Rotation as a source of asymmetry in the double-peak lightcurves of the bright EGRET pulsars
1
Copernicus Astronomical Center, Toruń, Poland
2
Dept. of Astronomy and Astrophysics, Nicholas Copernicus University, Toruń, Poland
Corresponding author: J. Dyks, jinx@ncac.torun.pl
Received:
10
December
2001
Accepted:
4
July
2002
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 ([CITE]),
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 β (where
β is the dimensionless local corotation velocity).
We find that even in the case
of nearly aligned rotators with spin periods of 
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
© ESO, 2002