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Swift-XRT follow-up of 2 unidentified INTEGRAL sources

ATel #3391; A. Malizia, R. Landi (INAF/IASF Bologna), A. Bazzano (INAF/IASF Rome), A. J. Bird (Univ. Southampton), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU)
on 31 May 2011; 14:31 UT
Credential Certification: Raffaella Landi (landi@iasfbo.inaf.it)

Subjects: X-ray, Gamma Ray, Request for Observations

In this telegram we report the X-ray follow-up observations performed with Swift-XRT of 2 unidentified INTEGRAL sources listed in Bird et al. 2010 (ApJS, 186, 1).

IGR J17472-7319

Within the IBIS error circle, XRT detects an X-ray source with coordinates R.A. (J2000) = 17h 43m 11.1s and Dec.(J2000) = -73d 19m 22.6s (5.0 arcsec positional uncertainty). The XRT detection is of 4.6 sigma in the 0.3-10 keV band and 2.4 sigma above 3 keV. This may be an overestimate given that the source appears to be slightly extended. No counterpart is found for this object at other wavelengths although an USNO-B1.0 source (USNO-B1.0 0166-0284769) with magnitude R ~18, is located only 7.7 arcsec from the Swift-XRT position. The Swift-XRT data are well fitted with a simple power law having a photon index ~2 and an observed 2-10 keV flux of ~ 1.1 x 10-13 erg cm-2 s-1.

IGR J23558-1047

XRT detected two X-ray sources whose positions are compatible with the IBIS error circle:

  • source #1: it is located within the 90% IBIS error circle at R.A.(J2000) = 23h 55m 58.3s and Dec. (J2000) = -10d 46m 42.24s with a positional uncertainty of 5.76 arcsec. It is detected in the 0.3-10 keV energy band at 4.1 sigma, but it is not observed above 3 keV. The XRT position is consistent both with an X-ray source belonging to the WGA Catalogue (1WGA J2355.9-1045) and with an object listed in the Million Quasars Catalog (MILLIQUAS) with magnitudes B and R ~19.0 and redshift 1.1. No optical and IR counterpart is found for this source. The XRT data analysis provides a good fit using a simple power law model with photon index ~1.9 and an observed 2-10 keV flux of ~8.4 10-14 erg cm-2 s-1.
  • source #2:This second source, located within the 99% IBIS error circle, is detected in the 0.3-10 keV band at 9 sigma and it is still observed above 3 keV at 2.3 sigma. The XRT position is R.A.(J2000) = 23h 55m 39.8s and Dec.(J2000) = -10d 53m 56.21s with 4.28 arcsec uncertainty. Within this positional error, we find a USNO-A2.0 object (USNO-A2.0 0750_21592353) having magnitudes R ~11.9 and B ~12.7, which is also a 2MASS source (2MASS J23554001-1053567) with magnitudes J ~10.3, H ~9.9, and K ~9.8 and a SDSS object SDSS J235540.01-105356.8 reported as a star in NED archive. Another SDSS object (SDSS J235539.87-105349.7) classified as a galaxy is also consistent with the XRT position. The XRT spectrum is quite poor and only the 2-10 keV observed flux of 1.6 x 10-13 erg cm-2 s-1 can be estimated.