Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 202) Show all publications
Yu, H.-F., Dereli-Begue, H. & Ryde, F. (2019). Bayesian Time-resolved Spectroscopy of GRB Pulses. Astrophysical Journal, 886(1), Article ID 20.
Open this publication in new window or tab >>Bayesian Time-resolved Spectroscopy of GRB Pulses
2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 886, no 1, article id 20Article in journal (Refereed) Published
Abstract [en]

We performed time-resolved spectroscopy on a sample of 38 single pulses from 37 gamma-ray bursts detected by the Fermi/Gamma-ray Burst Monitor during the first 9 yr of its mission. For the first time a fully Bayesian approach is applied. A total of 577 spectra are obtained and their properties studied using two empirical photon models, namely the cutoff power law (CPL) and Band model. We present the obtained parameter distributions, spectral evolution properties, and parameter relations. We also provide the result files containing this information for usage in further studies. It is found that the CPL model is the preferred model, based on the deviance information criterion and the fact that it consistently provides constrained posterior density maps. In contrast to previous works, the high-energy power-law index of the Band model, ?, has in general a lower value for the single pulses in this work. In particular, we investigate the individual spectrum in each pulse, that has the largest value of the low-energy spectral indexes, ?. For these 38 spectra, we find that 60% of the ? values are larger than ?2/3, and thus incompatible with synchrotron emission. Finally, we find that the parameter relations show a variety of behaviors. Most noteworthy is the fact that the relation between ? and the energy flux is similar for most of the pulses, independent of any evolution of the other parameters.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
Keywords
catalogs, gamma-ray burst: general, methods: statistical
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-265464 (URN)10.3847/1538-4357/ab488a (DOI)000499347600001 ()2-s2.0-85077333717 (Scopus ID)
Note

QC 20191217

Available from: 2019-12-17 Created: 2019-12-17 Last updated: 2020-03-09Bibliographically approved
Ahlgren, B., Larsson, J., Valan, V., Mortlock, D., Ryde, F. & Pe'er, A. (2019). Investigating Subphotospheric Dissipation in Gamma-Ray Bursts Using Joint Fermi-Swift Observations. Astrophysical Journal, 880(2), Article ID 76.
Open this publication in new window or tab >>Investigating Subphotospheric Dissipation in Gamma-Ray Bursts Using Joint Fermi-Swift Observations
Show others...
2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 880, no 2, article id 76Article in journal (Refereed) Published
Abstract [en]

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 Gamma-ray Burst Monitor (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 eight GRBs with known redshifts which are observed simultaneously with Fermi GBM and the Swift X-ray Telescope (XRT). This provides us with an energy range of 0.3. keV-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, Gamma, and the fireball luminosity, L-0,L-52, decrease while the fraction of dissipated energy, epsilon(d), increases 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.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
gamma-ray burst: general, methods: data analysis, radiation mechanisms: thermal
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-257565 (URN)10.3847/1538-4357/ab271b (DOI)000478778000004 ()2-s2.0-85071947863 (Scopus ID)
Note

QC 20190923

Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2019-09-23Bibliographically approved
Acuner, Z., Ryde, F. & Yu, H.-F. (2019). Non-dissipative photospheres in GRBs: spectral appearance in the Fermi/GBM catalogue. Monthly notices of the Royal Astronomical Society, 487(4), 5508-5519
Open this publication in new window or tab >>Non-dissipative photospheres in GRBs: spectral appearance in the Fermi/GBM catalogue
2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 487, no 4, p. 5508-5519Article in journal (Refereed) Published
Abstract [en]

A large fraction of gamma-ray burst (GRB) spectra are very hard below the peak. Indeed, the observed distribution of sub-peak power-law indices, alpha, has been used as an argument for a photospheric origin of GRB spectra. Here, we investigate what fraction of GRBs have spectra that are consistent with emission from a photopshere in a non-dissipative outflow. This is the simplest possible photospheric emission scenario. We create synthetic spectra, with a range of peak energies, by folding the theoretical predictions through the detector response of the FERMI/GBM detector. These simulated spectral data are fitted with typically employed empirical models. We find that the low-energy photon indices obtain values ranging -0.4 < alpha < 0.0, peaking at around -0.1, thus covering a non-negligible fraction of observed values. These values are significantly softer than the asymptotic value of the theoretical spectrum of alpha similar to 0.4. The reason for the alpha values to be much softer than expected, is the limitation of the empirical functions to capture the true curvature of the theoretical spectrum. We conclude that more than a quarter of the bursts in the GBM catalogue have at least one time-resolved spectrum, whose alpha values are consistent with spectra from a non-dissipative outflow, releasing its thermal energy at the photosphere. The fraction of spectra consistent with emission from the photosphere will increase even more if dissipation of kinetic energy in the flow occurs below the photosphere.

