arXiv subjects

Fronefield Crawford

Publications and source records attributed to Fronefield Crawford.

63 records · Page 4Linked to original sources

arXiv2004

A Low Cost Distributed Computing Approach to Pulsar Searches at a Small College

We describe a distributed processing cluster of inexpensive Linux machines developed jointly by the Astronomy and Computer Science departments at Haverford College which has been successfully used to search a large volume of data from a recent radio pulsar survey. Analysis of radio pulsar surveys requires significant computational resources to handle the demanding data storage and processing needs. One goal of this project was to explore issues encountered when processing a large amount of pulsar survey data with limited computational resources. This cluster, which was developed and activated in only a few weeks by supervised undergraduate summer research students, used existing decommissioned computers, the campus network, and a script-based, client-oriented, self-scheduled data distribution approach to process the data. This setup provided simplicity, efficiency, and "on-the-fly" scalability at low cost. The entire 570 GB data set from the pulsar survey was processed at Haverford over the course of a ten-week summer period using this cluster. We conclude that this cluster can serve as a useful computational model in cases where data processing must be carried out on a limited budget. We have also constructed a DVD archive of the raw survey data in order to investigate the feasibility of using DVD as an inexpensive and easily accessible raw data storage format for pulsar surveys. DVD-based storage has not been widely explored in the pulsar community, but it has several advantages. The DVD archive we have constructed is reliable, portable, inexpensive, and can be easily read by any standard modern machine.

cs.DC↗

arXiv2004

Three New Binary Pulsars Discovered With Parkes

We present three new binary pulsars discovered during a search for pulsations in 56 unidentified mid-latitude EGRET gamma-ray error boxes with the Parkes multibeam receiver. Timing observations of these sources is on-going with both the Parkes and the Green Bank telescopes. We discuss the place of these new systems in the population of binary pulsars and suggest that they are all somewhat atypical systems.

astro-ph↗

arXiv2004

PSR J2021+3651: A New Gamma-Ray Pulsar Candidate

The COS B high energy gamma-ray source 2CG 075+00, also known as GeV J2020+3658 or 3EG J2021+3716, has avoided identification with a low energy counterpart for over twenty years. We present a likely identification with the discovery and subsequent timing of a young and energetic pulsar, PSR J2021+3651, with the Wideband Arecibo Pulsar Processor at the Arecibo Observatory. PSR J2021+3651 has a rotation period P = 104ms and Pdot = 9.6 x 10^{-14}, implying a characteristic age T_c = 17kyr and a spin-down luminosity Edot = 3.4 x 10^{36} erg s^{-1}. The pulsar is also coincident with the ASCA source AX J2021.1+3651. The implied luminosity of the associated X-ray source suggests the X-ray emission is dominated by a pulsar wind nebula unresolved by ASCA. The pulsar's unexpectedly high dispersion measure DM = 371 pc cm^{-3} and the d > 10kpc DM distance pose a new question: is PSR J2021+3651 an extremely efficient gamma-ray pulsar at the edge of the Galaxy? This is a question for AGILE and GLAST to answer.

astro-ph↗

arXiv2004

New Pulsars Coincident With Unidentified Gamma-Ray Sources

We present the results of radio searches for pulsars within unidentified EGRET source error boxes. Using the Parkes multibeam system, we have surveyed 56 sources at Galactic latitudes |b| > 5 deg which do not appear to be associated with blazars. This population has been suggested to be distributed like the local star forming region known as the Gould Belt, the Galactic Halo, and/or the millisecond pulsars. We have discovered several new pulsars in this survey, including three new binary systems.

astro-ph↗

arXiv2003

A Comparison of Measured Crab and Vela Glitch Healing Parameters with Predictions of Neutron Star Models

There are currently two well-accepted models that explain how pulsars exhibit glitches, sudden changes in their regular rotational spin-down. According to the starquake model, the glitch healing parameter, Q, which is measurable in some cases from pulsar timing, should be equal to the ratio of the moment of inertia of the superfluid core of a neutron star (NS) to its total moment of inertia. Measured values of the healing parameter from pulsar glitches can therefore be used in combination with realistic NS structure models as one test of the feasibility of the starquake model as a glitch mechanism. We have constructed NS models using seven representative equations of state of superdense matter to test whether starquakes can account for glitches observed in the Crab and Vela pulsars, for which the most extensive and accurate glitch data are available. We also present a compilation of all measured values of Q for Crab and Vela glitches to date which have been separately published in the literature. We have computed the fractional core moment of inertia for stellar models covering a range of NS masses and find that for stable NSs in the realistic mass range 1.4 +/- 0.2 solar masses, the fraction is greater than 0.55 in all cases. This range is not consistent with the observational restriction Q < 0.2 for Vela if starquakes are the cause of its glitches. This confirms results of previous studies of the Vela pulsar which have suggested that starquakes are not a feasible mechanism for Vela glitches. The much larger values of Q observed for Crab glitches (Q > 0.7) are consistent with the starquake model predictions and support previous conclusions that starquakes can be the cause of Crab glitches.

