AstroNote 2026-42

The Follow-up X-ray Telescope on board the Einstein Probe (EP) conducted an 8 ks observation at the location of the Type Ic-BL supernova SN2026cha (Jayaraman et al., AstroNote 2026-29; Hinds et al., AstroNote 2026-31; Chrimes et al., AstroNote 2026-34) beginning at UTC 2026-02-17 18:00:48. SN2026cha exhibited an unusual light curve, with rapidly-evolving optical emission similar to SN2018gep (Pritchard et al. 2021) and iPTF16asu (Whitesides et al. 2017), with a clear blue shock cooling component.

We report a non-detection at the location of the transient, with an upper limit on the X-ray flux (across 0.5-10 keV) of 2.76 x 10^-14 erg/s/cm^2. At the redshift of this SN (z = 0.0393), this corresponds to an upper limit on the luminosity of roughly 10^41 erg/s. This is a lower luminosity than measured at a similar epoch for SN2006aj (Soderberg et al. 2006), which is around 6 x 10^41 erg/s at a similar redshift.

We also observed SN2026cha with the Very Large Array on 18 Feb 2026 at a mid-time of 07:44 UT in X band (10 GHz). We do not detect a source at this location, and place a 3σ upper limit of 15 µJy on the flux density, corresponding to a luminosity limit of 7 x 26 erg/s/Hz. This limit is a factor of ~2 lower than the radio emission associated with SN 2020bvc (Ho et al. 2020) and a factor of ~4 lower than the radio emission associated with XRF 060218/SN 2006aj (Soderberg et al. 2006), at a similar epoch and frequency. 

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).

We thank the staff at the NRAO for quickly approving these observations.