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INTEGRAL detection of a hard X-ray transient in NGC 6440

ATel #7098; E. Kuulkers (ESAC/ESA, Spain), E. Bozzo (ISDC, Switzerland), A. Bazzano (INAF/IAPS, Italy), V. Beckmann (APC, France), T. Bird (Southampton U., UK), A. Bodaghee (GCSU, USA), J. Chenevez (DTU Space, Denmark), M. Del Santo (INAF/IAPS, Italy), A. Domingo (CAB/INTA-CSIC, Spain), P. Jonker (SRON, The Netherlands), P. Kretschmar (ESA/ESAC, Spain), A. Paizis (INAF-IASF, Italy), K. Pottschmidt (UMBC/NASA GSFC, USA), C. Markwardt (GSFC, USA), C. Sanchez-Fernandez (ESA/ESAC, Spain), R. Wijnands (UvA, The Netherlands)
on 18 Feb 2015; 11:19 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Erik Kuulkers (Erik.Kuulkers@sciops.esa.int)

Subjects: Binary, Globular Cluster, Neutron Star, Transient, Variables, Pulsar

Referred to by ATel #: 7106, 7136, 7183, 10821

During INTEGRAL Galactic bulge monitoring (e.g., ATel #438) observations performed on UT 2015 February 17 at 12.53-16:45, IBIS/ISGRI detected renewed activity at hard X-rays from a transient within the Globular Cluster NGC 6440. The best determined position is: RA, Dec (J2000) = 267.208, -20.314 degrees, with an error radius of 2.4 arcmin (90% c.l.). Formally, there is no known X-ray source within the error circle, so we label the source as IGR J17488-2018.

The hard X-ray transient is detected at a significance of 11 (6.5) sigma on the IBIS/ISGRI mosaic in the 20-40 keV (40-80 keV) energy band. The IBIS/ISGRI spectrum (total exposure time of 12 ks) provides a photon index of 2.4 +/- 0.5 and a 20-100 keV flux of 4.8E-10 ergs/cm^2/s.

NGC 6440 was outside the JEM-X field-of-view for the entire observation.

The Globular Cluster NGC 6440 is known to host millisecond X-ray pulsars (see, e.g., ATel #2672), so it is possible that INTEGRAL detected an outburst from one of these sources. We can not rule out that one of the known X-ray sources just outside the error circle (such as MXB 1746-20 aka H1745-203) is experiencing an outburst. Note that Swift/BAT also detects enhanced activity from H1745-203 over the last days.

Further INTEGRAL observations in the direction of NGC 6440 are planned for the coming weeks. Swift ToO follow-up observations have been requested. Observations at other wavelengths are encouraged.