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On the nature of the SWIFT/INTEGRAL source SWIFT J1508.6-4953 (also PMN J1508-4953)

ATel #4167; R. Landi, L. Bassani, N. Masetti (INAF - IASF Bologna), A. Bazzano, P. Parisi (INAF - IAPS Rome), S. Drave, M. Goossens (University of Southampton)
on 12 Jun 2012; 15:55 UT
Credential Certification: Raffaella Landi (landi@iasfbo.inaf.it)

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

Referred to by ATel #: 4183

This source is listed in the recent INTEGRAL/IBIS 9-year Galactic Hard X-ray Survey (Krivonos et al. 2012, arXiv:1205.3941) and also appears in the BAT 58-month catalogue (http://heasarc.nasa.gov/docs/swift/results/bs58mon/).

It has been associated with the radio source PMN J1508-4953, also reported as a GeV emitter in the 2nd Fermi catalogue (Nolan et al. 2012, ApJS, 199, 31). We use archival Swift/XRT data to investigate its nature. XRT pointed at the region surrounding SWIFT J1508.6-4953 for a total exposure of ~11 ks.

There is only one X-ray source within the IBIS/BAT/LAT error circles; this object is located at RA(J2000) = 15h 08m 38.82s and Dec(J2000) = -49d 53m 02.9s (3.6 arcsec uncertainty, at 90% c.l.). It is detected at 22.7 and 13 sigma c.l. in the 0.3-10 keV energy range and above 3 keV, respectively. Its position is compatible with the faint ROSAT source 1RXS J150839.0-495304.

The XRT spectrum is well fitted with a power law having (NH(Gal) = 2.04 x 1021 cm-2) a photon index ~1.4 and an observed 2-10 keV flux of ~2.8 x 10-12 erg cm-2 s-1.

We note that SWIFT J1508.6-4953 is most likely an AGN of the Blazar type since it is a radio loud object (Log R = Log(L_5GHz/L_B)= 3.50) and has WISE colours (W2-W3 = 3.15 and W1-W2 = 1.26), typical of a gamma-ray emitting blazar (Massaro et al. 2012, ApJ, 750, 13). Indeed the source is reported in the 2nd Fermi AGN catalogue (Ackermann et al. 2011, ApJ, 743, 171) as an active galaxy of uncertain type.

All the observed features together with the fact that the Fermi spectrum has a photon index of 2.6, further suggest that SWIFT J1508.6-4953 could be a flat spectrum radio quasar.

We acknowledge the use of public data from the Swift data archive.