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Electromagnetic counterparts to structured jets from gravitational wave detected mergers

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journal contribution
posted on 24.07.2019, 15:24 by Gavin P. Lamb, Shiho Kobayashi
We show the peak magnitude for orphan afterglows from the jets of gravitational wave (GW) detected black hole/neutron star – neutron star (BH/NS–NS) mergers highly depend on the jet half-opening angle θj. Short γ-ray bursts (GRBs) with a homogeneous jet structure and θj > 10°, the orphan afterglow viewed at the typical inclination for a GW detected event, 38°, are brighter at optical frequencies than the comparable macronova emission. Structured jets, where the energetics and Lorentz factor Γ vary with angle from the central axis, may have low-Γ components where the prompt emission is suppressed; GW electromagnetic (EM) counterparts may reveal a population of failed-GRB orphan afterglows. Using a Monte Carlo method assuming an NS–NS detection limit we show the fraction of GW-EM counterparts from homogeneous, two-component, power-law structured and Gaussian jets where the variable structure models include a wide low energy and Γ component: for homogeneous jets, with a θj = 6° and typical short GRB parameters, we find r-band magnitude mr ≤ 21 counterparts for ∼13.6 per cent of GW detected mergers; where jet structure extends to a half-opening angle of 25°, two-component jets produce mr ≤ 21 counterparts in ∼30 per cent of GW detected mergers, power-law structured-jets result in ∼37 per cent and Gaussian jets with our parameters ∼13 per cent. We show the features in the light curves from orphan afterglows can be used to indicate the presence of extended structure.


This research was supported by Science and Technology Facilities Council (STFC) grants; GPL acknowledges support from Royal Astronomical Society (RAS) and International Astronomical Union (IAU) travel grants.



Monthly Notices of the Royal Astronomical Society, 2017, 472 (4), pp. 4953-4964 (12)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





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