GCN Circular 45547
Subject
EP260806a: VLA+ALMA radio detections
Event
Date
2026-09-10T14:49:26Z (5 days ago)
From
Anna Y Q Ho at Cornell University <ayh24@cornell.edu>
Via
Web form
Anna Ho, Cassie Sevilla, Michael Camilo (Cornell), Daniel Perley (LJMU) report:
We observed the position of the Einstein Probe transient EP260806a (Li et al. GCN 45299, Yang et al. GCN 45390), with the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) under joint VLA-ALMA program 26A-414 (PI Ho). The VLA observation began on 2026 September 5 UT (30 observer-frame days after discovery) at mean frequencies of 6, 10, 15, and 33 GHz, while the ALMA observation began on 2026 September 10 UT (35 observer-frame days after discovery) at mean frequencies of 104.5, 210, and 350 GHz.
From a preliminary analysis, we detect a bright radio source with a 10 GHz flux density of ~5.5 mJy and a 104.5 GHz flux density of ~50 mJy. The source position at 10 GHz is:
RA(J2000) = 00:49:13.571
Dec(J2000) = +35:33:39.59
This is consistent with the location of the optical counterpart of EP260806a (He et al. GCN 45300, de Ugarte Postigo et al. GCN 45302, Eyles-Ferris GCN 45303, Ma et al. GCN 45305, Li et al. GCN 45305, de Ugarte Postigo et al. GCN 45306, Anumarlapudi et al. GCN45312, Abidkhanov et al. GCN 45354, Hua et al. GCN 45385, Maksut et al. GCN 45389, Pankov et al. GCN 45396) and confirms the mm detection reported by NOEMA (de Ugarto Postigo et al. GCN 45541).
At the redshift of EP260806a, the VLA observation corresponds to a 10 GHz and 100 GHz luminosity of ~1E30 erg/s/Hz and ~1E31 erg/s/Hz, respectively. This luminosity is similar to the afterglows of relativistic jetted transients (e.g., gamma-ray bursts; Chandra & Frail 2012) while the positive spectral index across the radio bands at such a late time is similar to what has been observed in jetted tidal disruption events (e.g., Andreoni et al. 2022).
Additional followup is planned, and we thank the VLA and ALMA staff for quickly approving and executing these observations.