1,508 research outputs found
Green Bank Telescope Observations of the Eclipse of Pulsar "A" in the Double Pulsar Binary PSR J0737-3039
We report on the first Green Bank Telescope observations at 427, 820 and 1400
MHz of the newly discovered, highly inclined and relativistic double pulsar
binary. We focus on the brief eclipse of PSR J0737-3039A, the faster pulsar,
when it passes behind PSR J0737-3039B. We measure a frequency-averaged eclipse
duration of 26.6 +/- 0.6 s, or 0.00301 +/- 0.00008 in orbital phase. The
eclipse duration is found to be significantly dependent on radio frequency,
with eclipses longer at lower frequencies. Specifically, eclipse duration is
well fit by a linear function having slope (-4.52 +/- 0.03) x 10^{-7}
orbits/MHz. We also detect significant asymmetry in the eclipse. Eclipse
ingress takes 3.51 +/- 0.99 times longer than egress, independent of radio
frequency. Additionally, the eclipse lasts (40 +/- 7) x 10^{-5} in orbital
phase longer after conjunction, also independent of frequency. We detect
significant emission from the pulsar on short time scales during eclipse in
some orbits. We discuss these results in the context of a model in which the
eclipsing material is a shock-heated plasma layer within the slower PSR
J0737-3039B's light cylinder, where the relativistic pressure of the faster
pulsar's wind confines the magnetosphere of the slower pulsar.Comment: 12 pages, 3 figure
Pulsars in Globular Clusters with the SKA
Globular clusters are highly efficient radio pulsar factories. These pulsars
can be used as precision probes of the clusters' structure, gas content,
magnetic field, and formation history; some of them are also highly interesting
in their own right because they probe exotic stellar evolution scenarios as
well as the physics of dense matter, accretion, and gravity. Deep searches with
SKA1-MID and SKA1-LOW will plausibly double to triple the known population.
Such searches will only require one to a few tied-array beams, and can be done
during early commissioning of the telescope - before an all-sky pulsar survey
using hundreds to thousands of tied-array beams is feasible. With SKA2 it will
be possible to observe most of the active radio pulsars within a large fraction
of the Galactic globular clusters, an estimated population of 600 - 3700
observable pulsars (those beamed towards us). This rivals the total population
of millisecond pulsars that can be found in the Galactic field; fully
characterizing it will provide the best-possible physical laboratories as well
as a rich dynamical history of the Galactic globular cluster system.Comment: 15 pages, 5 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04
Constraining Parity Violation in Gravity with Measurements of Neutron-Star Moments of Inertia
Neutron stars are sensitive laboratories for testing general relativity,
especially when considering deviations where velocities are relativistic and
gravitational fields are strong. One such deviation is described by dynamical,
Chern-Simons modified gravity, where the Einstein-Hilbert action is modified
through the addition of the gravitational parity-violating Pontryagin density
coupled to a field. This four-dimensional effective theory arises naturally
both in perturbative and non-perturbative string theory, loop quantum gravity,
and generic effective field theory expansions. We calculate here Chern-Simons
modifications to the properties and gravitational fields of slowly spinning
neutron stars. We find that the Chern-Simons correction affects only the
gravitomagnetic sector of the metric to leading order, thus introducing
modifications to the moment of inertia but not to the mass-radius relation. We
show that an observational determination of the moment of inertia to an
accuracy of 10%, as is expected from near-future observations of the double
pulsar, will place a constraint on the Chern-Simons coupling constant of
\xi^{1/4} < 5 km, which is at least three-orders of magnitude stronger than the
previous strongest bound.Comment: 14 pages, 6 figures, replaced with version accepted for publication
in Phys. Rev.
PSR J2030+3641: radio discovery and gamma-ray study of a middle-aged pulsar in the now identified Fermi-LAT source 1FGL J2030.0+3641
In a radio search with the Green Bank Telescope of three unidentified low
Galactic latitude Fermi-LAT sources, we have discovered the middle-aged pulsar
J2030+3641, associated with 1FGL J2030.0+3641 (2FGL J2030.0+3640). Following
the detection of gamma-ray pulsations using a radio ephemeris, we have obtained
a phase-coherent timing solution based on gamma-ray and radio pulse arrival
times that spans the entire Fermi mission. With a rotation period of 0.2 s,
spin-down luminosity of 3e34 erg/s, and characteristic age of 0.5 Myr, PSR
J2030+3641 is a middle-aged neutron star with spin parameters similar to those
of the exceedingly gamma-ray-bright and radio-undetected Geminga. Its gamma-ray
flux is 1% that of Geminga, primarily because of its much larger distance, as
suggested by the large integrated column density of free electrons, DM=246
pc/cc. We fit the gamma-ray light curve, along with limited radio polarimetric
constraints, to four geometrical models of magnetospheric emission, and while
none of the fits have high significance some are encouraging and suggest that
further refinements of these models may be worthwhile. We argue that not many
more non-millisecond radio pulsars may be detected along the Galactic plane
that are responsible for LAT sources, but that modified methods to search for
gamma-ray pulsations should be productive -- PSR J2030+3641 would have been
found blindly in gamma rays if only >0.8 GeV photons had been considered, owing
to its relatively flat spectrum and location in a region of high soft
background.Comment: Accepted for publication in ApJ, 9 pages, 6 figure
The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197
We have observed the 5.54s anomalous X-ray pulsar XTE J1810-197 at radio,
millimeter, and infrared (IR) wavelengths, with the aim of learning about its
broad-band spectrum. At the IRAM 30m telescope, we have detected the magnetar
at 88 and 144GHz, the highest radio-frequency emission ever seen from a pulsar.
At 88GHz we detected numerous individual pulses, with typical widths ~2ms and
peak flux densities up to 45Jy. Together with nearly contemporaneous
observations with the Parkes, Nancay, and Green Bank telescopes, we find that
in late 2006 July the spectral index of the pulsar was -0.5<alpha<0 over the
range 1.4-144GHz. Nine dual-frequency Very Large Array and Australia Telescope
Compact Array observations in 2006 May-September are consistent with this
finding, while showing variability of alpha with time. We infer from the IRAM
observations that XTE J1810-197 remains highly linearly polarized at millimeter
wavelengths. Also, toward this pulsar, the transition frequency between strong
and weak scattering in the interstellar medium may be near 50GHz. At Gemini, we
detected the pulsar at 2.2um in 2006 September, at the faintest level yet
observed, K_s=21.89+-0.15. We have also analyzed four archival IR Very Large
Telescope observations (two unpublished), finding that the brightness
fluctuated within a factor of 2-3 over a span of 3 years, unlike the monotonic
decay of the X-ray flux. Thus, there is no correlation between IR and X-ray
flux, and it remains uncertain whether there is any correlation between IR and
radio flux.Comment: Accepted for publication in ApJ; contains improved discussion of
infrared uncertaintie
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