Einstein Probe detects fast X-ray transient identified as Type Ic-BL supernova SN 2026gzf

AI Summary

EP260321a was detected by Einstein Probe WXT on 2026-03-21 at 12:30:18 UTC with a soft X-ray spectrum (0.5-4 keV, SNR=7) and rapid decay, initially suggesting a possible supernova shock breakout. Rapid multi-wavelength follow-up identified an optical counterpart at z=0.0343 that brightened significantly over ~10 days, with spectroscopic observations confirming a Type Ic-BL supernova (SN 2026gzf) similar to GRB-associated supernovae like SN 1998bw and SN 2006aj. Radio observations detected emission at 6 GHz around day 13-22 post-trigger, while X-ray observations with Chandra at day 15 showed no significant X-ray afterglow, consistent with the supernova classification.

Measurements

Notices (1)

Einstein Probe WXT — GRB · Sat, 21 Mar 2026 12:30:18 GMT

GCN Circulars (33)

GCN-44412 — EP260321a · Mon, 27 Apr 2026 15:01:46 GMT
On April 26, 2026, the fast X-ray transient EP260321a was identified as a supernova, SN 2026gzf. Spectroscopic observations with the AZT-33IK telescope at Mondy revealed host galaxy emission lines and broad lines of the supernova, consistent with other reported measurements. The best fit with the SNID was SN 1997ef, SN 2006aj, SN 2002ap, and SN 1998bw supernovae.

GCN-44403 — EP260321a · Thu, 23 Apr 2026 17:14:05 GMT
The Australia Telescope Compact Array did not detect radio emission at the position of the optical counterpart of the transient event EP260321a. The corresponding 3-sigma flux density upper limits are 0.21, 0.15, 0.075, and 0.06 mJy at 17, 19, 21, and 23 GHz, respectively.

GCN-44357 — EP260321a · Mon, 20 Apr 2026 21:56:06 GMT
VLA radio follow-up of SN 2026gzf at 22 days post trigger.

GCN-44348 — EP260321A · Sun, 19 Apr 2026 09:06:27 GMT
ARIES team reports the detection of an optical afterglow from a gamma-ray burst (GRB) detected by EP-WXT satellite. The team obtained multiple frames with an exposure time of 300 seconds in the R filter. They stacked the images after alignment and detected an optical afterglow in their stacked image. The team obtained a preliminary magnitude of 17.14 +- 0.01 for the afterglow.

GCN-44295 — EP260321a · Tue, 14 Apr 2026 11:27:29 GMT
A new optical transient, designated as EP260321a, was detected at z = 0.0343. The transient is most likely a supernova and continues to rise in the J-band, indicating that it is near the maximum of the SN light curve.

GCN-44284 — EP260321a · Mon, 13 Apr 2026 10:24:49 GMT
SVOM/VT performed ToO observations of EP260321a, triggering by Einstein Probe. The optical counterpart showed a rise to a peak after trigger in both channels, followed by a decline. The peak in VT_B was at approximately 10.7 days post trigger.

GCN-44250 — EP260321a · Thu, 09 Apr 2026 22:11:06 GMT
The Chandra X-ray Observatory did not detect any X-ray source at the position of EP260321a, which is consistent with a non-detection. This observation is significant because it allows us to exclude known GRB X-ray afterglows from the Swift era, including GRB 060218, which is also located at ~150 Mpc.

GCN-44239 — EP260321a · Thu, 09 Apr 2026 01:06:49 GMT
Astronomical alert: EP260321a: VLA radio detection

GCN-44229 — EP260321a · Tue, 07 Apr 2026 14:50:36 GMT
Astronomical alert: EP260321a: Upper limits from VLA radio observations

GCN-44227 — EP260321a · Tue, 07 Apr 2026 11:11:53 GMT
Astronomical alert: EP260321a: uGMRT observations

GCN-44171 — EP260321a · Wed, 01 Apr 2026 05:05:57 GMT
Astronomical alert: EP260321a :Xinglong optical observations

GCN-44117 — EP260321a · Thu, 26 Mar 2026 07:29:39 GMT
Astronomical alert: EP260321a: JinShan near-infrared observations

