[ Previous | Next | ADS ]

Swift/XRT follow-up observations of unidentified INTEGRAL sources (1)

ATel #3271; R. Landi, L. Bassani, N. Masetti (INAF/IASF Bologna), A. Bazzano (INAF/IASF Rome), A. J. Bird (University of Southampton)
on 11 Apr 2011; 15:05 UT
Credential Certification: Raffaella Landi (landi@iasfbo.inaf.it)

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

We report the results of X-ray follow-up observations performed with Swift/XRT of 2 unidentified INTEGRAL sources listed in the INTEGRAL all sky survey (Krivonos et al. 2010, A&A, 523, 61).

IGR J12134-6015 (also SWIFT J1213.2-6020, see the link below.)

There is only one source, detected by XRT at 30 sigma confidence level (c.l.) in the 0.3-10 keV energy band (17 sigma c.l. above 3 keV), within the IBIS positional uncertainty: it is located at R.A.(J2000) = 12h 13m 23.95s and Dec.(J2000) = -60d 15m 15.5s (3.6 arcsec uncertainty). This position is compatible with that of the ROSAT Faint source 1RXS J121324.5-601458 and the XMM Slew source XMMSL1 J121323.5-601517. This X-ray source has only an infrared counterpart (2MASS 12132397-6015169) detected with magnitudes J ~16.4, H ~16.5 and K ~15.5. The average X-ray data are well modelled with a black body component with kT ~56 eV plus a flat (Gamma ~1.1) power law; the 2-10 keV flux is ~5 x 10-12 erg cm-2 s-1. The source shows strong variability (by a factor of 3) on a timescale of a few days.

IGR J16058-7253 (also SWIFT J1605.7-7250, see the link below.)

There are two sources detected by XRT and located within the IBIS positional uncertainty:

Source #1 is detected at ~9 sigma c.l. both in the 0.3-10 keV energy band and above 3 keV. It is is located at R.A.(J2000) = 16h 06m 06.66s and Dec.(J2000) = -72d 52m 42.3s (4.1 arcsec uncertainty). The XRT position is compatible with that of a USNO-A2.0 object (USNO-A2.0 0150_16011427) with magnitudes R ~15.7 and B ~16.8 and the 2MASS extended source (2MASX J16060682-7252418, magnitudes J ~15.0, H ~14.2 and K ~13.1), classified as a galaxy in NED.

The X-ray data are fitted with an absorbed (NH ~3 x 1023 cm-2) power law (Gamma fixed at 1.8) plus a second power law having the same photon index and passing only through Galactic absorption (NH = 7.89 x 1020 cm-2) to account for the presence of excess emission below 2 keV. The 2-10 keV flux is ~2 x 10-12 erg cm-2 s-1.

Source #2 is detected at ~15 sigma c.l. both in the 0.3-10 keV energy band and above 3 keV. Its position is at R.A.(J2000) = 16h 05m 22.84s and Dec.(J2000) = -72d 53m 55.4s (3.8 arcsec uncertainty). Again it coincides with a 2MASS extended source (2MASX J16052330-7253565, with magnitudes J ~13.3, H ~12.4 and K ~12.2) also classified as a galaxy in NED, and with a USNO-A2.0 object (USNO-A2.0 0150_15991912) with magnitudes R ~11.9 and B ~12.0. This source is also reported as a radio emitter in the SUMSS catalogue with a flux of 9.2 mJy at 36 cm. Also in this case the data are well modelled with an absorbed (NH ~2 x 1023 cm-2) power law (Gamma ~2.6) plus a second power law having the same photon index and passing only through Galactic absorption (NH = 7.94 x 1020 cm-2) to account for the presence of excess emission below 2 keV. The 2-10 keV flux is also ~2 x 10-12 erg cm-2 s-1.

Both are hard X-ray objects being clearly detected above 3 keV so that it is difficult at the present stage to state which one is the true association with the IBIS object; it is even possible that both galaxies contribute to the high energy emission.

The authors acknowledge the use of public data from the Swift data archive.

http://heasarc.nasa.gov/docs/swift/results/bs58mon/