分类： 天文学 >> 天文学 提交时间： 2023-02-19
N. D. R. Bhat
N. A. Swainston
S. J. McSweeney
M. Xue
B. W. Meyers
S. Kudale
S. Dai
S. E. Tremblay
W. van Straten
R. M. Shannon
K. R. Smith
M. Sokolowski
S. M. Ord
G. Sleap
A. Williams
P. J. Hancock
R. Lange
J. Tocknell
M. Johnston-Hollitt
D. L. Kaplan
摘要： In Paper I, we presented an overview of the Southern-sky MWA Rapid Two-metre (SMART) survey, including the survey design and search pipeline. While the combination of MWA's large field-of-view and the voltage capture system brings a survey speed of ~450 square degrees per hour, the survey progression relies on the availability of compact configuration of the Phase II array. Over the past few years, by taking advantage of multiple windows of opportunity when the compact configuration was available, we have advanced the survey to 75% completion. To date, about 10% of the data collected thus far have been processed for a first-pass search, where 10 minutes of observation is processed for dispersion measures out to 250 ${\rm pc\,cm^{-3}}$, to realise a shallow survey for long-period pulsars. The ongoing analysis has led to two new pulsar discoveries, as well as an independent discovery and a rediscovery of a previously incorrectly characterised pulsar, all from ~3% of the data for which candidate scrutiny is completed. Here we describe the strategies for further detailed follow-up including improved sky localisation and convergence to timing solution, and illustrate them using example pulsar discoveries. The processing has also led to re-detection of 120 pulsars in the SMART observing band, bringing the total number of pulsars detected to date with the MWA to 180, and these are used to assess the search sensitivity of current processing pipelines. The planned second-pass (deep survey) processing is expected to yield a three-fold increase in sensitivity for long-period pulsars, and a substantial improvement to millisecond pulsars by adopting optimal de-dispersion plans. The SMART survey will complement the highly successful Parkes High Time Resolution Universe survey at 1.2-1.5 GHz, and inform future large survey efforts such as those planned with the low-frequency Square Kilometre Array.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
N. D. R. Bhat
N. A. Swainston
S. J. McSweeney
M. Xue
B. W. Meyers
S. Kudale
S. Dai
S. E. Tremblay
W. van Straten
R. M. Shannon
K. R. Smith
M. Sokolowski
S. M. Ord
G. Sleap
A. Williams
P. J. Hancock
R. Lange
J. Tocknell
M. Johnston-Hollitt
D. L. Kaplan
摘要： We present an overview of the Southern-sky MWA Rapid Two-metre (SMART) pulsar survey that exploits the MWA's large field of view and voltage capture system to survey the sky south of 30 degree in declination for pulsars and fast transients in the 140-170 MHz band. The survey is enabled by the advent of the Phase II MWA's compact configuration, which offers an enormous efficiency in beam-forming and processing costs, thereby making an all-sky survey of this magnitude tractable with the MWA. Even with the long dwell times of the survey (4800 s), data collection can be completed in < 100 hours of telescope time, while still retaining the ability to reach a limiting sensitivity of ~2-3 mJy. Each observation is processed to generate ~5000-8000 tied-array beams that tessellate the full ~610 square degree field of view, which are then processed to search for pulsars. The voltage-capture recording allows a multitude of post hoc processing options including the reprocessing of data for higher time resolution. Due to the substantial computational cost in pulsar searches at low frequencies, processing is undertaken in multiple passes: in the first pass, a shallow survey is performed, where 10 minutes of each observation is processed, reaching about one-third of the full search sensitivity. Here we present the system overview and initial results. Further details including first pulsar discoveries and a census of low-frequency detections are presented in a companion paper. Future plans include deeper searches to reach the full sensitivity and acceleration searches to target binary and millisecond pulsars. Simulation analysis forecasts ~300 new pulsars upon the completion of full processing. The SMART survey will also generate a complete digital record of the low-frequency sky, which will serve as a valuable reference for future pulsar searches planned with the low-frequency Square Kilometre Array.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
D. R. Madison(1
2)
X.-J. Zhu(3
4)
G. Hobbs
W. Coles
R. M. Shannon(4
6)
J. Wang
C. Tiburzi(8
9
10
11)
R. N. Manchester
M. Bailes
N. D. R. Bhat
S. Burke-Spolaor
S.Dai
J. Dempsey
M. Keith
摘要： By regularly monitoring the most stable millisecond pulsars over many years, pulsar timing arrays (PTAs) are positioned to detect and study correlations in the timing behaviour of those pulsars. Gravitational waves (GWs) from supermassive black hole binaries (SMBHBs) are an exciting potentially detectable source of such correlations. We describe a straight-forward technique by which a PTA can be "phased-up" to form time series of the two polarisation modes of GWs coming from a particular direction of the sky. Our technique requires no assumptions regarding the time-domain behaviour of a GW signal. This method has already been used to place stringent bounds on GWs from individual SMBHBs in circular orbits. Here, we describe the methodology and demonstrate the versatility of the technique in searches for a wide variety of GW signals including bursts with unmodeled waveforms. Using the first six years of data from the Parkes Pulsar Timing Array, we conduct an all-sky search for a detectable excess of GW power from any direction. For the lines of sight to several nearby massive galaxy clusters, we carry out a more detailed search for GW bursts with memory, which are distinct signatures of SMBHB mergers. In all cases, we find that the data are consistent with noise.
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