GCN-44114 — EP260321a · Wed, 25 Mar 2026 21:30:19 GMT
Astronomical alert: EP260321a: Upper limits from a neutrino search with IceCube

GCN-44110 — EP260321a · Wed, 25 Mar 2026 09:38:42 GMT
Astronomical alert: EP260321a: J-band observations by the SYSU 80 cm infrared telescope

GCN-44107 — EP260321a · Tue, 24 Mar 2026 18:32:10 GMT
Astronomical alert: EP260321a: Gemini-South confirmation of a supernova

GCN-44108 — EP260321a · Tue, 24 Mar 2026 18:32:10 GMT
Astronomical alert: EP260321a: Gemini-South confirmation of a supernova

GCN-44105 — EP260321a · Tue, 24 Mar 2026 15:23:31 GMT
Astronomical alert: EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf

GCN-44103 — EP260321A · Tue, 24 Mar 2026 12:34:33 GMT
Astronomical alert: EP260321A: Mondy optical observations

GCN-44092 — EP260321a · Mon, 23 Mar 2026 17:12:25 GMT
Astronomers using the X-shooter spectrograph on the ESO VLT UT3 observed the variable point source AT2026gzf, associated with X-ray transient EP260321a, and detected broad features below 5000 Å, similar to those seen in early spectra of core-collapse supernovae. The detection of narrow absorption features due to Ca II at a redshift of 0.0344 rules out a Milky Way origin for this transient.

GCN-44091 — EP260321a · Mon, 23 Mar 2026 16:06:10 GMT
A team of international astronomers led by Antonio de Ugarte Postigo from LAM and UNAM reported the continued brightening of optical transient EP260321a using the DDRAGO imager on the COLIBRÍ telescope. The transient, first detected by Huang et al., has increased in brightness by approximately 1.3 magnitudes in the r-band since the previous observation. The latest measurement is r = 18.67 ± 0.02 mag, but the value may be affected by the underlying galaxy.

GCN-44089 — EP260321a · Mon, 23 Mar 2026 15:36:09 GMT
Astronomers report continued brightening of the emerging supernova candidate EP260321a, with a magnitude of 18.3 in the g-band, a significant increase from the initial measurement. The source is located in the direction of a blue variable source and is proposed to be associated with a supernova event based on its luminosity and spectroscopic observations.

GCN-44087 — EP260321a · Mon, 23 Mar 2026 11:26:51 GMT
Astronomers report the observation of a transient event, EP260321a, using the Thai Robotic Telescope network and the JinShan project. The transient, located in the galaxy SDSS J095942.88+002506.2, was first detected by the Einstein Probe and later confirmed by multiple observations. The source brightened significantly around the EP trigger time and then began to decay, consistent with a Shock Break-Out (SBO) of a SN-like event. In the second night of observation, the source re-brightened, suggesting the emergence of a SN-like main component that will likely continue to brighten in the coming days.

GCN-44084 — EP260321a · Sun, 22 Mar 2026 23:06:20 GMT
Astronomers using the Zwicky Transient Facility and Rubin Observatory have detected a new optical counterpart, ZTF26aaonmha (AT 2026gzf, magnitude 19.7), associated with the X-ray source EP260321a. The ZTF detection occurred 19 hours after the X-ray flare, while the Rubin detection showed variability around r = 23.8 mag, with a previous detection at r = 21.1 mag, 25 days before the X-ray event. The combined lightcurve can be found at <https://babamul.caltech.edu/objects/LSST/314003014107006318>. The team is pursuing follow-up observations to classify the source and validate the association.

GCN-44083 — EP260321a · Sun, 22 Mar 2026 21:30:52 GMT
Astronomers using the Gravitational-wave Optical Transient Observer (GOTO) detected a blue variable source, EP260321a, previously reported by other observatories. The source was observed using GOTO-South telescope and had a magnitude of 19.51 ± 0.1 AB mag in the L-band filter.

GCN-44082 — EP260321a · Sun, 22 Mar 2026 19:50:53 GMT
Astronomers using the ESO VLT observatory have identified the optical counterpart of the X-ray transient EP260321a, located at a redshift of 0.0343. The source, which is variable and has a magnitude of 19.5 in the R-band filter, is strongly associated with a galaxy and shows strong emission lines at the same redshift. The team suggests that this source may be the first example of an X-ray transient progenitor detected prior to explosion.

