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INTEGRAL detection of continued hard X-ray emission from MAXI J0911-655

ATel #10425; J.-G. Victor (ISDC, Switzerland), E. Kuulkers (ESA/ESTEC, Netherlands), L. Sidoli (INAF-IASF Milano, Italy), C. Sanchez-Fernandez (ESA/ESAC, Spain), K. Watanabe (FGCU, USA), L. Pavan, E. Bozzo (ISDC, Switzerland)
on 25 May 2017; 17:21 UT
Credential Certification: E. Bozzo (enrico.bozzo@unige.ch)

Subjects: X-ray, Gamma Ray, Binary, Neutron Star, Transient

During the observations performed in the direction of the Carina Region and IGR J11014-6103 between 2017 May 8 at 04:50 and May 24 at 17:39, INTEGRAL detected activity from the accreting millisecond X-ray pulsar (AMXP) MAXI J0911-655 (Sanna et al., 2017, A&A, 598, 34; Atel #8872, #8884, #8914, #8971, #8986, #9738, #9740).

The source was detected in the IBIS/ISGRI mosaic accumulated over the entire period at 18 sigma in the 20-40 keV energy band and 9 sigma in the 40-80 keV energy band. The source high energy spectrum could be well described (reduced chi^2/d.o.f. = 1.3/8) by a power law of photon index 3.0(-0.7,+1.1) and the correspondingly measured 20-100 keV X-ray flux was 1.3e-10 ergs/cm^2/s. The source was outside the JEM-X field of view for the entire observational period.

MAXI J0911-655 was discovered in outburst on 2016 February 19 and the monitoring carried out with Swift/XRT suggests that it did not go back to quiescence since then. The detection in the INTEGRAL data confirms that the source is still active after more than 450 days since the onset of the event, making MAXI J0911-655 the second AMXP after XTE J1807-294 displaying peculiarly long X-ray outbursts (not counting the case of the quasi-persistent HETE J1900.1-2455).

Further INTEGRAL observations in the direction of the source are planned for the coming days. Observations at softer energies are strongly encouraged to understand the origin of the long-lasting outburst.