Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Constrains on parameters of magnetic field decay for accreting isolated
  neutron stars   The influence of exponential magnetic field decay (MFD) on the spin evolution
of isolated neutron stars is studied. The ROSAT observations of several X-ray
sources, which can be accreting old isolated neutron stars, are used to
constrain the exponential and power-law decay parameters. We show that for the
exponential decay the ranges of minimum value of magnetic moment, $\mu_b$, and
the characteristic decay time, $t_d$, $\sim 10^{29.5}\ge \mu_b \ge 10^{28} {\rm
G} {\rm cm}^3$, $\sim 10^8\ge t_d \ge 10^7 {\rm yrs}$ are excluded assuming the
standard initial magnetic moment, $\mu_0=10^{30} {\rm G} {\rm cm}^3$. For these
parameters, neutron stars would never reach the stage of accretion from the
interstellar medium even for a low space velocity of the stars and a high
density of the ambient plasma. The range of excluded parameters increases for
lower values of $\mu_0$.
  We also show, that, contrary to exponential MFD, no significant restrictions
can be made for the parameters of power-law decay from the statistics of
isolated neutron star candidates in ROSAT observations.
  Isolated neutron stars with constant magnetic fields and initial values of
them less than $\mu_0 \sim 10^{29} {\rm G} {\rm cm}^3$ never come to the stage
of accretion.
  We briefly discuss the fate of old magnetars with and without MFD, and
describe parameters of old accreting magnetars.

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The categories of this paper are: cond-mat
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The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol