646 research outputs found
Millimeter interferometer observations of the magnetar 4U 0142+61
The Anomalous X‐ray Pulsar 4U 0142+61 is the only neutron star where it is believed that one of the long searched‐for ‘fallback’ disks has been detected in the mid‐IR by Wang et al. [1] using Spitzer. Such a disk originates from material falling back to the NS after the supernova. We search for cold circumstellar material in the 90 GHz continuum using the Plateau de Bure Interferometer. No millimeter flux is detected at the position of 4U 0142+61, the upper flux limit is 150 μJy corresponding to the 3σ noise rms level. The re‐processed Spitzer MIPS 24μm data presented previously by Wang et al. [2] show some indication of flux enhancement at the position of the neutron star, albeit below the 3σ statistical significance limit. At far infrared wavelengths the source flux densities are probably below the Herschel confusion limits
Extensive population synthesis of isolated neutron stars with field decay
We perform population synthesis studies of different types of neutron stars
taking into account the magnetic field decay. For the first time, we confront
our results with observations using {\it simultaneously} the Log N -- Log S
distribution for nearby isolated neutron stars, the Log N -- Log L distribution
for magnetars, and the distribution of radio pulsars in the --
diagram. We find that our theoretical model is consistent with all sets of data
if the initial magnetic field distribution function follows a log-normal law
with and . The
typical scenario includes about 10% of neutron stars born as magnetars,
significant magnetic field decay during the first million years of a NS life.
Evolutionary links between different subclasses may exist, although robust
conclusions are not yet possible.
We apply the obtained field distribution and the model of decay to study
long-term evolution of neuton stars till the stage of accretion from the
interstellar medium. It is shown that though the subsonic propeller stage can
be relatively long, initially highly magnetized neutron stars ( G) reach the accretion regime within the Galactic lifetime if their
kick velocities are not too large. The fact that in previous studies made 10
years ago, such objects were not considered results in a slight increase of the
Accretor fraction in comparison with earlier conclusions. Most of the neutron
stars similar to the Magnificent seven are expected to become accreting from
the interstellar medium after few billion years of their evolution. They are
the main predecestors of accreting isolated neutron stars.Comment: 4 pages, conference "Astrophysics of Neutron Stars - 2010" in honor
of M. Ali Alpar, Izmir, Turke
Chandra observations of the old pulsar PSR B1451-68
We present 35 ks Chandra ACIS observations of the 42 Myr old radio pulsar PSR
B1451-68. A point source is detected 0.32" +/- 0.73" from the expected radio
pulsar position. It has ~200 counts in the 0.3-8 keV energy range. We identify
this point source as the X-ray counterpart of the radio pulsar. PSR B1451-68 is
located close to a 2MASS point source, for which we derive 7% as the upper
limit on the flux contribution to the measured pulsar X-ray flux. The pulsar
spectrum can be described by either a power-law model with photon index
Gamma=2.4 (+0.4/-0.3) and a unrealistically high absorbing column density N(H)=
(2.5 (+1.2/-1.3)) * 10^(21) cm^-2, or by a combination of a kT=0.35
(+0.12/-0.07) keV blackbody and a Gamma = 1.4 +/- 0.5 power-law component for
N(H)[DM]= 2.6 * 10^(20) cm^-2, estimated from the pulsar dispersion measure. At
the parallactic, Lutz-Kelker bias corrected distance of 480 pc, the non-thermal
X-ray luminosities in the 0.3-8 keV energy band are either Lx(nonth)= (11.3 +/-
1.7) * 10^(29) erg/s or Lx(nonth)= (5.9 (+4.9/-5.0)) * 10^(29) erg/s,
respectively. This corresponds to non-thermal X-ray efficiencies of either
eta(nonth)= Lx(nonth) / (dE/dt) ~ 0.005 or 0.003, respectively.Comment: 19 pages, 9 figures, 2 tables, accepted by Ap
Space cowboys odyssey: beyond the Gould Belt
We present our new advanced model for population synthesis of close-by
cooling NSs. Detailed treatment of the initial spatial distribution of NS
progenitors and a detailed ISM structure up to 3 kpc give us an opportunity to
discuss the strategy to look for new isolated cooling NSs. Our main results in
this respect are the following: new candidates are expected to be identified
behind the Gould Belt, in directions to rich OB associations, in particular in
the Cygnus-Cepheus region; new candidates, on average, are expected to be
hotter than the known population of cooling NS. Besides the usual approach
(looking for soft X-ray sources), the search in 'empty' -ray error
boxes or among run-away OB stars may yield new X-ray thermally emitting NS
candidates.Comment: 3 pages, 2 figures, proceedings of the conference "40 Years of
Pulsars ", 12-17 August 2007, Montreal, Canad
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