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Publications (10 of 29) Show all publications
Larsson, J., D'Ammando, F., Falocco, S., Giroletti, M., Orienti, M., Piconcelli, E. & Righini, S. (2018). FBQS J1644+2619: multiwavelength properties and its place in the class of gamma-ray emitting Narrow Line Seyfert 1s. Monthly notices of the Royal Astronomical Society, 476(1), 43-55
Open this publication in new window or tab >>FBQS J1644+2619: multiwavelength properties and its place in the class of gamma-ray emitting Narrow Line Seyfert 1s
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 476, no 1, p. 43-55Article in journal (Refereed) Published
Abstract [en]

A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be gamma-ray emitters. Understanding the properties of these sources is of interest since the majority of NLSy1s are very different from typical blazars. Here, we present a multifrequency analysis of FBQS J1644+2619, one of the most recently discovered gamma-ray emitting NLSy1s. We analyse an similar to 80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multi-wavelength observations covering the radio-gamma-ray range. The spectral energy distribution of the source is similar to the other gamma-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterized by a hard photon index (Gamma = 1.66) above 2 keV and a soft excess at lower energies. The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonization in a warm, optically thick corona. We discuss our results in the context of the other gamma-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2018
Keywords
galaxies: active, galaxies: individual (FBQS J1644+2619), galaxies: jets, galaxies: Seyfert, X-rays: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-228113 (URN)10.1093/mnras/sty241 (DOI)000429276700004 ()2-s2.0-85043514539 (Scopus ID)
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-05-18Bibliographically approved
Valan, V., Larsson, J. & Ahlgren, B. (2018). Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitors. Monthly notices of the Royal Astronomical Society, 474(2), 2401-2418
Open this publication in new window or tab >>Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitors
2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 474, no 2, p. 2401-2418Article in journal (Refereed) Published
Abstract [en]

The early X-ray afterglows of gamma-ray bursts (GRBs) are usually well described by absorbed power laws. However, in some cases, additional thermal components have been identified. The origin of this emission is debated, with proposed explanations including supernova shock breakout, emission from a cocoon surrounding the jet, as well as emission from the jet itself. A larger sample of detections is needed in order to place constraints on these different models. Here, we present a time-resolved spectral analysis of 74 GRBs observed by Swift X-ray Telescope in a search for thermal components. We report six detections in our sample, and also confirm an additional three cases that were previously reported in the literature. The majority of these bursts have a narrow range of blackbody radii around similar to 2 x 10(12) cm, despite having a large range of luminosities (L-peak similar to 10(47)-10(51) erg s(-1)). This points to an origin connected to the progenitor stars, and we suggest that emission from a cocoon breaking out from a thick wind may explain the observations. For two of the bursts in the sample, an explanation in terms of late prompt emission from the jet is instead more likely. We also find that these thermal components are preferentially detected when the X-ray luminosity is low, which suggests that they may be hidden by bright afterglows in the majority of GRBs.

Place, publisher, year, edition, pages
Oxford University Press, 2018
Keywords
gamma-ray burst: general, X-rays: bursts
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-223805 (URN)10.1093/mnras/stx2920 (DOI)000424343600068 ()2-s2.0-85042616959 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20180307

Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-06-25Bibliographically approved
Nandi, S., Jamrozy, M., Roy, R., Larsson, J., Saikia, D. J., Baes, M. & Singh, M. (2017). Tale of J1328+2752: a misaligned double-double radio galaxy hosted by a binary black hole?. Monthly notices of the Royal Astronomical Society, 467(1), L56-L60
Open this publication in new window or tab >>Tale of J1328+2752: a misaligned double-double radio galaxy hosted by a binary black hole?
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2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 467, no 1, p. L56-L60Article in journal (Refereed) Published
Abstract [en]

We present a radio and optical study of the double-double radio galaxy J1328+2752 based on new low-frequency Giant Metrewave Radio Telescope observations and Sloan Digital Sky Survey (SDSS) data. The radio data were used to investigate the morphology and to perform a spectral index analysis. In this source, we find that the inner double is misaligned by similar to 30 degrees from the axis of the outer diffuse structure. The SDSS spectrum shows that the central component has double-peaked line profiles with different emission strengths. The average velocity offset of the two components is 235 +/- 10.5 kms(-1). The misaligned radio morphology along with the double-peaked emission lines indicate that this source is a potential candidate binary supermassive black hole. This study further supports mergers as a possible explanation for repeated jet activity in radio sources.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2017
Keywords
line: identification, line: profiles, galaxies: active, galaxies: individual: J1328+2752, galaxies: nuclei, radio continuum: galaxies
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-215485 (URN)10.1093/mnrasl/slw256 (DOI)000410063700012 ()2-s2.0-85018296806 (Scopus ID)
Note

