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Low Lorentz Factor Jets from Compact Stellar Mergers - Candidate Electromagnetic Counterparts to Gravitational Wave Sources

Lamb, GP and Kobayashi, S (2016) Low Lorentz Factor Jets from Compact Stellar Mergers - Candidate Electromagnetic Counterparts to Gravitational Wave Sources. ASTROPHYSICAL JOURNAL, 829 (2). ISSN 0004-637X

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Short gamma-ray bursts (GRBs) are believed to be produced by relativistic jets from mergers of neutron-stars (NS) or neutron-stars and black-holes (BH). If the Lorentz-factors Γ of jets from compact-stellar-mergers follow a similar power-law distribution to those observed for other high-energy astrophysical phenomena (e.g. blazars, AGN), the population of jets would be dominated by low-Γ outflows. These jets will not produce the prompt gamma-rays, but jet energy will be released as x-ray/optical/radio transients when they collide with the ambient medium. Using Monte Carlo simulations, we study the properties of such transients. Approximately 78% of merger-jets <300 Mpc result in failed-GRBs if the jet Γ follows a power-law distribution of index −1.75. X-ray/optical transients from failed-GRBs will have broad distributions of their characteristics: light-curves peak tp∼0.1−10 days after a merger; flux peaks for x-ray 10−6 mJy≲ Fx≲10−2 mJy; and optical flux peaks at 14≲ mg≲22. X-ray transients are detectable by Swift XRT, and ∼85% of optical transients will be detectable by telescopes with limiting magnitude mg≳21, for well localized sources on the sky. X-ray/optical transients are followed by radio transients with peak times narrowly clustered around tp∼10 days, and peak flux of ∼ 10−100 mJy at 10 GHz and ∼ 0.1 mJy at 150 MHz. By considering the all-sky rate of short GRBs within the LIGO/Virgo range, the rate of on-axis orphan afterglows from failed-GRB would be 2.6(26) per year for NS-NS(NS-BH) mergers, respectively. Since merger jets from gravitational-wave (GW) trigger events tend to be directed to us, a significant fraction of GW events could be associated with the on-axis orphan afterglow.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society and IOP Publishing
Date Deposited: 05 Aug 2016 10:35
Last Modified: 04 Sep 2021 12:37
DOI or Identification number: 10.3847/0004-637X/829/2/112
URI: https://researchonline.ljmu.ac.uk/id/eprint/4009

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