Color Me Intrigued: the Discovery of iPTF 16fnm, a Supernova 2002cx-like Object

Creators: Miller, A. A.; Kasliwal, M. M.; Cao, Y.; Adams, S. M.; Goobar, A.; Knežević, S.; Laher, R. R.; Lunnan, R.; Masci, F. J.; Nugent, P. E.; Perley, D. A.; Petrushevska, T.; Quimby, R. M.; Rebbapragada, U. D.; Sollerman, J.; Taddia, F.; Kulkarni, S. R.

Abstract

Modern wide-field, optical time-domain surveys must solve a basic optimization problem: maximize the number of transient discoveries or minimize the follow-up needed for the new discoveries. Here, we describe the Color Me Intrigued experiment, the first from the intermediate Palomar Transient Factory (iPTF) to search for transients simultaneously in the g_(PTF) and R_(PTF) bands. During the course of this experiment, we discovered iPTF 16fnm, a new member of the 02cx-like subclass of Type Ia supernovae (SNe). iPTF 16fnm peaked at M_(gPTF) = -15.09 ± 0.17 mag, making it the second-least-luminous known SN Ia. iPTF 16fnm exhibits all the hallmarks of the 02cx-like class: (i) low luminosity at peak, (ii) low ejecta velocities, and (iii) a non-nebular spectrum several months after peak. Spectroscopically, iPTF 16fnm exhibits a striking resemblance to two other low-luminosity 02cx-like SNe: SN 2007qd and SN 2010ae. iPTF 16fnm and SN 2005hk decline at nearly the same rate, despite a 3 mag difference in brightness at peak. When considering the full subclass of 02cx-like SNe, we do not find evidence for a tight correlation between peak luminosity and decline rate in either the g' or r' band. We measure the relative rate of 02cx-like SNe to normal SNe Ia and find r_(N02cx)/N_(Ia) = 33^(+158)_(-25)%. We further examine the g' − r' evolution of 02cx-like SNe and find that their unique color evolution can be used to separate them from 91bg-like and normal SNe Ia. This selection function will be especially important in the spectroscopically incomplete Zwicky Transient Facility/Large Synoptic Survey Telescope (LSST) era. Finally, we close by recommending that LSST periodically evaluate, and possibly update, its observing cadence to maximize transient science.

Additional Information

© 2017 The American Astronomical Society. Received 2017 March 27; revised 2017 September 11; accepted 2017 September 11; published 2017 October 12. This study has benefited from the suggestions of an anonymous referee. We thank K. Shen for a useful discussion on the color evolution of SNe Ia. R. Amanullah pointed us to several useful papers on the color evolution of SNe Ia, for which we are grateful. We wish to recognize J. Nordin, who helped us examine SEDm spectra. Finally, we thank J. D. Neill and A. Y. Q. Ho for providing detailed notes on the manuscript prior to submission. A.A.M. is funded by the Large Synoptic Survey Telescope Corporation in support of the Data Science Fellowship Program. The Intermediate Palomar Transient Factory project is a scientific collaboration among the California Institute of Technology, Los Alamos National Laboratory, the University of Wisconsin, Milwaukee, the Oskar Klein Center, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe. This work was supported by the GROWTH project funded by the National Science Foundation under grant No. 1545949. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Some of the data presented here were obtained in part with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOTSA. 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 NASA. 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. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Facilities: PO:1.2m - Palomar Observatory's 1.2 meter Samuel Oschin Telescope, PO:1.5 m (SEDm) - , Hale (DBSP) - , NOT (ALFOSC) - , Keck:I (LRIS) - .

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