QC 20171013

Available from: 2017-10-13 Created: 2017-10-13 Last updated: 2017-10-23Bibliographically approved
Abellán, F. J., Indebetouw, R., Marcaide, J. M., Gabler, M., Fransson, C., Spyromilio, J., . . . Woosley, S. E. (2017). Very Deep inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D. Astrophysical Journal Letters, 842(2), Article ID L24.
Open this publication in new window or tab >>Very Deep inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D
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2017 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 842, no 2, article id L24Article in journal (Refereed) Published
Abstract [en]

Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks ("nickel heating"). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.

Place, publisher, year, edition, pages
Institute of Physics Publishing, 2017
Keywords
hydrodynamics, Instabilities, ISM: supernova remnants, Supernovae: individual (SN 1987A) Supporting material: Animation
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-216454 (URN)10.3847/2041-8213/aa784c (DOI)000431000900001 ()2-s2.0-85021380728 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20171205

Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2018-05-14Bibliographically approved
D'Ammando, F., Orienti, M., Finke, J., Larsson, J., Giroletti, M. & Raiteri, C. M. (2016). A Panchromatic View of Relativistic Jets in Narrow-Line Seyfert 1 Galaxies. Galaxies, 4(3), Article ID 11.
Open this publication in new window or tab >>A Panchromatic View of Relativistic Jets in Narrow-Line Seyfert 1 Galaxies
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2016 (English)In: Galaxies, E-ISSN 2075-4434, Vol. 4, no 3, article id 11Article in journal (Refereed) Published
Abstract [en]

The discovery by the Large Area Telescope on board Fermi of variable -ray emission from radio-loud narrow-line Seyfert 1 (NLSy1) galaxies revealed the presence of a possible third class of Active Galactic Nuclei (AGN) with relativistic jets in addition to blazars and radio galaxies. Considering that NLSy1 are usually hosted in spiral galaxies, this finding poses intriguing questions about the nature of these objects and the formation of relativistic jets. We report on a systematic investigation of the -ray properties of a sample of radio-loud NLSy1, including the detection of new objects, using 7 years of Fermi-LAT data with the new Pass 8 event-level analysis. In addition we discuss the radio-to-very-high-energy properties of the -ray emitting NLSy1, their host galaxy, and black hole mass in the context of the blazar scenario and the unification of relativistic jets at different scales.

Place, publisher, year, edition, pages
MDPI AG, 2016
Keywords
galaxies: nuclei, galaxies: jets, galaxies: Seyfert, gamma-rays: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-196431 (URN)10.3390/galaxies4030011 (DOI)000385480600004 ()
Note

QC 20161129

Available from: 2016-11-29 Created: 2016-11-14 Last updated: 2017-11-29Bibliographically approved
Fransson, C., Larsson, J., Spyromilio, J., Leibundgut, B., McCray, R. & Jerkstrand, A. (2016). DISCOVERY OF MOLECULAR HYDROGEN IN SN 1987A. Astrophysical Journal Letters, 821(1), Article ID L5.
Open this publication in new window or tab >>DISCOVERY OF MOLECULAR HYDROGEN IN SN 1987A
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2016 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 821, no 1, article id L5Article in journal (Refereed) Published
Abstract [en]

Both CO and SiO have been observed at early and late phases in SN 1987A. H-2 was predicted to form at roughly the same time as these molecules, but was not detected at early epochs. Here, we report the detection of NIR lines from H-2 at 2.12 and 2.40 mu m in VLT/SINFONI spectra obtained between days 6489 and 10,120. The emission is concentrated to the core of the SN in contrast to Ha and approximately coincides with the [Si I]/[Fe II] emission detected previously in the ejecta. Different excitation mechanisms and power sources of the emission are discussed. From the nearly constant H-2 luminosities, we favor excitation resulting from the Ti-44 decay.

