Dr Kaustubh Rajwade

Abstract:

We present the discovery of 27 new Galactic transients made by the commensal MeerTRAP single pulse search programme at the MeerKAT telescope. We determine the location of 14 of these discoveries with arcsecond accuracy by imaging the data captured in the dedicated transient buffer. A preliminary estimate of the period was made for 8 sources using the arrival times of several pulses detected by MeerTRAP. The periods of these transients range between 0.78 s and 4 s. For the previously published MeerTRAP source MTP0040 (PSR J1357−6507), we are able to provide the position and period using new pulses detected since it was reported. We also estimate the radio fluences and discuss the burst rates derived from the commensal search detections. The accurate image-domain localizations were used to conduct follow-up observations and timing analysis. Furthermore, some follow-up observations revealed ordinary pulsar-like pulsed behavior for four of the new sources, illustrating the blurred separation between rotating radio transients and canonical pulsars. We also present coherent timing solutions for 4 sources, providing insight into their rotational properties and their place within the Galactic neutron star population.

Abstract:

We present the discovery of a second coherent radio burst from the thermally emitting neutron star 2XMM J104608.7–594306 in our follow-up observations with the Murriyang Ultra-Wideband Low receiver. This burst shows complex morphology with multiple components and wideband emission spanning from 704 to 4032 MHz. We measured a steep spectral index of . Our polarimetric analysis demonstrates that the burst is highly polarized with a linear and circular polarization fraction of 54 per cent and 22 per cent, respectively. We identified an orthogonal jump in the polarization position angles of the burst, resembling those seen in radio pulsars. We compared this burst with the first radio burst detected from the source with MeerKAT. These two bursts detected in a total of 40 h on source with MeerKAT and Murriyang, combined, show that 2XMM J104608.7–594306 can emit sporadic radio emission with luminosity jumps comparable to those seen in the bright bursts from SGR 1935+2154. This suggests that previously thought radio-quiet neutron stars such as X-ray dim isolated neutron stars and central compact objects could exhibit rare radio bursting activity.

Abstract:

The known population of non-accreting neutron stars is ever growing and currently consists of more than 3500 sources. Pulsar surveys with the SKAO telescopes will greatly increase the known population, adding radio pulsars to every subgroup in the radio-loud neutron star family. These discoveries will not only add to the current understanding of neutron star physics by increasing the sample of sources that can be studied, but will undoubtedly also uncover previously unknown types of sources that will challenge our theories of a wide range of physical phenomena. A broad variety of scientific studies will be made possible by a significantly increased known population of neutron stars, unravelling questions such as: How do isolated pulsars evolve with time; What is the connection between magnetars, high B-field pulsars, and the newly discovered long-period pulsars; How is a pulsar’s spin-down related to its radio emission; What is the nuclear equation of state? Increasing the known numbers of pulsars in binary or triple systems may enable both larger numbers and higher precision tests of gravitational theories and general relativity, as well as probing the neutron star mass distribution. The excellent sensitivity of the SKAO telescopes combined with the wide field of view, large numbers of simultaneous tied-array beams that will be searched in real time, wide range of observing frequencies, and the ability to form multiple sub-arrays will make the SKAO an excellent facility to undertake a wide range of neutron star research. In this paper, we give an overview of different types of neutron stars and discuss how the SKAO telescopes will aid in our understanding of the neutron star population.

Abstract:

This paper presents a comprehensive wideband study of FRB 20240619D focusing on its hyperactivity, rotation measure evolution, and the search for an associated persistent radio source. Using data from the MeerKAT, Murriyang, and Lovell telescopes, we analysed the spectral, temporal, and polarimetric properties of 1539 bursts. Our observations reveal a remarkably high burst rate of 161 bursts per hour in early August above a fluence value of 1.6 Jy ms as well as significant secular variations in rotation measure and diverse polarization characteristics, including high linear polarization fractions and occasional circular polarization. The burst activity also showed frequency dependence with approximately 61 per cent of the total number of bursts detected between 1300 and 1800 MHz. The burst activity of FRB 20240619D ceased abruptly after a period of intense activity lasting approximately 80 d, suggesting an episodic behaviour. Follow-up observations with MeerKAT and Australia Telescope Compact Array did not reveal an associated compact persistent radio source. Altogether, our results highlight the importance of continued long-term monitoring and multiwavelength observations in understanding the emission mechanisms and diversity of progenitor populations of fast radio bursts.

Abstract:

Accurately localizing fast radio bursts (FRBs) is essential for understanding their birth environments and for their use as cosmological probes. Recent advances in radio interferometry, particularly with MeerKAT, have enabled the localization of individual bursts with arcsecond precision. In this work, we present the localization of 15 apparently non-repeating FRBs detected with MeerKAT. Two of the FRBs, discovered in 2022, were localized in 8 s images from the projects that MeerTRAP was commensal to, while eight were localized using the transient buffer (TB) pipeline, and another one through SeeKAT, all with arcsecond precision. Four additional FRBs lacked TB triggers and sufficient signal, limiting their localization only to arcminute precision. For eight of the FRBs in our sample, we identify host galaxies with greater than 90 per cent confidence, and one with 80 per cent confidence, while two FRBs have ambiguous associations. We measured spectroscopic redshifts for six host galaxies, ranging from 0.33 to 0.85, demonstrating MeerKAT’s sensitivity to high-redshift FRBs. We modelled the spectral energy distributions of host galaxies with sufficient photometric coverage to derive their stellar population and star formation properties. This work represents one of the largest uniform samples of well-localized distant FRBs to date, laying the groundwork for using MeerKAT FRBs as cosmological probes and understand how FRB hosts evolve at high redshift.