618 research outputs found
Gravitational Wave Hotspots: Ranking Potential Locations of Single-Source Gravitational Wave Emission
The steadily improving sensitivity of pulsar timing arrays (PTAs) suggests
that gravitational waves (GWs) from supermassive black hole binary (SMBHB)
systems in the nearby universe will be de- tectable sometime during the next
decade. Currently, PTAs assume an equal probability of detection from every sky
position, but as evidence grows for a non-isotropic distribution of sources, is
there a most likely sky position for a detectable single source of GWs? In this
paper, a collection of galactic catalogs is used to calculate various metrics
related to the detectability of a single GW source resolv- able above a GW
background, assuming that every galaxy has the same probability of containing a
SMBHB. Our analyses of these data reveal small probabilities that one of these
sources is currently in the PTA band, but as sensitivity is improved regions of
consistent probability density are found in predictable locations, specifically
around local galaxy clusters.Comment: 9 pages, 9 figures, accepted for submission in Ap
The identification of the optical companion to the binary millisecond pulsar J0610-2100 in the Galactic field
We have used deep V and R images acquired at the ESO Very Large Telescope to
identify the optical companion to the binary pulsar PSR J0610-2100, one of the
black-widow millisecond pulsars recently detected by the Fermi Gamma-ray
Telescope in the Galactic plane. We found a faint star (V~26.7) nearly
coincident (\delta r ~0".28) with the pulsar nominal position. This star is
visible only in half of the available images, while it disappears in the
deepest ones (those acquired under the best seeing conditions), thus indicating
that it is variable. Although our observations do not sample the entire orbital
period (P=0.28 d) of the pulsar, we found that the optical modulation of the
variable star nicely correlates with the pulsar orbital period and describes a
well defined peak (R~25.6) at \Phi=0.75, suggesting a modulation due to the
pulsar heating. We tentatively conclude that the companion to PSR J0610-2100 is
a heavily ablated very low mass star (~ 0.02Msun) that completely filled its
Roche Lobe.Comment: 17 pages, 5 figures - Accepted for pubblication in Ap
Intrinsic and Reprocessed Optical Emission from the Companion to PSR J2051_0827
Hubble Space Telescope observations of the companion to the eclipsing millisecond pulsar PSR J2051-0827 have revealed its "dark" side. The R magnitude at minimum is ~26, while the difference between the side heated by the impinging pulsar radiation and the unirradiated side is ~3.3 mag. For the first time, these data show that there is an asymmetry in the optical light curve of the companion. Furthermore, significant variability is seen in the companion brightness measured after optical maximum on successive orbits. The data are modeled by a gravitationally distorted low-mass secondary star that is irradiated by the pulsar wind. These model fits indicate that the system is only mildly inclined (i ~ 40°) and the unilluminated side of the companion has a temperature likely less than 3000 K
Pulsed X-ray Emission from Pulsar A in the Double Pulsar System J0737-3039
The double pulsar system J0737-3039 is not only a test bed for General Relativity and theories of gravity, but also provides a unique laboratory for probing the relativistic winds of neutron stars. Recent X-ray observations have revealed a point source at the position of PSR J0737-3039, but have failed to detect pulsations or orbital modulation. Here we report on Chandra X-ray Observatory High Resolution Camera observations of the double pulsar. We detect deeply modulated, double-peaked X-ray pulses at the period of PSR J0737-3039A, similar in appearance to the observed radio pulses. The pulsed fraction is approximately 70%. Although purely non-thermal emission is consistent with the data, the X-ray pulse morphology of A, in combination with previously reported spectral properties of the X-ray emission, suggests the existence of both non-thermal magnetospheric emission and a broad sinusoidal thermal emission component from the neutron star surface. No pulsations are detected from pulsar B, and there is no evidence for orbital modulation. The absence of orbital modulation is consistent with theoretical expectations of a Poynting-dominated relativistic wind at the termination shock between the magnetosphere of B and the wind from A, and with the small fraction of the energy outflow from A intercepted by the termination shock
Discovery of Gamma-ray Pulsations from the Transitional Redback PSR J1227-4853
The 1.69 ms spin period of PSR J1227-4853 was recently discovered in radio
observations of the low-mass X-ray binary XSS J12270-4859 following the
announcement of a possible transition to a rotation-powered millisecond pulsar
state, inferred from decreases in optical, X-ray, and gamma-ray flux from the
source. We report the detection of significant (5) gamma-ray pulsations
after the transition, at the known spin period, using ~1 year of data from the
Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The
gamma-ray light curve of PSR J1227-4853 can be fit by one broad peak, which
occurs at nearly the same phase as the main peak in the 1.4 GHz radio profile.
The partial alignment of light-curve peaks in different wavebands suggests that
at least some of the radio emission may originate at high altitude in the
pulsar magnetosphere, in extended regions co-located with the gamma-ray
emission site. We folded the LAT data at the orbital period, both pre- and
post-transition, but find no evidence for significant modulation of the
gamma-ray flux. Analysis of the gamma-ray flux over the mission suggests an
approximate transition time of 2012 November 30. Continued study of the pulsed
emission and monitoring of PSR J1227-4853, and other known redback systems, for
subsequent flux changes will increase our knowledge of the pulsar emission
mechanism and transitioning systems.Comment: 5 figures, 1 table, accepted for publication in ApJ, updated to
reflect accepted version and add additional coautho
Microarcsecond VLBI pulsar astrometry with PSR II. parallax distances for 57 pulsars
We present the results of PSR, a large astrometric project targeting
radio pulsars using the Very Long Baseline Array (VLBA). From our astrometric
database of 60 pulsars, we have obtained parallax-based distance measurements
for all but 3, with a parallax precision of typically 40 as and
approaching 10 as in the best cases. Our full sample doubles the number of
radio pulsars with a reliable (5) model-independent distance
constraint. Importantly, many of the newly measured pulsars are well outside
the solar neighbourhood, and so PSR brings a near-tenfold increase in the
number of pulsars with a reliable model-independent distance at kpc.
Using our sample along with previously published results, we show that even the
most recent models of the Galactic electron density distribution model contain
significant shortcomings, particularly at high Galactic latitudes. When
comparing our results to pulsar timing, two of the four millisecond pulsars in
our sample exhibit significant discrepancies in the estimates of proper motion
obtained by at least one pulsar timing array. With additional VLBI observations
to improve the absolute positional accuracy of our reference sources and an
expansion of the number of millisecond pulsars, we will be able to extend the
comparison of proper motion discrepancies to a larger sample of pulsar
reference positions, which will provide a much more sensitive test of the
applicability of the solar system ephemerides used for pulsar timing. Finally,
we use our large sample to estimate the typical accuracy attainable for
differential astrometry with the VLBA when observing pulsars, showing that for
sufficiently bright targets observed 8 times over 18 months, a parallax
uncertainty of 4 as per arcminute of separation between the pulsar and
calibrator can be expected.Comment: updated to version accepted by ApJ: 30 pages, 20 figures, 9 table
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