Discovery of an intermediate-luminosity red transient in M51 and its likely dust-obscured, infrared-variable progenitor

Bibliographic Details
Title: Discovery of an intermediate-luminosity red transient in M51 and its likely dust-obscured, infrared-variable progenitor
Authors: Jencson, Jacob E., Adams, Scott M., Bond, Howard E., van Dyk, Schuyler D., Kasliwal, Mansi M., Bally, John, Blagorodnova, Nadejda, De, Kishalay, Fremling, Christoffer, Yao, Yuhan, Fruchter, Andrew, Rubin, David, Barbarino, Cristina, Sollerman, Jesper, Miller, Adam A., Hicks, Erin K. S., Malkan, Matthew A., Andreoni, Igor, Bellm, Eric C., Buchheim, Robert, Dekany, Richard, Feeney, Michael, Frederick, Sara, Gal-Yam, Avishay, Gehrz, Robert D., Giomi, Matteo, Graham, Matthew J., Green, Wayne, Hale, David, Hankins, Matthew J., Hanson, Mark, Helou, George, Ho, Anna Y. Q., Hung, T., Jurić, Mario, Kendurkar, Malhar R., Kulkarni, S. R., Lau, Ryan M., Masci, Frank J., Neill, James D., Quin, Kevin, Riddle, Reed L., Rusholme, Ben, Sims, Forrest, Smith, Nathan, Smith, Roger M., Soumagnac, Maayane T., Tachibana, Yutaro, Tinyanont, Samaporn, Walters, Richard, Watson, Stanley, Williams, Robert E.
Source: The Astrophysical Journal Letters, 880 (2019) L20
Publication Year: 2019
Collection: Astrophysics
Subject Terms: Astrophysics - Solar and Stellar Astrophysics
More Details: We present the discovery of an optical transient (OT) in Messier 51, designated M51 OT2019-1 (also ZTF19aadyppr, AT 2019abn, ATLAS19bzl), by the Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed luminosity of $M_r=-13$ (${\nu}L_{\nu}=9\times10^6~L_{\odot}$), in the luminosity gap between novae and typical supernovae (SNe). Spectra during the outburst show a red continuum, Balmer emission with a velocity width of $\approx400$ km s$^{-1}$, Ca II and [Ca II] emission, and absorption features characteristic of an F-type supergiant. The spectra and multiband light curves are similar to the so-called "SN impostors" and intermediate-luminosity red transients (ILRTs). We directly identify the likely progenitor in archival Spitzer Space Telescope imaging with a $4.5~\mu$m luminosity of $M_{[4.5]}\approx-12.2$ and a $[3.6]-[4.5]$ color redder than 0.74 mag, similar to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive monitoring of M51 with Spitzer further reveals evidence for variability of the progenitor candidate at [4.5] in the years before the OT. The progenitor is not detected in pre-outburst Hubble Space Telescope optical and near-IR images. The optical colors during outburst combined with spectroscopic temperature constraints imply a higher reddening of $E(B-V)\approx0.7$ mag and higher intrinsic luminosity of $M_r\approx-14.9$ (${\nu}L_{\nu}=5.3\times10^7~L_{\odot}$) near peak than seen in previous ILRT candidates. Moreover, the extinction estimate is higher on the rise than on the plateau, suggestive of an extended phase of circumstellar dust destruction. These results, enabled by the early discovery of M51 OT2019-1 and extensive pre-outburst archival coverage, offer new clues about the debated origins of ILRTs and may challenge the hypothesis that they arise from the electron-capture induced collapse of extreme asymptotic giant branch stars.
Comment: 21 pages, 5 figures, published in ApJL
Document Type: Working Paper
DOI: 10.3847/2041-8213/ab2c05
Access URL: http://arxiv.org/abs/1904.07857
Accession Number: edsarx.1904.07857
Database: arXiv
More Details
DOI:10.3847/2041-8213/ab2c05