GCN-44081 — EP260321a · Sun, 22 Mar 2026 15:49:58 GMT
A team of astronomers led by National Central University reported their optical observations of the fast X-ray transient EP260321a using the 1m LOT at Lulin Observatory. They detected a variable star, SDSS J095942.88+002506.2, but no new transient was identified. The team used the Kinder pipeline and AutoPhOT to analyze the data and measured magnitudes of 19.18 and 18.77 in the r and g filters, respectively. The absence of an optical counterpart 23 hours after the initial X-ray detection and the weak X-ray flux suggest that the emission may originate from the variable star itself, possibly a supersoft X-ray binary or a strong stellar flare.

GCN-44079 — EP260321a · Sun, 22 Mar 2026 13:12:22 GMT
A team of astronomers led by Runduo Liang and Wenxiong Li used the Las Cumbres 1m telescope at Cerro Tololo Inter-American Observatory to search for an optical transient identified by the Einstein Probe WXT trigger. They did not detect any uncataloged source within the refined position of the transient, setting a 3-sigma upper limit of ~20.8 mag in the r-band.

GCN-44076 — EP260321a · Sun, 22 Mar 2026 07:01:20 GMT
A team of international astronomers using the COLIBRÍ telescope at the Observatorio Astronómico Nacional in Mexico reported non-detection of any new optical source at the position of the Einstein Probe X-ray transient EP260321a, down to the following 5-sigma upper limits in the g, r, and z filters: g > 23.8, r > 23.8, z > 22.8. These limits are consistent with previous reports and unable to confirm the presence of a shock breakout as proposed by Huang et al.

GCN-44075 — EP260321a · Sun, 22 Mar 2026 04:32:32 GMT
The Einstein Probe (EP) mission detected a fast X-ray transient, EP260321a, with the Wide-field X-ray Telescope (WXT) and the Follow-up X-ray Telescope (FXT). The transient exhibited a soft X-ray spectrum, rapid decay, and a high luminosity, suggesting a possible supernova shock breakout candidate. No optical counterpart has been detected yet, and further multi-band follow-up observations are encouraged.

GCN-44074 — EP260321a · Sun, 22 Mar 2026 02:34:27 GMT
The SVOM/VT team reported a non-detection of an optical transient in the field of EP260321a, detected by EP/WXT, using the SVOM/VT telescope. No uncataloged source was found within the error box of FXT with magnitude upper limits of 22.8 mag (VT_R) and 23.0 mag (VT_B) after 1.92 hours since the trigger. The stellar source and galaxy reported by Kinder were detected with no significant variability.

GCN-44070 — EP260321a · Sat, 21 Mar 2026 17:18:54 GMT
Astronomers using the Kinder collaboration observed a blue variable star and set a 3-sigma upper limit of r = 23.1 mag for new sources within the error circle of the fast X-ray transient EP260321a. The galaxy SDSS J095942.88+002506.2, located at z = 0.0343, lies within the EP FXT localisation region. If EP260321 is associated with this galaxy, no new source brighter than an absolute magnitude of M ~ -12.6 mag at t-t0 = 1.13 hours after the FXT trigger was detected.

GCN-44069 — EP260321a · Sat, 21 Mar 2026 13:54:25 GMT
The MASTER-Net team at Moscow State University and collaborators reported non-detection of a transient object EP260321a using the MASTER-Tunka robotic telescope in Russia. Observations were initiated 194 seconds after the notice time and 2105 seconds after the trigger time, with upper limits ranging from 18.8 to 19.1 mag in the clear filter. The observation and reduction are ongoing.

GCN-44068 — EP260321a · Sat, 21 Mar 2026 13:01:43 GMT
The Einstein Probe mission has detected an X-ray transient, EP260321a, using its Wide-field X-ray Telescope (WXT). The transient, located at R.A. = 149.894 deg, DEC = 0.397 deg (J2000), triggered an automatic follow-up observation with the Follow-up X-ray Telescope (FXT), which detected an uncatalogued X-ray source at R.A. = 149.9260 deg, DEC = 0.4181 deg (J2000). Further information will be provided once telemetry data is received.