General information
GRB 260111A is a long-duration gamma-ray burst detected by Fermi/GBM and recovered/localized by Swift/BAT-GUANO, with follow-up identifying a likely X-ray/optical afterglow candidate. Optical imaging at later times indicates the candidate faded below deep limits, strengthening the afterglow association.
Wavelength coverage
- Gamma-ray: Fermi/GBM reported T90 ~31 s (50–300 keV), spectral fit with cutoff power law (index ~-0.7, Epeak ~140 keV), and fluence ~2.3e-6 erg/cm^2 (10–1000 keV).
- X-ray: Swift-XRT observed at ~T0+94–105 ks and detected an uncatalogued source (source #2) with flux ~1.56e-13 erg/cm^2/s (0.3–10 keV).
- Optical: Multiple facilities reported limits (MASTER-Net, GOTO) and COLIBRÍ detected an uncatalogued source in r/z consistent with XRT source #2, later fading below r>24.4 and z>23.0.
No observations were mentioned in UV, near-IR, mid-IR, radio, mm/sub-mm.
Lightcurve and spectrum
- Prompt duration: T90 ~31 s (Fermi/GBM, 50–300 keV) and T90 ~33 (+13/-12) s (GECAM-B, 70–6000 keV).
- Prompt spectrum: cutoff power law with index -0.7 ± 0.3 and Epeak 140 ± 30 keV (time-averaged T0-18 to T0+52 s).
- Prompt fluence: (2.3 ± 0.3)e-6 erg/cm^2 (10–1000 keV); 1 s peak photon flux 2.4 ± 0.2 ph/s/cm^2 (10–1000 keV).
- X-ray flux: (1.56 [+0.66, -0.53])e-13 erg/cm^2/s (0.3–10 keV; observed).
- Optical: COLIBRÍ measured r = 22.87 ± 0.07 and z = 22.33 ± 0.14 at ~17.6–20.9 h post-trigger, and later reported non-detection at ~4.8 d with r > 24.4 and z > 23.0 (3σ), consistent with fading.
Redshift
What’s special vs typical
A plausible optical afterglow candidate is supported by a later-time disappearance in deep r/z imaging (~5 days post-trigger), helping solidify the counterpart identification despite limited X-ray fading evidence in the reported interval.