Place, publisher, year, edition, pages
Institute of Physics Publishing, 2016
Keywords
molecular processes, supernovae: general, supernovae: individual (SN 1987A)
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-185973 (URN)10.3847/2041-8205/821/1/L5 (DOI)000373812000005 ()2-s2.0-84964264800 (Scopus ID)
Note

QC 20160509

Available from: 2016-05-09 Created: 2016-04-29 Last updated: 2017-11-30Bibliographically approved
Topchiev, N. P., Larsson, J., Pearce, M., Ryde, F., Zverev, V. G. & et al., . (2016). The GAMMA-400 gamma-ray telescope for precision gamma-ray emission investigations. In: INTERNATIONAL CONFERENCE ON PARTICLE PHYSICS AND ASTROPHYSICS (ICPPA-2015), PTS 1-4: . Paper presented at International Conference on Particle Physics and Astrophysics (ICPPA), Moscow, 2015. Institute of Physics (IOP)
Open this publication in new window or tab >>The GAMMA-400 gamma-ray telescope for precision gamma-ray emission investigations
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2016 (English)In: INTERNATIONAL CONFERENCE ON PARTICLE PHYSICS AND ASTROPHYSICS (ICPPA-2015), PTS 1-4, Institute of Physics (IOP), 2016Conference paper, Published paper (Refereed)
Abstract [en]

The GAMMA-400 gamma-ray telescope with excellent angular and energy resolutions is designed to search for signatures of dark matter in the fluxes of gamma-ray emission and electrons + positrons. Precision investigations of gamma-ray emission from Galactic Center, Crab, Vela, Cygnus, Geminga, and other regions will be performed, as well as diffuse gamma-ray emission, along with measurements of high-energy electron + positron and nuclei fluxes. Furthermore, it will study gamma-ray bursts and gamma-ray emission from the Sun during periods of solar activity. The GAMMA-400 energy range is expected to be from similar to 20 MeV up to TeV energies for gamma rays, up to 10 TeV for electrons + positrons, and up to 10(15) eV for cosmic-ray nuclei. For 100-GeV gamma rays, the GAMMA-400 angular resolution is similar to 0.01 degrees and energy resolution is similar to 1%; the proton rejection factor is similar to 5x10(5). GAMMA-400 will be installed onboard the Russian space observatory.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2016
Series
Journal of Physics Conference Series ; 675
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-185736 (URN)10.1088/1742-6596/675/3/032009 (DOI)000372460100075 ()2-s2.0-84964788343 (Scopus ID)
Conference
International Conference on Particle Physics and Astrophysics (ICPPA), Moscow, 2015
Note

QC 20160426

Available from: 2016-04-26 Created: 2016-04-26 Last updated: 2016-11-03Bibliographically approved
Larsson, J., Fransson, C., Spyromilio, J., Leibundgut, B., Challis, P., Chevalier, R. A., . . . Wheeler, J. C. (2016). THREE-DIMENSIONAL DISTRIBUTION OF EJECTA IN SUPERNOVA 1987A AT 10,000 DAYS. Astrophysical Journal, 833(2), Article ID 147.
Open this publication in new window or tab >>THREE-DIMENSIONAL DISTRIBUTION OF EJECTA IN SUPERNOVA 1987A AT 10,000 DAYS
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2016 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 833, no 2, article id 147Article in journal (Refereed) Published
Abstract [en]

Due to its proximity, SN. 1987A offers a unique opportunity to directly observe the geometry of a stellar explosion as it unfolds. Here we present spectral and imaging observations of SN. 1987A obtained similar to 10,000 days after the explosion with HST/STIS and VLT/SINFONI at optical and near-infrared wavelengths. These observations allow us to produce the most detailed 3D map of Ha to date, the first 3D maps for [Ca II] lambda lambda 7292, 7324, [O I] lambda lambda 6300, 6364, and Mg. II lambda lambda 9218, 9244, as well as new maps for [Si I]+[Fe II] 1.644 mu m and He I 2.058 mu m. A comparison with previous observations shows that the [Si I]+[Fe II] flux and morphology have not changed significantly during the past ten years, providing evidence that this line is powered by Ti-44. The time evolution of Ha shows that it is predominantly powered by X-rays from the ring, in agreement with previous findings. All lines that have sufficient signal show a similar large-scale 3D structure, with a north-south asymmetry that resembles a broken dipole. This structure correlates with early observations of asymmetries, showing that there is a global asymmetry that extends from the inner core to the outer envelope. On smaller scales, the two brightest lines, Ha and [Si I]+[Fe II] 1.644 mu m, show substructures at the level of similar to 200-1000 km s(-1) and clear differences in their 3D geometries. We discuss these results in the context of explosion models and the properties of dust in the ejecta.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keywords
supernovae: general, supernovae: individual (SN 1987A)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-200759 (URN)10.3847/1538-4357/833/2/147 (DOI)000391169600022 ()2-s2.0-85007543316 (Scopus ID)
Note

