1,073 research outputs found
A Search for Pulsars in Quiescent Soft X-Ray Transients. I
We have carried out a deep search at 1.4 GHz for radio pulsed emission from
six soft X-ray transient sources observed during their X-ray quiescent phase.
The commonly accepted model for the formation of the millisecond radio pulsars
predicts the presence of a rapidly rotating, weakly magnetized neutron star in
the core of these systems. The sudden drop in accretion rate associated with
the end of an X-ray outburst causes the Alfv\`en surface to move outside the
light cylinder, allowing the pulsar emission process to operate. No pulsed
signal was detected from the sources in our sample. We discuss several
mechanisms that could hamper the detection and suggest that free-free
absorption from material ejected from the system by the pulsar radiation
pressure could explain our null result.Comment: accepted by Ap
The 69 ms Radio Pulsar Near the Supernova Remnant RCW 103
We report the detection of the radio pulsar counterpart to the 69 ms X-ray
pulsar discovered near the supernova remnant RCW 103 (G332.4-0.4). Our
detection confirms that the pulsations arise from a rotation-powered neutron
star, which we name PSR J1617-5055. The observed barycentric period derivative
confirms that the pulsar has a characteristic age of only 8 kyr, the sixth
smallest of all known pulsars. The unusual apparent youth of the pulsar and its
proximity to a young remnant requires that an association be considered.
Although the respective ages and distances are consistent within substantial
uncertainties, the large inferred pulsar transverse velocity is difficult to
explain given the observed pulsar velocity distribution, the absence of
evidence for a pulsar wind nebula, and the symmetry of the remnant. Rather, we
argue that the objects are likely superposed on the sky; this is reasonable
given the complex area. Without an association, the question of where is the
supernova remnant left behind following the birth of PSR J1617-5055 remains
open. We also discuss a possible association between PSR J1617-5055 and the
gamma-ray source 2CG 333+01. Though an association is energetically plausible,
it is unlikely given that EGRET did not detect 2CG 333+01.Comment: 18 pages, 2 encapsulated Postscript figures, uses AAS LaTeX style
files. Accepted for publication in The Astrophysical Journal Letter
A Shapiro delay detection in the binary system hosting the millisecond pulsar PSR J1910-5959A
PSR J1910-5959A is a binary pulsar with a helium white dwarf companion
located about 6 arcmin from the center of the globular cluster NGC6752. Based
on 12 years of observations at the Parkes radio telescope, the relativistic
Shapiro delay has been detected in this system. We obtain a companion mass Mc =
0.180+/-0.018Msun (1sigma) implying that the pulsar mass lies in the range
1.1Msun <= Mp <= 1.5Msun. We compare our results with previous optical
determinations of the companion mass, and examine prospects for using this new
measurement for calibrating the mass-radius relation for helium white dwarfs
and for investigating their evolution in a pulsar binary system. Finally we
examine the set of binary systems hosting a millisecond pulsar and a low mass
helium white dwarf for which the mass of both stars has been measured. We
confirm that the correlation between the companion mass and the orbital period
predicted by Tauris & Savonije reproduces the observed values but find that the
predicted Mp - Pb correlation over-estimates the neutron star mass by about
0.5Msun in the orbital period range covered by the observations. Moreover, a
few systems do not obey the observed Mp - Pb correlation. We discuss these
results in the framework of the mechanisms that inhibit the accretion of matter
by a neutron star during its evolution in a low-mass X-ray binary.Comment: 4 figures, 2 tables, accepted for publication in the Astrophysical
Journa
Timing of Millisecond Pulsars in NGC 6752: Evidence for a High Mass-to-Light Ratio in the Cluster Core
Using pulse timing observations we have obtained precise parameters,
including positions with about 20 mas accuracy, of five millisecond pulsars in
NGC 6752. Three of them, located relatively close to the cluster center, have
line-of-sight accelerations larger than the maximum value predicted by the
central mass density derived from optical observation, providing dynamical
