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Color Me Intrigued: The Discovery of iPTF 16fnm, an SN 2002cx-like Object

  • Author(s): Miller, AA
  • Kasliwal, MM
  • Cao, Y
  • Adams, SM
  • Goobar, A
  • Knežević, S
  • Laher, RR
  • Lunnan, R
  • Masci, FJ
  • Nugent, PE
  • Perley, DA
  • Petrushevska, T
  • Quimby, RM
  • Rebbapragada, UD
  • Sollerman, J
  • Taddia, F
  • Kulkarni, SR
  • et al.
Abstract

© 2017. The American Astronomical Society. All rights reserved. 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 MgPTF = -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 rN02cx N1a = 33-25+1.58%. 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.

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