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Issue A&A
Volume 393, Number 2, October II 2002
Page(s) 511 - 521
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021051



A&A 393, 511-521 (2002)
DOI: 10.1051/0004-6361:20021051

Rotation as a source of asymmetry in the double-peak lightcurves of the bright EGRET pulsars

J. Dyks1 and B. Rudak1, 2

1  Copernicus Astronomical Center, Torun, Poland
2  Dept. of Astronomy and Astrophysics, Nicholas Copernicus University, Torun, Poland

(Received 10 December 2001 / Accepted 4 July 2002)

Abstract
We investigate the role of rotational effects in inducing asymmetry present above ~5 GeV in the double-peak lightcurves of the bright EGRET pulsars: Vela, Crab, and Geminga. According to Thompson (2001), the trailing peak dominates over the leading peak above ~5 GeV consistently for all three pulsars, even though this is not the case over the entire energy range of EGRET, i.e. above ~100 MeV. We present the results of Monte Carlo simulations of electromagnetic cascades in a pulsar magnetosphere within a single-polar-cap scenario with rotationally-induced propagation effects of the order of $\beta$ (where $\beta$ is the dimensionless local corotation velocity). We find that even in the case of nearly aligned rotators with spin periods of $P\sim 0.1$ s rotation may lead to asymmetric (with respect to the magnetic axis) magnetic photon absorption which in turn leads to asymmetric gamma-ray pulse profiles. The resulting features - softer spectrum of the leading peak and the dominance of the trailing peak above ~5 GeV - agree qualitatively with the EGRET data of the bright gamma-ray pulsars.


Key words: stars: rotation -- stars: pulsars: general

Offprint request: J. Dyks, jinx@ncac.torun.pl

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