QC 20170209

Available from: 2017-02-09 Created: 2017-02-09 Last updated: 2017-11-29Bibliographically approved
Ahlgren, B., Larsson, J., Nymark, T., Ryde, F. & Pe'er, A. (2015). Confronting GRB prompt emission with a model for subphotospheric dissipation. Monthly Notices of the Royal Astronomical Society: Letters, 454(1), L31-L35
Open this publication in new window or tab >>Confronting GRB prompt emission with a model for subphotospheric dissipation
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2015 (English)In: Monthly Notices of the Royal Astronomical Society: Letters, ISSN 1745-3925, Vol. 454, no 1, p. L31-L35Article in journal (Refereed) Published
Abstract [en]

The origin of the prompt emission in gamma-ray bursts (GRBs) is still an unsolved problem and several different mechanisms have been suggested. Here, we fit Fermi GRB data with a photospheric emission model which includes dissipation of the jet kinetic energy below the photosphere. The resulting spectra are dominated by Comptonization and contain no significant contribution from synchrotron radiation. In order to fit to the data, we span a physically motivated part of the model's parameter space and create DREAM (Dissipation with Radiative Emission as A table Model), a table model for XSPEC. We show that this model can describe different kinds of GRB spectra, including GRB 090618, representing a typical Band function spectrum, and GRB 100724B, illustrating a double peaked spectrum, previously fitted with a Band+blackbody model, suggesting they originate from a similar scenario. We suggest that the main difference between these two types of bursts is the optical depth at the dissipation site.

Place, publisher, year, edition, pages
Oxford University Press, 2015
Keywords
Gamma-ray burst: general, Gamma-ray burst: individual: GRB 090618, Gamma-ray burst: individual: GRB 100724B, Radiation mechanisms: thermal
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-181222 (URN)10.1093/mnrasl/slv114 (DOI)000378922200006 ()2-s2.0-84944884952 (Scopus ID)
Note

QC 20160203

Available from: 2016-02-03 Created: 2016-01-29 Last updated: 2017-03-09Bibliographically approved
Larsson, J., Racusin, J. L. & Burgess, J. M. (2015). Evidence for jet launching close to the black hole in GRB 101219b: A Fermi grb dominated by thermal emission. Astrophysical Journal Letters, 800(2), Article ID L34.
Open this publication in new window or tab >>Evidence for jet launching close to the black hole in GRB 101219b: A Fermi grb dominated by thermal emission
2015 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 800, no 2, article id L34Article in journal (Refereed) Published
Abstract [en]

We present observations by the Fermi Gamma-Ray Space Telescope Gamma-Ray Burst Monitor (GBM) of the nearby (z = 0.55) GRB 101219B. This burst is a long GRB, with an associated supernova and with a blackbody (BB) component detected in the early afterglow observed by the Swift X-ray Telescope (XRT). Here we show that the prompt gamma-ray emission has a BB spectrum, making this the second such burst observed by Fermi GBM. The properties of the BB, together with the redshift and our estimate of the radiative efficiency makes it possible to calculate the absolute values of the properties of the outflow. We obtain an initial Lorentz factor G = 138 +/- 8, a photospheric radius r(phot) = 4.4 +/- 1.9 x 10(11) cm, and a launch radius r(0) = 2.7 +/- 1.6 x 10(7) cm. The latter value is close to the black hole and suggests that the jet has a relatively unobstructed path through the star. There is no smooth connection between the BB components seen by GBM and XRT, ruling out the scenario that the late emission is due to high-latitude effects. In the interpretation that the XRT BB is prompt emission due to late central engine activity, the jet either has to be very wide or have a clumpy structure where the emission originates from a small patch. Other explanations for this component, such as emission from a cocoon surrounding the jet, are also possible.

Keywords
gamma-ray burst, general, gamma-ray burst, individual (GRB 101219B), radiation mechanisms, thermal
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-161955 (URN)10.1088/2041-8205/800/2/L34 (DOI)000349692900015 ()2-s2.0-84923641901 (Scopus ID)
Note

QC 20150408

Available from: 2015-04-08 Created: 2015-03-20 Last updated: 2017-12-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-0065-2933

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