Bulk Lorentz factors of gamma-ray bursts

Ghirlanda, G.; Nappo, F.; Ghisellini, G.; Melandri, A.; Marcarini, G.; Nava, Lara; Salafia, O. S.; Campana, S.; Salvaterra, R.

doi:10.1051/0004-6361/201731598

Cited by 120 publications

(176 citation statements)

References 143 publications

Supporting

Mentioning

149

Contrasting

Order By: Relevance

“…As compared to the standard values that are generally invoked for the prompt emitting region, the values we have inferred point to much larger radii, a much weaker magnetic field, quite large Γ (e.g. Ghirlanda et al 2018), and relatively low values of N e . The inferred location of the emitting region is very similar to the typical deceleration radius R dec .…”

Section: Discussionsupporting

confidence: 49%

Prompt optical emission as a signature of synchrotron radiation in gamma-ray bursts

Oganesyan

Nava

Ghirlanda

et al. 2019

A&A

Self Cite

100

124

View full text Add to dashboard Cite

Information on the spectral shape of prompt emission in gamma-ray bursts (GRB) is mostly available only at energies 10 keV, where the main instruments for GRB detection are sensitive. The origin of this emission is still very uncertain because of the apparent inconsistency with synchrotron radiation, which is the most obvious candidate, and the resulting need for considering less straightforward scenarios. The inclusion of data down to soft X-rays (∼ 0.5 keV), which are available only in a small fraction of GRBs, has firmly established the common presence of a spectral break in the low-energy part of prompt spectra, and even more importantly, the consistency of the overall spectral shape with synchrotron radiation in the moderately fast-cooling regime, the low-energy break being identified with the cooling frequency. In this work we further extend the range of investigation down to the optical band. In particular, we test the synchrotron interpretation by directly fitting a theoretically derived synchrotron spectrum and making use of optical to gamma-ray data. Secondly, we test an alternative model that considers the presence of a black-body component at ∼keV energies, in addition to a non-thermal component that is responsible for the emission at the spectral peak (100 keV-1 MeV). We find that synchrotron radiation provides a good description of the broadband data, while models composed of a thermal and a non-thermal component require the introduction of a low-energy break in the non-thermal component in order to be consistent with optical observations. Motivated by the good quality of the synchrotron fits, we explore the physical parameter space of the emitting region. In a basic prompt emission scenario we find quite contrived solutions for the magnetic field strength (5 G < B < 40 G) and for the location of the region where the radiation is produced (R γ > 10 16 cm). We discuss which assumptions of the basic model would need to be relaxed in order to achieve a more natural parameter space.

show abstract

Section: Discussionsupporting

confidence: 49%

Prompt optical emission as a signature of synchrotron radiation in gamma-ray bursts

Oganesyan

Nava

Ghirlanda

et al. 2019

A&A

Self Cite

100

124

View full text Add to dashboard Cite

show abstract

“…The level of dissipation was found to be around ∼ 5%, consistent with the internal shock scenario, and the luminosity and Lorentz factor of the model were found to be correlated. The latter has independently been reported in other studies (Lü et al 2012;Ghirlanda et al 2018). In our study there was no correlation between the fitted Band function α and β parameters and any properties of the fits using the DREAM model.…”

Section: Introductionsupporting

confidence: 88%

“…For this study we have expanded the model with additional grid points in Γ, extending the range down to 50 from 100 and from 500 up to 1000. We added these grid points to obtain a better coverage of values of Γ inferred from observations (Ghirlanda et al 2018). We have also added one additional grid point in L 0,52 , at 1000.…”

Section: Table Modelmentioning

confidence: 99%

Investigating Subphotospheric Dissipation in Gamma-Ray Bursts Using Joint Fermi–Swift Observations

Ahlgren

Larsson

Valan

et al. 2019

ApJ

View full text Add to dashboard Cite

The jet photosphere has been proposed as the origin for the gamma-ray burst (GRB) prompt emission. In many such models, characteristic features in the spectra appear below the energy range of the Fermi GBM detectors, so joint fits with X-ray data are important in order to assess the photospheric scenario. Here we consider a particular photospheric model which assumes localized subphotospheric dissipation by internal shocks in a non-magnetized outflow. We investigate it using Bayesian inference and a sample of 8 GRBs with known redshifts which are observed simultaneously with Fermi GBM and Swift XRT. This provides us with an energy range of 0.3 keV to 40 MeV and much tighter parameter constraints. We analyze 32 spectra and find that 16 are well described by the model. We also find that the estimates of the bulk Lorentz factor, Γ, and the fireball luminosity, L 0,52 , decrease while the fraction of dissipated energy, ε d , increase in the joint fits compared to GBM only fits. These changes are caused by a small excess of counts in the XRT data, relative to the model predictions from fits to GBM only data. The fact that our limited implementation of the physical scenario yields 50% accepted spectra is promising, and we discuss possible model revisions in the light of the new data. Specifically, we argue that the inclusion of significant magnetization, as well as removing the assumption of internal shocks, will provide better fits at low energies.

show abstract

“…We adopt p = 2.2 and εe = 0.1 as canonical values (Beniamini & van der Horst 2017). We also assumed a gamma-ray efficiency of ηγ = 0.2 (Beniamini et al 2015) to convert the gamma-ray energy released into blastwave kinetic energy E kin , and an outflow Lorentz factor Γ=300 (Ghirlanda, et al 2018).…”

Section: X-ray Constraintsmentioning

confidence: 99%

Short gamma-ray bursts within 200 Mpc

Dichiara

Troja

O’Connor

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We present a systematic search for short-duration gamma-ray bursts (GRBs) in the local Universe based on 14 years of observations with the Neil Gehrels Swift Observatory. We cross-correlate the GRB positions with the GLADE catalogue of nearby galaxies, and find no event at a distance 100 Mpc and four plausible candidates in the range 100 Mpc D 200 Mpc. Although affected by low statistics, this number is higher than the one expected for chance alignments to random galaxies, and possibly suggests a physical association between these bursts and nearby galaxies. By assuming a local origin, we use these events to constrain the range of properties for X-ray counterparts of neutron star mergers. Optical upper limits place tight constraints on the onset of a blue kilonova, and imply either low masses ( 10 −3 M ⊙ ) of lanthanidepoor ejecta or unfavorable orientations (θ obs 30 deg). Finally, we derive that the all-sky rate of detectable short GRBs within 200 Mpc is 1.3 +1.7 −0.8 yr −1 (68% confidence interval), and discuss the implications for the GRB outflow structure. If these candidates are instead of cosmological origin, we set a upper limit of 2.0 yr −1 (90% confidence interval) to the rate of nearby events detectable with operating gamma-ray observatories, such as Swift and Fermi.

show abstract

Bulk Lorentz factors of gamma-ray bursts

Cited by 120 publications

References 143 publications

Prompt optical emission as a signature of synchrotron radiation in gamma-ray bursts

Prompt optical emission as a signature of synchrotron radiation in gamma-ray bursts

Investigating Subphotospheric Dissipation in Gamma-Ray Bursts Using Joint Fermi–Swift Observations

Short gamma-ray bursts within 200 Mpc

Contact Info

Product

Resources

About