Constraint on pulsar wind properties from induced Compton scattering off radio pulses

• Published in: Progress of theoretical and experimental physics Vol. 2013; no. 12; pp. 123 - 123E01
• Main Authors: Tanaka, Shuta J., Takahara, Fumio
• Format: Journal Article
• Language: English
• Published: Oxford University Press 17-12-2013
• Subjects: E15; J21; E11; E33
• ISSN: 2050-3911; 2050-3911
• DOI: 10.1093/ptep/ptt108

Pulsar winds have longstanding problems in energy conversion and pair cascade processes, which determine the magnetization
, the pair multiplicity
, and the bulk Lorentz factor
of the wind. We study induced Compton scattering by a relativistically moving cold plasma to constrain the wind properties by imposing that radio pulses from the pulsar itself are not scattered by the wind, as was first studied by Wilson and Rees [D. B. Wilson and M. J. Rees, Mon. Not. R. Astron. Soc., 185, 297 (1978)]. We find that relativistic effects cause a significant increase or decrease of the scattering coefficient depending on scattering geometry. Applying this to the Crab, we consider the uncertainties of the inclination angle of the wind velocity with respect to the radio beam
and the emission region size
, which determines the opening angle of the radio beam. We obtain the lower limit
(
 cm) at the light cylinder
for an inclined wind
10^{-2.7}$]]>
. For an aligned wind
, we require
10^{2.7}$]]>
at
and an additional constraint
10^{3.4}r^{1/5}_{{\mathrm {e}},3}(1+\sigma)^{-1/10}$]]>
at the characteristic scattering radius
 cm, within which the 'lack of time' effect prevents scattering. Considering the lower limit
suggested by recent studies of the Crab Nebula, for
 cm, we obtain the most optimistic constraint
and
, which are independent of
when
and
at
.