evidence for a central mass-to-light ratio >~ 10, much higher than for any
other globular cluster. It is likely that the other two millisecond pulsars
have been ejected out of the core to their present locations at 1.4 and 3.3
half-mass radii, respectively, suggesting unusual non-thermal dynamics in the
cluster core.Comment: Accepted by ApJ Letter. 5 pages, 2 figures, 1 tabl
Formation of "Lightnings" in a Neutron Star Magnetosphere and the Nature of RRATs
The connection between the radio emission from "lightnings" produced by the
absorption of high-energy photons from the cosmic gamma-ray background in a
neutron star magnetosphere and radio bursts from rotating radio transients
(RRATs) is investigated. The lightning length reaches 1000 km; the lightning
radius is 100 m and is comparable to the polar cap radius. If a closed
magnetosphere is filled with a dense plasma, then lightnings are efficiently
formed only in the region of open magnetic field lines. For the radio emission
from a separate lightning to be observed, the polar cap of the neutron star
must be directed toward the observer and, at the same time, the lightning must
be formed. The maximum burst rate is related to the time of the plasma outflow
from the polar cap region. The typical interval between two consecutive bursts
is ~100 s. The width of a single radio burst can be determined both by the
width of the emission cone formed by the lightning emitting regions at some
height above the neutron star surface and by a finite lightning lifetime. The
width of the phase distribution for radio bursts from RRATs, along with the
integrated pulse width, is determined by the width of the bundle of open
magnetic field lines at the formation height of the radio emission. The results
obtained are consistent with the currently available data and are indicative of
a close connection between RRATs, intermittent pulsars, and extreme nullers.Comment: 24 pages, no figures, references update
Discovery of Pulsations and a Possible Spectral Feature in the X-ray Emission from Rotating Radio Transient J1819-1458
PSR J1819-1458 is a rotating radio transient (RRAT) source with an inferred
surface dipole magnetic field strength of 5e13 G and a 4.26-s spin period. We
present XMM-Newton observations of the X-ray counterpart of this source, CXOU
J181939.1-145804, in which we identify pulsations and a possible spectral
feature. The X-ray pulsations are at the period predicted by the radio
ephemeris, providing an unambiguous identification with the radio source and
confirmation of its neutron star nature. The X-ray pulse has a 0.3-5 keV pulsed
fraction of 34% and is aligned with the expected phase of the radio pulse. The
X-ray spectrum is fit well by an absorbed blackbody with kT = 0.14 keV with the
addition of an absorption feature at 1 keV, with total absorbed flux of 1.5e-13
ergs/cm^2/s (0.3-5 keV). This absorption feature is well modeled by a Gaussian
or resonant cyclotron scattering model, but its significance is dependent on
the choice of continuum model. We find no evidence for any X-ray bursts or
aperiodic variability on timescales of 6 ms to the duration of the observation
and can place the most stringent limit to date of < 3e-9 ergs/cm^2/s on the
absorbed 0.3-5 keV flux of any bursts.Comment: 5 figures, accepted by Ap
Discovery of a Young Radio Pulsar in a Relativistic Binary Orbit
We report on the discovery of PSR J1141-6545, a radio pulsar in an eccentric,
relativistic 5-hr binary orbit. The pulsar shows no evidence for being
recycled, having pulse period P = 394 ms, characteristic age tau_c = 1.4 x 10^6
yr, and inferred surface magnetic dipole field strength B = 1.3 x 10^12 G. From
the mass function and measured rate of periastron advance, we determine the
total mass in the system to be (2.300 +/- 0.012) solar masses, assuming that
the periastron advance is purely relativistic. Under the same assumption, we
constrain the pulsar's mass to be M_p < 1.348 solar masses and the companion's
mass to be M_c > 0.968 solar masses (both 99% confidence). Given the total
system mass and the distribution of measured neutron star masses, the companion
is probably a massive white dwarf which formed prior to the birth of the
pulsar. Optical observations can test this hypothesis.Comment: 18 pages, 4 figures, Accepted for Publication in Ap
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