ORCID Profile
0000-0002-5654-2744
Current Organisations
University of Southampton
,
University of Amsterdam
,
University of Oxford
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Publisher: MDPI AG
Date: 24-04-2023
Abstract: The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide.
Publisher: Oxford University Press (OUP)
Date: 13-04-2022
Abstract: We report on the detection of MKT J174641.0−321404, a new radio transient found in untargeted searches of wide-field MeerKAT radio images centred on the black hole X-ray binary H1743−322. MKT J174641.0−321404 is highly variable at 1.3 GHz and was detected three times during 11 observations of the field in late 2018, reaching a maximum flux density of 590 ± 60 µJy. We associate this radio transient with a high proper motion, M dwarf star SCR 1746−3214 12 pc away from the Sun. Multiwavelength observations of this M dwarf indicate flaring activity across the electromagnetic spectrum, consistent with emission expected from dMe stars, and providing upper limits on quiescent brightness in both the radio and X-ray regimes. TESS photometry reveals a rotational period for SCR 1746−3214 of 0.2292 ± 0.0025 d, which at its estimated radius makes the star a rapid rotator, comparable to other low-mass systems. Dedicated spectroscopic follow up confirms the star as a mid-late spectral M dwarf with clear magnetic activity indicated by strong H α emission. This transient’s serendipitous discovery by MeerKAT, along with multiwavelength characterization, make it a prime demonstration of both the capabilities of the current generation of radio interferometers and the value of simultaneous observations by optical facilities such as MeerLICHT. Our results build upon the literature of M dwarfs’ flaring behaviour, particularly relevant to the habitability of their planetary systems.
Publisher: American Astronomical Society
Date: 06-2022
Abstract: We present a detailed study of the evolution of the Galactic black hole transient GRS 1716−249 during its 2016–2017 outburst at optical (Las Cumbres Observatory), mid-infrared (Very Large Telescope), near-infrared (Rapid Eye Mount telescope), and ultraviolet (the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope) wavelengths, along with archival radio and X-ray data. We show that the optical/near-infrared and UV emission of the source mainly originates from a multi-temperature accretion disk, while the mid-infrared and radio emission are dominated by synchrotron emission from a compact jet. The optical/UV flux density is correlated with the X-ray emission when the source is in the hard state, consistent with an X-ray irradiated accretion disk with an additional contribution from the viscous disk during the outburst fade. We find evidence for a weak, but highly variable jet component at mid-infrared wavelengths. We also report the long-term optical light curve of the source and find that the quiescent i ′ -band magnitude is 21.39 ± 0.15 mag. Furthermore, we discuss how previous estimates of the system parameters of the source are based on various incorrect assumptions, and so are likely to be inaccurate. By comparing our GRS 1716−249 data set to those of other outbursting black hole X-ray binaries, we find that while GRS 1716−249 shows similar X-ray behavior, it is noticeably optically fainter, if the literature distance of 2.4 kpc is adopted. Using several lines of reasoning, we argue that the source distance is further than previously assumed in the literature, likely within 4–17 kpc, with a most likely range of ∼4–8 kpc.
Publisher: American Astronomical Society
Date: 10-2023
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Rob Fender.