From Discovery to the First Month of the Type II Supernova 2023ixf: High and Variable Mass Loss in the Final Year before Explosion

Abstract

We present the discovery of the Type II supernova SN 2023ixf in M101 and follow-up photometric and spectroscopic observations, respectively, in the first month and week of its evolution. Our discovery was made within a day of estimated first light, and the following light curve is characterized by a rapid rise (≈5 days) to a luminous peak (M V ≈ − 18.2 mag) and plateau (M V ≈ − 17.6 mag) extending to 30 days with a fast decline rate of ≈0.03 mag day−1. During the rising phase, U − V color shows blueward evolution, followed by redward evolution in the plateau phase. Prominent flash features of hydrogen, helium, carbon, and nitrogen dominate the spectra up to ≈5 days after first light, with a transition to a higher ionization state in the first ≈2 days. Both the U−V color and flash ionization states suggest a rise in the temperature, indicative of a delayed shock breakout inside dense circumstellar material (CSM). From the timescales of CSM interaction, we estimate its compact radial extent of ∼(3–7) × 1014 cm. We then construct numerical light-curve models based on both continuous and eruptive mass-loss scenarios shortly before explosion. For the continuous mass-loss scenario, we infer a range of mass-loss history with 0.1–1.0 M ⊙ yr−1 in the final 2−1 yr before explosion, with a potentially decreasing mass loss of 0.01–0.1 M ⊙ yr−1 in ∼0.7–0.4 yr toward the explosion. For the eruptive mass-loss scenario, we favor eruptions releasing 0.3–1 M ⊙ of the envelope at about a year before explosion, which result in CSM with mass and extent similar to the continuous scenario. We discuss the implications of the available multiwavelength constraints obtained thus far on the progenitor candidate and SN 2023ixf to our variable CSM models.

The SN 2023ixf Progenitor in M101. I. Infrared Variability

“…As shown by Davies et al (2022, see their Figure 3), mid-IR emission from the pre-SN outburst models stays almost constant, while the optical and near-IR bands may be significantly affected and thereby provide the best diagnostic for such outbursts. The MMT/MMIRS J-and K-band observations taken less than two weeks prior to the SN explosion appear to follow the general variability trend in the near-IR going back 16 yr based on the WFCAM and NIRI data (Figure 6), thus supporting the result obtained by other groups that there was likely no pre-SN outburst (Dong et al 2023;Hiramatsu et al 2023;Jencson et al 2023;Kilpatrick et al 2023;Neustadt et al 2023). There are not enough deep optical observations of the progenitor prior to explosion to measure the variability that is typically present for RSGs in this wavelength regime.…”

The Preexplosion Environments and the Progenitor of SN 2023ixf from the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX)

“…(2023),Lundquist et al (2023),Smith et al (2023), andHiramatsu et al (2023), and it is not significantly different from our preexplosion measurement of E(B − V ) = 0.03 ± 0.06 in the regions of r < 1″. Niu et al 2023 measure the preexplosion extinction of the environment within r < 4 5 as E(B − V ) = 0.15mag using the resolved stars in the Hubble Space Telescope (HST) images.…”

“…SN 2023ixf was reported on 2023 May 19.727 UT in M101 (NGC 5457; Itagaki 2023) and was classified as a Type II SN (Perley et al 2023). Being the SN event of the smallest distance in the past decade, intensive archival observations are available to identify the progenitor and to constrain the preexplosion environment (e.g., Dong et al 2023;Hiramatsu et al 2023;Jacobson-Galan et al 2023;Jencson et al 2023;Kilpatrick et al 2023;Neustadt et al 2023;Pledger & Shara 2023;Soker 2023;Soraisam et al 2023;Van Dyk et al 2023).…”

Early Spectroscopy and Dense Circumstellar Medium Interaction in SN 2023ixf

“…All of the comparison SNe are Type IIP/L SNe with the exception of SN 2013cu, which is a Type IIb (Leonard et al 2000;Gal-Yam et al 2014;Terreran et al 2016Terreran et al , 2022Yaron et al 2017;Tartaglia et al 2021). Their light curves show similarly shallow linear declines in V band, with SN 2013cu being the steepest (Bianciardi et al 2023;Hiramatsu et al 2023;Jacobson-Galan et al 2023;Teja et al 2023;Yamanaka et al 2023).…”