4 research outputs found
On the anomalously large extension of the Pulsar Wind Nebula HESS J1825-137
The very high energy (VHE) gamma-ray emission reported from a number of
pulsar wind nebulae (PWNe) is naturally explained by the inverse Compton
scattering of multi-TeV electrons. However, the physical dimensions of some
gamma-ray-emitting PWNe significantly exceed the scales anticipated by the
standard hydrodynamical paradigm of PWN formation. The most "disturbing" case
in this regard is HESS J1825-137, which extends to distances
from the central pulsar PSR J1826-1334. If the gamma-ray
emission is indeed produced inside the PWN, but not by electrons that escaped
the nebula and diffuse in the interstellar medium (ISM), the formation of such
an anomalously extended plerion could be realized, in a diluted environment
with the hydrogen number density . In this
paper, we explore an alternative scenario assuming that the pulsar responsible
for the formation of the nebula initially had a very short rotation period. In
this case, the sizes of both the PWN and the surrounding supernova remnant
depend on the initial pulsar period, the braking index, and the ISM density. To
check the feasibility of this scenario, we study the parameter space that would
reproduce the size of HESS J1825-137. We show that this demand can be achieved
if the braking index is small, and the pulsar birth period is short,
. This scenario can reproduce the wind termination
position, which is expected at , only in a dense
environment with . The requirement of the dense
surrounding gas is supported by the presence of molecular clouds found in the
source vicinity.Comment: 15 pages, 6 figures, ApJ accepte
Gamma Ray Signal from the Pulsar Wind in the Binary Pulsar system PSR B1259-63/LS2883
Binary pulsar systems emit potentially detectable components of gamma ray
emission due to Comptonization of the optical radiation of the companion star
by relativistic electrons of the pulsar wind, both before and after termination
of the wind. The recent optical observations of binary pulsar system PSR
B1259-63/LS 2883 revealed radiation properties of the companion star which
differ significantly from previous measurements. In this paper we study the
implications of these observations for the interaction rate of the unshocked
pulsar wind with the stellar photons and the related consequences for fluxes of
high energy (HE) and very high energy (VHE) gamma rays. We show that the signal
should be strong enough to be detected with Fermi close to the periastron
passage, unless the pulsar wind is strongly anisotropic or the Lorentz factor
of the wind is smaller than or larger that . The higher luminosity
of the optical star also has two important implications: (i) attenuation of
gamma rays due to photon-photon pair production, and (ii) Compton drag of the
unshocked wind. While the first effect has an impact on the lightcurve of VHE
gamma rays, the second effect may significantly decrease the energy available
for particle acceleration after termination of the wind.Comment: 17 pages, 6 figure