Kavli Affiliate: Nathan P. Lourie
| Summary:
In March 2026, the Einstein Probe (EP) discovered its most nearby (z = 0.0343) Fast X-ray Transient (FXT), EP260321a, the first EP FXT to provide a strong match to expectations for X-ray ”shock breakout” (SBO) emission. Here, we present our multi-wavelength follow-up campaign of EP260321a and its broad-line Type Ic (Ic-BL) supernova (SN) counterpart, SN 2026gzf, the first Type Ic-BL SN with a definitive X-ray SBO. We show that our radio follow-up extending over 5.8 – 54.5 days post-FXT rules out an on-axis jet counterpart of isotropic-equivalent kinetic energy $E_K > 10^49$ erg for circumburst densities $n > 10^-2~rm cm^-3$ and constrains radio synchrotron emission from the fastest-moving SN ejecta. In addition, we derive the properties of SN 2026gzf and its host galaxy from our well-sampled optical data and compare them with those of optically discovered Type Ic-BL SNe, finding that SN2026gzf is well within the 90% confidence interval across all properties. We further fit SN 2026gzf’s light curve with five different physical models, and determine that combined emission from both interaction with circumstellar material (CSM) and $^56$Ni radioactive decay provides the best fit with plausible model parameters. Finally, using the rate of Ic-BL SNe from the ZTF Bright Transient Survey and assuming all Type Ic-BL SNe produce EP260321a-like FXTs, we infer an expected rate of EP-detected SBOs of 4.4 – 16 year$^-1$. This is inconsistent at the 90% confidence level with current EP detection rates, potentially indicating that most Type Ic-BL SNe produce less luminous X-ray SBO signals compared to EP 260321a.
| Search Query: arXiv Query: search_query=au:”Lourie Nathan P.”&id_list=&start=0&max_results=10
Read More