ORCID Profile
0000-0002-8094-6108
Current Organisations
Queen's University Belfast
,
University of Oxford
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Publisher: Springer Science and Business Media LLC
Date: 30-11-2022
Publisher: Research Square Platform LLC
Date: 10-06-2022
DOI: 10.21203/RS.3.RS-1700217/V1
Abstract: The tidal forces of a black hole can rip apart a star that passes too close to it, resulting in a stellar Tidal Disruption Event (TDE, (1)). In some such encounters, the black hole can launch a powerful relativistic jet (2-6). If this jet fortuitously aligns with our line of sight, the overall brightness is Doppler boosted by several orders of magnitude. Consequently, such on-axis relativistic TDEs have the potential to unveil cosmological (redshift z ) quiescent black holes and are ideal test beds to understand the radiative mechanisms operating in super-Eddington jets. Here, we present multi-wavelength (X-ray, UV, optical, and radio) observations of the optically discovered transient AT 2022cmc at z=1.193 (7). Its unusual X-ray properties, including a peak observed luminosity of 48 erg s -1 , systematic variability on timescales as short as 1000 seconds, and overall duration lasting more than 30 days in the rest-frame are traits associated with relativistic TDEs. This makes AT 2022cmc only the fourth member of this rare class and the first one identified in the optical and with well-s led optical data. The X-ray to radio spectral energy distributions spanning 5-50 days after discovery can be explained as synchrotron emission from a relativistic jet (radio), synchrotron self-Compton (X-rays), and thermal emission similar to that seen in low-redshift TDEs (UV/optical). Our modeling implies a beamed, highly relativistic jet akin to blazars (e.g., (8,9)) but requires extreme matter-domination, i.e, high ratio of electron-to-magnetic field energy densities in the jet, and challenges our theoretical understanding of jets. This work provides one of the best multi-wavelength datasets of a newborn relativistic jet to date and will be invaluable for testing more sophisticated jet models, and for identifying more such events in transient surveys.
Publisher: American Astronomical Society
Date: 06-2023
Abstract: We report observations of the optical counterpart of the long gamma-ray burst GRB 221009A. Due to the extreme rarity of being both nearby ( z = 0.151) and highly energetic ( E γ ,iso ≥ 10 54 erg), GRB 221009A offers a unique opportunity to probe the connection between massive star core collapse and relativistic jet formation across a very broad range of γ -ray properties. Adopting a phenomenological power-law model for the afterglow and host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian model comparison techniques to determine the likelihood of an associated supernova (SN) contributing excess flux to the optical light curve. Though not conclusive, we find moderate evidence ( K Bayes = 10 1.2 ) for the presence of an additional component arising from an associated SN, SN 2022xiw, and find that it must be substantially fainter ( % as bright at the 99% confidence interval) than SN 1998bw. Given the large and uncertain line-of-sight extinction, we attempt to constrain the SN parameters ( M Ni , M ej , and E KE ) under several different assumptions with respect to the host galaxy’s extinction. We find properties that are broadly consistent with previous GRB-associated SNe: M Ni = 0.05–0.25 M ⊙ , M ej = 3.5–11.1 M ⊙ , and E KE = (1.6–5.2) × 10 52 erg. We note that these properties are weakly constrained due to the faintness of the SN with respect to the afterglow and host emission, but we do find a robust upper limit on M Ni of M Ni 0.36 M ⊙ . Given the tremendous range in isotropic gamma-ray energy release exhibited by GRBs (seven orders of magnitude), the SN emission appears to be decoupled from the central engine in these systems.
Publisher: American Astronomical Society
Date: 31-03-2020
Publisher: American Astronomical Society
Date: 29-07-2021
Publisher: American Association for the Advancement of Science (AAAS)
Date: 09-06-2023
Abstract: Long-duration gamma-ray bursts (GRBs) are powerful cosmic explosions, signaling the death of massive stars. Among them, GRB 221009A is by far the brightest burst ever observed. Because of its enormous energy ( E iso ≈ 10 55 erg) and proximity ( z ≈ 0.15), GRB 221009A is an exceptionally rare event that pushes the limits of our theories. We present multiwavelength observations covering the first 3 months of its afterglow evolution. The x-ray brightness decays as a power law with slope ≈ t −1.66 , which is not consistent with standard predictions for jetted emission. We attribute this behavior to a shallow energy profile of the relativistic jet. A similar trend is observed in other energetic GRBs, suggesting that the most extreme explosions may be powered by structured jets launched by a common central engine.
Publisher: American Astronomical Society
Date: 02-2023
Abstract: We present observations and analysis of the hostless and luminous Type Ia supernova 2022ilv, illustrating it is part of the 2003fg-like family, often referred to as super-Chandrasekhar (Ia-SC) explosions. The Asteroid Terrestrial-impact Last Alert System light curve shows evidence of a short-lived, pulse-like early excess, similar to that detected in another luminous Type Ia supernova (SN 2020hvf). The light curve is broad, and the early spectra are remarkably similar to those of SN 2009dc. Adopting a redshift of z = 0.026 ± 0.005 for SN 2022ilv based on spectral matching, our model light curve requires a large 56 Ni mass in the range 0.7–1.5 M ⊙ and a large ejecta mass in the range 1.6–2.3 M ⊙ . The early excess can be explained by fast-moving SN ejecta interacting with a thin, dense shell of circumstellar material close to the progenitor (∼10 13 cm) a few hours after the explosion. This may be realized in a double-degenerate scenario, wherein a white dwarf merger is preceded by the ejection of a small amount (∼10 −3 –10 −2 M ⊙ ) of hydrogen and helium-poor tidally stripped material. A deep pre-explosion Pan-STARRS1 stack indicates no host galaxy to a limiting magnitude of r ∼ 24.5. This implies a surprisingly faint limit for any host of M r ≳ −11, providing further evidence that these types of explosions occur predominantly in low-metallicity environments.
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 James Gillanders.