{
  "id": "2103.05209",
  "version": "v1",
  "published": "2021-03-09T04:07:13.000Z",
  "updated": "2021-03-09T04:07:13.000Z",
  "title": "Rapid-response radio observations of short GRB 181123B with the Australia Telescope Compact Array",
  "authors": [
    "G. E. Anderson",
    "M. E. Bell",
    "J. Stevens",
    "M. D. Aksulu",
    "J. C. A. Miller-Jones",
    "A. J. van der Horst",
    "R. A. M . J. Wijers",
    "A. Rowlinson",
    "A. Bahramian",
    "P. J. Hancock",
    "J. -P. Macquart",
    "S. D. Ryder",
    "R. M. Plotkin"
  ],
  "comment": "15 pages, 7 figures, accepted for publication in MNRAS",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We introduce the Australia Telescope Compact Array (ATCA) rapid-response mode by presenting the first successful trigger on the short-duration gamma-ray burst (GRB) 181123B. Early-time radio observations of short GRBs may provide vital insights into the radio afterglow properties of Advanced LIGO- and Virgo-detected gravitational wave events, which will in turn inform follow-up strategies to search for counterparts within their large positional uncertainties. The ATCA was on target within 12.6 hr post-burst, when the source had risen above the horizon. While no radio afterglow was detected during the 8.3 hr observation, we obtained force-fitted flux densities of $7 \\pm 12$ and $15 \\pm 11~\\mu$Jy at 5.5 and 9 GHz, respectively. Afterglow modelling of GRB 181123B showed that the addition of the ATCA force-fitted radio flux densities to the Swift X-ray Telescope detections provided more stringent constraints on the fraction of thermal energy in the electrons (log$\\epsilon_e = -0.75^{+0.39}_{-0.40}$ rather than log$\\epsilon_e = -1.13^{+0.82}_{-1.2}$ derived without the inclusion of the ATCA values), which is consistent with the range of typical $\\epsilon_e$ derived from GRB afterglow modelling. This allowed us to predict that the forward shock may have peaked in the radio band $\\sim10$ days post-burst, producing detectable radio emission $\\gtrsim3-4$ days post-burst. Overall, we demonstrate the potential for extremely rapid radio follow-up of transients and the importance of triggered radio observations for constraining GRB blast wave properties, regardless of whether there is a detection, via the inclusion of force-fitted radio flux densities in afterglow modelling efforts.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-03-09T04:07:13.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "australia telescope compact array",
      "rapid-response radio observations",
      "short grb 181123b",
      "force-fitted radio flux densities",
      "grb blast wave properties"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 15,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}