A Radio Flare in the Long-lived Afterglow of the Distant Short GRB 210726A: Energy Injection or a Reverse Shock from Shell Collisions?

The Astrophysical Journal American Astronomical Society 970:2 (2024) 139

Authors:

Genevieve Schroeder, Lauren Rhodes, Tanmoy Laskar, Anya Nugent, Alicia Rouco Escorial, Jillian C Rastinejad, Wen-fai Fong, Alexander J van der Horst, Péter Veres, Kate D Alexander, Alex Andersson, Edo Berger, Peter K Blanchard, Sarah Chastain, Lise Christensen, Rob Fender, David A Green, Paul Groot, Ian Heywood, Assaf Horesh, Luca Izzo, Charles D Kilpatrick, Elmar Körding, Amy Lien

Abstract:

We present the discovery of the radio afterglow of the short gamma-ray burst (GRB) 210726A, localized to a galaxy at a photometric redshift of z ∼ 2.4. While radio observations commenced ≲1 day after the burst, no radio emission was detected until ∼11 days. The radio afterglow subsequently brightened by a factor of ∼3 in the span of a week, followed by a rapid decay (a “radio flare”). We find that a forward shock afterglow model cannot self-consistently describe the multiwavelength X-ray and radio data, and underpredicts the flux of the radio flare by a factor of ≈5. We find that the addition of substantial energy injection, which increases the isotropic kinetic energy of the burst by a factor of ≈4, or a reverse shock from a shell collision are viable solutions to match the broadband behavior. At z ∼ 2.4, GRB 210726A is among the highest-redshift short GRBs discovered to date, as well as the most luminous in radio and X-rays. Combining and comparing all previous radio afterglow observations of short GRBs, we find that the majority of published radio searches conclude by ≲10 days after the burst, potentially missing these late-rising, luminous radio afterglows.

Neutral hydrogen lensing simulations in the hubble frontier fields

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 532:3 (2024) 3236-3251

Authors:

Tariq Blecher, Roger Deane, Danail Obreschkow, Ian Heywood

MeerKAT observations of starburst galaxies and AGNs within the core of XMMXCS J2215.9−1738 at z = 1.46

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 532:2 (2024) 2842-2859

Authors:

DY Klutse, M Hilton, I Heywood, I Smail, AM Swinbank, K Knowles, SP Sikhosana

Discovery of the Optical and Radio Counterpart to the Fast X-Ray Transient EP 240315a

The Astrophysical Journal Letters American Astronomical Society 969:1 (2024) L14

Authors:

JH Gillanders, L Rhodes, S Srivastav, F Carotenuto, J Bright, ME Huber, HF Stevance, SJ Smartt, KC Chambers, T-W Chen, R Fender, A Andersson, AJ Cooper, PG Jonker, FJ Cowie, T de Boer, N Erasmus, MD Fulton, H Gao, J Herman, C-C Lin, T Lowe, EA Magnier, H-Y Miao

Abstract:

Fast X-ray Transients (FXTs) are extragalactic bursts of soft X-rays first identified ≳10 yr ago. Since then, nearly 40 events have been discovered, although almost all of these have been recovered from archival Chandra and XMM-Newton data. To date, optical sky surveys and follow-up searches have not revealed any multiwavelength counterparts. The Einstein Probe, launched in 2024 January, has started surveying the sky in the soft X-ray regime (0.5–4 keV) and will rapidly increase the sample of FXTs discovered in real time. Here we report the first discovery of both an optical and radio counterpart to a distant FXT, the fourth source publicly released by the Einstein Probe. We discovered a fast-fading optical transient within the 3′ localization radius of EP 240315a with the all-sky optical survey ATLAS, and our follow-up Gemini spectrum provides a redshift, z = 4.859 ± 0.002. Furthermore, we uncovered a radio counterpart in the S band (3.0 GHz) with the MeerKAT radio interferometer. The optical (rest-frame UV) and radio luminosities indicate that the FXT most likely originates from either a long gamma-ray burst or a relativistic tidal disruption event. This may be a fortuitous early mission detection by the Einstein Probe or may signpost a mode of discovery for high-redshift, high-energy transients through soft X-ray surveys, combined with locating multiwavelength counterparts.

MeerKAT discovery of a double radio relic and odd radio circle: connecting cluster and galaxy merger shocks

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 531:3 (2024) 3357-3372

Authors:

Bärbel S Koribalski, Angie Veronica, Klaus Dolag, Thomas H Reiprich, Marcus Brüggen, Ian Heywood, Heinz Andernach, Ralf-Jürgen Dettmar, Matthias Hoeft, Xiaoyuan Zhang, Esra Bulbul, Christian Garrel, Gyula IG Józsa, Jayanne English