Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the origin of the bi-drifting subpulse phenomenon in pulsars   The unique and highly unusual drift feature reported for PSR J0815+0939,
wherein one component's subpulses drift in the direction opposite of the
general trend, is a veritable challenge to pulsar theory. In this paper, we
observationally quantify the drift direction throughout its profile, and find
that the second component is the only one that exhibits "bi-drifting", meaning
that only second component moves in the direction opposite of the others. We
here present a model that shows that the observed bi-drifting phenomenon
follows from the insight that the discharging regions, i.e. sparks, do not
rotate around the magnetic axis per se, but rather around the point of electric
potential extremum at the polar cap: minimum in the pulsar case
($\mathbf{\Omega} \cdot \mathbf{B} < 0$) and maximum in the antipulsar case
($\mathbf{\Omega} \cdot \mathbf{B} > 0$). We show that a purely dipolar surface
magnetic field cannot exhibit bi-drifting behaviour, though certain non-dipolar
configurations can. We can distinguish two types of solutions, with relatively
low ($\sim 10^{12} \,{\rm G}$) and high ($\sim 10^{14} \,{\rm G}$) surface
magnetic fields. Depending on the strength of the surface magnetic field, the
radius of the curvature of magnetic field lines ranges from $10^{5} \,{\rm cm}$
to $10^{7}\,{\rm cm}$. Pulsar \J~allows us to gain an understanding of the
polar-cap conditions essential for plasma generation processes in the inner
acceleration region, by linking the observed subpulse shift to the underlying
spark motion.

2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
23
The categories of this paper are: solv-int
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph