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INTEGRAL observations of the Be/X-ray binary 4U 0115+63 in outburst

ATel #9159; A. Postel (ISDC, University of Geneva, Switzerland), L. Ducci (IAAT, Germany, ISDC, University of Geneva, Switzerland), C. Sanchez, J. Keajava, E. Kuulkers (ESA/ESAC, Spain), R. Diehl (MPE, Germany), K. Watanabe (Florida Gulf Coast University, USA), C. Ferrigno (ISDC, University of Geneva, Switzerland)
on 15 Jun 2016; 21:30 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)

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

Referred to by ATel #: 9172

During the observations of the Cas A and Tycho supernova remnant regions, INTEGRAL has serendipitously detected the prototypical Be/X-ray binary 4U 0115+63 undergoing a new outburst. A significant increase in the source flux has been clearly measured since 2016-06-08 by both the IBIS and JEM-X instruments. These findings confirm the similar results reported by using Swift/BAT, MAXI/GSC, and Fermi/GBM (ATEL #9149).

The source fluxes recorded by INTEGRAL in the past days are summarized below and expressed in mCrab. All uncertainties are given at 1σ confidence level and are only statistical.

Revolution 1688 (2016-06-08 03:59 - 2016-06-10 08:13 UTC)
3-10 keV 28±2
10-20 keV 29±7
20-40 keV 10.2±0.6 keV
40-80 keV < 3 at 3σ c.l.

Rev. 1689 (2016-06-10 19:43 - 2016-06-13 00:02 UTC)
20-40 keV 27±1
40-80 keV 10±1

Rev. 1690 (2016-06-13 13:59 - 2016-06-15 15:53 UTC)
3-10 keV 51±3
10-20 keV 66±9
20-40 keV 24.9±0.7
40-80 keV 3±1

Note that 4U 0115+63 was outside the field of view of the JEM-X instrument during the INTEGRAL revolutions 1689. The source has decreased its luminosity by a factor about two during the last revolution (20-40 keV), suggesting that the current outburst is of type I and linked to the source periastron passage on 2016-06-07 (Bildsten et al, 1997).

INTEGRAL will continue monitoring the region around 4U 0115+63 during the next weeks. Observations in other energy domains are encouraged.