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Publications (10 of 69) Show all publications
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, 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
Keyword
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, 1728-1732 p.Article 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, 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
Keyword
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, L43- p.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.

Keyword
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, 42-47 p.Article 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.

Keyword
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, 51-54 p.Article 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, 17- p.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.

Keyword
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
Axelsson, M. (2013). Photospheric emission from gamma-ray bursts. In: EAS Publications Series: . Paper presented at 2012 Gamma-Ray Burst Symposium, GRB 2012; Malaga, Spain, 8-12 October 2012 (pp. 53-57). .
Open this publication in new window or tab >>Photospheric emission from gamma-ray bursts
2013 (English)In: EAS Publications Series, 2013, 53-57 p.Conference paper, Published paper (Refereed)
Abstract [en]

In spite of extensive research over the past decades, a complete physical picture of the origin of the prompt gamma-ray burst emission is still lacking. During recent years, evidence has been accumulating that the jet photosphere plays an important role. In this paper we summarize the lessons learned from Fermi observations regarding the behavior of the photosphere and discuss why photospheric emission does not necessarily appear as blackbody radiation. We concentrate on two strong and important bursts, GRB 090902B and GRB 110721A, which serve as examples of the standard appearance photospheric emission may have in gamma-ray burst spectra.

Series
EAS Publications Series, ISSN 1633-4760 ; 61
Keyword
Black body radiation, Gamma ray bursts, Photospheric emission, Physical pictures, Antenna radiation, Gamma rays, Stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-139962 (URN)10.1051/eas/1361006 (DOI)000323183700007 ()2-s2.0-84887077384 (Scopus ID)
Conference
2012 Gamma-Ray Burst Symposium, GRB 2012; Malaga, Spain, 8-12 October 2012
Note

QC 20140116

Available from: 2014-01-16 Created: 2014-01-16 Last updated: 2014-01-23Bibliographically approved
Ackermann, M., Ajello, M., Asano, K., Axelsson, M., Baldini, L., Ballet, J., . . . Yang, Z. (2013). The first Fermi-Lat gamma-ray burst catalog. Astrophysical Journal Supplement Series, 209(1), 11.
Open this publication in new window or tab >>The first Fermi-Lat gamma-ray burst catalog
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2013 (English)In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 209, no 1, 11- p.Article in journal (Refereed) Published
Abstract [en]

In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy (greater than or similar to 20 MeV) gamma-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above similar to 20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

Keyword
catalogs, gamma-ray burst: general, methods: data analysis
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-136487 (URN)10.1088/0067-0049/209/1/11 (DOI)000326571000011 ()2-s2.0-84887959508 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Note

QC 20131210

Available from: 2013-12-10 Created: 2013-12-05 Last updated: 2017-12-06Bibliographically approved
Iyyani, S., Ryde, F., Axelsson, M., Burgess, J. M., Guiriec, S., Larsson, J., . . . Rosquist, K. (2013). Variable jet properties in GRB 110721A: time resolved observations of the jet photosphere. Monthly notices of the Royal Astronomical Society, 433(4), 2739-2748.
Open this publication in new window or tab >>Variable jet properties in GRB 110721A: time resolved observations of the jet photosphere
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2013 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 433, no 4, 2739-2748 p.Article in journal (Refereed) Published
Abstract [en]

Fermi Gamma-ray Space Telescope observations of GRB 110721A have revealed two emission components from the relativistic jet: emission from the photosphere, peaking at similar to 100 keV, and a non-thermal component, which peaks at similar to 1000 keV. We use the photospheric component to calculate the properties of the relativistic outflow. We find a strong evolution in the flow properties: the Lorentz factor decreases with time during the bursts from G similar to 1000 to similar to 150 (assuming a redshift z = 2; the values are only weakly dependent on unknown efficiency parameters). Such a decrease is contrary to the expectations from the internal shocks and the isolated magnetar birth models. Moreover, the position of the flow nozzle measured from the central engine, r(0), increases by more than two orders of magnitude. Assuming a moderately magnetized outflow we estimate that r(0) varies from 10(6) to similar to 10(9) cm during the burst. We suggest that the maximal value reflects the size of the progenitor core. Finally, we show that these jet properties naturally explain the observed broken power-law decay of the temperature which has been reported as a characteristic for gamma-ray burst pulses.

Keyword
gamma-ray burst: individual: GRB 110721A
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-127493 (URN)10.1093/mnras/stt863 (DOI)000322405900004 ()2-s2.0-84881118688 (Scopus ID)
Note

QC 20130902

Available from: 2013-09-02 Created: 2013-08-30 Last updated: 2017-06-22Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4378-8785

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