An SKA precursor view of X-ray binary jets

In this PhD thesis, we use the Square Kilometre Array precursor telescopes, including the Murchison Widefield Array (MWA), the Australian Square Kilometre Array Pathfinder, and MeerKAT, to study the jets of black hole X-ray binaries (BH-XRBs), through both broadband spectra and neutral hydrogen absorption measurements. We constrained the kinematic distance of two BH-XRBs. We made the first MWA detections of both transient and compact jets in BH-XRBs, from which we determined the jet physical parameters

The study of thermonuclear X-ray bursts in accreting millisecond pulsar MAXI J1816-195 with NuSTAR and NICER

The millisecond pulsar MAXI J1816--195 was recently discovered by MAXI in 2022 May. We have studied different properties of the pulsar using data from NuSTAR and NICER observations. The position of the source is measured by NuSTAR as RA = $18^h 16^m 52^s.40$, Dec = $-19^o37^{'} 58^{''}.35$. The unstable burning of accreted material on the surface of neutron stars induces thermonuclear (Type-I) bursts. Several thermonuclear bursts have been detected from the source during the outburst. We study the evolution of burst profile with flux and energy using NuSTAR and NICER observations. During the NuSTAR observation, a total of four bursts were detected from the source. The duration of each burst was around $\sim$ 30 s and the ratio of peak to persistent count rate is $\sim$ 26 as seen from the NuSTAR data. The thermonuclear bursts are modeled to determine the burst timing parameters using a sharp linear rise and exponential decay function. The burst profiles show a relatively long tail in lower energies. The hardness ratio during the thermonuclear bursts shows significant variation as observed by NuSTAR. We successfully model the broadband burst-resolved spectra with a combination of an absorbed blackbody along with a non-thermal component to account for the persistent emission. The burst-resolved spectral parameters show significant evolution during the burst. During the peak of the burst, the Eddington luminosity is found to be $\sim 3.7 \times 10^{38}$ erg s$^{-1}$. The burst-resolved spectral parameters provide a source distance of $8.5\pm1.2$ kpc for isotropic burst emission.Comment: 13 pages, 9 figures, 4 tables, comments are welcom

Re-awakening of GRS 1716–249 after 23 yr, observed by Swift/XRT and NuSTAR

In this work, we present a spectral and temporal analysis of Swift/XRT and NuSTAR observations of GRS 1716–249 during its recent 2016–2017 outburst. This low-mass X-ray binary underwent an extraordinary outburst after a long quiescence of 23 yr, since its last major outburst in 1993. The source was observed over two different epochs during 2017 April 7 and 10. The best-fitting joint spectral fitting in the energy range 0.5–79.0 keV indicates that the spectrum is best described by relatively cold, weak disc blackbody emission, dominant thermal Comptonization emission, and a relativistically broadened fluorescent iron K α emission line. We observed a clear indication of a Compton hump around 30 keV. We also detected an excess feature of 1.3 keV. Assuming a lamp-post geometry of the corona, we constrained the inner disc radius for both observations to 11.92^(+8.62)_(−11.92) R_(ISCO) (i.e. an upper limit) and 10.39^(+9.51)_(−3.02) R_(ISCO)(where R_(ISCO) ≡ radius of the innermost stable circular orbit) for the first epoch (E1) and second epoch (E2), respectively. A significant (5σ) type C quasi-periodic oscillation (QPO) at 1.20 ± 0.04 Hz is detected for the first time for GRS 1716–249, which drifts to 1.55 ± 0.04 Hz (6σ) at the end of the second observation. The derived spectral and temporal properties show a positive correlation between the QPO frequency and the photon index

An HI absorption distance to the black hole candidate X-ray binary MAXI J1535-571

With the Australian Square Kilometre Array Pathfinder (ASKAP) we monitored the black hole candidate X-ray binary MAXI J1535--571 over seven epochs from 21 September to 2 October 2017. Using ASKAP observations, we studied the HI absorption spectrum from gas clouds along the line-of-sight and thereby constrained the distance to the source. The maximum negative radial velocities measured from the HI absorption spectra for MAXI J1535--571 and an extragalactic source in the same field of view are $-69\pm4$ km s$^{-1}$ and $-89\pm4$ km s$^{-1}$, respectively. This rules out the far kinematic distance ($9.3^{+0.5}_{-0.6}$ kpc), giving a most likely distance of $4.1^{+0.6}_{-0.5}$ kpc, with a strong upper limit of the tangent point at $6.7^{+0.1}_{-0.2}$ kpc. At our preferred distance, the peak unabsorbed luminosity of MAXI J1535--571 was $>78$ per cent of the Eddington luminosity, and shows that the soft-to-hard spectral state transition occurred at the very low luminosity of 1.2 -- 3.4 $\times$ 10$^{-5}$ times the Eddington luminosity. Finally, this study highlights the capabilities of new wide-field radio telescopes to probe Galactic transient outbursts, by allowing us to observe both a target source and a background comparison source in a single telescope pointing.Comment: Revised after favorable referee report from MNRAS Letter

Re-awakening of GRS 1716-249 after 23 yr, observed by Swift/XRT and NuSTAR

In this work, we present a spectral and temporal analysis of Swift/XRT and NuSTAR observations of GRS 1716–249 during its recent 2016–2017 outburst. This low-mass X-ray binary underwent an extraordinary outburst after a long quiescence of 23 yr, since its last major outburst in 1993. The source was observed over two different epochs during 2017 April 7 and 10. The best-fitting joint spectral fitting in the energy range 0.5–79.0 keV indicates that the spectrum is best described by relatively cold, weak disc blackbody emission, dominant thermal Comptonization emission, and a relativistically broadened fluorescent iron K α emission line. We observed a clear indication of a Compton hump around 30 keV. We also detected an excess feature of 1.3 keV. Assuming a lamp-post geometry of the corona, we constrained the inner disc radius for both observations to 11.92+8.62 −11.92 RISCO (i.e. an upper limit) and 10.39+9.51 −3.02 RISCO (where RISCO ≡ radius of the innermost stable circular orbit) for the first epoch (E1) and second epoch (E2), respectively. A significant (5σ) type C quasi-periodic oscillation (QPO) at 1.20 ± 0.04 Hz is detected for the first time for GRS 1716–249, which drifts to 1.55 ± 0.04 Hz (6σ) at the end of the second observation. The derived spectral and temporal properties show a positive correlation between the QPO frequency and the photon inde

An H i absorption distance to the black hole candidate X-ray binary MAXI J1535-571

With the Australian Square Kilometre Array Pathfinder (ASKAP) we monitored the black hole candidate X-ray binary MAXI J1535-571 over seven epochs from 2017 September 21 to October 2. Using ASKAP observations, we studied the H i absorption spectrum from gas clouds along the line of sight and thereby constrained the distance to the source. The maximum negative radial velocities measured from the H i absorption spectra for MAXI J1535-571 and an extragalactic source in the same field of view are -69 ± 4 and -89 ± 4 km s-1, respectively. This rules out the far kinematic distance (9.3+0.5 -0.6 kpc), giving a most likely distance of 4.1+0.6 -0.5 kpc, with a strong upper limit of the tangent point at 6.7+0.1 -0.2 kpc. At our preferred distance, the peak unabsorbed luminosity of MAXI J1535-571 was >78 per cent of the Eddington luminosity, and shows that the soft-to-hard spectral state transition occurred at the very low luminosity of (1.2-3.4) × 10-5 times the Eddington luminosity. Finally, this study highlights the capabilities of new wide-field radio telescopes to probe Galactic transient outbursts, by allowing us to observe both a target source and a background comparison source in a single telescope pointing