CaltechAUTHORS
Published February 10, 2018 | Version Published + Submitted
Journal Article Open

iPTF Archival Search for Fast Optical Transients

Creators

  • 1. ROR icon California Institute of Technology
  • 2. ROR icon Lawrence Berkeley National Laboratory
  • 3. ROR icon University of California, Merced
  • 4. ROR icon University of Maryland, College Park
  • 5. ROR icon Liverpool John Moores University
  • 6. ROR icon University of Washington
  • 7. ROR icon University of Wisconsin–Milwaukee
  • 8. ROR icon Weizmann Institute of Science
  • 9. ROR icon Instituto de Astrofísica de Andalucía
  • 10. ROR icon Infrared Processing and Analysis Center
  • 11. ROR icon Stockholm University

Abstract

There has been speculation about a class of relativistic explosions with an initial Lorentz factor Γ_(init) smaller than that of classical gamma-ray bursts (GRBs). These "dirty fireballs" would lack prompt GRB emission but could be pursued via their optical afterglow, appearing as transients that fade overnight. Here we report a search for such transients (that fade by 5-σ in magnitude overnight) in four years of archival photometric data from the intermediate Palomar Transient Factory (iPTF). Our search criteria yielded 50 candidates. Of these, two were afterglows to GRBs that had been found in dedicated follow-up observations to triggers from the Fermi GRB Monitor. Another (iPTF14yb) was a GRB afterglow discovered serendipitously. Eight were spurious artifacts of reference image subtraction, and one was an asteroid. The remaining 38 candidates have red stellar counterparts in external catalogs. The photometric and spectroscopic properties of the counterparts identify these transients as strong flares from M dwarfs of spectral type M3–M7 at distances of d ≈ 0.15–2.1 kpc; three counterparts were already spectroscopically classified as late-type M stars. With iPTF14yb as the only confirmed relativistic outflow discovered independently of a high-energy trigger, we constrain the all-sky rate of transients that peak at m = 18 and fade by Δm = 2 mag in Δt = 3 hr to be 680 yr^(-1), with a 68% confidence interval of 119-2236, yr^(-1). This implies that the rate of visible dirty fireballs is at most comparable to that of the known population of long-duration GRBs.

Additional Information

© 2018 American Astronomical Society. Received 2017 December 5. Accepted 2018 January 24. Published 2018 February 9. It is a pleasure to thank Yi Cao, Jim Davenport, Adam Miller, Yuguang Chen, Harish Vendantham, Lynne Hillenbrand, and Trevor David for helpful discussions and assistance. We are grateful to the anonymous referee for constructive feedback that improved the quality of the paper. A.Y.Q.H. was supported by a National Science Foundation Graduate Research Fellowship under grant No. DGE1144469. D.A.K. acknowledges support from from the Spanish research project AYA 2014-58381-P and the Juan de la Cierva Incorporacíon fellowship IJCI-2015-261. This work was supported by the GROWTH project funded by the National Science Foundation under PIRE grant No. 1545949. 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 research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013).

Attached Files

Published - Ho_2018_ApJL_854_L13.pdf

Submitted - 1712.00949.pdf

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Additional details

Identifiers

Eprint ID
84762
Resolver ID
CaltechAUTHORS:20180209-095826158

Related works

Describes
https://arxiv.org/abs/1712.00949 (URL)

Funding

NSF Graduate Research Fellowship
DGE-1144469
Ministerio de Educación y Ciencia (MEC)
AYA 2014-58381-P
Juan de la Cierva Incorporacíon
IJCI-2015-261
NSF
AST-1545949

Dates

Created
2018-02-09
Created from EPrint's datestamp field
Updated
2021-11-15
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
Palomar Transient Factory, Infrared Processing and Analysis Center (IPAC), Astronomy Department, Division of Geological and Planetary Sciences (GPS)