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INTEGRAL detection of enhanced activity from the HMXB 4U 2206+543

ATel #10519; L. Di Gesu (ISDC, Switzerland) R. Diehl (MPE, Germany) C. Sanchez-Fernandez (ESAC, Spain) K. Watanabe (Florida Gulf Coast University, USA) C. Ferrigno (ISDC, Switzerland)
on 22 Jun 2017; 20:47 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)

Subjects: X-ray, Gamma Ray, Binary, Variables, Pulsar

Referred to by ATel #: 10568

During the observations performed in the direction of Cassiopea A/Tycho SNR, the gamma-ray observatory INTEGRAL detected enhanced activity from the high mass X-ray binary 4U 2206+543.

INTEGRAL has continuously observed this field since 2017 June 8 at 9:48 UTC. 4U 2206+543 was located in the outer part of the imager IBIS field of view and out of the X-ray monitor JEM-X reach, at off axis angle larger than nine degrees. During the satellite revolution 1829 ( 2017-06-18 21:43 - 2017-06-20 07:04 UTC ), 4U 2206+543 was detected by the detector IBIS/ISGRI at a significance level of 27σ, with a flux of 56±2 mCrab and 38±4 mCrab in the 20-40 and 40-80 keV bands, respectively. These values were obtained from the mosaicked images and the uncertainties are only statistical at one sigma confidence level. Before that time and during the current campaign, the typical upper limits ranged from 10 to 20 mCrab, while in the ongoing satellite revolution (1830 , which started on 2017-06-20 18:13 UTC), the source was still detected, but at a lower significance (11σ). The corresponding flux is 18±2 mCrab and 15±3 mCrab, in the 20-40 and 40-80 keV energy bands, respectively.

In revolution 1829, when the source flared up, the IBIS spectrum above 30 keV was well modeled by a power-law with a photon index of 3.0±0.4 and 20-100 keV flux of 6.5×10-10 erg/cm2/s. At the best of our knowledge, this flare was the brightest caught with INTEGRAL and exceeds the typical luminosity by a factor roughly ten. A complete analysis of INTEGRAL data from 2005 to 2011 about this slow X-ray pulsar (PS=5558 s) appeared in Wang (2013; MNRAS, 432, p. 954), while from the Swift/BAT Hard X-ray Transient Monitor, we can infer that the source exceeds the flux level reported in this telegram only for about 1% of the measurements and reached at most 85 mCrab in the 15-50 keV band over the past 12 years. A more detailed data analysis is on-going.

Further INTEGRAL observation in the direction Cassiopea A/Tycho SNR are already planned for the coming days.