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Two new hard X-ray sources IGR J18151-1052 and IGR J17009+3559 discovered with INTEGRAL

ATel #2170; R. Krivonos, S. Tsygankov, R. Sunyaev (MPA/IKI), S. Melnikov, I. Bikmaev (KSU/AST), M. Pavlinsky, R. Burenin (IKI)
on 21 Aug 2009; 19:58 UT
Credential Certification: Roman Krivonos (krivonos@mpa-garching.mpg.de)

Subjects: Optical, X-ray

Referred to by ATel #: 2193

We report detection of two new hard X-ray sources IGR J18151-1052 and IGR J17009+3559. The sources were detected on images of the on-going hard X-ray survey performed with INTEGRAL/IBIS (Krivonos et al. 2007, A&A, 475, 775). The source sky positions were estimated from INTEGRAL data as:

IGR J18151-1052 R.A.=18h15m09.60s, Decl.=-10d52m48.0s,
IGR J17009+3559 R.A.=17h01m00.00s, Decl.=35d59m24.0s,
(equinox 2000.0, uncertainty 4 arcmin).

The source fluxes in the 17-60 keV band are equal to 0.54+/-0.10 mCrab and 0.96+/-0.20 mCrab, respectively. We assume that 1 mCrab in 17-60 keV energy band corresponds to 1.43e-11 erg/s/cm^2.

IGR J18151-1052 --- The source was observed by our request with SWIFT/XRT for 5151 seconds in photon counting mode on 2009 August 18 to determine a refined position (obsid 00031463001). In ~2 arcmin away from the INTEGRAL position we detect bright source with sky coordinates R.A.=18h15m03.99s, Decl.=-10:51:31.81 (uncertainty 4.2 arcsec). We failed to find any bright counterpart in existing optical surveys, as well as in ROSAT all-sky survey. However the faint object is apparently seen on DSS II red plate at RA,Dec = 18:15:03.82 -10:51:34.6 (J2000).

The source has a 1-10 keV count rate of 0.018 c/s. A preliminary X-ray spectrum has significantly measured points only above ~2 keV which indirectly explains lack of its detection in ROSAT archive. The quality of spectrum is poor, but rising part above 2 keV is apparently seen. A power-law fit of the spectrum gives a photon index Gamma = -0.8 (-0.8, +0.6).

Basing on preliminary spectral analysis, we conclude that IGR~J18151-1052 may have any type of obscured objects detected in a variety with INTEGRAL/IBIS, e.g. AGN, HMXB or CV. We estimated equivalent photoabsorption column density from the shape of source X-ray spectrum fixing photon index at 1.0 and 2.0. For these cases we have nHL = 3.4 (-2.0, +5.1)x 10^22 and 5.7 (-2.7, +8.3)x 10^22, respectively. These values are much higher than that in the Galactic interstellar medium, which is ~5x10^21 cm^-2 according to Dickey and Lockman, (1990).

IGR J17009+3559 --- The source was observed to refine its position by SWIFT/XRT for 4896 seconds in PC mode on 2009 August 12 (obsid 00031462001). In ~1.5 arcmin away from the INTEGRAL position we found weak source with sky coordinates R.A.=17h00m53.1617s, Decl.=+35d59m51.3370s (uncertainty ~5 arcsec). The source has a 1-10 keV count rate of 0.05 c/s.

The following optical observations were made with the Russian-Turkish 1.5-m telescope (RTT-150, Bakirlitepe, TUBITAK National Observatory, Turkey) by using TFOSC instrument on 2009 August 18. The optical companion of IGR J17009+3559 source is probably found to be galaxy 2MASX J17005297+3559560.

The optical spectrum of this object is typical for X-ray bright optically normal galaxy (XBONG). A few weak emission lines are detected above strong stellar background ([O III ] 4959, [N II] 6584, [S II] blend of 6717,6731). Using both emission and absorption lines (NaD, MgB, G-band, H,K CaII) we measured the redshift of this object as z=0.112+/-0.003. Rc filter RTT150 image reveals the galaxy (Rc ~ 17 mag) with a core of Rc ~ 17.5-18.0 mag. Taking into account the insignificant Galactic extinction in the direction of this AGN (E(B-V) ~ 0.03 mag) IGR J17009+3559 is good candidate to highly absorbed sources population discovered by INTEGRAL.

We encourage follow-up observations of both sources at all possible wavelengths.

The authors acknowledge the SWIFT/XRT Team for scheduling observations of INTEGRAL sources.

INTEGRAL all-sky survey, online catalog of X-Ray sources.