Is spectral width a reliable measure of GRB emission physics?

Burgess, J. Michael

doi:10.1051/0004-6361/201935140

Cited by 25 publications

(20 citation statements)

References 48 publications

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“…The data of POLAR do not allow to determine the nature of the PA evolution for the two GRBs for which hints of it were found. The data are compatible with both random variations as well as a single 90 • change [104]. Finer time binning or higher statistics within the time bins are required to fully resolve this.…”

Section: Time-resolved Measurementsmentioning

confidence: 68%

“…This may become a problem in instances where such models are unable to capture the intrinsic complexity of the underlying data. Therefore, an arguably better approach is to directly fit physical models to the raw data to derive spectral parameters and remove any bias [103][104][105][106]. Such an approach has led to alleviating some of the issues encountered by the optically thin synchrotron model, where it was shown that direct spectral fits (in count space rather than energy space) with synchrotron emission from cooling power-law electrons can explain the low-energy spectral slopes as well as the spectral width of the peak [107].…”

Section: Optically-thin Synchrotron Emissionmentioning

confidence: 99%

“…Both for the instrument response and the data format, a standardized format is proposed similar to that used in spectrometry, and the tool can therefore easily be adapted for other polarimeters. The tool has been used first to analyze GRB 170114A [104] in detail using POLAR data, and subsequently to produce the full GRB catalog published by POLAR [187]. The POLAR data used for this analysis is furthermore public https://www.astro.unige.ch/polar/grb-light-curves (accessed on 25 August 2014), allowing further analysis by anyone interested as well as to perform rigorous tests of the validity of the different POLAR results.…”

Section: Need For Public Analysis Tools and Datamentioning

confidence: 99%

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GRB Polarization: A Unique Probe of GRB Physics

2021

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Over half a century from the discovery of gamma-ray bursts (GRBs), the dominant radiation mechanism responsible for their bright and highly variable prompt emission remains poorly understood. Spectral information alone has proven insufficient for understanding the composition and main energy dissipation mechanism in GRB jets. High-sensitivity polarimetric observations from upcoming instruments in this decade may help answer such key questions in GRB physics. This article reviews the current status of prompt GRB polarization measurements and provides comprehensive predictions from theoretical models. A concise overview of the fundamental questions in prompt GRB physics is provided. Important developments in gamma-ray polarimetry including a critical overview of different past instruments are presented. Theoretical predictions for different radiation mechanisms and jet structures are confronted with time-integrated and time-resolved measurements. The current status and capabilities of upcoming instruments regarding the prompt emission are presented. The very complimentary information that can be obtained from polarimetry of X-ray flares as well as reverse-shock and early to late forward-shock (afterglow) emissions are highlighted. Finally, promising directions for overcoming the inherent difficulties in obtaining statistically significant prompt-GRB polarization measurements are discussed, along with prospects for improvements in the theoretical modeling, which may lead to significant advances in the field.

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Section: Time-resolved Measurementsmentioning

confidence: 68%

Section: Optically-thin Synchrotron Emissionmentioning

confidence: 99%

Section: Need For Public Analysis Tools and Datamentioning

confidence: 99%

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GRB Polarization: A Unique Probe of GRB Physics

2021

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“…Simultaneous optical observations of the prompt γ-ray emission [45,61,66] provided interesting constraints on the broad-band spectral shape, the Lorentz factor, or the emission geometry. Detailed studies have been performed also on the shape of the prompt emission spectra, both on the sharpness of the peaks [176] as well as the conclusive answers provided by spectral fits with physical models [12,24,28,175] rather than empirical functions (like band, or cut-off power laws). Combined GBM and POLAR measurements of GRB 170111A provided further support for a synchrotron origin by revealing a smooth polarisation angle swing in concert with a declining peak energy [27].…”

Section: Glast/fermimentioning

confidence: 99%

Half-a-century of gamma-ray astrophysics at the Max-Planck Institute for Extraterrestrial Physics

