Radio afterglows of very high-energy gamma-ray bursts 190829A and 180720B
Monthly Notices of the Royal Astronomical Society Oxford University Press 496:3 (2020) 3326-3335
Abstract:
We present high-cadence multifrequency radio observations of the long gamma-ray burst (GRB) 190829A, which was detected at photon energies above 100 GeV by the High Energy Stereoscopic System (H.E.S.S.). Observations with the Meer Karoo Array Telescope (MeerKAT, 1.3 GHz) and Arcminute Microkelvin Imager – Large Array (AMI-LA, 15.5 GHz) began one day post-burst and lasted nearly 200 d. We used complementary data from Swift X-Ray Telescope (XRT), which ran to 100 d post-burst. We detected a likely forward shock component with both MeerKAT and XRT up to over 100 d post-burst. Conversely, the AMI-LA light curve appears to be dominated by reverse shock emission until around 70 d post-burst when the afterglow flux drops below the level of the host galaxy. We also present previously unpublished observations of the other H.E.S.S.-detected GRB, GRB 180720B from AMI-LA, which shows likely forward shock emission that fades in less than 10 d. We present a comparison between the radio emission from the three GRBs with detected very high energy (VHE) gamma-ray emission and a sensitivity-limited radio afterglow sample. GRB 190829A has the lowest isotropic radio luminosity of any GRB in our sample, but the distribution of luminosities is otherwise consistent, as expected, with the VHE GRBs being drawn from the same parent distribution as the other radio-detected long GRBs.LOFAR 144-MHz follow-up observations of GW170817
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 494:4 (2020) 5110-5117
Radio afterglows of Very High Energy Gamma-ray Bursts
Proceedings of the International Astronomical Union Cambridge University Press (CUP) 16:S363 (2020) 220-223
Relativistic X-ray jets from the black hole X-ray binary MAXI J1820+070
Astrophysical Journal Letters American Astronomical Society 895:2 (2020) L31
Abstract:
The black hole MAXI J1820+070 was discovered during its 2018 outburst and was extensively monitored across the electromagnetic spectrum. Following the detection of relativistic radio jets, we obtained four Chandra X-ray observations taken between 2018 November and 2019 June, along with radio observations conducted with the Very Large Array and MeerKAT arrays. We report the discovery of X-ray sources associated with the radio jets moving at relativistic velocities with a possible deceleration at late times. The broadband spectra of the jets are consistent with synchrotron radiation from particles accelerated up to very high energies (>10 TeV) by shocks produced by the jets interacting with the interstellar medium. The minimal internal energy estimated from the X-ray observations for the jets is ~10^41 erg, significantly larger than the energy calculated from the radio flare alone, suggesting most of the energy is possibly not radiated at small scales but released through late-time interactions.A radio parallax to the black hole X-ray binary MAXI J1820+070
Monthly Notices of the Royal Astronomical Society: Letters Oxford University Press (OUP) 493:1 (2020) l81-l86