分类： 天文学 >> 天文学 提交时间： 2023-02-19
M. C. Bezuidenhout
C. J. Clark
R. P. Breton
B. W. Stappers
E. D. Barr
M. Caleb
W. Chen
F. Jankowski
M. Kramer
K. Rajwade
M. Surnis
摘要： Multi-element interferometers such as MeerKAT, which observe with high time resolution and have a wide field-of-view, provide an ideal opportunity to perform real-time, untargeted transient and pulsar searches. However, because of data storage limitations, it is not always feasible to store the baseband data required to image the field of a discovered transient or pulsar. This limits the ability of surveys to effectively localise their discoveries and may restrict opportunities for follow-up science, especially of one-off events like some Fast Radio Bursts (FRBs). Here we present a novel maximum-likelihood estimation approach to localising transients and pulsars detected in multiple MeerKAT tied-array beams at once, which we call Tied Array Beam Localisation (TABLo), as well as a Python implementation of the method named SeeKAT. We provide real-world examples of SeeKAT's use as well as a Monte Carlo analysis to show that it is capable of localising single pulses detected in beamformed MeerKAT data to (sub-)arcsecond precision.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
J. C. Andrianjafy
N. Heeralall-Issur
A. A. Deshpande
K. Golap
P. Woudt
M. Caleb
E. D. Barr
W. Chen
F. Jankowski
M. Kramer
B. W. Stappers
J. Wu
摘要： We present the analysis of radio interferometric 2-s images from a MeerKAT observation of the repeating fast radio burst FRB121102 on September 2019, during which 11 distinct pulses have been previously detected using high time and frequency resolution data cubes. In this work, we detected 6 out of the 11 bursts in the image plane at 1.48 GHz with a minimum peak signal-to-noise ratio (S/N) of 5 {\sigma} and a fluence detection limit of 0.512 Jy ms. These constitute the first detections of a fast radio burst (FRB) or a radio transient using 2-s timescale images with MeerKAT data. Analysis of the fitted burst properties revealed a weighted average precision of 1 arcsec in the localization of the bursts. The accurate knowledge of FRB positions is essential for identifying their host galaxy and understanding their mysterious nature which is still unresolved to this day. We also produced 2-s images at 1.09 GHz but yielded no detection which we attributed to the spectral structure of the pulses that are mostly higher in strength in the upper frequencies. We also explore a new approach to difference imaging analysis (DIA) to search for transients and find that our technique has the potential to reduce the number of candidates and could be used to automate the detection of FRBs in the image plane for future MeerKAT observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
A. Corongiu
V. Venkatraman Krishnan
P. C. C. Freire
M. Kramer
A. Possenti
M. Geyer
A. Ridolfi
F. Abbate
M. Bailes
E. D. Barr
V. Balakrishnan
S. Buchner
D. J. Champion
W. Chen
B. V. Hugo
A. Karastergiou
A. G. Lyne
R. N. Manchester
P. V. Padmanabh
A. Parthasarathy
摘要： PSRJ1910-5959A (J1910A) is a binary millisecond pulsar in a 0.837 day circular orbit around a helium white dwarf (HeWD) companion. This pulsar is located 6.3 arcmin away from the centre of the globular cluster NGC6752. Given the large offset, the association of the pulsar to NGC6752 has been debated. We have made use of two decades of archival Parkes 64-m "Murriyang" telescope data and recently carried out observations with the MeerKAT telescope. We obtained Pulse times of arrival using standard data reduction techniques and analysed using Bayesian pulsar timing techniques. We analysed the pulsar's total intensity and polarisation profile, to study the interstellar scattering along the line of sight, and the pulsar's geometry by applying the rotating vector model. We obtain precise measurements of several post-Keplerian parameters: the range $r=0.202(6)T_\odot$ and shape s=0.999823(4) of the Shapiro delay, from which we infer the orbital inclination to be $88.9^{+0.15}_{-0.14}\deg$ and the masses of both the pulsar and the companion to be $1.55(7)M_{\odot}$ and $0.202(6)M_{\odot}$ respectively; a secular change in the orbital period $\dot{P}_{\rm b}=-53^{+7.4}_{-6.0}\times 10^{-15}$\,s\,s$^{-1}$ that proves the association to NGGC6752 and a secular change in the projected semi-major axis of the pulsar $\dot{x}= -40.7^{+7.3}_{-8.2}\times10^{-16}$\,s\,s$^{-1}$ that is likely caused by the spin-orbit interaction from a misaligned HeWD spin, at odds with the likely isolated binary evolution of the system. We also discuss some theoretical models for the structure and evolution of WDs in NS-WD binaries by using J1910A's companion as a test bed. J1910A is a rare system for which several parameters of both the pulsar and the HeWD companion can be accurately measured. As such, it is a test bed to discriminate between alternative models for HeWD structure and cooling.
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