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Fermi LAT Continuous Observations of the PSR B1259-63 Region

ATEL # 3054; A. A. Abdo (NRC Research Associate, resident at NRL), J. E. Grove (NRL), Richard Dubois (SLAC), G. A. Caliandro (IEEC-CSIC) on behalf of the Fermi Large Area Telescope Collaboration
on 24 Nov 2010; 1:41 UT
Password Certification: J. Eric Grove (

Subjects: Gamma Ray, >GeV, Binaries, Pulsars, Transients

We provide further information on searches for GeV activity from the system PSR B1259-63 as it approaches periastron passage. Periodic routine estimates of the significance of any detection are being made as part of a multi-wavelength campaign, and they show no significant detections prior to or subsequent to the time reported by Tam et al. in ATEL #3046 (2010-11-18 00:00:00 to 2010-11-21 00:04:42 UTC). For the indicated three-day interval, an excess of gamma-ray emission positionally consistent with PSR B1259-63 has a likelihood test statistic (TS) of 14. For the two free parameters of the spectral model this corresponds to a single-trial chance probability of ~0.1%. Furthermore, we judge that the detection significance should be diluted by a factor of ~10 trials, given that any positive excess within at least the preceding month would have been considered of equal interest. The chance probability of such an event is thus of order 1%, which we consider to be too high to establish a secure detection. To avoid false positives, we adopt the conservative position that a secure detection in LAT data requires a substantially higher confidence level or continued detection over a longer interval. We note that there is no significant detection (TS < 1) of PSR B1259-63 in the subsequent interval (2010-11-21 00:04:42 to 2010-11-22 23:56:38 UTC), so that the continued rise in flux predicted in ATEL #3046 has not been detected. For completeness we report that we performed this likelihood analysis in a 15-deg radius region surrounding the system, modeling the Galactic diffuse background and all point sources from the Fermi Large Area Telescope First Source Catalog (Abdo et al. 2010, ApJS, 188, 405). Fermi operates in an all-sky scanning mode, and the LAT team will continue its planned close monitoring of this source through the coming months. For this source, the Fermi LAT contact person is Aous Abdo ( The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

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