Place, publisher, year, edition, pages
Oxford University Press, 2019
Keywords
radiation mechanisms: thermal, methods: data analysis, methods: numerical, gamma-ray burst: general
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-255552 (URN)10.1093/mnras/stz1356 (DOI)000475888500077 ()2-s2.0-85070069004 (Scopus ID)
Note

QC 20190805

Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2020-03-09Bibliographically approved
Ryde, F., Yu, H.-F., Dereli-Begue, H., Lundman, C., Pe'er, A. & Li, L. (2019). On the alpha-intensity correlation in gamma-ray bursts: subphotospheric heating with varying entropy. Monthly notices of the Royal Astronomical Society, 484(2), 1912-1925
Open this publication in new window or tab >>On the alpha-intensity correlation in gamma-ray bursts: subphotospheric heating with varying entropy
Show others...
2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 484, no 2, p. 1912-1925Article in journal (Refereed) Published
Abstract [en]

The emission mechanism during the prompt phase in gamma-ray bursts (GRBs) can be investigated through correlations between spectral properties. Here, we revisit the correlation relating the instantaneous flux, F, and the photon index below the spectral break, alpha, in individual emission pulses, by studying the 38 most prominent pulses in the Fermi/Gamma-ray Burst Monitor GRB catalogue. First, we search for signatures of the bias in the determination of alpha due to the limited spectral coverage (window effect) expected in the synchrotron case. The absence of such a characteristic signature argues against the simplest synchrotron models. We instead find that the observed correlation between F and alpha can, in general, be described by the relation F(t) proportional to e(k alpha(t)), for which the median k = 3. We suggest that this correlation is a manifestation of subphotospheric heating in a flow with a varying entropy. Around the peak of the light curve, a large entropy causes the photosphere to approach the saturation radius, leading to an intense emission with a narrow spectrum. As the entropy decreases the photosphere secedes from the saturation radius, and weaker emission with a broader spectrum is expected. This simple scenario naturally leads to a correlated variation of the intensity and spectral shape, covering the observed range.

Place, publisher, year, edition, pages
Oxford University Press, 2019
Keywords
gamma-ray burst: general, gamma-ray burst: individual, radiation mechanism: thermal, methods: data analysis
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-249863 (URN)10.1093/mnras/stz083 (DOI)000462302600034 ()2-s2.0-85063384317 (Scopus ID)
Note

QC 20190426

Available from: 2019-04-26 Created: 2019-04-26 Last updated: 2019-04-26Bibliographically approved
Pearce, M., Eliasson, L., Iyer, N., Kiss, M., Kushwah, R., Larsson, J., . . . Xie, F. (2019). Science prospects for SPHiNX - A small satellite GRB polarimetry mission. Astroparticle physics, 104, 54-63
Open this publication in new window or tab >>Science prospects for SPHiNX - A small satellite GRB polarimetry mission
Show others...
2019 (English)In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 104, p. 54-63Article in journal (Refereed) Published
Abstract [en]

Gamma-ray bursts (GRBs) are exceptionally bright electromagnetic events occurring daily on the sky. The prompt emission is dominated by X-/gamma-rays. Since their discovery over 50 years ago, GRBs are primarily studied through spectral and temporal measurements. The properties of the emission jets and underlying processes are not well understood. A promising way forward is the development of missions capable of characterising the linear polarisation of the high-energy emission. For this reason, the SPHiNX mission has been developed for a small-satellite platform. The polarisation properties of incident high-energy radiation (50-600 keV) are determined by reconstructing Compton scattering interactions in a segmented array of plastic and Gd3Al2Ga3O12(Ce) (GAGG(Ce)) scintillators. During a two-year mission, similar to 200 GRBs will be observed, with similar to 50 yielding measurements where the polarisation fraction is determined with a relative error <= 10%. This is a significant improvement compared to contemporary missions. This performance, combined with the ability to reconstruct GRB localisation and spectral properties, will allow discrimination between leading classes of emission models.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Polarimetry, X-ray, Gamma-ray burst, Small satellite
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-238104 (URN)10.1016/j.astropartphys.2018.08.007 (DOI)000447479300004 ()2-s2.0-85052499332 (Scopus ID)
Note

