GCN Circular 45984

R. Maccary (University of Ferrara) on behalf of a larger collaboration report:

We determined the minimum variability timescale (MVT) of GRB 261017A (Fermi GBM team, GCN 45973

) from the Fermi/GBM light curve (NaI detectors 3, 4, 6, and 7) following the prescriptions of Camisasca et al. (2023), i.e. as the minimum full width half maximum (FWHM_min) of all statistically significant pulses, and found FWHM_min = 31 (-8, +11) ms. Combined with the T90~9.2 s (Fermi GBM team, GCN 45976

Loading...

 

 

), in the T90-FWHM_min plot GRB 261017A (green square in the Figure at this link https://drive.google.com/file/d/1KuegJmDUVT0LSCSNSdl47arSIPbaKbdB/view?usp=drive_link) lies in the region populated by other long-lasting merger candidates, such as also GRB 230307A. The MVT corresponds to a feature found at ~2.9 s (see https://drive.google.com/file/d/16Sh5ua-Jc3eqS4GeIlQv2bAZgMFcZ7Cb/view?usp=drive_link).

In addition, with a fluence of 1.22e-5 erg cm-2 and a peak energy Ep~1024 keV (Fermi GBM team, GCN 45976

), the positions of GRB 261017A in the Epi-Eiso plane at different redshifts seem to be more compatible with Type-I rather than with Type-II GRBs (see Figure at this link https://drive.google.com/file/d/1txeRPoWaA0bIfNknlq8OOEXjrAcC3Uj1/view?usp=drive_link).

References:

• Minimum variability timescale (MVT): Camisasca et al., 2023,https://doi.org/10.1051/0004-6361/202245657
  Loading...

   

   
  ; Maccary et al., 2025,A&A,https://doi.org/10.1051/0004-6361/202555418
  Loading...