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Fermi/LAT and Swift/XRT detection of increased activity from the binary system PSR B1259-63/SS 2883

ATEL # 3046; P.H.T. Tam, A.K.H. Kong, R.H.H. Huang (NTHU, Taiwan), C.Y. Hui (Chungnam, Korea)
on 21 Nov 2010; 7:15 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Albert Kong (

Subjects: X-ray, Gamma Ray, Request for Observations, Binaries, Pulsars
Referred to by ATEL #: 3054

We report on the gamma-ray detection by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope from the sky position of the binary system PSR B1259-63/SS2883. A preliminary analysis of the region around the system has resulted in a detection significance of about 4 standard deviations using data taken between 2010-11-18 00:00:00 (UT) to 2010-11-21 00:04:42 (UT).

Based on the same data set and using a single power law model for the source, the averaged gamma-ray flux is around 4 x 10^-8 photons/s/cm^2 over the energy range 300 MeV to 100 GeV and the photon index is about 1.7. We note that the gamma-ray flux from the binary system has increased over the last few days and we expect the flux to increase further in the coming days. Note that an earlier LAT observations this year did not reveal any emission from the source (ATel #2780).

Swift/XRT observed the region around PSR B1259-63 starting on 2010 Nov 20 05:02 (UT) for about 3.8 ks. The source spectrum of PSR B1259-63 is best described by an absorbed power-law with N_H=6.9(+5.5,-4.2)e21 cm^-2 (90% confidence) and a photon index of 1.3+/-0.4 (reduced chi2/dof=0.51/14). The absorbed 1-10 keV flux is around 6.5e-12 erg/s/cm^2. The Swift observation hence suggests an increasing X-ray flux compared to previous observation taken on 2010 Aug 8 (ATel #2782), and similar harderning behavior has been seen during the first, pre-periastron passage of the disk (Chernyakova et al. 2006, 2009).

PSR B1259-63 will pass through the periastron of its companion star SS 2883 in 2010 mid-Dec. The increase of X-ray and gamma-ray flux therefore occurs around the time when the pulsar enters the equatorial disk of the Be stars.

Multiwavelength observations of the source are strongly encouraged.

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R. E. Rutledge , Editor
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