QC 20190111

Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-11Bibliographically approved
Ahlgren, B., Larsson, J., Ahlberg, E., Lundman, C., Ryde, F. & Pe'er, A. (2019). Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario. Monthly notices of the Royal Astronomical Society, 485, 474-497
Open this publication in new window or tab >>Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario
Show others...
2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, p. 474-497Article in journal (Refereed) Published
Abstract [en]

It has been suggested that the prompt emission in gamma-ray bursts (GRBs) could be described by radiation from the photosphere in a hot fireball. Such models must be tested by directly fitting them to data. In this work we use data from the Fermi Gamma-ray Space Telescope and consider a specific photospheric model, in which the kinetic energy of a low-magnetization outflow is dissipated locally by internal shocks below the photosphere. We construct a table model with a physically motivated parameter space and fit it to time-resolved spectra of the 36 brightest Fermi GRBs with a known redshift. We find that about two-thirds of the examined spectra cannot be described by the model, as it typically underpredicts the observed flux. However, since the sample is strongly biased towards bright GRBs, we argue that this fraction will be significantly lowered when considering the full population. From the successful fits we find that the model can reproduce the full range of spectral slopes present in the sample. For these cases we also find that the dissipation consistently occurs at a radius of ∼1012 cm and that only a few per cent efficiency is required. Furthermore, we find a positive correlation between the fireball luminosity and the Lorentz factor. Such a correlation has been previously reported by independent methods. We conclude that if GRB spectra are due to photospheric emission, the dissipation cannot only be the specific scenario we consider here.

Keywords
gamma-ray burst
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-245227 (URN)10.1093/mnras/stz110 (DOI)000466786400034 ()2-s2.0-85070108669 (Scopus ID)
Note

QC 20190308

Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2020-03-09Bibliographically approved
Samuelsson, F., Begue, D., Ryde, F. & Pe'er, A. (2019). The Limited Contribution of Low- and High-luminosity Gamma-Ray Bursts to Ultra-high-energy Cosmic Rays. Astrophysical Journal, 876(2), Article ID 93.
Open this publication in new window or tab >>The Limited Contribution of Low- and High-luminosity Gamma-Ray Bursts to Ultra-high-energy Cosmic Rays
2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 876, no 2, article id 93Article in journal (Refereed) Published
Abstract [en]

The acceleration site for ultra-high-energy cosmic rays (UHECRs) is still an open question despite extended research. In this paper, we reconsider the prompt phase of gamma-ray bursts (GRBs) as a possible candidate for this acceleration and constrain the maximum proton energy in optically thin synchrotron and photospheric models, using properties of the prompt photon spectra. We find that neither of the models favors acceleration of protons to 10(20) eV in high-luminosity bursts. We repeat the calculations for low-luminosity GRBs (llGRBs) considering both protons and completely stripped iron and find that the highest obtainable energies are < 10(19) eV and < 10(20) eV for protons and iron respectively, regardless of the model. We conclude therefore that for our fiducial parameters, GRBs, including low-luminosity bursts, contribute little to nothing to the UHECRs observed. We further constrain the conditions necessary for an association between UHECRs and llGRBs and find that iron can be accelerated to 1020 eV in photospheric models, given very efficient acceleration and/or a small fractional energy given to a small fraction of accelerated electrons. This will necessarily result in high prompt optical fluxes, and the detection of such a signal could therefore be an indication of successful UHECR acceleration at the source.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
cosmic rays, gamma-ray burst: general
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-252607 (URN)10.3847/1538-4357/ab153c (DOI)000467460700004 ()2-s2.0-85067286419 (Scopus ID)
Note

QC 20190610

Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2020-03-09Bibliographically approved
Sharma, V., Iyyani, S., Bhattacharya, D., Chattopadhyay, T., Rao, A. R., Aarthy, E., . . . Pe'er, A. (2019). Time-varying Polarized Gamma-Rays from GRB 160821A: Evidence for Ordered Magnetic Fields. Astrophysical Journal Letters, 882(1), Article ID L10.
Open this publication in new window or tab >>Time-varying Polarized Gamma-Rays from GRB 160821A: Evidence for Ordered Magnetic Fields
Show others...
2019 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 882, no 1, article id L10Article in journal (Refereed) Published
Abstract [en]

