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Publications (10 of 198) Show all publications
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 ()
Note

QC 20190805

Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-05Bibliographically 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
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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
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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
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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 ()
Note

QC 20190308

Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2019-05-29Bibliographically 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 ()
Note

QC 20190610

Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2019-06-10Bibliographically 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

QC20190418

Available from: 2019-04-18 Created: 2019-04-18 Last updated: 2019-04-18Bibliographically approved
Li, L., Wu, X.-F., Lei, W.-H., Dai, Z.-G., Lian, E.-W. & Ryde, F. (2018). Constraining the Type of Central Engine of GRBs with Swift Data. Astrophysical Journal Supplement Series, 236(2), Article ID 26.
Open this publication in new window or tab >>Constraining the Type of Central Engine of GRBs with Swift Data
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2018 (English)In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 236, no 2, article id 26Article in journal (Refereed) Published
Abstract [en]

The central engine of gamma-ray bursts (GRBs) is poorly constrained. There exist two main candidates: a fast-rotating black hole and a rapidly spinning magnetar. Furthermore, X-ray plateaus are widely accepted to be the energy injection into the external shock. In this paper, we systematically analyze the Swift/XRT light curves of 101 GRBs having plateau phases and known redshifts (before 2017 May). Since a maximum energy budget (similar to 2 x 10(52) erg) exists for magnetars but not for black holes, this provides a good clue to identifying the type of GRB central engine. We calculate the isotropic kinetic energy E-K,(iso) and the isotropic X-ray energy release E-X,E-iso for individual GRBs. We identify three categories based on how likely a black hole harbors a central engine: "Gold" (9 out of 101; both E-X,E-iso and E-K,E-iso exceed the energy budget), "Silver" (69 out of 101; E-X,E-iso less than the limit but E-K,E-iso greater than the limit), and "Bronze" (23 out of 101; the energies are not above the limit). We then derive and test the black hole parameters with the Blandford-Znajek mechanism, and find that the observations of the black hole candidate ("Gold" + "Silver") samples are consistent with the expectations of the black hole model. Furthermore, we also test the magnetar candidate ("Bronze") sample with the magnetar model, and find that the magnetar surface magnetic field (B-p) and initial spin period (P-0) fall into reasonable ranges. Our analysis indicates that if the magnetar wind is isotropic, a magnetar central engine is possible for 20% of the analyzed GRBs. For most GRBs, a black hole is most likely operating.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
methods: statistical, reference systems, X-rays: ISM
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-230421 (URN)10.3847/1538-4365/aabaf3 (DOI)000432546100002 ()
Note

QC 20180619

Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-06-19Bibliographically approved
Ajello, M., Allafort, A., Axelsson, M., Baldini, L., Barbiellini, G., Baring, M. G., . . . Zaharijas, G. (2018). Fermi-LAT Observations of LIGO/Virgo Event GW170817. Astrophysical Journal, 861(2), Article ID 88.
Open this publication in new window or tab >>Fermi-LAT Observations of LIGO/Virgo Event GW170817
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2018 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 861, no 2, article id 88Article in journal (Refereed) Published
Abstract [en]

We present the Fermi Large Area Telescope (LAT) observations of the binary neutron star merger event GW170817 and the associated short gamma-ray burst (SGRB) GRB 170817A detected by the Fermi Gamma-ray Burst Monitor. The LAT was entering the South Atlantic Anomaly at the time of the LIGO/Virgo trigger (t(GW)) and therefore cannot place constraints on the existence of high-energy (E > 100 MeV) emission associated with the moment of binary coalescence. We focus instead on constraining high-energy emission on longer timescales. No candidate electromagnetic counterpart was detected by the LAT on timescales of minutes, hours, or days after the LIGO/Virgo detection. The resulting flux upper bound (at 95% C. L.) from the LAT is 4.5. x. 10(-10) erg cm(-2) s(-1) in the 0.1-1 GeV range covering a period from tGW. +. 1153 s to t(GW). +. 2027 s. At the distance of GRB 170817A, this flux upper bound corresponds to a luminosity upper bound of 9.7. x. 10(43) erg s(-1), which is five orders of magnitude less luminous than the only other LAT SGRB with known redshift, GRB 090510. We also discuss the prospects for LAT detection of electromagnetic counterparts to future gravitational-wave events from Advanced LIGO/Virgo in the context of GW170817/GRB 170817A.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2018
Keywords
gamma-ray burst: general, gamma rays: general, gravitational waves
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-232611 (URN)10.3847/1538-4357/aac515 (DOI)000437822700010 ()2-s2.0-85050685077 (Scopus ID)
Note

