Strong Carbon Features and a Red Early Color in the Underluminous Type Ia SN 2022xkq

Pearson, Jeniveve and Sand, David and Lundqvist, Peter and Galbany, Lluís and Andrews, J.E. and Bostroem, K. Azalee and Dong, Yize and Hoang, Emily and Hosseinzadeh, Griffin and Janzen, Daryl and Jencson, Jacob and Lundquist, Michael and Mehta, Darshana and Meza, Nicolas and Shrestha, Manisha and VALENTI, Stefano and Wyatt, Samuel and Anderson, Joseph and Ashall, Chris and Auchettl, Katie and Baron, Edward and Blondin, Stéphane and Burns, Christopher R. and CAI, YONGZHI and Chen, Ting-Wan and Chomiuk, Laura and Coulter, David and Cross, Dane and Davis, Kyle and de Jaeger, Thomas and DerKacy, James M and Desai, Dhvanil D. and Dimitriadis, Georgios and Do, Aaron and Farah, Joseph R. and Foley, Ryan and Gromadzki, Mariusz and Gutiérrez, Claudia P. and Haislip, Joshua and Hernández, Jonay I. González and Hinkle, Jason and Hoogendam, Willem and Howell, D. Andrew and Hoeflich, Peter and Hsiao, Eric Y. and Huber, Mark E. and Jha, Saurabh W and Jiménez-Palau, Cristina and Kilpatrick, Charles and Kouprianov, Vladimir and Kumar, Sahana and Kwok, Lindsey and Larison, Conor and LeBaron, Natalie and Saux, Xavier Le and Lu, Jing and McCully, Curtis and Mera, Tyco and Milne, Peter and Modjaz, Maryam and Morrell, Nidia Irene and Müller-Bravo, Tomás E. and Newsome, Megan and Nicholl, Matt and Gonzalez, Estefania Padilla and Payne, Anna and Pellegrino, Craig and Phan, Kim and Pineda-García, Jonathan and Piro, Anthony and Piscarreta, Lara and Polin, Abigail and Reichart, Daniel and Rojas-Bravo, Cesar and Ryder, Stuart D and Salmaso, Irene and Schwab, Michaela and Shahbandeh, Melissa and Shappee, Benjamin and Siebert, Matthew and Smith, Nathan and Strader, Jay and Taggart, Kirsty and Terreran, Giacomo and Tinyanont, Samaporn and Tucker, Michael and Valerin, Giorgio and Young, David (2024) Strong Carbon Features and a Red Early Color in the Underluminous Type Ia SN 2022xkq. The Astrophysical Journal, 960 (1): 29. ISSN 0004-637X

Abstract

We present optical, infrared, ultraviolet, and radio observations of SN 2022xkq, an underluminous fast-declining Type Ia supernova (SN Ia) in NGC 1784 (D ≈ 31 Mpc), from <1 to 180 days after explosion. The high-cadence observations of SN 2022xkq, a photometrically transitional and spectroscopically 91bg-like SN Ia, cover the first days and weeks following explosion, which are critical to distinguishing between explosion scenarios. The early light curve of SN 2022xkq has a red early color and exhibits a flux excess that is more prominent in redder bands; this is the first time such a feature has been seen in a transitional/91bg-like SN Ia. We also present 92 optical and 19 near-infrared (NIR) spectra, beginning 0.4 days after explosion in the optical and 2.6 days after explosion in the NIR. SN 2022xkq exhibits a long-lived C i 1.0693 μm feature that persists until 5 days post-maximum. We also detect C iiλ6580 in the pre-maximum optical spectra. These lines are evidence for unburnt carbon that is difficult to reconcile with the double detonation of a sub-Chandrasekhar mass white dwarf. No existing explosion model can fully explain the photometric and spectroscopic data set of SN 2022xkq, but the considerable breadth of the observations is ideal for furthering our understanding of the processes that produce faint SNe Ia.