GRB 160821A is the third most energetic gamma-ray burst observed by the Fermi gamma-ray space telescope. Based on the observations made by the Cadmium Zinc Telluride Imager on board AstroSat, here we report the most conclusive evidence to date of (i) high linear polarization (66(27)(+26)%; 5.3 sigma detection), and (ii) variation of polarization angle with time, occurring twice during the rise and decay phase of the burst at 3.5 sigma and 3.1 sigma detections, respectively. All confidence levels are reported for two parameters of interest. These observations strongly suggest synchrotron radiation produced in magnetic field lines that are highly ordered on angular scales of 1/Gamma, where Gamma is the Lorentz factor of the outflow.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-260183 (URN)10.3847/2041-8213/ab3a48 (DOI)000484250100005 ()2-s2.0-85072612704 (Scopus ID)
Note

QC 20190930

Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2019-09-30Bibliographically approved
Acuner, Z. & Ryde, F. (2018). Appearances of the jet photosphere in GRB spectra. In: 14th Marcel Grossman Meeting On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories, Proceedings: . Paper presented at 14th Marcel Grossman Meeting On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories, 12 July 2015 through 18 July 2015 (pp. 2921-2930). World Scientific Publishing Co. Pte. Ltd.
Open this publication in new window or tab >>Appearances of the jet photosphere in GRB spectra
2018 (English)In: 14th Marcel Grossman Meeting On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories, Proceedings, World Scientific Publishing Co. Pte. Ltd. , 2018, p. 2921-2930Conference paper, Published paper (Refereed)
Abstract [en]

There are several strong arguments for considering photospheric emission in GRBs. Here, we describe the two main appearances of the photospheric emission that are currently discussed. In the multi-component models the photosphere only contributes to a part of the spectrum, while the main part is due to optically-thin synchrotron emission. In the photospheric emission models the whole emission spectrum is from the photosphere: The emission spectrum has been altered due to subphotospheric dissipation and/or off-axis emission. In many cases, though, it is difficult to distinguish between these models on a purely statistical ground. Therefore, more detailed predictions from different physical scenarios should be tested on the observations.

Place, publisher, year, edition, pages
World Scientific Publishing Co. Pte. Ltd., 2018
Keywords
GRBs, Thermal emission, Astrophysics, Emission spectroscopy, Emission spectrums, Multicomponent model, Off-axis, Photospheric emission, Physical scenario, Synchrotron emission, Thermal emissions, Relativity
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-247441 (URN)2-s2.0-85059092983 (Scopus ID)9789813226593 (ISBN)
Conference
14th Marcel Grossman Meeting On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories, 12 July 2015 through 18 July 2015
Note

QC 20190418

Available from: 2019-04-18 Created: 2019-04-18 Last updated: 2020-01-15Bibliographically approved
Acuner, Z. & Ryde, F. (2018). Clustering of gamma-ray burst types in the Fermi GBM catalogue: indications of photosphere and synchrotron emissions during the prompt phaseShow affiliations. Monthly Notices of the Royal Astronomical Society, 475(2), 1708-1724, Article ID stx3106.
Open this publication in new window or tab >>Clustering of gamma-ray burst types in the Fermi GBM catalogue: indications of photosphere and synchrotron emissions during the prompt phaseShow affiliations
2018 (English)In: Monthly Notices of the Royal Astronomical Society, Vol. 475, no 2, p. 1708-1724, article id stx3106Article in journal (Refereed) Published
Abstract [en]

Many different physical processes have been suggested to explain the prompt gamma-ray emission in gamma-ray bursts (GRBs). Although there are examples of both bursts with photospheric and synchrotron emission origins, these distinct spectral appearances have not been generalized to large samples of GRBs. Here, we search for signatures of the different emission mechanisms in the full Fermi Gamma-ray Space Telescope/GBM (Gamma-ray Burst Monitor) catalogue. We use Gaussian Mixture Models to cluster bursts according to their parameters from the Band function (α, β, and Epk) as well as their fluence and T90. We find five distinct clusters. We further argue that these clusters can be divided into bursts of photospheric origin (2/3 of all bursts, divided into three clusters) and bursts of synchrotron origin (1/3 of all bursts, divided into two clusters). For instance, the cluster that contains predominantly short bursts is consistent of photospheric emission origin. We discuss several reasons that can determine which cluster a burst belongs to: jet dissipation pattern and/or the jet content, or viewing angle.

National Category
Natural Sciences
Research subject
Physics, Atomic, Subatomic and Astrophysics
Identifiers
urn:nbn:se:kth:diva-265525 (URN)10.1093/mnras/stx3106 (DOI)000427345900019 ()2-s2.0-85045976276 (Scopus ID)
Note

QC 20191212

Available from: 2019-12-12 Created: 2019-12-12 Last updated: 2020-02-19Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9769-8016

Search in DiVA

Show all publications