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

Yassine, M.; Piron, F.; Daigne, F.; Mochkovitch, R.; Longo, F.; Omodei, N.; Vianello, G.

doi:10.1051/0004-6361/201937057

Cited by 10 publications

(6 citation statements)

References 58 publications

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“…However, recent studies show that the Band function is a poor model for the physical emission spectra (e.g., Burgess et al (2015), Burgess et al (2019a), Zhang et al (2019b) ) and should only be used as a qualitative description of the spectra such as the peak energy and flux. However, Yassine et al (2019) also show that the Band function may not adequately model the true peak energy either. The use of physical models to perform the analysis, as in Burgess et al (2019b), would be preferable to avoid overinterpretation of the spectral parameters found using empirical models.…”

Section: Catalog Analysismentioning

confidence: 96%

The POLAR gamma-ray burst polarization catalog

Kole

Angelis²,

Berlato³

et al. 2020

A&A

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Context. Despite over 50 years of research, many open questions remain about the origin and nature of gamma-ray bursts (GRBs). Linear polarization measurements of the prompt emission of these extreme phenomena have long been thought to be key to answering a range of these questions. The POLAR detector was designed to produce the first set of detailed and reliable linear polarization measurements in the 50 − 500 keV energy range. During late 2016 and early 2017, POLAR detected a total of 55 GRBs. The analysis results of 5 of these GRBs have been reported, and were found to be consistent with a low or unpolarized flux. However, previous reports by other collaborations found high levels of linear polarization, including some as high as 90%. Aims. We study the linear polarization for the 14 GRBs observed by POLAR for which statistically robust inferences are possible. Additionally, time-resolved polarization studies are performed on GRBs with sufficient apparent flux. Methods. A publicly available polarization analysis tool, developed within the Multi-Mission Maximum Likelihood framework (3ML), was used to produce statistically robust results. The method allows spectral and polarimetric data from POLAR to be combined with spectral data from the Fermi Gamma-ray Burst Monitor (Fermi-GBM) and the Neil Gehrels Swift Observatory (hereafter Swift) to jointly model the spectral and polarimetric parameters. Results. The time-integrated analysis finds all results to be compatible with low or zero polarization with the caveat that, when timeresolved analysis is possible within individual pulses, we observe moderate linear polarization with a rapidly changing polarization angle. Therefore, time-integrated polarization results, while pointing to lower polarization, are potentially an artifact of summing over the changing polarization signal and thus washing out the true moderate polarization. We therefore caution against overinterpretation of any time-integrated results inferred herein and encourage the community to wait for more detailed polarization measurements from forthcoming missions such as POLAR-2 and LEAP.

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Section: Catalog Analysismentioning

confidence: 96%

The POLAR gamma-ray burst polarization catalog

Kole

Angelis²,

Berlato³

et al. 2020

A&A

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“…In this analysis, threeML offered the full accuracy of the LAT unbinned likelihood technique, which is lost during the binning in space and energy that is required by pyXSPEC. We considered the spectral models Band [5] and ISSM [6], both having four parameters. Additionally, we considered the models obtained by multiplying these functions by a high-energy exponential cutoff (∝ 𝑒 −𝐸/𝐸 𝑐𝑢𝑡 ).…”

Section: Analysis Proceduresmentioning

confidence: 99%

Constraining the prompt emission region and the ejecta speed of the distant GRB 220101A

Scotton¹,

Piron²,

Omodei³

et al. 2023

Proceedings of 7th Heidelberg International Symposium on High-Energy Gamma-Ray Astronomy — PoS(Gamma2022)

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GRB 220101A is the most distant gamma-ray burst detected by Fermi-LAT to date (z = 4.618). It is a very energetic event, with an equivalent isotropic energy 𝐸 𝑖𝑠𝑜 ∼ 3.3 × 10 54 erg. We jointly analysed Fermi-GBM and LAT data with two analysis chains and obtained consistent results. They reveal a spectral break below 100 MeV in the LAT Low Energy (LLE) range during the prompt emission, associated with fast variability, which suggests that the spectral attenuation is caused by internal opacity to pair creation. Regardless of the nature of the emission processes, we find that the keV and MeV emissions were produced co-spatially above and close to the photosphere, with a moderate Lorentz factor Γ 𝑏𝑢𝑙𝑘 ∼ 100. Here we present this study and compare our findings with other LAT-detected bursts with similar properties.

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“…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%

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

Cited by 10 publications

References 58 publications

The POLAR gamma-ray burst polarization catalog

The POLAR gamma-ray burst polarization catalog

Constraining the prompt emission region and the ejecta speed of the distant GRB 220101A

GRB Polarization: A Unique Probe of GRB Physics

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