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Ajello, M., Arimoto, M., Axelsson, M., Baldini, L., Barbiellini, G., Bastieri, D., . . . Zimmer, S. (2019). A Decade of Gamma-Ray Bursts Observed by Fermi-LAT: The Second GRB Catalog. Astrophysical Journal, 878(1), Article ID 52.
Open this publication in new window or tab >>A Decade of Gamma-Ray Bursts Observed by Fermi-LAT: The Second GRB Catalog
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2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 878, no 1, article id 52Article in journal (Refereed) Published
Abstract [en]

The Large Area Telescope (LAT) aboard the Fermi spacecraft routinely observes high-energy emission from gamma-ray bursts (GRBs). Here we present the second catalog of LAT-detected GRBs, covering the first 10 yr of operations, from 2008 to 2018 August 4. A total of 186 GRBs are found; of these, 91 show emission in the range 30-100 MeV (17 of which are seen only in this band) and 169 are detected above 100 MeV. Most of these sources were discovered by other instruments (Fermi/GBM, Swift/BAT, AGILE, INTEGRAL) or reported by the Interplanetary Network (IPN); the LAT has independently triggered on four GRBs. This catalog presents the results for all 186 GRBs. We study onset, duration, and temporal properties of each GRB, as well as spectral characteristics in the 100 MeV-100 GeV energy range. Particular attention is given to the photons with the highest energy. Compared with the first LAT GRB catalog, our rate of detection is significantly improved. The results generally confirm the main findings of the first catalog: the LAT primarily detects the brightest GBM bursts, and the high-energy emission shows delayed onset as well as longer duration. However, in this work we find delays exceeding 1 ks and several GRBs with durations over 10 ks. Furthermore, the larger number of LAT detections shows that these GRBs not only cover the high-fluence range of GBM-detected GRBs but also sample lower fluences. In addition, the greater number of detected GRBs with redshift estimates allows us to study their properties in both the observer and rest frames. Comparison of the observational results with theoretical predictions reveals that no model is currently able to explain all results, highlighting the role of LAT observations in driving theoretical models.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2019
Keywords
catalogs, gamma-ray burst: general, methods: data analysis
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-254502 (URN)10.3847/1538-4357/ab1d4e (DOI)000471624300001 ()
Note

QC 20190715

Available from: 2019-07-15 Created: 2019-07-15 Last updated: 2019-10-08Bibliographically approved
Yamada, S., Axelsson, M., Ishisaki, Y., Konami, S., Takemura, N., Kelley, R. L., . . . Szymkowiak, A. (2019). Poisson vs. Gaussian statistics for sparse X-ray data: Application to the soft X-ray spectrometer. Publications of the Astronomical Society of Japan, 71(4), Article ID 75.
Open this publication in new window or tab >>Poisson vs. Gaussian statistics for sparse X-ray data: Application to the soft X-ray spectrometer
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2019 (English)In: Publications of the Astronomical Society of Japan, ISSN 0004-6264, E-ISSN 2053-051X, Vol. 71, no 4, article id 75Article in journal (Refereed) Published
Abstract [en]

Reliable results when fitting X-ray data require proper consideration of the statistics involved. We probe the impact of Gaussian versus Poisson statistics at low count levels using both the standard chi(2) method and maximum likelihood based on Poisson studied and quantified through simulated spectra with known properties. We then test the results through analysis of Mn K alpha calibration data taken with the flight spare microcalorimeter for the Hitomi soft X-ray spectrometer. Through comparison with simulations, our results show that the chi(2) method tends to give overly optimistic estimates of the detector energy resolution, in particular when there are few counts. Given an energy resolution of similar to 5eV and a line with about 100 photons, the line width becomes similar to 10% lower in the chi(2) method than in Poisson statistics. This is a consequence of the uncertainties being dominated by counting statistics, and therefore highlights the need to choose the appropriate fit statistic.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2019
Keywords
instrumentation: detectors, methods: data analysis, methods: statistical
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-259454 (URN)10.1093/pasj/psz053 (DOI)000482425000009 ()2-s2.0-85070811248 (Scopus ID)
Note

