Post-Periastron Gamma Ray Flare from PSR~B1259-63/LS 2883 as a Result of Comptonization of the Cold Pulsar Wind

Details Post-Periastron Gamma Ray Flare from PSR~B1259-63/LS 2883 as a Result of Comptonization of the Cold Pulsar Wind Post-Periastron Gamma Ray Flare from PSR~B1259-63/LS 2883 as a Result of Comptonization of the Cold Pulsar Wind

2011-07-25

arxiv.org/abs/1107.4833v1

Astronomy and Astrophysics

Astrophysics

High Energy Astrophysical Phenomena

12 pages, 3 figures

Scientific paper

The recent detection of gamma rays with the {\it Fermi} Large Area Telescope (LAT) from the binary system PSR B1259-63/LS2883 provides unique information about the pulsar wind. Although the nature of the weak gamma-ray signal detected at the periastron passage remains uncertain, the reported fluxes allow robust constraints on the Lorentz factor $\Gamma_0$ of the pulsar wind. Unless the latter is strongly anisotropic, the range of $\Gamma_0$ between $10^4$ and $3\times 10^5$ is excluded by the {\it Fermi} data. Moreover, we argue that the "surprise" gamma ray flare detected by {\it Fermi} after several weeks of the periastron passage can be explained by inverse Compton (IC) emission of the cold pulsar wind with $\Gamma_0 \approx 10^4$. The combination of two independent effects, both linked to the circumstellar disk, is a principal element in the proposed scenario. The first is related to radiation of the shocked stellar disk which in the close vicinity of the pulsar can provide a dense photon target for the IC scattering. The second effect is related to the strong impact of the surrounding medium ram pressure on location of the termination shock. Inside the disk, the pulsar termination shock stands close to the pulsar; consequently the "early" termination results in suppression of gamma-ray luminosity of the wind. When the pulsar escapes the disk, a fast transformation of the termination shock occurs leading to a significant increase of the pulsar wind zone towards the observer and, consequently to an enhancement of the gamma ray production rate.

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