ZTF20aajnksq (AT2020blt): A Fast Optical Transient at $z approx 2.9$ With No Detected Gamma-Ray Burst Counterpart. (arXiv:2006.10761v3 [astro-ph.HE] UPDATED)

ZTF20aajnksq (AT2020blt): A Fast Optical Transient at $z approx 2.9$ With No Detected Gamma-Ray Burst Counterpart. (arXiv:2006.10761v3 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Ho_A/0/1/0/all/0/1">Anna Y. Q. Ho</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Perley_D/0/1/0/all/0/1">Daniel A. Perley</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Beniamini_P/0/1/0/all/0/1">Paz Beniamini</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Cenko_S/0/1/0/all/0/1">S. Bradley Cenko</a> (3 and 4), <a href="http://arxiv.org/find/astro-ph/1/au:+Kulkarni_S/0/1/0/all/0/1">S. R. Kulkarni</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Andreoni_I/0/1/0/all/0/1">Igor Andreoni</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Singer_L/0/1/0/all/0/1">Leo P. Singer</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+De_K/0/1/0/all/0/1">Kishalay De</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Kasliwal_M/0/1/0/all/0/1">Mansi M. Kasliwal</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Fremling_C/0/1/0/all/0/1">Christoffer Fremling</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Bellm_E/0/1/0/all/0/1">Eric C. Bellm</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Dekany_R/0/1/0/all/0/1">Richard Dekany</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Delacroix_A/0/1/0/all/0/1">Alexandre Delacroix</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Duev_D/0/1/0/all/0/1">Dmitry A. Duev</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Goldstein_D/0/1/0/all/0/1">Daniel A. Goldstein</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Golkhou_V/0/1/0/all/0/1">V. Zach Golkhou</a> (5 and 7), <a href="http://arxiv.org/find/astro-ph/1/au:+Goobar_A/0/1/0/all/0/1">Ariel Goobar</a> (8), <a href="http://arxiv.org/find/astro-ph/1/au:+Graham_M/0/1/0/all/0/1">Matthew Graham</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Hale_D/0/1/0/all/0/1">David Hale</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Kupfer_T/0/1/0/all/0/1">Thomas Kupfer</a> (9), <a href="http://arxiv.org/find/astro-ph/1/au:+Laher_R/0/1/0/all/0/1">Russ R. Laher</a> (10), <a href="http://arxiv.org/find/astro-ph/1/au:+Masci_F/0/1/0/all/0/1">Frank J. Masci</a> (10), <a href="http://arxiv.org/find/astro-ph/1/au:+Miller_A/0/1/0/all/0/1">A. A. Miller</a> (11 and 12), <a href="http://arxiv.org/find/astro-ph/1/au:+Neill_J/0/1/0/all/0/1">James D. Neill</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Riddle_R/0/1/0/all/0/1">Reed Riddle</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Rusholme_B/0/1/0/all/0/1">Ben Rusholme</a> (10), <a href="http://arxiv.org/find/astro-ph/1/au:+Shupe_D/0/1/0/all/0/1">David L. Shupe</a> (10), <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_R/0/1/0/all/0/1">Roger Smith</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Sollerman_J/0/1/0/all/0/1">Jesper Sollerman</a> (13), <a href="http://arxiv.org/find/astro-ph/1/au:+Roestel_J/0/1/0/all/0/1">Jan van Roestel</a> (1) ((1) Caltech, (2) LJMU, (3) NASA Goddard, (4) UMD, (5) DIRAC Institute, (6) COO, (7) eScience Institute, (8) OKC Physics, (9) Kavli Institute UCSB, (10) IPAC, (11) CIERA, (12) Adler, (13) OKC Astronomy)

We present ZTF20aajnksq (AT2020blt), a fast-fading ($Delta r=2.4$ mag in
$Delta t=1.3$ days) red ($g-rapprox0.6$ mag) and luminous ($M_{1626}=-25.9$)
optical transient at $z=2.9$ discovered by the Zwicky Transient Facility (ZTF).
AT2020blt shares several features in common with afterglows to long-duration
gamma-ray bursts (GRBs): (1) an optical light curve well-described by a broken
power-law with a break at $t_mathrm{j}=1$ day (observer-frame); (2) a luminous
$(L_X = 10^{46}$ $mathrm{erg}$ $mathrm{s}^{-1})$ X-ray counterpart; and (3)
luminous ($L_nu = 4 times 10^{31}$ $mathrm{erg}$ $mathrm{sec}^{-1}$
$mathrm{Hz}^{-1}$ at 10 GHz) radio emission. However, no GRB was detected in
the 0.74d between the last ZTF non-detection ($r > 20.64$) and the first ZTF
detection ($r = 19.57$), with an upper limit on the isotropic-equivalent
gamma-ray energy release of $E_{gamma,mathrm{iso}} < 7 times 10^{52}$ erg.
AT2020blt is thus the third afterglow-like transient discovered without a
detected GRB counterpart (after PTF11agg and ZTF19abvizsw) and the second
(after ZTF19abvizsw) with a redshift measurement. We conclude that the
properties of AT2020blt are consistent with a classical (initial Lorentz factor
$Gamma_0 gtrsim 100$) on-axis GRB that was missed by high-energy satellites.
Furthermore, by estimating the rate of transients with light curves similar to
that of AT2020blt in ZTF high-cadence data, we agree with previous results that
there is no evidence for an afterglow-like phenomenon that is significantly
more common than classical GRBs. We conclude by discussing the status and
future of fast-transient searches in wide-field high-cadence optical surveys.

http://arxiv.org/icons/sfx.gif