QC 20190920

Available from: 2019-09-20 Created: 2019-09-20 Last updated: 2019-09-20Bibliographically 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
Racusin, J. L., Burns, E., Goldstein, A., Connaughton, V., Wilson-Hodge, C. A., Jenke, P., . . . Wood, M. (2017). SEARCHING THE GAMMA-RAY SKY FOR COUNTERPARTS TO GRAVITATIONAL WAVE SOURCES: FERMI GAMMA-RAY BURST MONITOR. AND LARGE AREA TELESCOPE OBSERVATIONS OF LVT151012 AND GW151226. Astrophysical Journal, 835(1), Article ID 82.
Open this publication in new window or tab >>SEARCHING THE GAMMA-RAY SKY FOR COUNTERPARTS TO GRAVITATIONAL WAVE SOURCES: FERMI GAMMA-RAY BURST MONITOR. AND LARGE AREA TELESCOPE OBSERVATIONS OF LVT151012 AND GW151226
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2017 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 835, no 1, article id 82Article in journal (Refereed) Published
Abstract [en]

We present the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) observations of the LIGO binary black hole merger event GW151226 and candidate LVT151012. At the time of the LIGO triggers on LVT151012 and GW151226, GBM was observing 68% and 83% of the localization regions, and LAT was observing 47% and 32%, respectively. No candidate electromagnetic counterparts were detected by either the GBM or LAT. We present a detailed analysis of the GBM and LAT data over a range of timescales from seconds to years, using automated pipelines and new techniques for characterizing the flux upper bounds across large areas of the sky. Due to the partial GBM and LAT coverage of the large LIGO localization regions at the trigger times for both events, differences in source distances and masses, as well as the uncertain degree to which emission from these sources could be beamed, these non-detections cannot be used to constrain the variety of theoretical models recently applied to explain the candidate GBM counterpart to GW150914.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017
Keywords
gamma rays: general, gravitational waves, methods: observational
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-202778 (URN)10.3847/1538-4357/835/1/82 (DOI)000393455400082 ()
Note

QC 20170307

Available from: 2017-03-07 Created: 2017-03-07 Last updated: 2017-11-29Bibliographically approved
Moretti, E. & Axelsson, M. (2016). Signs of magnetic acceleration and multizone emission in GRB 080825C. Monthly notices of the Royal Astronomical Society, 458(2), 1728-1732
Open this publication in new window or tab >>Signs of magnetic acceleration and multizone emission in GRB 080825C
2016 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 458, no 2, p. 1728-1732Article in journal (Refereed) Published
Abstract [en]

One of the major results from the study of gamma-ray bursts with the Fermi Gamma-ray Space Telescope has been the confirmation that several emission components can be present in the energy spectrum. Here, we reanalyse the spectrum of GRB 080825C using data from the Fermi-Large Area Telescope (LAT) and Gamma-ray Burst Monitor instruments. Although fairly weak, it is the first gamma-ray burst detected by the Fermi-LAT. We improve on the original analysis by using the LAT Low Energy events covering the 30–100 MeV band. We find evidence of an additional component above the main emission peak (modelled using a Band function) with a significance of 3.5σ in two out of the four time bins. The component is well fitted by a Planck function, but shows unusual behaviour: the peak energy increases in the prompt emission phase, reaching energies of several MeV. This is the first time such a trend has been seen, and implies that the origin of this component is different from those previously detected. We suggest that the two spectral components likely arise in different regions of the outflow, and that strong constraints can be achieved by assuming one of them originates from the photosphere. The most promising model appears to be that the high-energy peak is the result of photospheric emission in a Poynting flux dominated outflow where the magnetization increases with time.

