_version_ 1866912472620859392
author Srinivasaragavan, Gokul P.
Hamidani, Hamid
Schroeder, Genevieve
Sarin, Nikhil
Ho, Anna Y. Q.
Piro, Anthony L.
Cenko, S. Bradley
Anand, Shreya
Sollerman, Jesper
Perley, Daniel A.
Maeda, Keiichi
O'Connor, Brendan
Kuncarayakti, Hanindyo
Miller, M. Coleman
Ahumada, Tomás
Vail, Jada L.
Duffell, Paul
Dastidar, Ranadeep Ghosh
Andreoni, Igor
Bochenek, Aleksandra
Brennan, Seán J.
Carney, Jonathan
Chen, Ping
Freeburn, James
Gal-Yam, Avishay
Jacobson-Galán, Wynn
Kasliwal, Mansi M.
Li, Jiaxuan
Li, Maggie L.
Sravan, Niharika
Warshofsky, Daniel E.
author_facet Srinivasaragavan, Gokul P.
Hamidani, Hamid
Schroeder, Genevieve
Sarin, Nikhil
Ho, Anna Y. Q.
Piro, Anthony L.
Cenko, S. Bradley
Anand, Shreya
Sollerman, Jesper
Perley, Daniel A.
Maeda, Keiichi
O'Connor, Brendan
Kuncarayakti, Hanindyo
Miller, M. Coleman
Ahumada, Tomás
Vail, Jada L.
Duffell, Paul
Dastidar, Ranadeep Ghosh
Andreoni, Igor
Bochenek, Aleksandra
Brennan, Seán J.
Carney, Jonathan
Chen, Ping
Freeburn, James
Gal-Yam, Avishay
Jacobson-Galán, Wynn
Kasliwal, Mansi M.
Li, Jiaxuan
Li, Maggie L.
Sravan, Niharika
Warshofsky, Daniel E.
contents We present optical, radio, and X-ray observations of EP250108a/SN 2025kg, a broad-line Type Ic supernova (SN Ic-BL) accompanying an Einstein Probe (EP) fast X-ray transient (FXT) at $z=0.176$. EP250108a/SN 2025kg possesses a double-peaked optical light curve and its spectrum transitions from a blue underlying continuum to a typical SN Ic-BL spectrum over time. We fit a radioactive decay model to the second peak of the optical light curve and find SN parameters that are consistent with the SNe Ic-BL population, while its X-ray and radio properties are consistent with those of low-luminosity GRB (LLGRB) 060218/SN 2006aj. We explore three scenarios to understand the system's multi-wavelength emission -- (a) SN ejecta interacting with an extended circumstellar medium (CSM), (b) the shocked cocoon of a collapsar-driven jet choked in its stellar envelope, and (c) the shocked cocoon of a collapsar-driven jet choked in an extended CSM. Models (b) and (c) can explain the optical light curve and are also consistent with the radio and X-ray observations. We favor model (c) because it can self-consistently explain both the X-ray prompt emission and first optical peak, but we do not rule out model (b). From the properties of the first peak in model (c), we find evidence that EP250108a/SN 2025kg interacts with an extended CSM, and infer an envelope mass $M_{\rm e} \sim 0.1\,\rm M_\odot$ and radius $R_{\rm e} \sim 4 \times 10^{13}$ cm. EP250108a/SN 2025kg's multi-wavelength properties make it a close analog to LLGRB 060218/SN 2006aj, and highlight the power of early follow-up observations in mapping the environments of massive stars prior to core collapse.
format Preprint
id arxiv_https___arxiv_org_abs_2504_17516
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle EP250108a/SN 2025kg: A Jet-Driven Stellar Explosion Interacting With Circumstellar Material
Srinivasaragavan, Gokul P.
Hamidani, Hamid
Schroeder, Genevieve
Sarin, Nikhil
Ho, Anna Y. Q.
Piro, Anthony L.
Cenko, S. Bradley
Anand, Shreya
Sollerman, Jesper
Perley, Daniel A.
Maeda, Keiichi
O'Connor, Brendan
Kuncarayakti, Hanindyo
Miller, M. Coleman
Ahumada, Tomás
Vail, Jada L.
Duffell, Paul
Dastidar, Ranadeep Ghosh
Andreoni, Igor
Bochenek, Aleksandra
Brennan, Seán J.
Carney, Jonathan
Chen, Ping
Freeburn, James
Gal-Yam, Avishay
Jacobson-Galán, Wynn
Kasliwal, Mansi M.
Li, Jiaxuan
Li, Maggie L.
Sravan, Niharika
Warshofsky, Daniel E.
High Energy Astrophysical Phenomena
We present optical, radio, and X-ray observations of EP250108a/SN 2025kg, a broad-line Type Ic supernova (SN Ic-BL) accompanying an Einstein Probe (EP) fast X-ray transient (FXT) at $z=0.176$. EP250108a/SN 2025kg possesses a double-peaked optical light curve and its spectrum transitions from a blue underlying continuum to a typical SN Ic-BL spectrum over time. We fit a radioactive decay model to the second peak of the optical light curve and find SN parameters that are consistent with the SNe Ic-BL population, while its X-ray and radio properties are consistent with those of low-luminosity GRB (LLGRB) 060218/SN 2006aj. We explore three scenarios to understand the system's multi-wavelength emission -- (a) SN ejecta interacting with an extended circumstellar medium (CSM), (b) the shocked cocoon of a collapsar-driven jet choked in its stellar envelope, and (c) the shocked cocoon of a collapsar-driven jet choked in an extended CSM. Models (b) and (c) can explain the optical light curve and are also consistent with the radio and X-ray observations. We favor model (c) because it can self-consistently explain both the X-ray prompt emission and first optical peak, but we do not rule out model (b). From the properties of the first peak in model (c), we find evidence that EP250108a/SN 2025kg interacts with an extended CSM, and infer an envelope mass $M_{\rm e} \sim 0.1\,\rm M_\odot$ and radius $R_{\rm e} \sim 4 \times 10^{13}$ cm. EP250108a/SN 2025kg's multi-wavelength properties make it a close analog to LLGRB 060218/SN 2006aj, and highlight the power of early follow-up observations in mapping the environments of massive stars prior to core collapse.
title EP250108a/SN 2025kg: A Jet-Driven Stellar Explosion Interacting With Circumstellar Material
topic High Energy Astrophysical Phenomena
url https://arxiv.org/abs/2504.17516