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First hard X-ray detection of AX J1949.8+2534

ATel #8250; V. Sguera (INAF-IASF Bologna, Italy), A. Bazzano (INAF-IAPS Roma, Italy), L. Sidoli (INAF-IASF MIlano, Italy)
on 5 Nov 2015; 16:19 UT
Credential Certification: Eleonora Torresi (torresi@iasfbo.inaf.it)

Subjects: X-ray, Transient

The unidentified X-ray source AX J1949.8+2534 was within the field of view of the IBIS/ISGRI instrument onboard INTEGRAL for an effective exposure time of about 14 ks during recent observations of the Cygnus region performed between 1 Nov 08:28 (UTC) and 2 Nov 15:47 (UTC). We found that IBIS/ISGRI detected hard X-ray activity from AX J1949.8+2534 at about 7.3 sigma level (22-60 keV) with coordinates RA (J2000) = 297.48 and Dec (J2000) = 25.57 (3.9 arcmin uncertainty radius), such IBIS/ISGRI position is consistent with the ASCA position of AX J1949.8+2534 (Sugizaki et al. 2001, ApJSS, 134, 77). The source was also covered by the JEM-X monitor, in the combined JEM-X1+JEM-X2 mosaic it was barely detected at about 4.2 sigma level (3-10 keV) with an average flux of 2.7+/-0.6 mCrab or about 4 x 10-11 erg cm-2 s-1 (effective exposure of about 4.5 ks). The IBIS/ISGRI spectrum is very well fitted by a power law with photon index 2.4+/-0.8 and average flux of about 1.0 x 10-10 erg cm-2 s-1 (22-60 keV).

INTEGRAL performed further observations in the direction of AX J1949.8+2534 during recent Galactic Plane Scans from 3 Nov 06:11 (UTC) and 3 Nov 23:24 (UTC). However, the source was in the field of view of IBIS/ISGRI for an effective exposure time of only 3.3 ks and it was not significantly detected. We estimate a 22-60 keV 3 sigma upper limit of about 7 mCrab or 7 x 10-11 erg cm-2 s-1 (assuming a Crab-like spectrum).

As from information reported in the fourth IBIS/ISGRI catalog (Bird et al. 2010, ApJs, 186, 1), the region of the sky including AX J1949.8+2534 has been observed for a total of about 1.1 Ms, no source was detected in the total mosaic providing a 3 sigma upper limit of 0.6 mCrab or 4.5 x 10-12 erg cm-2 s-1 (20-40 keV) for persistent emission. When assuming the source flux in the same energy band as measured by IBIS/ISGRI in the current detection (7.5 x 10-11 erg cm-2 s-1) we can infer a dynamic range greater than at least 16.