Place, publisher, year, edition, pages
Oxford University Press, 2016
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-184153 (URN)10.1093/mnras/stw432 (DOI)000374569600046 ()2-s2.0-84963838545 (Scopus ID)
Note

QC 20160419

Available from: 2016-03-29 Created: 2016-03-29 Last updated: 2017-11-30Bibliographically approved
Sofitta, P., Pearce, M., Axelsson, M., Chauvin, M., Burgess, M., Kiss, M., . . . et al., . (2016). XIPE the X-ray Imaging Polarimetry Explorer. In: Proceedings of SPIE: . Paper presented at Conference on Space Telescopes and Instrumentation - Ultraviolet to Gamma Ray, Edinburgh, SCOTLAND, JUN 26-JUL 01, 2016. SPIE - International Society for Optical Engineering, 9905, Article ID UNSP 990515.
Open this publication in new window or tab >>XIPE the X-ray Imaging Polarimetry Explorer
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2016 (English)In: Proceedings of SPIE, SPIE - International Society for Optical Engineering, 2016, Vol. 9905, article id UNSP 990515Conference paper, Published paper (Refereed)
Abstract [en]

XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to X-ray Astronomy. At the time of writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the polarimetry window in high energy Astrophysics after more than 4 decades thanks to a detector that efficiently exploits the photoelectric effect and to X-ray optics with large effective area. XIPE uniqueness is time-spectrally-spatially- resolved X-ray polarimetry as a breakthrough in high energy astrophysics and fundamental physics. Indeed the payload consists of three Gas Pixel Detectors at the focus of three X-ray optics with a total effective area larger than one XMM mirror but with a low weight. The payload is compatible with the fairing of the Vega launcher. XIPE is designed as an observatory for X- ray astronomers with 75% of the time dedicated to a Guest Observer competitive program and it is organized as a consortium across Europe with main contributions from Italy, Germany, Spain, United Kingdom, Poland, Sweden.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2016
Keywords
Gas Pixel Detector, Polarimetry, X-ray Astronomy, X-ray optics
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:kth:diva-202016 (URN)10.1117/12.2233046 (DOI)000387731500030 ()2-s2.0-85003741930 (Scopus ID)978-1-5106-0189-5 (ISBN)978-1-5106-0190-1 (ISBN)
Conference
Conference on Space Telescopes and Instrumentation - Ultraviolet to Gamma Ray, Edinburgh, SCOTLAND, JUN 26-JUL 01, 2016
Note

QC 20170216

Available from: 2017-02-16 Created: 2017-02-16 Last updated: 2017-02-16Bibliographically approved
Burgess, J. M., Preece, R. D., Ryde, F., Veres, P., Meszaros, P., Connaughton, V., . . . Zhu, S. (2014). An observed correlation between thermal and non-thermal emission in gamma-ray bursts. Astrophysical Journal Letters, 784(2), L43
Open this publication in new window or tab >>An observed correlation between thermal and non-thermal emission in gamma-ray bursts
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2014 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, Vol. 784, no 2, p. L43-Article in journal (Refereed) Published
Abstract [en]

Recent observations by the Fermi Gamma-ray Space Telescope have confirmed the existence of thermal and non-thermal components in the prompt photon spectra of some gamma-ray bursts (GRBs). Through an analysis of six bright Fermi GRBs, we have discovered a correlation between the observed photospheric and non-thermal gamma-ray emission components of several GRBs using a physical model that has previously been shown to be a good fit to the Fermi data. From the spectral parameters of these fits we find that the characteristic energies, E-p and kT, of these two components are correlated via the relation E-p proportional to T-alpha which varies from GRB to GRB. We present an interpretation in which the value of the index alpha indicates whether the jet is dominated by kinetic or magnetic energy. To date, this jet composition parameter has been assumed in the modeling of GRB outflows rather than derived from the data.

