74 research outputs found
X-Rays from the Nearby Solitary Millisecond Pulsar PSR J0030+0451 - the Final ROSAT Observations
We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+0451.
The pulsar was one of the last targets observed in DEC-98 by the ROSAT PSPC.
X-ray pulses are detected on a level and make the source the
millisecond pulsar detected in the X-ray domain. The pulsed fraction
is found to be . The X-ray pulse profile is characterized by two
narrow peaks which match the gross pulse profile observed at 1.4 GHz. Assuming
a Crab-like spectrum the X-ray flux is in the range
erg s cm ( keV), implying an X-ray efficiency of
.Comment: Accepted for publication in Ap
Detection, Localization and Characterization of Gravitational Wave Bursts in a Pulsar Timing Array
Efforts to detect gravitational waves by timing an array of pulsars have
focused traditionally on stationary gravitational waves: e.g., stochastic or
periodic signals. Gravitational wave bursts --- signals whose duration is much
shorter than the observation period --- will also arise in the pulsar timing
array waveband. Sources that give rise to detectable bursts include the
formation or coalescence of supermassive black holes (SMBHs), the periapsis
passage of compact objects in highly elliptic or unbound orbits about a SMBH,
or cusps on cosmic strings. Here we describe how pulsar timing array data may
be analyzed to detect and characterize these bursts. Our analysis addresses, in
a mutually consistent manner, a hierarchy of three questions: \emph{i}) What
are the odds that a dataset includes the signal from a gravitational wave
burst? \emph{ii}) Assuming the presence of a burst, what is the direction to
its source? and \emph{iii}) Assuming the burst propagation direction, what is
the burst waveform's time dependence in each of its polarization states?
Applying our analysis to synthetic data sets we find that we can \emph{detect}
gravitational waves even when the radiation is too weak to either localize the
source of infer the waveform, and \emph{detect} and \emph{localize} sources
even when the radiation amplitude is too weak to permit the waveform to be
determined. While the context of our discussion is gravitational wave detection
via pulsar timing arrays, the analysis itself is directly applicable to
gravitational wave detection using either ground or space-based detector data.Comment: 43 pages, 13 figures, submitted to ApJ
Optimization of NANOGrav's Time Allocation for Maximum Sensitivity to Single Sources
Pulsar Timing Arrays (PTAs) are a collection of precisely timed millisecond
pulsars (MSPs) that can search for gravitational waves (GWs) in the nanohertz
frequency range by observing characteristic signatures in the timing residuals.
The sensitivity of a PTA depends on the direction of the propagating
gravitational wave source, the timing accuracy of the pulsars, and the
allocation of the available observing time. The goal of this paper is to
determine the optimal time allocation strategy among the MSPs in the North
American Nanohertz Observatory for Gravitational Waves (NANOGrav) for a single
source of GW under a particular set of assumptions. We consider both an
isotropic distribution of sources across the sky and a specific source in the
Virgo cluster. This work improves on previous efforts by modeling the effect of
intrinsic spin noise for each pulsar. We find that, in general, the array is
optimized by maximizing time spent on the best-timed pulsars, with sensitivity
improvements typically ranging from a factor of 1.5 to 4.Comment: Accepted by Astrophyiscal Journa
Optimizing Pulsar Timing Arrays to Maximize Gravitational Wave Single Source Detection: a First Cut
Pulsar Timing Arrays (PTAs) use high accuracy timing of a collection of low
timing noise pulsars to search for gravitational waves in the microhertz to
nanohertz frequency band. The sensitivity of such a PTA depends on (a) the
direction of the gravitational wave source, (b) the timing accuracy of the
pulsars in the array and (c) how the available observing time is allocated
among those pulsars. Here, we present a simple way to calculate the sensitivity
of the PTA as a function of direction of a single GW source, based only on the
location and root-mean-square residual of the pulsars in the array. We use this
calculation to suggest future strategies for the current North American
Nanohertz Observatory for Gravitational Waves (NANOGrav) PTA in its goal of
detecting single GW sources. We also investigate the affects of an additional
pulsar on the array sensitivity, with the goal of suggesting where PTA pulsar
searches might be best directed. We demonstrate that, in the case of single GW
sources, if we are interested in maximizing the volume of space to which PTAs
are sensitive, there exists a slight advantage to finding a new pulsar near
where the array is already most sensitive. Further, the study suggests that
more observing time should be dedicated to the already low noise pulsars in
order to have the greatest positive effect on the PTA sensitivity. We have made
a web-based sensitivity mapping tool available at http://gwastro.psu.edu/ptasm.Comment: 14 pages, 3 figures, accepted by Ap
- …