Schönfelder

Greiner

2021

EPJ H

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Gamma-ray astronomy has been one of the prime scientific research fields of the Max-Planck Institute for Extraterrestrial Physics (MPE) from its beginning. Over the years, the entire gamma-ray energy range accessible from space was explored. The purpose of this review article is to summarise the achievements of the gamma-ray group at MPE during the last 50+ years. This covers a substantial part of the general history of space-based gamma-ray astronomy, for which both, general review articles (e.g. Pinkau in Exp Astron 5: 157, 2009; Schönfelder in AN 323: 524, 2002; Trimble in AIP Conf Proc 304: 40, 1994) and a detailed tabular list of events and missions (Leonard and Gehrels in https://heasarc.gsfc.nasa.gov/docs/history, version 1.0.8, 2009), have been compiled. Here, we describe the gamma-ray activities at MPE from the beginning till the present, reviewing the tight interplay between new technological developments towards new instruments and scientific progress in understanding gamma-ray sources in the sky. This covers (i) the early development of instruments and their tests on half a dozen balloon flights, (ii) the involvement in the most important space missions at the time, i.e. ESA’s COS-B satellite, NASA’s Compton Gamma-ray Observatory and Fermi Space Telescope, as well as ESA’s INTEGRAL observatory, (iii) the participation in several other missions such as TD-1, Solar Maximum Mission, or Ulysses, and (iv) the complementary ground-based optical instruments OPTIMA and GROND to enhance selected science topics (pulsars, gamma-ray bursts). With the gradual running-out of institutional support since 2010, gamma-ray astrophysics as a main research field has now come to an end at MPE.

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“…In addition, the authors did not attempt to fit this theoretical model to the data, which might introduce instrumental biases in the comparison with the Band fit results. Direct fits of the synchrotron emission model to GRB prompt spectra have been performed by Zhang et al (2016) and Burgess (2019), who showed that the line-of-death and spectralsharpness issues are likely artefacts due to the use of the Band function (see also Ronchi et al 2020). Fitting the spectra with simpler versions of the synchrotron emission model or with empirical functions featuring a low-energy spectral break, especially on a broad energy range extending down to the X-ray and/or optical domain, appears able to reconcile the observations with the synchrotron theory as well, showing the expected transition from fast to slow cooling (Oganesyan et al 2017(Oganesyan et al , 2018(Oganesyan et al , 2019Ravasio et al 2018Ravasio et al , 2019.…”

Section: Introductionmentioning

confidence: 99%

A new fitting function for GRB MeV spectra based on the internal shock synchrotron model

Yassine

Piron

Daigne

et al. 2020

A&A

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Aims. The physical origin of the gamma-ray burst (GRB) prompt emission is still a subject of debate. Internal shock models have been widely explored, owing to their ability to explain most of the high-energy properties of this emission phase. While the Band function or other phenomenological functions are commonly used to fit GRB prompt emission spectra, we propose a new parametric function that is inspired by an internal shock physical model. We use this function as a proxy of the model to compare it easily to GRB observations. Methods. We built a parametric function that represents the spectral form of the synthetic bursts provided by our internal shock synchrotron model (ISSM). We simulated the response of the Fermi instruments to the synthetic bursts and fit the obtained count spectra to validate the ISSM function. Then, we applied this function to a sample of 74 bright GRBs detected by the Fermi GBM, and we computed the width of their spectral energy distributions around their peak energy. For comparison, we also fit the phenomenological functions that are commonly used in the literature. Finally, we performed a time-resolved analysis of the broadband spectrum of GRB 090926A, which was jointly detected by the Fermi GBM and LAT. This spectrum has a complex shape and exhibits a power-law component with an exponential cutoff at high energy, which is compatible with inverse Compton emission attenuated by gamma-ray internal absorption. Results. This work proposes a new parametric function for spectral fitting that is based on a physical model. The ISSM function reproduces 81% of the spectra in the GBM bright GRB sample, versus 59% for the Band function, for the same number of parameters. It gives also relatively good fits to the GRB 090926A spectra. The width of the MeV spectral component that is obtained from the fits of the ISSM function is slightly larger than the width from the Band fits, but it is smaller when observed over a wider energy range. Moreover, all of the 74 analyzed spectra are found to be significantly wider than the synthetic synchrotron spectra. We discuss possible solutions to reconcile the observations with the internal shock synchrotron model, such as an improved modeling of the shock microphysics or more accurate spectral measurements at MeV energies.

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Is spectral width a reliable measure of GRB emission physics?

Cited by 25 publications

References 48 publications

GRB Polarization: A Unique Probe of GRB Physics

GRB Polarization: A Unique Probe of GRB Physics

Half-a-century of gamma-ray astrophysics at the Max-Planck Institute for Extraterrestrial Physics

A new fitting function for GRB MeV spectra based on the internal shock synchrotron model

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