Keywords
gamma-ray burst: general, radiation mechanisms: non-thermal, radiation mechanisms: thermal
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-145271 (URN)10.1088/2041-8205/784/2/L43 (DOI)000333333400026 ()2-s2.0-84897013356 (Scopus ID)
Note

QC 20140515

Available from: 2014-05-15 Created: 2014-05-15 Last updated: 2017-06-22Bibliographically approved
Ackermann, M., Ajello, M., Asano, K., Atwood, W. B., Axelsson, M., Baldini, L., . . . Cummings, J. R. (2014). Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A. Science, 343(6166), 42-47
Open this publication in new window or tab >>Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A
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2014 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 343, no 6166, p. 42-47Article in journal (Refereed) Published
Abstract [en]

The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest gamma-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

Keywords
Large-Area Telescope, High-Energy Emission, Spectral Component, Afterglows, Prompt
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-140369 (URN)10.1126/science.1242353 (DOI)000329162000042 ()2-s2.0-84896723186 (Scopus ID)
Note

QC 20140124

Available from: 2014-01-24 Created: 2014-01-23 Last updated: 2017-12-06Bibliographically approved
Preece, R., Burgess, J. M., von Kienlin, A., Bhat, P. N., Briggs, M. S., Byrne, D., . . . Zhu, S. (2014). The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks. Science, 343(6166), 51-54
Open this publication in new window or tab >>The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks
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2014 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 343, no 6166, p. 51-54Article in journal (Refereed) Published
Abstract [en]

Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 seconds is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-140370 (URN)10.1126/science.1242302 (DOI)000329162000044 ()2-s2.0-84896700289 (Scopus ID)
Note

QC 20140123

Available from: 2014-01-23 Created: 2014-01-23 Last updated: 2017-12-06Bibliographically approved
Burgess, J. M., Preece, R. D., Connaughton, V., Briggs, M. S., Goldstein, A., Bhat, P. N., . . . Vianello, G. (2014). Time-resolved analysis of fermi gamma-ray bursts with fast- and slow-cooled synchrotron photon models. Astrophysical Journal, 784(1), 17
Open this publication in new window or tab >>Time-resolved analysis of fermi gamma-ray bursts with fast- and slow-cooled synchrotron photon models
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2014 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 784, no 1, p. 17-Article in journal (Refereed) Published
Abstract [en]

Time-resolved spectroscopy is performed on eight bright, long gamma-ray bursts (GRBs) dominated by single emission pulses that were observed with the Fermi Gamma-Ray Space Telescope. Fitting the prompt radiation of GRBs by empirical spectral forms such as the Band function leads to ambiguous conclusions about the physical model for the prompt radiation. Moreover, the Band function is often inadequate to fit the data. The GRB spectrum is therefore modeled with two emission components consisting of optically thin non-thermal synchrotron radiation from relativistic electrons and, when significant, thermal emission from a jet photosphere, which is represented by a blackbody spectrum. To produce an acceptable fit, the addition of a blackbody component is required in five out of the eight cases. We also find that the low-energy spectral index a is consistent with a synchrotron component with a = -0.81 +/- 0.1. This value lies between the limiting values of a = -2/3 and a = -3/2 for electrons in the slow-and fast-cooling regimes, respectively, suggesting ongoing acceleration at the emission site. The blackbody component can be more significant when using a physical synchrotron model instead of the Band function, illustrating that the Band function does not serve as a good proxy for a non-thermal synchrotron emission component. The temperature and characteristic emission-region size of the blackbody component are found to, respectively, decrease and increase as power laws with time during the prompt phase. In addition, we find that the blackbody and non-thermal components have separate temporal behaviors as far as their respective flux and spectral evolutions.

Keywords
acceleration of particles, gamma-ray burst: general, gamma rays: stars, methods: data analysis, radiation mechanisms: non-thermal, radiation mechanisms: thermal
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-146157 (URN)10.1088/0004-637X/784/1/17 (DOI)000335457000017 ()2-s2.0-84896793258 (Scopus ID)
Note

QC 20140609

Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2017-12-05Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4378-8785

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