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New outburst from the bursting pulsar GRO J1744-28

ATel #14689; I. Mereminskiy(1), S. Tsygankov(2, 1), S. Molkov(1), A. Semena(1), A. Lutovinov(1) (1: Space Research Institute RAS, Moscow, Russia; 2: University of Turku, Finland)
on 9 Jun 2021; 11:42 UT
Credential Certification: Ilya Mereminskiy (i.a.mereminskiy@gmail.com)

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

Referred to by ATel #: 14695

The Swift/BAT transient monitor data (Krimm et al., 2013) indicated that nearly a week ago GRO J1744-28 went in the new outburst and reached the flux of about 80 mCrab (about 10-9 erg/cm2/s) in the hard X-ray band (15-50 keV) on June 04, 2021.

Given the source's peculiarity and rareness of its outbursts (with the previous one registered in 2017, ATel#10073) and also its location in a very crowded Galactic Center region, we initiated a short follow-up observation with Swift/XRT in order to confirm the correctness of association of the observed hard X-rays excess with GRO J1744-28.

Swift/XRT observed the source on June 08, 2021 in the PC mode with an exposure of about 300s. There is a bright source (approx. 6 counts per second in the 0.3-10 keV band) at a position coinciding with the known location of GRO J1744-28. Its X-ray spectrum is hard and heavily absorbed, with estimated NH=9(+4-3)x1022 cm-2 and photon index of 1.1 (+0.7-0.6). The unabsorbed 0.3-10 keV flux is about 1.5x10-9 erg/cm2/s, which corresponds to the luminosity of 1037 erg/s assuming the distance to the source of 8 kpc.

We, therefore, conclude that GRO J1744-28 entered a new outburst. Multiwavelength observations are strongly encouraged to study this enigmatic source.

We are grateful to the Swift team for rapid scheduling of our observation. The XRT data was processed with online tools (Evans et al., 2009, 2014) provided by UK Swift Science Data Centre at the University of Leicester.