Alice P. Curtin (McGill University) for the CHIME/FRB Collaboration:
At 15:36:21 UTC on 15 November 2023, GRB 231115A was detected by Fermi/GBM (Fermi GBM Team, GCN 35035 & 35044), INTEGRAL (P. D'Avanzo et al., GCN 35036, S. Mereghetti et al., GCN 35037), Glowbug (C. C. Cheung et al., GCN 35045), and Insight-HXMT (Insight-HXMT team, GCN 35060). The position of GRB 231115A (RA=149.00, DEC=69.68 with an uncertainty of 2 arcmin) is consistent with that of the M82 galaxy (S. Mereghetti et al. GCN 35037). Additionally, the spectrotemporal properties of GRB 231115A suggest it is likely due to a magnetar giant flare (Fermi/GBM Team, GCN 35044, S. Ronchini et al., GCN 35065).
At the time of the high-energy (HE) emission, GRB 231115A was ~20 degrees from the meridian of the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project (CHIME/FRB). No radio emission was detected from the source at the time of the HE emission. In addition to searching for radio emission at the time of the Fermi/GBM trigger, we also searched within the CHIME/FRB database for bursts from this position within the last two years, yet did not find any definitive astrophysical associations.
Using a pipeline described in Curtin et al. (2023), we constrain the FRB-like radio emission from this source in the 400-800 MHz band to be <260 Jy or <720 Jy ms (assuming a 10 ms pulse width) at the time of the Fermi/GBM trigger. The HE fluence reported by Fermi/GBM in the 10-1000 keV range is (6.3 +/- 0.4)e-7 erg/cm^2 (Fermi/GBM Team, GCN 35044). This implies a radio-to-HE emission ratio of <4.5e-9 (unitless assuming a 400 MHz bandwidth). Additionally, using a luminosity distance of 3.5 Mpc to the M82 galaxy (P. D'Avanzo et al. 2023, GCN 35036), our derived radio flux limit corresponds to an upper limit on the radio luminosity of <3.8e30 erg s^-1 Hz^-1.
While GRB 231115A was ~20 degrees from the meridian of CHIME/FRB at the time of the Fermi/GBM trigger, it transited directly overhead CHIME/FRB at 14:18:45 UTC on 15 November 2023. Thus, our best radio constraints for this source are ~80 minutes prior to the Fermi/GBM trigger. As no radio emission was similarly detected at this time, we constrain the radio flux at this time to be <0.5 Jy and the fluence to be <1.2 Jy ms assuming a burst width of 10 ms. This corresponds to a radio luminosity limit of <7.3e27 erg s^-1 Hz^-1 and a radio-to-HE fluence ratio of <7.6e-12 (unitless assuming a 400 MHz bandwidth).
Curtin, A.P., Tendulkar, S.P., Josephy, A., et al., 2023, ApJ, 954, 154. doi:10.3847/1538-4357/ace52f