PSR J2032+4127/MT91 213 on approach to periastron: X-ray & optical monitoring

ATel #10920; Coe M. J. (Southampton University), Steele IA (LJMU), Ho WCG (Southampton University), Stappers B (Manchester University), Lyne AG (Manchester University), Halpern JP (Columbia University), Ray PS (NRL), Johnson TL (GMU), Ng C-Y (Hong Kong University), Kerr M (NRL)
on 2 Nov 2017; 08:53 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Malcolm Coe (mjcoe@soton.ac.uk)

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Swift XRT monitoring of the ~50 year binary system PSR J2032+4127/MT91 213 shows a dramatic decrease in the X-ray flux as the system is in the final stages of approach to periastron (13 November 2017). The X-ray flux from this gamma-ray binary system has fallen sharply by a factor of two in the last few days in complete contrast to the steady X-ray flux rise seen over the past 150 - 200 days. In addition, the H alpha equivalent width has fallen by a factor of two in the last 150 days, down to a recent value of -7.4 Angstrom seen by FRODOSPEC on the Liverpool Telescope on 31 Oct 2017. Though the rapid decrease in the X-ray flux probably implies obscuration of the X-ray signal by the circumstellar disk of the OB star, the reason for the decrease in H alpha emission is not so clear. A similar X-ray behaviour is seen in the system PSR B1259-63 on the approach to periastron, though it is not yet clear whether gamma-ray flares seen in that system will also occur in PSR J2032+4127. Detailed monitoring of this system will continue over the next few weeks at many wavebands, including FERMI which has not yet seen any change in the gamma-ray flux from the system. The current Swift/XRT lightcurve can be seen here: www.soton.ac.uk/~mjcoe/xrt.pdf