QC 20180801

Available from: 2018-08-01 Created: 2018-08-01 Last updated: 2018-10-16Bibliographically approved
Pe'Er, A. & Ryde, F. (2018). Photospheric emission in gamma-ray bursts. 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. 806-840). World Scientific Publishing Co. Pte. Ltd.
Open this publication in new window or tab >>Photospheric emission in gamma-ray bursts
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. 806-840Conference paper, Published paper (Refereed)
Abstract [en]

A major breakthrough in our understanding of gamma-ray bursts (GRB) prompt emission physics occurred in the last few years, with the realization that a thermal component accompanies the over-all nonthermal prompt spectra. This thermal part is important by itself, as it provides direct probe of the physics in the innermost outflow regions. It further has an indirect importance, as a source of seed photons for inverse-Compton scattering, thereby it contributes to the nonthermal part as well. In this short review, we highlight some key recent developments. Observationally, although so far it was clearly identified only in a minority of bursts, there is indirect evidence that a thermal component exists in a very large fraction of GRBs, possibly close to 100%. Theoretically, the existence of a thermal component has a large number of implications as a probe of underlying GRB physics. Some surprising implications include its use as a probe of the jet dynamics, geometry and magnetization.

Place, publisher, year, edition, pages
World Scientific Publishing Co. Pte. Ltd., 2018
Keywords
Gamma-rays bursts, Hydrodynamics, Radiation mechanism: nonthermal, Radiation mechanism: thermal
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-246524 (URN)2-s2.0-85059070608 (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 20190329

Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2019-03-29Bibliographically approved
Amati, L., O'Brien, P., Gotz, D., Bozzo, E., Tenzer, C., Frontera, F., . . . Zicha, J. (2018). The THESEUS space mission concept: science case, design and expected performances. Advances in Space Research, 62(1), 191-244
Open this publication in new window or tab >>The THESEUS space mission concept: science case, design and expected performances
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2018 (English)In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 62, no 1, p. 191-244Article in journal (Refereed) Published
Abstract [en]

THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. These goals will be achieved through a unique combination of instruments allowing GRB and X-ray transient detection over a broad field of view (more than 1 sr) with 0.5-1 arcmin localization, an energy band extending from several MeV down to 0.3 keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7 m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing the main open issues in cosmology such as, e.g., star formation rate and metallicity evolution of the inter-stellar and intra-galactic medium up to redshift similar to 10, signatures of Pop III stars, sources and physics of re-ionization, and the faint end of the galaxy luminosity function. In addition, it will provide unprecedented capability to monitor the X-ray variable sky, thus detecting, localizing, and identifying the electromagnetic counterparts to sources of gravitational radiation, which may be routinely detected in the late '20s/early '30s by next generation facilities like aLIGO/ aVirgo, eLISA, KAGRA, and Einstein Telescope. THESEUS will also provide powerful synergies with the next generation of multi-wavelength observatories (e.g., LSST, ELT, SKA, CTA, ATHENA).

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Gamma-ray: bursts, Cosmology: observations, Dark ages, Re-ionization, First stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-232234 (URN)10.1016/j.asr.2018.03.010 (DOI)000436889000016 ()2-s2.0-85046789580 (Scopus ID)
Note

QC 20180718

Available from: 2018-07-18 Created: 2018-07-18 Last updated: 2018-07-18Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9769-8016

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