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New hard X-ray source IGRJ19566+0326 discovered with INTEGRAL

ATel #7506; A. M.Cherepashchuk (SAI MSU, Moscow), S. V.Molkov (IKI, Moscow), A. A.Lutovinov (IKI, Moscow), K. A.Postnov (SAI MSU, Moscow)
on 14 May 2015; 14:34 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Alexander Lutovinov (aal@hea.iki.rssi.ru)

Subjects: X-ray, Gamma Ray, Transient

Referred to by ATel #: 7520, 7524, 8143, 8146, 8197, 8529

A previously unknown hard X-ray source has been discovered with the IBIS/ISGRI telescope on board INTEGRAL. The source was detected during deep observations of the microquasar SS433 (PI Cherepashchuk) carried out on May 6-13, 2015. The S/N ratio for this source at the mosaic image was 6 standard deviations in the 20-60 keV energy band and its flux was equal to 4.1+/-0.7 mCrab (corresponding to 5.5+/-0.9 E-11 erg/s/cm2) in the same band. The source best-fit position was found to be R.A.=19h 56m 33s, Decl.=+3d 26m 32s (equinox 2000.0, uncertainty 3').

Independently, MAXI/GSC detected a new faint transient MAXIJ1957+032 with the position consistent with that of IGRJ19566+0326 (Atel #7504).

Thanks to a very prompt response of the SWIFT team on the TOO request, the source had been observed during 3ks with XRT in Photon Counting (PC) mode at 23:05 UT on May 13, 2015. The only source has been found in FOV at the following location: R.A.(J2000) = 19h 56m 38.8s, Decl(J2000) = +3d 26m 42s with an estimated uncertainty of 3.5 arc-seconds radius (90% confidence). This position is well inside the INTEGRAL error box.

The source is bright with an estimated 0.3-10 keV flux of (1.18+/-0.05) e-11 erg/s/cm2, uncorrected for absorption. Its spectrum can be fitted by an absorbed power-law model, with the following parameters: NH = (0.35+/-0.05) e22 cm-2, photon index = 2.92+/-0.13. Simple extrapolation of the XRT spectrum to the 20-60 keV (INTEGRAL) energy band gives us approximately five times lower flux value than measured with INTEGRAL, that can be connected with the decay of a possible outburst or more complex spectrum shape.

An USNO B1 source with R=19.15 (R.A.=19h 56m 38.92s, Decl=+3d 26m 41.8s, J2000) falls within the Swift/XRT error box.

We encourage multiwavelength follow-up observations of this source.