EP260530a — All Circulars

Xinglong optical observations Junjie-Jin (NAOC), Yiming-Mao (NAOC), Junjun-Jia (NAOC), Pengliang-Du (NAOC), Yu-Zhang (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report:

We obtained an optical spectrum of the Einstein Probe transient EP260530a (Wu et al., ATel #17824) using the Xinglong 2.16-m telescope. The observations targeted the optical counterpart candidate, AT 2026nwl, discovered by GOTO (TNS Astronomical Transient Report No. 306622).

The observation was carried out on 2026 June 1 at 12:53:59 UT with BFOSC using the G4 grism and a 2.3-arcsec slit. The exposure time was 1800 s. The spectrum shows clear narrow emission lines from hydrogen and helium.

Marion Guelfand (CPPM), Camila Angulo (UNAM), Noémie Globus (UNAM), Alan M. Watson (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM),  Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM)  report:

We observed the field of the optical source AT 2026nwl, discovered by GOTO (Godson et al., TNS Astronomical Transient Report No. 306622), associated with EP260530a (Wu et al., ATel #17824), further observed by COLIBRÍ (Globus et al., GCN Circ. 44759) and KAIT (Zheng et al., GCN Circ. 44775), and classified as a CV (Pursiainen et al., TNS Classification Report No. 23885), with the DDRAGO two-channel wide-field imager mounted on the COLIBRÍ telescope. We observed from 2026-06-02 04:19 to 07:11 UTC (from 79.21 to 82.15 hours after the GOTO discovery) and obtained 24 minutes of exposure in each of the g, r, and i filters, and 72 minutes of exposure in the z filter.

The data were reduced and coadded with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

We continue to detect the source at the following preliminary magnitudes:

g = 15.77 +/- 0.01,
r = 15.87 +/- 0.01,
i = 15.98 +/- 0.01,
z = 16.07 +/- 0.01.


We observe a quasi-periodic modulation of the light curve in the different photometric bands with a characteristic timescale of approximately 1 hour, typical of certain classes of accreting binary stars, and a peak-to-valley amplitude of about 0.1 mag Further observations and analysis are ongoing.

We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.

WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and

Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:


The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at

Lick Observatory, observed the field of EP260530a (Wu et al.,

ATel #17824) on May 31 and again on Jun 02 UT. A set of clear

(roughly R) filter images were obtained. We clearly detected the

bright CV outburst associated with AT 2026nwl (TNS Astronomical

Transient Report 306622, 306654; TNS Classification Reports 23885;

Globus et al., GCN 44759).  We measure its brightness decayed from

14.4 +/- 0.1 mag (Vega) at 0.98d after the burst, to 15.6 +/- 0.1

mag at 2.95d after the burst.

Noémie Globus (UNAM), Damien Dornic (CPPM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), , Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:

We observed the field of the Einstein Probe X-ray transient EP260530a (Wu et al., ATel #17824) with the DDRAGO two-channel wide-field imager mounted on the COLIBRÍ telescope. The observations targeted the optical counterpart candidate, AT 2026nwl, discovered by GOTO (TNS Astronomical Transient Report No. 306622) and associated with EP260530a. We observed from 2026-06-01 04:59 to 06:02 UTC (from (55.93 to 56.97 hours after the GOTO discovery) and obtained 11, 23, 10, 24, and 20 minutes of exposure in the g, r, i, z, and y filters, respectively.

The data were reduced and coadded with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

We detect the optical counterpart previously reported by GOTO (AT 2026nwl). The source is measured at the following preliminary magnitudes:

g = 15.22 +/- 0.01,
r = 15.33 +/- 0.01,
i = 15.41 +/- 0.01,
z = 15.52 +/- 0.01,
y = 15.58 +/- 0.01.

The source is brighter than the magnitude of L = 17.03 at 2026-05-29 21:04 UTC reported by the GOTO team (TNS Astronomical Transient Report 306622), but fainter than the unfiltered magnitude of 14.46 at 2026-05-31 05:24 UTC reported by Sokolovsky et al (TNS Astronomical Transient Report 306654). If the transient has a simple rise and decay, this suggests that it has already reached its maximum.

The source shows blue colors, consistent with both a CV and an FBOT.

During the 55 minutes of our observations, the source shows a smooth rise from r = 15.35 to r = 15.28 followed by a smooth fall again to r = 15.36. Similar behavior is also seen in the other filters. This variability is reminiscent of that seen in CVs.

We encourage spectroscopic observations to determine the redshift of this source and its likely nature.

We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.