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Swift/XRT observations of PSR B1259-63 after the 2017 periastron passage

ATel #10973; Partha Sarathi Pal, P. H. Thomas Tam, Xinbo He (Sun Yat-sen Univ.)
on 15 Nov 2017; 11:23 UT
Credential Certification: P.H.Thomas Tam (grbtom@gmail.com)

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

PSR B1259-63, orbiting the massive star LS 2883, has passed the periastron on 22 Sept 2017 (MJD 58018). SWIFT/XRT has observed this source once every 3-7 days since end of August (results before periastron was posted on Atel #10775). We analyzed a circular region of 47 arcsec centered on PSR B1259-63. We observed an increase in 0.3-10 keV flux from around 1.3e-11 erg/s/cm^2 (0.17+-0.02 cts/s) on 28 Sept 2017 to 5.9e-11 erg/s/cm^2 (0.72+-0.04 cts/s) on 17 Oct 2017 within 20 days. The flux rate decreased to 2.1e-11 erg/s/cm^2 on 30 Oct 2017. In consecutive days, during the onset of the GeV flares, increase in X-ray flux was seen. The 2017 observations may indicate flux evolution, e.g., a delay of the X-ray peak, different from 2014.

The GeV flares in 2017 have been reported by, e.g., ATel #10925, #10972.

Since there are some differences both in X-rays and gamma-rays seen this year compared to previous periastron passages, multi-wavelength observations of this object in the current as well as future periastron passages are crucial to get better understanding of the behavior of this unique binary system.

We thank the SWIFT/XRT team to schedule observations of this object.