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No gamma-ray flare detected from the Be-pulsar binary PSR B1259-63 so far

ATel #10918; J. Zhou, Y. Xing, Z. Wang (SHAO)
on 2 Nov 2017; 01:57 UT
Credential Certification: YI XING (yixing@shao.ac.cn)

Subjects: Gamma Ray, Binary, Pulsar

Referred to by ATel #: 10924, 10925, 10972

We are monitoring the Be-pulsar binary system PSR B1259-63 from analyzing Fermi/LAT data, as the pulsar passes through the periastron of its 3.4 year long orbit. During the 2010 and 2014 periastron passages, the system started to have a bright gamma-ray flare 30 days after periastron. This time, the Fermi/LAT detection of pre-periastron and early post-periastron emission from the system has been reported in ATel #10775 and #10818, respectively. Our analysis shows that there was an emission peak 11 days after periastron, which has a flux of 7.5x10^-7 ph/cm^2/s (0.1--300 GeV). The enhanced emission gradually decayed to a level of 4x10^-7 ph/cm^2/s in 5 days, stayed at the level for 9 days, and then became undetectable (TS < 9)in the LAT data of any 7 days time bins. In other words, 26--43 days after periastron (2017 Oct. 17 to now), the system can not be detected in the data of 7 days time bins. We report the result to alert: the binary system may have different behaviour in this 2017 periastron passage, as no bright flare has been seen >40 days after periastron. From our likelihood analysis, the power law describing the source's emission has photon index values consistent with the ones obtained in the previous periastron passages.