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Black Hole

Lensing of space time around a black hole. At Oxford we study black holes observationally and theoretically on all size and time scales - it is some of our core work.

Credit: ALAIN RIAZUELO, IAP/UPMC/CNRS. CLICK HERE TO VIEW MORE IMAGES.

Ian Heywood

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Research theme

  • Astronomy and astrophysics

Sub department

  • Astrophysics

Research groups

  • Galaxy formation and evolution
  • MeerKAT
  • Pulsars, transients and relativistic astrophysics
  • The Square Kilometre Array (SKA)
  • Breakthrough Listen
ian.heywood@physics.ox.ac.uk
  • About
  • Publications

MeerKAT follow-up of enigmatic GLEAM 4-Jy (G4Jy) sources

Monthly Notices of the Royal Astronomical Society Oxford University Press 518:3 (2022) 4290-4309

Authors:

Precious K Sejake, Sarah V White, Ian Heywood, Kshitij Thorat, Hertzog L Bester, Sphesihle Makhathini, Bernie Fanaroff

Abstract:

We present the results from studying 140 radio sources in the GLEAM (GaLactic and Extragalactic All-sky MWA [Murchison Widefield Array]) 4-Jy (G4Jy) Sample. These sources were followed-up with MeerKAT to assess their radio morphology and enable host-galaxy identification, as existing radio images of 25 to 45-arcsec resolution do not provide sufficient information. We refer to these sources as the MeerKAT-2019 subset. The aim is to identify the host galaxy of these sources by visually inspecting the overlays comprising radio data from four surveys (at 150, 200, 843/1400, and 1300 MHz). Our morphological classification and host-galaxy identification relies upon the ∼7-arcsec resolution images from MeerKAT (1300 MHz). Through the visual inspection of the overlays, 14 radio sources in the MeerKAT-2019 subset have wide-angle tail (WAT) morphology, 10 are head-tail, and 5 have X-, S-/Z-shaped morphology. Most of the remaining sources have the radio morphology of typical symmetric lobes. Of 140 sources, we find host galaxies for 98 sources, leaving 42 with no identified host galaxy. These 42 sources still have ambiguous identification even with higher resolution images from MeerKAT.
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MIGHTEE: deep 1.4 GHz source counts and the sky temperature contribution of star forming galaxies and active galactic nuclei

Monthly Notices of the Royal Astronomical Society Oxford University Press 520:2 (2022) 2668-2691

Authors:

Cl Hale, Ih Whittam, Mj Jarvis, Pn Best, Nl Thomas, I Heywood, M Prescott, N Adams, J Afonso, Fangxia An, Raa Bowler, Jd Collier, Rhw Cook, R Davé, Bs Frank, M Glowacki, Pw Hatfield, S Kolwa, Cc Lovell, N Maddox, L Marchetti, Lk Morabito, E Murphy, I Prandoni, Z Randriamanakoto, Ar Taylor

Abstract:

We present deep 1.4 GHz source counts from ∼5 deg2 of the continuum Early Science data release of the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey down to S1.4GHz ∼15 μJy. Using observations over two extragalactic fields (COSMOS and XMM-LSS), we provide a comprehensive investigation into correcting the incompleteness of the raw source counts within the survey to understand the true underlying source count population. We use a variety of simulations that account for: errors in source detection and characterisation, clustering, and variations in the assumed source model used to simulate sources within the field and characterise source count incompleteness. We present these deep source count distributions and use them to investigate the contribution of extragalactic sources to the sky background temperature at 1.4 GHz using a relatively large sky area. We then use the wealth of ancillary data covering a subset of the COSMOS field to investigate the specific contributions from both active galactic nuclei (AGN) and star forming galaxies (SFGs) to the source counts and sky background temperature. We find, similar to previous deep studies, that we are unable to reconcile the sky temperature observed by the ARCADE 2 experiment. We show that AGN provide the majority contribution to the sky temperature contribution from radio sources, but the relative contribution of SFGs rises sharply below 1 mJy, reaching an approximate 15-25 per cent contribution to the total sky background temperature (Tb ∼100 mK) at ∼15 μJy.
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Search and identification of transient and variable radio sources using MeerKAT observations: a case study on the MAXI J1820+070 field

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 517:2 (2022) 2894-2911

Authors:

A Rowlinson, J Meijn, J Bright, AJ van der Horst, S Chastain, S Fijma, R Fender, I Heywood, RAMJ Wijers, PA Woudt, A Andersson, GR Sivakoff, E Tremou, LN Driessen
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Radio observations of the Black Hole X-ray Binary EXO 1846-031 re-awakening from a 34-year slumber

Monthly Notices of the Royal Astronomical Society Oxford University Press 517:2 (2022) 2801-2817

Authors:

Dra Williams, Se Motta, R Fender, Jca Miller-Jones, J Neilsen, Jr Allison, J Bright, I Heywood, Pfl Jacob, L Rhodes, E Tremou, Pa Woudt, J van den Eijnden, F Carotenuto, Da Green, D Titterington, Aj van der Horst, P Saikia

Abstract:

We present radio [1.3 GHz MeerKAT, 4–8 GHz Karl G. Jansky Very Large Array (VLA), and 15.5 GHz Arcminute Microkelvin Imager Large Array (AMI-LA)] and X-ray (Swift and MAXI) data from the 2019 outburst of the candidate Black Hole X-ray Binary (BHXB) EXO 1846−031. We compute a Hardness–Intensity diagram, which shows the characteristic q-shaped hysteresis of BHXBs in outburst. EXO 1846−031 was monitored weekly with MeerKAT and approximately daily with AMI-LA. The VLA observations provide sub-arcsecond-resolution images at key points in the outburst, showing moving radio components. The radio and X-ray light curves broadly follow each other, showing a peak on ∼MJD 58702, followed by a short decline before a second peak between ∼MJD 58731–58739. We estimate the minimum energy of these radio flares from equipartition, calculating values of Emin ∼ 4 × 1041 and 5 × 1042 erg, respectively. The exact date of the return to ‘quiescence’ is missed in the X-ray and radio observations, but we suggest that it likely occurred between MJD 58887 and 58905. From the Swift X-ray flux on MJD 58905 and assuming the soft-to-hard transition happened at 0.3–3 per cent Eddington, we calculate a distance range of 2.4–7.5 kpc. We computed the radio:X-ray plane for EXO 1846−031 in the ‘hard’ state, showing that it is most likely a ‘radio-quiet’ BH, preferentially at 4.5 kpc. Using this distance and a jet inclination angle of θ = 73◦, the VLA data place limits on the intrinsic jet speed of βint = 0.29c, indicating subluminal jet motion.
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Radio observations of the Black Hole X-ray Binary EXO 1846-031 re-awakening from a 34-year slumber

(2022)

Authors:

DRA Williams, SE Motta, R Fender, JCA Miller-Jones, J Neilsen, JR Allison, J Bright, I Heywood, PFL Jacob, L Rhodes, E Tremou, P Woudt, J van den Eijnden, F Carotenuto, DA Green, D Titterington, AJ van der Horst, P Saikia
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