TY - JOUR
T1 - The Peculiar Ca-rich SN2019ehk
T2 - Evidence for a Type IIb Core-collapse Supernova from a Low-mass Stripped Progenitor
AU - De, Kishalay
AU - Fremling, U. Christoffer
AU - Gal-Yam, Avishay
AU - Yaron, Ofer
AU - Kasliwal, Mansi M.
AU - Kulkarni, S. R.
N1 - We thank S. Hachinger for providing the model spectral sequences used in this work. We thank the anonymous referee for a careful reading of the manuscript that significantly improved the quality of the paper. We thank W. Jacobson-Galan for providing the spectral sequence of SN 2019ehk. We thank J. Sollerman and C. Fransson for constructive comments on this manuscript. We thank L. Bildsten and A. Polin for valuable discussions. We thank D. Perley for assistance with lpipe. M.M.K. acknowledges generous support from the David and Lucille Packard Foundation. This work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant No. 1545949. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. A.G.Y.'s research is supported by the EU via ERC grant No. 725161, the ISF GW excellence center, an IMOS space infrastructure grant and BSF/Transformative and GIF grants, as well as The Benoziyo Endowment Fund for the Advancement of Science, the Deloro Institute for Advanced Research in Space and Optics, The Veronika A. Rabl Physics Discretionary Fund, Paul and Tina Gardner, Yeda-Sela and the WIS-CIT joint research grant; A.G.Y. is the recipient of the Helen and Martin Kimmel Award for Innovative Investigation.
PY - 2021/1
Y1 - 2021/1
N2 - The nature of the peculiar "Ca-rich" SN 2019ehk in the nearby galaxy M100 remains unclear. Its origin has been debated as either a stripped core-collapse supernova or a thermonuclear helium detonation event. Here, we present very late-time photometry of the transient obtained with the Keck I telescope at 280 days from peak light. Using the photometry to perform accurate flux calibration of a contemporaneous nebular phase spectrum, we measure an [O I] luminosity of (0.19-1.08) x 10(38) erg s(-1) and [Ca II] luminosity of (2.7-15.6) x 10(38) erg s(-1) over the range of the uncertain extinction along the line of sight and distance to the host galaxy. We use these measurements to derive lower limits on the synthesized oxygen mass of 0.004-0.069 M. The oxygen mass is a sensitive tracer of the progenitor mass for core-collapse supernovae, and our estimate is consistent with explosions of very low-mass CO cores of 1.45-1.5 M, corresponding to He core masses of 1.8-2.0 M. We present high-quality peak light optical spectra of the transient and highlight features of hydrogen in both the early ("flash") and photospheric phase spectra that suggest the presence of greater than or similar to 0.02 M of hydrogen in the progenitor at the time of explosion. The presence of H, together with the large [Ca II]/[O I] ratio (10-15) in the nebular phase, is consistent with SN 2019ehk being a Type IIb core-collapse supernova from a stripped low-mass (9-9.5 M) progenitor, similar to the Ca-rich SN IIb iPTF 15eqv. These results provide evidence for a likely class of "Ca-rich" core-collapse supernovae from stripped low-mass progenitors in star-forming environments, distinct from the thermonuclear Ca-rich gap transients in old environments.
AB - The nature of the peculiar "Ca-rich" SN 2019ehk in the nearby galaxy M100 remains unclear. Its origin has been debated as either a stripped core-collapse supernova or a thermonuclear helium detonation event. Here, we present very late-time photometry of the transient obtained with the Keck I telescope at 280 days from peak light. Using the photometry to perform accurate flux calibration of a contemporaneous nebular phase spectrum, we measure an [O I] luminosity of (0.19-1.08) x 10(38) erg s(-1) and [Ca II] luminosity of (2.7-15.6) x 10(38) erg s(-1) over the range of the uncertain extinction along the line of sight and distance to the host galaxy. We use these measurements to derive lower limits on the synthesized oxygen mass of 0.004-0.069 M. The oxygen mass is a sensitive tracer of the progenitor mass for core-collapse supernovae, and our estimate is consistent with explosions of very low-mass CO cores of 1.45-1.5 M, corresponding to He core masses of 1.8-2.0 M. We present high-quality peak light optical spectra of the transient and highlight features of hydrogen in both the early ("flash") and photospheric phase spectra that suggest the presence of greater than or similar to 0.02 M of hydrogen in the progenitor at the time of explosion. The presence of H, together with the large [Ca II]/[O I] ratio (10-15) in the nebular phase, is consistent with SN 2019ehk being a Type IIb core-collapse supernova from a stripped low-mass (9-9.5 M) progenitor, similar to the Ca-rich SN IIb iPTF 15eqv. These results provide evidence for a likely class of "Ca-rich" core-collapse supernovae from stripped low-mass progenitors in star-forming environments, distinct from the thermonuclear Ca-rich gap transients in old environments.
UR - http://www.scopus.com/inward/record.url?scp=85100306267&partnerID=8YFLogxK
U2 - 10.3847/2041-8213/abd627
DO - 10.3847/2041-8213/abd627
M3 - مقالة
SN - 2041-8205
VL - 907
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1
M1 - 18
ER -