510 research outputs found
Finding (or not) New Gamma-ray Pulsars with GLAST
Young energetic pulsars will likely be the largest class of Galactic sources
observed by GLAST, with many hundreds detected. Many will be unknown as radio
pulsars, making pulsation detection dependent on radio and/or x-ray
observations or on blind periodicity searches of the gamma-rays. Estimates for
the number of pulsars GLAST will detect in blind searches have ranged from tens
to many hundreds. I argue that the number will be near the low end of this
range, partly due to observations being made in a scanning as opposed to a
pointing mode. This paper briefly reviews how blind pulsar searches will be
conducted using GLAST, what limits these searches, and how the computations and
statistics scale with various parameters.Comment: 3 pages, 2 figures, for the Proceedings of the First GLAST Symposium
(5-8 Feb 2007
A compact steep spectrum radio source in NGC1977
A compact steep spectrum radio source (J0535-0452) is located in the sky
coincident with a bright optical rim in the HII region NGC1977. J0535-0452 is
observed to be mas in angular size at 8.44 GHz. The spectrum for the
radio source is steep and straight with a spectral index of -1.3 between 330
and 8440 MHz. No 2 \mu m IR counter part for the source is detected. These
characteristics indicate that the source may be either a rare high redshift
radio galaxy or a millisecond pulsar (MSP). Here we investigate whether the
steep spectrum source is a millisecond pulsar.The optical rim is believed to be
the interface between the HII region and the adjacent molecular cloud. If the
compact source is a millisecond pulsar, it would have eluded detection in
previous pulsar surveys because of the extreme scattering due to the HII
region--molecular cloud interface. The limits obtained on the angular
broadening along with the distance to the scattering screen are used to
estimate the pulse broadening. The pulse broadening is shown to be less than a
few msec at frequencies \gtsim 5 GHz. We therefore searched for pulsed
emission from J0535-0452 at 14.8 and 4.8 GHz with the Green Bank Telescope
(GBT). No pulsed emission is detected to 55 and 30 \mu Jy level at 4.8 and 14.8
GHz. Based on the parameter space explored by our pulsar search algorithm, we
conclude that, if J0535-0452 is a pulsar, then it could only be a binary MSP of
orbital period \ltsim 5 hrs.Comment: Accepted for publication in A&A (3pages, 1 fig
The Massive Pulsar PSR J1614-2230: Linking Quantum Chromodynamics, Gamma-ray Bursts, and Gravitational Wave Astronomy
The recent measurement of the Shapiro delay in the radio pulsar PSR
J1614-2230 yielded a mass of 1.97 +/- 0.04 M_sun, making it the most massive
pulsar known to date. Its mass is high enough that, even without an
accompanying measurement of the stellar radius, it has a strong impact on our
understanding of nuclear matter, gamma-ray bursts, and the generation of
gravitational waves from coalescing neutron stars. This single high mass value
indicates that a transition to quark matter in neutron-star cores can occur at
densities comparable to the nuclear saturation density only if the quarks are
strongly interacting and are color superconducting. We further show that a high
maximum neutron-star mass is required if short duration gamma-ray bursts are
powered by coalescing neutron stars and, therefore, this mechanism becomes
viable in the light of the recent measurement. Finally, we argue that the
low-frequency (<= 500 Hz) gravitational waves emitted during the final stages
of neutron-star coalescence encode the properties of the equation of state
because neutron stars consistent with this measurement cannot be centrally
condensed. This will facilitate the measurement of the neutron star equation of
state with Advanced LIGO/Virgo.Comment: Accepted for publication in ApJ
Twenty Years of Searching for (and Finding) Globular Cluster Pulsars
Globular clusters produce orders of magnitude more millisecond pulsars per
unit mass than the Galactic disk. Since the first cluster pulsar was uncovered
twenty years ago, at least 138 have been identified - most of which are binary
millisecond pulsars. Because of their origins involving stellar encounters,
many of these systems are exotic objects that would never be observed in the
Galactic disk. Examples include pulsar-main sequence binaries, extremely rapid
rotators (including the current record holder), and millisecond pulsars in
highly eccentric orbits. These systems are allowing new probes of the
interstellar medium, the equation of state of material at supra-nuclear
density, the mass distribution of neutron stars, and the dynamics of globular
clusters.Comment: 9 pages, 6 figures. Submitted review for the "40 Years of Pulsars"
conference in Montreal, Aug 2007. To be published by the AI
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