118 research outputs found
Modeling the X-rays from the Central Compact Object PSR J1852+0040 in Kesteven 79: Evidence for a Strongly Magnetized Neutron Star
I present modeling of the X-ray pulsations from the central compact object
(CCO) PSR J1852+0040 in the Galactic supernova remnant Kesteven 79. In the
context of thermal surface radiation from a rotating neutron star, a
conventional polar cap model can reproduce the broad, large-amplitude X-ray
pulse only with a "pencil plus fan" beam emission pattern, which is
characteristic of strongly magnetized (10^12 Gauss) neutron star
atmospheres, substantially stronger than the ~10^10 Gauss external dipole field
inferred from the pulsar spin-down rate. This discrepancy can be explained by
an axially displaced dipole. For other beaming patterns, it is necessary to
invoke high-aspect-ratio emitting regions that are greatly longitudinally
elongated, possibly due to an extremely offset dipole. For all assumed emission
models, the existence of strong internal magnetic fields (10^14}
Gauss) that preferentially channel internal heat to only a portion of the
exterior is required to account for the implied high-temperature contrast
across the stellar surface. This lends further observational evidence in
support of the "hidden" strong magnetic field scenario, in which CCOs possess
strong submerged magnetic fields that are substantially stronger than the
external dipole field, presumably due to burial by fallback of supernova
ejecta. I also conduct phase-resolved X-ray spectroscopy and find no evidence
for prominent spin-phase-dependent absorption features that could be produced
by cyclotron absorption/scattering.Comment: 12 pages, 7 figures; accepted for publication in the Astrophysical
Journa
Deep XMM-Newton Spectroscopic and Timing Observations of the Isolated Radio Millisecond Pulsar PSR J0030+0451
We present deep XMM-Newton EPIC spectroscopic and timing X-ray observations
of the nearby solitary radio millisecond pulsar, PSR J0030+0451. Its emission
spectrum in the 0.1-10 keV range is found to be remarkably similar to that of
the nearest and best studied millisecond pulsar, PSR J0437-4715, being well
described by a predominantly thermal two-temperature model plus a faint hard
tail evident above ~2 keV. The pulsed emission in the 0.3-2 keV band is
characterized by two broad pulses with pulsed fraction ~60-70%, consistent with
a mostly thermal origin of the X-rays only if the surface polar cap radiation
is from a light-element atmosphere. Modeling of the thermal pulses permits us
to place constraints on the neutron star radius of R>10.7 (95% confidence) and
R>10.4 km (at 99.9% confidence) for M=1.4 M_sun.Comment: 8 pages, 7 figures; accepted for publication in The Astrophysical
Journa
The Light Curve and Internal Magnetic Field of the Mode-Switching Pulsar PSR B0943+10
A number of radio pulsars exhibit intriguing mode-switching behavior. Recent
observations of PSR B0943+10 revealed correlated radio and X-ray mode switches,
providing a new avenue for understanding this class of objects. The large X-ray
pulse fraction observed during the radio quiet phase (Q mode) was previously
interpreted as a result of changing obscuration of X-rays by dense
magnetosphere plasma. We show that the large X-ray pulse fraction can be
explained by including the beaming effect of a magnetic atmosphere, while
remaining consistent with the dipole field geometry constrained by radio
observations. We also explore a more extreme magnetic field configuration,
where a magnetic dipole displaced from the center of the star produces two
magnetic polar caps of different sizes and magnetic field strengths. These
models are currently consistent with data in radio and X-rays and can be tested
or constrained by future X-ray observations.Comment: 5 pages, 5 figures, submitted to ApJ
X-ray and -ray Studies of the Millisecond Pulsar and Possible X-ray Binary/Radio Pulsar Transition Object PSR J1723-2837
We present X-ray observations of the "redback" eclipsing radio millisecond
pulsar and candidate radio pulsar/X-ray binary transition object PSR
J1723-2837. The X-ray emission from the system is predominantly non-thermal and
exhibits pronounced variability as a function of orbital phase, with a factor
of ~2 reduction in brightness around superior conjunction. Such temporal
behavior appears to be a defining characteristic of this variety of peculiar
millisecond pulsar binaries and is likely caused by a partial geometric
occultation by the main-sequence-like companion of a shock within the binary.
There is no indication of diffuse X-ray emission from a bow shock or pulsar
wind nebula associated with the pulsar. We also report on a search for point
source emission and -ray pulsations in Fermi Large Area Telescope data
using a likelihood analysis and photon probability weighting. Although PSR
J1723-2837 is consistent with being a -ray point source, due to the
strong Galactic diffuse emission at its position a definitive association
cannot be established. No statistically significant pulsations or modulation at
the orbital period are detected. For a presumed source detection, the implied
-ray luminosity is 5% of its spin-down power. This indicates
that PSR J1723-2837 is either one of the least efficient -ray producing
millisecond pulsars or, if the detection is spurious, the -ray emission
pattern is not directed towards us.Comment: 10 pages, 6 figures; accepted for publication in the Astrophysical
Journa
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