Low-frequency spectra of gamma-ray bursts

Katz, J. I.

doi:10.1086/187523

Cited by 261 publications

(236 citation statements)

References 23 publications

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“…• verify the strongest prediction of the synchrotron theory of a low energy spectral shape not evolving and fixed to −2/3 (Katz et al 1994). For clarity we first present the results for the time integrated (Sect.…”

Section: Resultsmentioning

confidence: 58%

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Time resolved spectral analysis of bright gamma ray bursts

Ghirlanda

Celotti

Ghisellini

2002

A&A

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Abstract. We present the time integrated and time resolved spectral analysis of a sample of bright bursts selected with F peak ≥ 20 phot cm −2 s −1 from the BATSE archive. We fitted four different spectral models to the pulse time integrated and time resolved spectra. We compare the low energy slope of the fitted spectra with the prediction of the synchrotron theory [predicting photon spectra softer than N(E) ∝ E −2/3 ], and test, through direct spectral fitting, the synchrotron shock model. We point out that differences in the parameters distribution can be ascribed to the different spectral shape of the models employed and that in most cases the spectrum can be described by a smoothly curved function. The synchrotron shock model does not give satisfactory fits to the time averaged and time resolved spectra. Finally, we derive that the synchrotron low energy limit is violated in a considerable number of spectra both during the rise and decay phase around the peak.

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Section: Resultsmentioning

confidence: 58%

“…Alternative spectral models -and in particular the predictions for synchrotron emission (Katz 1994;Crider et al 1997a,b) -have also been recently tested on a large sample of time resolved spectra by Preece and collaborators (Preece et al 2000).…”

Section: Introductionmentioning

confidence: 99%

Time resolved spectral analysis of bright gamma ray bursts

Ghirlanda

Celotti

Ghisellini

2002

A&A

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“…The gamma-ray burst GRB 970228 [1,2] has been observed after a delay of [8][9][10][11][12][13][14][15][16][17] hours in x rays [3] and of 17 hours in visible light [4]. This marks the first detection of emission at lower frequencies following the gamma-ray observation of a gamma-ray burst (GRB) and the first detection of any visible counterpart to a GRB.…”

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confidence: 99%

“…It also leads to a specific prediction for its spectrum, which may be roughly tested with the data at hand. The instantaneous spectrum of a relativistic shock is predicted [15,16] to be F n~n 1͞3 . The spectrum integrated over the radiative decay of the electrons' energy is predicted [17] to be F n~n 21͞2 .…”

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confidence: 99%

Implications of the Visible and X-Ray Counterparts to GRB 970228

1998

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We propose that the visible and x-ray emission associated with the cosmic gamma-ray burst GRB 970228 but following it by hours and days was produced by a weaker continuation of the processes which produced the gamma-ray burst itself. This hypothesis predicts an instantaneous spectrum F n~n 21͞2 , resulting from radiative cooling of synchrotron-emitting electrons, at frequencies from the infrared to x rays and higher. The limited data support this prediction. [S0031-9007(98) The gamma-ray burst GRB 970228 [1,2] has been observed after a delay of 8-17 hours in x rays [3] and of 17 hours in visible light [4]. This marks the first detection of emission at lower frequencies following the gamma-ray observation of a gamma-ray burst (GRB) and the first detection of any visible counterpart to a GRB. We consider possible delayed visible and x-ray emission mechanisms, and conclude that the activity by the source of the GRB continued at a much reduced intensity for at least a day. There are hints of such continued activity in other GRB, and future observations can decide if this is true of GRB in general. The observed simultaneous multiband spectrum of GRB 970228 agrees with the predictions of relativistic shock theory when the flux is integrated over a time longer than that required for a radiating electron to lose its energy.Several mechanisms for the continuing x-ray emission of GRB 970228 should be considered. The simplest possibility is that the relativistic particles required to explain a GRB will collide with a surrounding dilute medium. This process has been suggested [5] as the source of the gamma-ray emission itself. These models face, however, a serious problem. The observed duration of x-ray emission [3] is roughly 1000 times the reported gamma-ray duration [1], despite a ratio of only ϳ50 in the observed frequency n obs . Most models of this type predict a much steeper decrease in frequency as a function of time. A specific calculation [6] predicts, for example, a time scale of emission~n 25͞12 obs . One can consider, alternatively, models in which hot electrons cool, and emit lower energy photons. These models face the same problem. For example, a model [7] in which relativistic electrons radiate their energy in a constant magnetic field predicts a time scale~n 21͞2obs . Another alternative model of the x-ray emission, thermal bremsstrahlung (as in a supernova remnant), may also be excluded because the required power ϳ10 45 erg͞s (at a cosmological redshift of a few tenths) would require an unachievable particle density .10 10 cm 23 even if the maximum plausible mass of 1M Ø is radiating.Instead, we suggest that the observed brief intense gamma-ray emission of a GRB is only the "tip of an iceberg"; it emits gamma rays at a much lower level for time of order a day following (and perhaps preceding) the intense outburst. GRB detectors necessarily have high backgrounds because they must have very broad angular acceptance; these high backgrounds, lack of angular discrimination, and necessarily short integration tim...

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“…The discovery of GRB afterglow emission in X-ray (Costa et al 1997), optical (van Paradijs et al 1997) and radio wavelengths (Frail et al 1997) confirmed (Waxman 1997, Wijers, Rees & Mészáros 1997, standard model predictions of afterglow (Paczyński & Rhoads 1993, Kats 1994, Vietri 1997) that results from the collision of the expanding fireball with surrounding medium.…”

Section: Introductionmentioning

confidence: 94%

Efficiency and Spectrum of Internal $\gamma$ -Ray Burst Shocks

Spada¹,

Guetta²,

Waxman³

Gamma-Ray Bursts in the Afterglow Era

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We present an analysis of the Internal Shock Model of GRBs, where gamma-rays are produced by internal shocks within a relativistic wind. We show that observed GRB characteristics impose stringent constraints on wind and source parameters. We find that a significant fraction, of order 20%, of the wind kinetic energy can be converted to radiation, provided the distribution of Lorentz factors within the wind has a large variance and provided the minimum Lorentz factor is > Γ ± ≈ 10 2.5 L 2/9 52 , where L = 10 52 L 52 erg s −1 is the wind luminosity. For a high, > 10%, efficiency wind, spectral energy breaks in the 0.1 to 1 MeV range are obtained for sources with dynamical time R/c ∼ < 1 ms, suggesting a possible explanation for the observed clustering of spectral break energies in this range. The lower limit Γ ± to wind Lorenz factor and the upper limit ≈ 1(R/10 7 cm) −5/6 MeV to observed break energies are set by Thomson optical depth due to e ± pairs produced by synchrotron photons. Natural consequences of the model are absence of bursts with peak emission energy significantly exceeding 1 MeV, and existence of low luminosity bursts with low, 1 keV to 10 keV, break energies.

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Low-frequency spectra of gamma-ray bursts

Cited by 261 publications

References 23 publications

Time resolved spectral analysis of bright gamma ray bursts

Time resolved spectral analysis of bright gamma ray bursts

Implications of the Visible and X-Ray Counterparts to GRB 970228

Efficiency and Spectrum of Internal $\gamma$ -Ray Burst Shocks

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