1,078 research outputs found
Two-photon annihilation in the pair formation cascades in pulsar polar caps
The importance of the photon-photon pair production process () to form pair production cascades in pulsar
polar caps is investigated within the framework of the Ruderman-Sutherland
vacuum gap model. It is found that this process is unimportant if the polar
caps are not hot enough, but will play a non-negligible role in the pair
formation cascades when the polar cap temperatures are in excess of the
critical temperatures, , which are around when
s and will slowly increase with increasing periods. Compared with the
process, it is found that the two-photon annihilation process may
ignite a central spark near the magnetic pole, where sparks can not
be formed due to the local weak curvatures. This central spark is large if the
gap is dominated by the ``resonant ICS mode''. The possible connection of these
central sparks with the observed pulsar ``core'' emission components is
discussed.Comment: 7 pages, 3 Postscript figures, LaTex, accepted for publication in
Astronomy and Astrophysic
Is Gamma-ray Absorption by Induced Electric Fields Important in the Pulsar Magnetospheres?
Although the unified formula for gamma-ray absorption process involving both
the magnetic field and a perpendicular electric field derived by Daugherty &
Lerche (1975) is correct, we argued in this paper that their conclusion that
the induced electric fields are important in the pair formation process in the
pulsar magnetospheres is wrong and misleading. The key point is that usually
the direction of a gamma photon at the emission point observed in the
laboratory frame should be (v/c, 0, [1-(v/c)^2]^{1/2}) rather than (0, 0, 1),
where v is the co-rotating velocity. This emission direction is just the one
which results in zero attenuation coefficient of the gamma photon. Calculation
shows that after the photon has moved a distance, its direction lead to the
result that the induced electric field is also of minor importance. Thus only
gamma-B process is the important mechanism for the pair production in the
pulsar magnetospheres. The implications of the modification by ejecting the
induced electric field are also discussed.Comment: 4 pages, 2 Postscript figures, LaTeX, some miscomments on the
references of Harding et al are modified, Accepted for publication in
Astronomy and Astrophysics Letter
What if pulsars are born as strange stars?
The possibility and the implications of the idea, that pulsars are born as
strange stars, are explored. Strange stars are very likely to have atmospheres
with typical mass of but bare polar caps almost
throughout their lifetimes, if they are produced during supernova explosions. A
direct consequence of the bare polar cap is that the binding energies of both
positively and negatively charged particles at the bare quark surface are
nearly infinity, so that the vacuum polar gap sparking scenario as proposed by
Ruderman & Sutherland should operate above the cap, regardless of the sense of
the magnetic pole with respect to the rotational pole. Heat can not accumulate
on the polar cap region due to the large thermal conductivity on the bare quark
surface. We test this ``bare polar cap strange star'' (BPCSS) idea with the
present broad band emission data of pulsars, and propose several possible
criteria to distinguish BPCSSs from neutron stars.Comment: 31 pages in Latex. Accepted by AstroParticle Physic
Deformation and -theoretic Index Formulae on Boundary Groupoids
Boundary groupoids were introduced by the second author, which can be used to
model many analysis problems on singular spaces. In order to investigate index
theory on boundary groupoids, we introduce the notion of {\em a deformation
from the pair groupoid}.Under the assumption that a deformation from the pair
groupoid exists for Lie groupoid ,
we construct explicitly a deformation index map relating the analytic index on
and the index on the pair groupoid. We apply this map to boundary
groupoids of the form , where is an exponential Lie group,
to obtain index formulae for (fully) elliptic (pseudo)-differential operators
on , with the aid of the index formula by M. J. Pflaum, H.
Posthuma, and X. Tang. These results recover and generalize our previous
results for renormalizable boundary groupoids via the method of renormalized
trace
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