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INTEGRAL detection of the symbiotic star RT Cru during a bright hard X-ray state

ATel #3887; V. Sguera (INAF/IASF Bologna Italy), S. P. Drave (Univ. of Southampton, UK), L. Sidoli (INAF/IASF Milano), M. Fiocchi (INAF/IASF Roma), J. L. Sokoloski (Columbia University, USA), A. J. Bird (Univ. of Southampton), A. Bazzano (INAF/IASF Roma), L. Bassani (INAF/IASF Bologna), E. Kuulkers (ESAC/ESA, Spain), A. Malizia (INAF/IASF Bologna), L. Natalucci (INAF/IASF Roma) and A. Tarana (INAF/IASF Roma)
on 25 Jan 2012; 19:30 UT
Credential Certification: Sebastian Drave (sd805@soton.ac.uk)

Subjects: X-ray, Gamma Ray, Request for Observations, Binary, Transient, Variables

Referred to by ATel #: 8448

We report the detection with the IBIS/ISGRI telescope on board INTEGRAL of the hard X-ray emitting symbiotic star RT Cru (also known as IGR J12349-6434). The source was detected during the Galactic Plane scan observations performed between 2012 January 20, 11:26 (UTC) and January 23, 02:34 (UTC). It was inside the field of view of IBIS/ISGRI for a total on-source time of about 21 ks leading to a detection significance of 6.2 sigma in the energy band 18-40 keV and 5.9 sigma in the energy band 18-60 keV. A fit to the IBIS/ISGRI spectrum (18-60 keV) with a power law model resulted in a good fit (reduced chi_sq = 1.02 for 15 degrees of freedom) with a photon index of 2.4 (+1.6, -1.4) and a flux of 1.3 x 10E-10 erg cmE-2 sE-1 (18-60 keV). We note that the average flux of the source in the energy band 18-40 keV (13+/-2 mCrab) is a factor of 3.4 brighter than that reported in the same energy band in the 4th IBIS catalog (2.3 Ms exposure). RT Cru appears to be entered a new bright hard X-ray state like that observed by INTEGRAL in 2003-2004 (ATel #519). Following the INTEGRAL detection, we asked for a Swift/XRT follow-up observation. RT Cru was detected at about 16 sigma level on 24 January 2012 at 18:53:58 (UTC) with a net exposure time of 1978 s. An absorbed power law model provided an acceptable fit to the 0.2-10 keV spectrum (reduced chi_sq = 0.876 for 9 degrees of freedom) with a photon index of -0.36 (+0.47, -0.51), an absorption of NH<1.78 x 10E22 cmE-2 and an unabsorbed flux of 8.2 x 10E-11 erg cmE-2 sE-1 (1-10 keV). There is a possible hint of an iron line centered at 6.15 (+0.26, -0.14) KeV with EW = 480 eV. We encourage follow-up observations of this source at all wavelengths, especially at radio to look for synchrotron emission.