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 (landi@iasfbo.inaf.it)

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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).

IGR J18219-1347

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.

IGR J16336-4733

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 (N_H ~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.

SWIFT J2037.2+4151

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 (N_H ~3 x 10²² cm^-2) 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.