67 research outputs found
Pulsar population synthesis using palfa detections and pulsar search collaboratory discoveries including a wide DNS system and a nearby MSP
Using the ensemble of detections from pulsar surveys, we can learn about the sizes and characteristics of underlying populations. In this thesis, I analyze results from the Pulsar Arecibo L-band Feed Array (PALFA) precursor and Green Bank Telescope 350 MHz Drift Scan surveys; I examine survey sensitivity to see how detections can inform pulsar population models, I look at new ways of including young scientists -- high school students -- in the discovery process and I present timing solutions for students\u27 discoveries (including a nearby millisecond pulsar and a pulsar in a wide-orbit double neutron star system).;The PALFA survey is on-going and uses the ALFA 7-beam receiver at 1400 MHz to search both inner and outer Galactic sectors visible from Arecibo (32° ?£? 77° and 168° ?£? 214°) close to the Galactic plane (|b| ? 5°) for pulsars. The PALFA precursor survey observed a subset of this region, (|b| ? 1°) and detected 45 pulsars, including one known millisecond pulsar (MSP) and 11 previously unknown, long-period (normal) pulsars. I assess the sensitivity of the PALFA precursor survey and use the number of normal pulsar and MSP detections to infer the size of each underlying Galactic population. Based on 44 normal pulsar detections and one MSP, we constrain each population size to 107,000+36,000-25,000 and 15,000 +85,000-6,000 respectively with 95% confidence. Based on these constraints, we predict yields for the full PALFA survey and find a deficiency in normal pulsar detections, possibly due to radio frequency interference and/or scintillation, neither of which are currently accounted for in population simulations.;The GBT 350 MHz Drift Scan survey collected data in the summer of 2007 while the GBT was stationary, undergoing track replacement. Results discussed here come from ~20% of the survey data, which were processed and donated to the Pulsar Search Collaboratory (PSC). The PSC is a joint outreach program between WVU and NRAO, involving high school students in the pulsar discovery process -- hands-on, cutting-edge research -- to foster their interest in pursuing Science, Technology, Engineering and Mathematics (STEM) related career paths. The PSC began in 2008; since then, over 100 teachers and 2,500 students from 18 states have participated and discovered seven pulsars. Of these seven, J1400--1431, a bright, nearby MSP shows promising characteristics for inclusion in pulsar timing arrays, which aim to detect gravitational waves by precisely timing an array of MSPs. Two others -- J1821+0155, a disrupted recycled pulsar and J1930--1852 show interesting properties due to interactions with binary companions. PSR J1930--1852 is a partially-recycled, first-to-evolve pulsar in a double neutron star (DNS) system with a high-eccentricity 45 day orbit. Its spin period and orbital period are factors of 2 and 3 higher, respectively, than any previously-known, primary DNS pulsars. We measure the relativistic advance of periastron o=0.00078(4), implying a total system mass of Mtot =2.59(4), which is consistent with other DNS systems. PSR J1930--1852\u27s spin and orbital parameters, however, challenge current DNS evolution models, making it an important system for further investigation
A Pilot Study of Nulling in 22 Pulsars Using Mixture Modeling
The phenomenon of pulsar nulling, observed as the temporary inactivity of a
pulsar, remains poorly understood both observationally and theoretically. Most
observational studies that quantify nulling employ a variant of Ritchings
(1976)'s algorithm which can suffer significant biases for pulsars where the
emission is weak. Using a more robust mixture model method, we study pulsar
nulling in a sample of 22 recently discovered pulsars, for which we publish the
nulling fractions for the first time. These data clearly demonstrate biases of
the former approach and show how an otherwise non-nulling pulsar can be
classified as having significant nulls. We show that the population-wide
studies that find a positive correlation of nulling with pulsar
period/characteristic age can similarly be biased because of the bias in
estimating the nulling fraction. We use our probabilistic approach to find the
evidence for periodicity in the nulls in a subset of three pulsars in our
sample. In addition, we also provide improved timing parameters for 17 of the
22 pulsars that had no prior follow-up.Comment: Accepted for publication in the Astrophysical Journal (ApJ
Serendipitous Discovery of PSR J1431-6328 as a Highly-Polarized Point Source with the Australian SKA Pathfinder
We identified a highly-polarized, steep-spectrum radio source in a deep image
with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope at 888
MHz. After considering and rejecting a stellar origin for this source, we
discovered a new millisecond pulsar (MSP) using observations from the Parkes
radio telescope. This pulsar has period 2.77 ms and dispersion measure 228.27
pc/cm**3. Although this pulsar does not yet appear to be particularly
remarkable, the short spin period, wide profile and high dispersion measure do
make it relatively hard to discover through traditional blind periodicity
searches. Over the course of several weeks we see changes in the barycentric
period of this pulsar that are consistent with orbital motion in a binary
system, but the properties of any binary need to be confirmed by further
observations. While even a deep ASKAP survey may not identify large numbers of
new MSPs compared to the existing population, it would be competitive with
existing all-sky surveys and could discover interesting new MSPs at high
Galactic latitude without the need for computationally-expensive all-sky
periodicity searches.Comment: ApJ, in pres
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
The Green Bank North Celestial Cap Pulsar Survey. III. 45 New Pulsar Timing Solutions
We provide timing solutions for 45 radio pulsars discovered by the Robert C. Byrd Green Bank Telescope. These pulsars were found in the Green Bank North Celestial Cap pulsar survey, an all-GBT-sky survey being carried out at a frequency of 350 MHz. We include pulsar timing data from the Green Bank Telescope and Low Frequency Array. Our sample includes five fully recycled millisecond pulsars (MSPs, three of which are in a binary system), a new relativistic double neutron star system, an intermediate-mass binary pulsar, a mode-changing pulsar, a 138 ms pulsar with a very low magnetic field, and several nulling pulsars. We have measured two post-Keplerian parameters and thus the masses of both objects in the double neutron star system. We also report a tentative companion mass measurement via Shapiro delay in a binary MSP. Two of the MSPs can be timed with high precision and have been included in pulsar timing arrays being used to search for low-frequency gravitational waves, while a third MSP is a member of the black widow class of binaries. Proper motion is measurable in five pulsars, and we provide an estimate of their space velocity. We report on an optical counterpart to a new black widow system and provide constraints on the optical counterparts to other binary MSPs. We also present a preliminary analysis of nulling pulsars in our sample. These results demonstrate the scientific return of long timing campaigns on pulsars of all types
Bayesian Solar Wind Modeling with Pulsar Timing Arrays
Using Bayesian analyses we study the solar electron density with the NANOGrav
11-year pulsar timing array (PTA) dataset. Our model of the solar wind is
incorporated into a global fit starting from pulse times-of-arrival. We
introduce new tools developed for this global fit, including analytic
expressions for solar electron column densities and open source models for the
solar wind that port into existing PTA software. We perform an ab initio
recovery of various solar wind model parameters. We then demonstrate the
richness of information about the solar electron density, , that can be
gleaned from PTA data, including higher order corrections to the simple
model associated with a free-streaming wind (which are informative probes of
coronal acceleration physics), quarterly binned measurements of and a
continuous time-varying model for spanning approximately one solar cycle
period. Finally, we discuss the importance of our model for chromatic noise
mitigation in gravitational-wave analyses of pulsar timing data and the
potential of developing synergies between sophisticated PTA solar electron
density models and those developed by the solar physics community.Comment: 22 pages, 7 figures, Submitted to Ap
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