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Title: RADIO FLARES FROM GAMMA-RAY BURSTS

Abstract

We present predictions of centimeter and millimeter radio emission from reverse shocks (RSs) in the early afterglows of gamma-ray bursts (GRBs) with the goal of determining their detectability with current and future radio facilities. Using a range of GRB properties, such as peak optical brightness and time, isotropic equivalent gamma-ray energy, and redshift, we simulate radio light curves in a framework generalized for any circumburst medium structure and including a parameterization of the shell thickness regime that is more realistic than the simple assumption of thick- or thin-shell approximations. Building on earlier work by Mundell et al. and Melandri et al. in which the typical frequency of the RS was suggested to lie at radio rather than optical wavelengths at early times, we show that the brightest and most distinct RS radio signatures are detectable up to 0.1–1 day after the burst, emphasizing the need for rapid radio follow-up. Detection is easier for bursts with later optical peaks, high isotropic energies, lower circumburst medium densities, and at observing frequencies that are less prone to synchrotron self-absorption effects—typically above a few GHz. Given recent detections of polarized prompt gamma-ray and optical RS emission, we suggest that detection of polarized radio/millimeter emissionmore » will unambiguously confirm the presence of low-frequency RSs at early time.« less

Authors:
; ; ;  [1];  [2]; ;  [3];  [4];  [5]
  1. Astrophysics Research Institute, Liverpool John Moores University, Liverpool, L3 5RF (United Kingdom)
  2. Department of Astrophysics, School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv (Israel)
  3. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana (Slovenia)
  4. Department of Physics and Earth Sciences, University of Ferrara, Via Saragat, 1, I-44122 Ferrara (Italy)
  5. INAF/Brera Astronomical Observatory, via Bianchi 46, I-23807, Merate (Italy)
Publication Date:
OSTI Identifier:
22522285
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 806; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AFTERGLOW; BRIGHTNESS; COSMIC GAMMA BURSTS; COSMIC RADIO SOURCES; DENSITY; DETECTION; DIAGRAMS; EMISSION SPECTRA; GAMMA RADIATION; GHZ RANGE; RED SHIFT; SELF-ABSORPTION; VISIBLE RADIATION

