Spectral evolution of GRB pulses

Kargatis, Vincent E.; Liang, Edison; Nasa, Nasa; Cass, Ucsd

doi:10.1007/bf00658611

Cited by 18 publications

(24 citation statements)

References 6 publications

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“…As mentioned above, Kargatis et al (1995) found a central value ofγ ∼ 1.7, which is somewhat lower than ours. However, their sample of 28 pulses was taken from 15 multi-pulse GRBs.…”

Section: The Distribution Of Plhic Indices Among Burstscontrasting

confidence: 78%

“…Kargatis et al (1995) found the PLHIC in 28 pulse decays from 15 bursts, out of a total of 26 GRBs with prominent pulses studied. The distribution of the correlation index peaks at 1.7 and has a substantial spread.…”

Section: The Relation Between Hardness and Intensitymentioning

confidence: 92%

“…In studies of the spectral/temporal evolution, other workers (e.g., Kargatis et al 1995;Liang & Kargatis 1996) have fixed the parameters α and β to reduce the estimated uncertainties of E pk . For instance, the parameter values of the time-integrated spectrum can be used.…”

Section: Track Jumps and Overlapping Pulsesmentioning

confidence: 99%

“…However, this has been done for the Hardness-Fluence Correlation by Liang & Kargatis (1996) and by Crider et al (1999). Corresponding studies of the HIC have been mainly discussed in Kargatis et al (1995).…”

Section: Introductionmentioning

confidence: 99%

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On the Hardness‐Intensity Correlation in Gamma‐Ray Burst Pulses

Borgonovo

Ryde

2001

ApJ

115

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We study the hardness-intensity correlation (HIC) in gamma-ray bursts (GRBs). In particular, we analyze the decay phase of pulse structures in their light curves. The study comprises a sample of 82 long pulses selected from 66 long bursts observed by the Burst And Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory. We find that at least 57% of these pulses have HICs that can be well described by a power law. A number of the other cases can still be explained with the power law model if various limitations of the observations are taken into account.The distribution of the power law indices γ, obtained by modeling the HIC of pulses from different bursts, is broad with a mean of 1.9 and a standard deviation of 0.7. We also compare indices among pulses from the same bursts and find that their distribution is significantly narrower. The probability p of a random coincidence is shown to be very small (< 2 × 10 −5 ). In most cases, the indices are equal to within the uncertainties. These results demand a physical model to be able to reproduce multiple pulses with similar characteristics for an individual burst, but with a large diversity for pulses from an ensemble of bursts. This is particularly relevant when comparing the external versus the internal models.In our analysis, we also use a new method for studying the hardness-intensity correlation, in which the intensity is represented by the peak value of the EF E spectrum, where E is the energy and F E is the energy flux spectrum. We compare it to the traditional method in which the intensity over a finite energy range is used instead, which may be an incorrect measure of the bolometric intensity. This new method gives stronger correlations and is useful in the study of various aspects of the HIC. In particular, it produces a better agreement between indices of different pulses within the same burst. Also, we find that some pulses exhibit a track jump in their HICs, in which the correlation jumps between two power laws with the same index. We discuss the possibility that the track jump is caused by strongly overlapping pulses. Based on our findings, the constancy of the index is proposed to be used as a tool for pulse identification in overlapping pulses and examples of its application are given.

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“…As mentioned above, Kargatis et al (1995) found a central value ofγ ∼ 1.7, which is somewhat lower than ours. However, their sample of 28 pulses was taken from 15 multi-pulse GRBs.…”

Section: The Distribution Of Plhic Indices Among Burstscontrasting

confidence: 78%

Section: The Relation Between Hardness and Intensitymentioning

confidence: 92%

Section: Track Jumps and Overlapping Pulsesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the Hardness‐Intensity Correlation in Gamma‐Ray Burst Pulses

Borgonovo

Ryde

2001

ApJ

115

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“…Recently, quantitative studies of the spectral behavior of GRB pulses were made by many authors [17,[30][31][32][33]. It was found that the hardness-intensity correlation obtained from the statistical analysis was regarded as a result of the spectral evolution, could be accounted for by the curvature effect [17].…”

Section: Introductionmentioning

confidence: 99%

Hardness ratio evolutionary curves of gamma-ray bursts expected by the curvature effect

