10 keV) X-ray source detected only at 2.5 sigma c.l., which disappears at soft energies (0.3-3 keV); it is located at RA(J2000) = 16h 41m 19.31s and Dec(J2000) = -40d 47m 31.84s (7.7 arcsec uncertainty). The XRT location is compatible with a USNO-A2.0 object having magnitude R ~15.6; this object is also listed in the 2MASS survey with magnitudes I ~13.65, H ~13.23 and K ~13.27. Unfortunately, because of the low signal-to-noise ratio of the source, we can only infer a 2-10 keV flux of 6.2 x 10-14 erg cm-2 s-1, assuming a simple power law model with the photon index fixed at 1.8.
Both XRT and IBIS instrument show a weak and persistent source, nevertheless, to better investigate its nature we suggest further deeper X-ray observations.
NVSS image of IGR J05255-0711