General information
GRB 260601B was detected at 2026-06-01 19:12:46-49 UTC by multiple high-energy instruments and is strongly associated with the Einstein Probe transient EP260601a through time and localization consistency. The prompt event lasts roughly 70 s and is described as unusually hard, with some teams noting it may resemble the atypical long-duration, Type I-like class exemplified by GRB 060614.
Wavelength coverage
- Gamma-ray / hard X-ray: Detected by GECAM-B, CALET/CGBM, NuSTAR CsI shields, and Insight-HXMT/HE; GECAM-B reports 70-6000 keV coverage and CALET gives 40-1000 keV timing properties.
- Soft X-ray: Einstein Probe/WXT detected the associated transient EP260601a, which provides the localization used in some analyses.
- Optical: SVOM/VT detected the counterpart in VT_B (400-650 nm) and VT_R (650-1000 nm) at about 13.7-14.7 hr after trigger.
- Near-infrared: WINTER observed in J band at about 16 hr post-trigger and reported a 5-sigma upper limit of J > 18.8 AB.
Bands with no observations mentioned in the provided circulars: radio, ultraviolet, and spectroscopy.
Lightcurve and spectrum
- GECAM-B reports a possible precursor, then a short pulse followed by long emission, with T90 = 66.5 +2.5/-3.5 s.
- CALET/CGBM reports a multi-peaked light curve starting at T+0.1 s, peaking at T+4.9 s, ending at T+101.4 s, with T90 = 70.0 +/- 4.7 s and T50 = 21.9 +/- 1.0 s in 40-1000 keV.
- NuSTAR reports a short peak followed by a long burst lasting about 75 s, with a peak count rate of about 2500 cps over a baseline of about 1000 cps; marginal evidence is also seen above 100 keV in the CZT detectors.
- Insight-HXMT/HE reports a similar precursor plus short pulse plus long emission morphology with T90 = 76.0 +4.5/-4.0 s.
- GECAM-B finds the time-averaged spectrum from T0-8 s to T0+90 s is best fit by a power law with exponential cutoff, with photon index -1.36 +0.05/-0.05 and Epeak = 3600 +830/-770 keV.
- For the main pulse (T0+1 s to T0+5 s), GECAM-B finds photon index -1.10 +0.14/-0.15 and Epeak = 715 +249/-162 keV.
- GECAM-B reports the extended emission is even harder than the initial pulse and is clearly detected above 1 MeV.
- The reported fluence is (1.03 +/- 0.02)E-04 erg/cm^2 in 10-1000 keV.
- SVOM/VT measured the optical counterpart at VT_B = 23.4 +/- 0.3 AB and VT_R = 21.43 +/- 0.15 AB around 14.6 hr after trigger.
Redshift
A tentative redshift of about z ~ 4 was suggested from the red optical color seen by SVOM/VT; this is a color-based estimate rather than a spectroscopic measurement.
What’s special vs typical
This burst stands out because several teams explicitly note an unusual combination of long duration and very hard prompt emission, with a temporal profile compared to GRB 060614. GECAM-B further argues it could be a possible long-duration Type I GRB, which is a more atypical interpretation than for an ordinary long GRB.