Long GRB 261017A detected by Fermi GBM and Swift with complex multi-peaked structure

AI Summary

GRB 261017A was triggered on 2026-10-17 at 16:05:05 UT by Fermi GBM (trigger 813945910) and confirmed by Swift BAT. The burst exhibits a long duration (~9-11 seconds T90) with multiple overlapping pulses and a secondary weaker emission phase, with peak energy ~1024 keV and fluence 1.22×10⁻⁵ erg/cm². Swift-XRT localized the source to RA 09h19m36.83s, Dec +12°38'16.0" with 2.5 arcsec uncertainty. Minimum variability timescale of 31 ms and spectral properties suggest possible compact object merger origin, though classification remains ambiguous between Type-I and Type-II GRBs. Multiple optical/infrared follow-up observations detected no significant afterglow, with upper limits ranging from r~21.0 to L>21.0 mag.

Measurements

Notices (1)

Fermi GBM — GRB · Sat, 17 Oct 2026 16:05:05 GMT

GCN Circulars (14)

GCN-45990 — GRB 261017A · Mon, 19 Oct 2026 14:57:57 GMT
The Konus-Wind instrument detected a long-duration gamma-ray burst (GRB 261017A) on October 26, 2019, at 16:05:06.065 UT. The burst had a multipeaked structure lasting approximately 10.8 seconds and was observed up to ~3 MeV, with a total fluence of 1.96x10^-5 erg/cm2.

GCN-45988 — GRB 261017A · Mon, 19 Oct 2026 13:42:13 GMT
The Swift/UVOT telescope detected a possible source consistent with the XRT position of GRB 261017A, with preliminary detections and upper limits provided in various filters. The source exhibited variability and sometimes appeared double, suggesting it might not be a point source.

GCN-45987 — GRB 261017A · Mon, 19 Oct 2026 11:45:33 GMT
A 28cm optical telescope in Chengde, China, observed the field of GRB 261017A approximately 1.1 days after its detection by Fermi/GBM and Swift, but no significant source was detected at the X-ray counterpart position, leading to a 5-sigma upper limit of L > 21.0 mag. This non-detection is consistent with existing optical/infrared constraints, and further observations are encouraged due to the potential classification of GRB 261017A as a merger-driven long-duration GRB.

GCN-45986 — GRB 261017A · Mon, 19 Oct 2026 07:20:14 GMT
Observations of GRB 261017A with the 1.3-m Devasthal Fast Optical Telescope (DFOT) did not detect an optical source at the enhanced Swift-XRT position, yielding a 5-sigma upper limit of magnitude >22.5 in the R filter. The observations were conducted approximately 6.87 hours after the Swift trigger, providing insights into the early behavior of the gamma-ray burst.

GCN-45985 — GRB 261017A · Sun, 18 Oct 2026 23:24:53 GMT
A gamma-ray burst, GRB 261017A, was detected and analyzed by the Swift-BAT team. The burst exhibited multiple overlapping pulses and a weaker secondary set of pulses, with a total duration (T90) of approximately 89.36 seconds, and a power-law spectral index of 1.09.

GCN-45984 — GRB 261017A · Sun, 18 Oct 2026 15:46:59 GMT
The Gamma-Ray Burst GRB 261017A has been analyzed to have a minimum variability timescale of 31 ms, suggesting it may originate from a compact object merger. Its characteristics, including a fluence of 1.22e-5 erg cm-2 and a peak energy of ~1024 keV, are more consistent with Type-I GRBs, which are typically associated with such mergers.

GCN-45982 — GRB 261017A · Sun, 18 Oct 2026 11:14:16 GMT
The SYSU 80cm infrared telescope observed the field of GRB 261017A, detected by Fermi and Swift, and did not detect any new source within the enhanced Swift-XRT error circle, with a 5-sigma limiting magnitude of J = 18.6 mag (Vega). The observations were conducted approximately 4.15 hours after the BAT trigger.

GCN-45980 — GRB 261017A · Sun, 18 Oct 2026 08:27:49 GMT
The MITSuME 50-cm telescope Akeno observed the field of GRB 261017A, detected by Fermi and Swift, but did not detect any obvious point sources within the Swift/XRT error region, setting optical upper limits of g'>20.1, Rc>20.3, and Ic>19.7. The observations were conducted in three optical bands (g', Rc, and Ic) and started approximately 1.01 hours after the initial trigger.

GCN-45979 — GRB 261017A · Sun, 18 Oct 2026 07:57:11 GMT
The Swift-XRT team has analyzed data from GRB 261017A, revealing a complex light curve with multiple power-law decays. The initial decay index is 1.7, steepening to 5.0 at 100 seconds post-trigger, and then to 1.12 at 260 seconds. The photon spectral index is 1.16, with a total absorption column consistent with the Galactic value.

GCN-45978 — GRB 261017A · Sun, 18 Oct 2026 03:53:39 GMT
The NEXT telescope at Nanshan, China, observed the field of GRB 261017A, detected by Fermi and Swift, but found no optical transient within the enhanced Swift-XRT error circle, setting an upper limit of r ~ 21.0 magnitude. This non-detection occurred 5.67 hours post-burst.

GCN-45977 — GRB 261017A · Sun, 18 Oct 2026 01:19:55 GMT
The Swift-XRT team has reported an enhanced X-ray position for the gamma-ray burst GRB 261017A, with coordinates RA (J2000): 09h 19m 36.83s and Dec (J2000): +12d 38' 16.0" and an uncertainty of 2.5 arcsec. This position was determined using XRT Photon Counting mode data and UVOT images, and may be further refined with additional data.

GCN-45976 — GRB 261017A · Sun, 18 Oct 2026 00:51:46 GMT
On 17 October 2026, the Fermi Gamma-ray Burst Monitor (GBM) detected a gamma-ray burst, GRB 261017A, which was also observed by the Swift BAT. The burst had a duration of about 9.2 seconds and a peak energy of 1024 keV, with a fluence of 1.22E-05 erg/cm^2 and a peak photon flux of 4.3 ph/s/cm^2.

GCN-45974 — GRB 261017A · Sat, 17 Oct 2026 16:18:01 GMT
The Swift Burst Alert Telescope (BAT) detected a gamma-ray burst, GRB 261017A, on 26/10/17 at 16:05:05 UT. The burst had a complex structure lasting about 11 seconds and a peak count rate of approximately 3000 counts/sec. The XRT instrument located a bright, uncatalogued X-ray source within the BAT error circle, but no optical afterglow was detected by the UVOT.

GCN-45973 — GRB 261017A · Sat, 17 Oct 2026 16:15:32 GMT
The Fermi Gamma-ray Burst Monitor (GBM) detected a likely long gamma-ray burst (GRB 261017A) on October 17, 2026, at 16:05:05 UT. The event was located at RA = 141.9, Dec = 14.8 (J2000) with a statistical uncertainty of 2.4 degrees.