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The symbiotic star RT Cru entered a new hard X-ray state as detected by INTEGRAL

ATel #8448; V. Sguera (INAF-IASF Bologna, Italy), A. J. Bird (Univ. of Southampton, UK), L. Sidoli (INAF-IASF Milano, Italy)
on 22 Dec 2015; 11:14 UT
Credential Certification: Eleonora Torresi (torresi@iasfbo.inaf.it)

Subjects: X-ray, Binary, Star

The symbiotic star RT Cru (also known as IGR J12349-6434) was in the field of view of INTEGRAL during recent observations of the Musca region performed between 11 Dec 17:54 (UTC) and 17 Dec 20:43 (UTC).

The source was detected by IBIS/ISGRI at 8 sigma level (22-60 keV) with an average flux of 6.10+/-0.76 mCrab (34 ks of effective exposure time). The IBIS/ISGRI spectrum (22-60 keV) is reasonably fitted by a power law with photon index 2.7+/-0.7 and average flux equal to 5 x 10-11 erg cm-2 s-1 (20-40 keV). RT Cru was not significantly detected by IBIS/ISGRI when previously observed on 22 Nov. We note that the above flux value is a factor of about 2 higher than that reported in the same energy band in the 4th IBIS catalog (2.3 Ms exposure). RT Cru appears to have entered a new bright hard X-ray state like that observed by INTEGRAL in 2003-2004 (ATel #519) and 2012 (ATel #3887). The inspection of these observations at shorter timescales (i.e. at ScW level, typically 2 ks exposure) revealed a possible hard fast flare detected at about 6 sigma level (22-60 keV) on 12 Dec, from 10:55 to 11:55 (UTC). The average flux during this flare is a factor of about 2 higher than that measured from the total observation.

RT Cru was also inside the field of view of the JEM-X monitor. The source was not detected in the combined JEM-X1+JEM-X2 mosaic (total effective exposure of about 30 ks). We derive a 3 sigma upper limit of about 1 mCrab (or 1.2 x 10-11 erg cm-2 s-1) in the band 3-10 keV.

We encourage follow-up observations of this source.