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A mildly relativistic outflow from the energetic, fast-rising blue optical transient CSS161010 in a dwarf galaxy

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  • D. L. Coppejans
  • R. Margutti
  • G. Terreran
  • A. J. Nayana
  • E. R. Coughlin
  • T. Laskar
  • K. D. Alexander
  • M. Bietenholz
  • D. Caprioli
  • P. Chandra
  • M. Drout
  • D. Frederiks
  • C. Frohmaier
  • K. Hurley
  • C. S. Kochanek
  • M. MacLeod
  • A. Meisner
  • P. E. Nugent
  • A. Ridnaia
  • D. J. Sand
  • And 18 others
  • D. Svinkin
  • C. Ward
  • S. Yang
  • A. Baldeschi
  • I. V. Chilingarian
  • Y. Dong
  • C. Esquivia
  • W. Fong
  • C. Guidorzi
  • P. Lundqvist
  • D. Milisavljevic
  • K. Paterson
  • D. E. Reichart
  • B. Shappee
  • M. C. Stroh
  • S. Valenti
  • A. Zauderer
  • B. Zhang
We present X-ray and radio observations of the Fast Blue Optical Transient CRTS-CSS161010 J045834−081803 (CSS161010 hereafter) at t = 69–531 days. CSS161010 shows luminous X-ray (L x ~ 5 × 1039 erg s−1) and radio (L ν ~ 1029 erg s−1 Hz−1) emission. The radio emission peaked at ~100 days post-transient explosion and rapidly decayed. We interpret these observations in the context of synchrotron emission from an expanding blast wave. CSS161010 launched a mildly relativistic outflow with velocity Γβc ≥ 0.55c at ~100 days. This is faster than the non-relativistic AT 2018cow (Γβc ~ 0.1c) and closer to ZTF18abvkwla (Γβc ≥ 0.3c at 63 days). The inferred initial kinetic energy of CSS161010 (E k ≿ 1051 erg) is comparable to that of long gamma-ray bursts, but the ejecta mass that is coupled to the mildly relativistic outflow is significantly larger (∼0.01-0.1 M). This is consistent with the lack of observed γ-rays. The luminous X-rays were produced by a different emission component to the synchrotron radio emission. CSS161010 is located at ~150 Mpc in a dwarf galaxy with stellar mass M * ~ 107 M and specific star formation rate sSFR ~ 0.3 Gyr−1. This mass is among the lowest inferred for host galaxies of explosive transients from massive stars. Our observations of CSS161010 are consistent with an engine-driven aspherical explosion from a rare evolutionary path of a H-rich stellar progenitor, but we cannot rule out a stellar tidal disruption event on a centrally located intermediate-mass black hole. Regardless of the physical mechanism, CSS161010 establishes the existence of a new class of rare (rate < 0.4% of the local core-collapse supernova rate) H-rich transients that can launch mildly relativistic outflows.
Original languageEnglish
Article numberL23
Number of pages15
JournalAstrophysical Journal Letters
Issue number1
Publication statusPublished - 26 May 2020


  • Coppejans_2020_ApJL_895_L23

    Rights statement: D. L. Coppejans et al. 'A Mildly Relativistic Outflow from the Energetic, Fast-rising Blue Optical Transient CSS161010 in a Dwarf Galaxy.' 2020 ApJL 895 L23. © 2020 The American Astronomical Society. All rights reserved. Reproduced by permission of the AAS.

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