Qin

Fan

et al. 2006

Phys. Rev. D

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Hardness ratio evolutionary curves of gamma-ray bursts expected by the curvature effect AbstractWe have investigated the gamma-ray bursts (GRBs) pulses with a fast rise and an exponential decay phase, assumed to arise from relativistically expending fireballs, and found that the curvature effect influences the evolutionary curve of the corresponding hardness ratio (hereafter HRC). We find, due to the curvature effect, the evolutionary curve of the pure hardness ratio (when the background count is not included) would peak at the very beginning of the curve, and then would undergo a drop-to-rise-to-decay phase. In the case of the raw hardness ratio (when the background count is included), the curvature effect would give rise to several types of evolutionary curve, depending on the hardness of a burst. For a soft burst, an upside-down pulse of its raw HRC would be observed; for a hard burst, its raw HRC shows a pulse-like profile with a sinkage in its decaying phase; for a very hard burst, the raw HRC possesses a pulse-like profile without a sinkage in its decaying phase. For a pulse-like raw HRC as shown in the case of the hard and very hard bursts, its peak would appear in advance of that of the corresponding light curve, which was observed previously in some GRBs. For illustration, we have studied here the HRC of GRB 920216, GRB 920830 and GRB 990816 in detail. The features of the raw HRC expected in the hard burst are observed in these bursts. A fit to the three bursts shows that the curvature effect alone could indeed account for the predicted characteristics of HRCs. In addition, we find that the observed hardness ratio tends to be harder at the beginning of the pulses than what the curvature effect could predict and be softer at the late time of the pulses. We believe this is an evidence showing the existence of intrinsic hard-to-soft radiation which might be due to the acceleration-to-deceleration mode of shocks.PACS numbers: 98.70. Rz,

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Spectral evolution in gamma-ray bursts: Predictions of the internal shock model and comparison to observations

Bošnjak

Daigne

2014

A&A

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Context. Several trends have been identified in the prompt gamma-ray burst (GRB) emission: e.g. hard-to-soft evolution, pulse width evolution with energy, time lags, and hardness-intensity and hardness-fluence correlations. Recently, Fermi has significantly extended the spectral coverage of GRB observations and improved the characterization of this spectral evolution. Aims. We want to study how internal shocks can reproduce these observations. In this model the emission comes from the synchrotron radiation of shock accelerated electrons, and the spectral evolution is governed by the evolution of the physical conditions in the shocked regions.Methods. We present a comprehensive set of simulations of a single pulse and investigate the impact of the model parameters, related to the shock microphysics and to the initial conditions in the ejecta. Results. We find general qualitative agreement between the model and the various observations used for the comparison. All these properties or relations are governed by the evolution of the peak energy and photon indices of the spectrum. In addition, we identify the conditions for quantitative agreement. We find that the best agreement is obtained for (i) steep electron slopes (p > ∼ 2.7); (ii) microphysics parameters varying with shock conditions so that more electrons are accelerated in stronger shocks; and (iii) steep variations in the initial Lorentz factor in the ejecta. When simulating short GRBs by contracting all timescales, all other parameters being unchanged, we show that the hardness-duration correlation is reproduced, as well as the evolution with duration of the pulse properties. Finally, we investigate the signature at high energy of these different scenarios and find distinct properties -delayed onset, longer emission, and flat spectrum in some cases -suggesting that internal shocks could have a significant contribution to the prompt LAT emission. Conclusions. Spectral evolution is an important property of GRBs that is not easily reproduced in most models for the prompt emission. We find that the main observed features can be accounted for in a quantitative way within the internal shock model. However, the current uncertainties on shock acceleration in the mildly relativistic regime and relativistic ejection by compact sources prevent us from deciding if one or several of the proposed scenario are viable. By combining observations over the whole spectral range of Fermi, it may be possible in the future to identify specific signatures imprinted by this uncertain underlying physics.

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Spectral evolution of GRB pulses

Cited by 18 publications

References 6 publications

On the Hardness‐Intensity Correlation in Gamma‐Ray Burst Pulses

On the Hardness‐Intensity Correlation in Gamma‐Ray Burst Pulses

Hardness ratio evolutionary curves of gamma-ray bursts expected by the curvature effect

Spectral evolution in gamma-ray bursts: Predictions of the internal shock model and comparison to observations

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