Prospects for GRB Afterglow Discovery with the Eric and Wendy Schmidt Observatory System

Two time domain surveys, recently funded as part of the Eric and Wendy Schmidt Observatory System; the Argus Array, in the optical, and the Deep Synoptic Array (DSA), in the radio, will transform gamma-ray burst (GRB) science via the serendipitous discovery of hundreds of GRB afterglows per year. In this work, we simulate DSA and Argus observations of GRB afterglows. We find that, of the long-duration GRBs (LGRBs) detected by the Fermi Gamma-ray Burst Monitor, $(24 \pm 2)\%$ will yield afterglow detections with Argus and $(42 \pm 3)\%$ with DSA, corresponding to rate of $47 \pm 4$ and $82 \pm 7$ per year respectively. We also compute rates for both upcoming and proposed GRB monitors; the forthcoming StarBurst Multi-messenger Pioneer, with $62 \pm 5$ detections per year in Argus and $117 \pm 8$ detections per year in DSA and the Moon Burst Energetics All-sky Monitor (MoonBEAM) concept, with $62 \pm 6$ per year in Argus and $105 \pm 10$ per year in DSA. The observatory system will detect also 116$\pm$8 optical and 217$\pm$15 radio afterglows per year, independent of GRB triggers, exceeding the current annual rate with global follow-up. Afterglow counterparts to short-duration GRBs, originating from neutron star mergers, will be detected at $5$-$10$% of the LGRB afterglow rate, which is promising for multi-messenger detections of gravitational wave sources and constraining the neutron star merger rate. The Argus Array, with its second-minute cadence, will detect afterglows before they peak $\sim 18\%$ of the time which will dramatically increase the sample of observed reverse shock and prompt optical emission.