Citation Formats

Kopač, D., Mundell, C. G., Kobayashi, S., Virgili, F. J., Harrison, R., Japelj, J., Gomboc, A., Guidorzi, C., and Melandri, A., E-mail: D.Kopac@ljmu.ac.uk. RADIO FLARES FROM GAMMA-RAY BURSTS. United States: N. p., 2015. Web. doi:10.1088/0004-637X/806/2/179.
Kopač, D., Mundell, C. G., Kobayashi, S., Virgili, F. J., Harrison, R., Japelj, J., Gomboc, A., Guidorzi, C., & Melandri, A., E-mail: D.Kopac@ljmu.ac.uk. RADIO FLARES FROM GAMMA-RAY BURSTS. United States. doi:10.1088/0004-637X/806/2/179.
Kopač, D., Mundell, C. G., Kobayashi, S., Virgili, F. J., Harrison, R., Japelj, J., Gomboc, A., Guidorzi, C., and Melandri, A., E-mail: D.Kopac@ljmu.ac.uk. 2015. "RADIO FLARES FROM GAMMA-RAY BURSTS". United States. doi:10.1088/0004-637X/806/2/179.
@article{osti_22522285,
title = {RADIO FLARES FROM GAMMA-RAY BURSTS},
author = {Kopač, D. and Mundell, C. G. and Kobayashi, S. and Virgili, F. J. and Harrison, R. and Japelj, J. and Gomboc, A. and Guidorzi, C. and Melandri, A., E-mail: D.Kopac@ljmu.ac.uk},
abstractNote = {We present predictions of centimeter and millimeter radio emission from reverse shocks (RSs) in the early afterglows of gamma-ray bursts (GRBs) with the goal of determining their detectability with current and future radio facilities. Using a range of GRB properties, such as peak optical brightness and time, isotropic equivalent gamma-ray energy, and redshift, we simulate radio light curves in a framework generalized for any circumburst medium structure and including a parameterization of the shell thickness regime that is more realistic than the simple assumption of thick- or thin-shell approximations. Building on earlier work by Mundell et al. and Melandri et al. in which the typical frequency of the RS was suggested to lie at radio rather than optical wavelengths at early times, we show that the brightest and most distinct RS radio signatures are detectable up to 0.1–1 day after the burst, emphasizing the need for rapid radio follow-up. Detection is easier for bursts with later optical peaks, high isotropic energies, lower circumburst medium densities, and at observing frequencies that are less prone to synchrotron self-absorption effects—typically above a few GHz. Given recent detections of polarized prompt gamma-ray and optical RS emission, we suggest that detection of polarized radio/millimeter emission will unambiguously confirm the presence of low-frequency RSs at early time.},
doi = {10.1088/0004-637X/806/2/179},
journal = {Astrophysical Journal},
number = 2,
volume = 806,
place = {United States},
year = 2015,
month = 6
}
  • Data on solar gamma-ray flares, including 24 flares with gamma-ray lines, recorded up to June 1982, are analyzed. It is shown that from the point of view of radio emission the differences between flares with and without gamma-ray lines has a purely quantitative character: the former are accompanied by the most intense microwave bursts. Meter type II bursts are not a distinctive feature of flares with gamma-ray lines. Pulsed flares, regardless of the presence or absence of gamma-ray lines, are not accompanied by significant proton fluxes at the earth. On the whole, contrary to the popular opinion in the literature,more » flares with gamma-ray lines do not display a deficit of proton flux in interplanetary space in comparison with similar flares without gamma-ray lines. The results of quantitative diagnostics of proton flares based on radio bursts are not at variance with the presence of flares without detectable gamma-ray emission in lines but with a pronounced increase in the proton flux at the earth. 23 references.« less
  • We have reexamined the relationship between ''U-shaped'' peak flux density microwave spectra and solar proton events for approx.200 large (Sp(> or =2 GHz)> or =800 solar flux units (sfu) microwave bursts (1965-1979). The radio spectra fell into two basic classes: U-shaped, with two maxima (> or =800 sfu) in the range from 200 MHz to > or =10 GHz (59% of all events), and cutoff spectra, with a maximum > or =800 sfu at f> or =2 GHz and Sp (200 MHz)<100 sfu (18%). Nine percent of the events had ''intermediate'' spectra with a maximum > or =800 sfu atmore » f> or =2 GHz and 100 sfu < or =Sp (200 MHz)<800 sfu. We were unable to classify 15% of the events because of incomplete data. The associations of the three classes of spectra with type II (and/or type IV) meter wavelength bursts and >10-MeV proton events of any size (> or =0.01 protons cm/sup -2/ s/sup -1/ sr/sup -1/) are as follows: U-shaped: type II/IV (90% of large microwave bursts with U-shaped spectra are associated with type II/IV events), protons (77%); intermediate: type II/IV (78%), protons (73%); and cutoff, type II/IV (22%), protons (33%). These statistics affirm various lines of evidence linking coronal shock waves and interplanetary proton events. They also suggest that the meter wavelength branch of the U-shaped spectrum may be attributable to second-phase (versus flash phase) accelerated electrons.« less
  • The light from a shock breakout of stellar explosions, which carries a wealth of information, strongly depends on the shock velocity at the time of the breakout. The emission from Newtonian breakouts, typical in regular core-collapse supernovae (SNe), has been explored extensively. However, a large variety of explosions result in mildly or ultrarelativistic breakouts, where the observed signature is unknown. Here we calculate the luminosity and spectrum produced by relativistic breakouts. In order to do so, we improve the analytic description of relativistic radiation-mediated shocks and follow the system from the breakout itself, through the planar phase and into themore » spherical phase. We limit our calculation to cases where the post-breakout acceleration of the gas ends during the planar phase (i.e., the final gas Lorentz factor {approx}< 30). We find that spherical relativistic breakouts produce a flash of gamma rays with energy, E{sub bo}, temperature, T{sub bo}, and duration, t{sup obs} b{sub o}, that provide the breakout radius ( Almost-Equal-To 5 R{sub Sun }(t{sup obs}{sub bo}/10 s)(T{sub bo}/50 keV){sup 2}) and the Lorentz factor ( Almost-Equal-To T{sub bo}/50 keV). They also always satisfy a relativistic breakout relation (t{sup obs}{sub bo}/20 s) {approx} (E{sub bo}/10{sup 46} erg){sup 1/2}(T{sub bo}/50 keV){sup -2.68}. The breakout flare is typically followed, on longer timescales, by X-rays that carry a comparable energy. We apply our model to a variety of explosions, including Type Ia and .Ia SNe, accretion-induced collapse, energetic SNe, and gamma-ray bursts (GRBs). We find that all these events produce detectable gamma-ray signals, some of which may have already been seen. Some particular examples are: (1) relativistic shock breakouts provide a natural explanation to the energy, temperature, and timescales of low-luminosity GRBs. Indeed, all observed low-luminosity GRBs satisfy the relativistic breakout relation. (2) Nearby broad-line Type Ib/c (like SN 2002ap) may produce a detectable {gamma}-ray signal. (3) Galactic Type Ia SNe may produce detectable {gamma}-ray flares. We conclude that relativistic shock breakouts provide a generic process for the production of gamma-ray flares.« less