astro-ph↗

arXiv2003

Radio Polarization of the Young High-Magnetic-Field Pulsar PSR J1119-6127

We have investigated the radio polarization properties of PSR J1119-6127, a recently discovered young radio pulsar with a large magnetic field. Using pulsar-gated radio imaging data taken at a center frequency of 2496 MHz with the Australia Telescope Compact Array, we have determined a rotation measure for the pulsar of +842 +/- 23 rad m^-2. These data, combined with archival polarimetry data taken at a center frequency of 1366 MHz with the Parkes telescope, were used to determine the polarization characteristics of PSR J1119-6127 at both frequencies. The pulsar has a fractional linear polarization of ~75% and ~55% at 1366 and 2496 MHz, respectively, and the profile consists of a single, wide component. This pulse morphology and high degree of linear polarization are in agreement with previously noticed trends for young pulsars (e.g., PSR J1513-5908). A rotating-vector (RV) model fit of the position angle (PA) of linear polarization over pulse phase using the Parkes data suggests that the radio emission comes from the leading edge of a conal beam. We discuss PSR J1119-6127 in the context of a recent theoretical model of pulsar spin-down which can in principle be tested with polarization and timing data from this pulsar. Geometric constraints from the RV fit are currently insufficient to test this model with statistical significance, but additional data may allow such a test in the future.

astro-ph↗

arXiv2002

PSR J2021+3651: A Young Radio Pulsar Coincident with an Unidentified EGRET Gamma-ray Source

We report on a deep search for radio pulsations toward five unidentified ASCA X-ray sources coincident with EGRET gamma-ray sources. This search has led to the discovery of a young and energetic pulsar using data obtained with the new Wideband Arecibo Pulsar Processor. PSR J2021+3651 is likely associated with the X-ray source AX J2021.1+3651, which in turn is likely associated with the COS B high energy gamma-ray source 2CG 075+00, also known as GeV J2020+3658 or 3EG J2021+3716. PSR J2021+3651 has a rotation period P = 104 ms and P_dot = 9.6x10^{-14}, implying a characteristic age ~17 kyr and a spin-down luminosity E_dot ~ 3.4x10^{36}ergs/s. The dispersion measure DM ~ 371 pc cm^{-3} is by far the highest of any observed pulsar in the Galactic longitude range 55 < l < 80. This DM suggests a distance d > 10 kpc, and a high gamma-ray efficiency of \~15%, but the true distance may be closer if there is a significant contribution to the DM from excess gas in the Cygnus region. The implied luminosity of the associated X-ray source suggests the X-ray emission is dominated by a pulsar wind nebula unresolved by ASCA.

astro-ph↗

arXiv2000

A radio supernova remnant associated with the young pulsar J1119-6127

We report on Australia Telescope Compact Array observations in the direction of the young high magnetic-field pulsar J1119-6127. In the resulting images we identify a non-thermal radio shell of diameter 15', which we classify as a previously uncatalogued young supernova remnant, G292.2-0.5. This supernova remnant is positionally coincident with PSR J1119-6127, and we conclude that the two objects are physically associated. No radio emission is detected from any pulsar wind nebula (PWN) associated with the pulsar; our observed upper limits are consistent with the expectation that high magnetic-field pulsars produce radio nebulae which fade rapidly. This system suggests a possible explanation for the lack of an associated radio pulsar and/or PWN in many supernova remnants.

astro-ph↗

arXiv2000

A Search for Sub-millisecond Pulsations in Unidentified FIRST and NVSS Radio Sources

We have searched 92 unidentified sources from the FIRST and NVSS 1400 MHz radio survey catalogs for radio pulsations at 610 MHz. The selected radio sources are bright, have no identification with extragalactic objects, are point-like and are more than 5% linearly polarized. Our search was sensitive to sub-millisecond pulsations from pulsars with dispersion measures (DMs) less than 500 pc cm-3 in the absence of scattering. We have detected no pulsations from these sources and consider possible effects which might prevent detection. We conclude that as a population, these sources are unlikely to be pulsars.

astro-ph↗