GRB 260527A

General information

GRB 260527A is a short/hard GRB detected by multiple gamma-ray instruments and associated with the Einstein Probe transient EP260527a, supported by timing/localization consistency and IPN triangulation. An X-ray source and an optical/NIR counterpart were identified within the EP localization region.

Wavelength coverage

• Gamma-ray: Konus-Wind, GECAM-B, CALET/CGBM, Insight-HXMT/HE, and Glowbug reported a short (T90 ~0.2–0.5 s), multi-peaked burst with spectral measurements (Band fit reported by Konus-Wind).
• X-ray: Einstein Probe/FXT detected an uncatalogued X-ray source within the WXT error circle with an absorbed power-law fit and reported 0.5–10 keV flux.
• Optical/NIR: SVOM/VT, NOT, VLT (imaging and spectroscopy), Gemini-S, FTW, plus additional limits (MDM J-band, LOT r-band, and Wendelstein r-band) reported detections/constraints from ~21 hr to ~2.6 days post-trigger.
• Radio: VLA reported a ~3σ detection of a ~50 µJy source at 6 GHz near the optical position. No UV or millimeter/submillimeter observations were mentioned.

Lightcurve and spectrum

• Prompt duration reported as T90 = 0.40 (+0.02/-0.04) s (GECAM-B), T90 = 0.19 +/- 0.04 s (CALET/CGBM, 40–1000 keV), and T90 = 0.50 (+0.30/-0.11) s (Insight-HXMT/HE), with multi-peaked structure.
• Konus-Wind time-averaged spectrum (T0 to T0+0.064 s) fit by a Band model with alpha = -0.67(-0.36,+0.46), beta = -2.13(-0.85,+0.36), Ep = 541(-204,+367) keV; fluence 1.99(-0.46,+0.57)x10^-6 erg/cm^2 (20 keV–10 MeV).
• EP/FXT reported an absorbed power-law X-ray spectrum (photon index 2.6 +1.2/-0.7 with Galactic NH fixed) and unabsorbed 0.5–10 keV flux ~7.7(+3.7/-3.9)x10^-14 erg/s/cm^2.
• Optical/NIR photometry includes VT_B = 22.32 +/- 0.22 and VT_R = 21.77 +/- 0.19 AB mag at ~21.8 hr; i ~23.17 AB and z ~23.25 AB at ~40 hr (NOT); z ~23.1 and J ~23.0 AB at ~41 hr (VLT); i ~23.2 AB at ~43 hr (Gemini-S); r ~23.1 AB at ~1.57 d (FTW). Reported non-detections include J > 18.4 AB at ~23 hr (MDM), r > 21.1 AB at ~33.7 hr (LOT), and r > 24.0 AB at ~2.6 d (Wendelstein).

Redshift

VLT/X-shooter spectroscopy reported weak emission features consistent with [OII] 3727, suggesting a tentative redshift z ~ 0.80 for the transient/host. A galaxy ~13 arcsec from the transient position has a DESI DR1 redshift z = 0.3656 (reported chance-coincidence probability Pcc ~ 0.09).

What’s special vs typical

• Especially well-constrained association between a short GRB (multiple gamma-ray detections and IPN triangulation) and an identified X-ray/optical counterpart.
• A tentative spectroscopic redshift is reported, but host identification remains uncertain due to alternative nearby-galaxy association possibilities.