Ref HAL: in2p3-00377697_v1
DOI: 10.1126/SCIENCE.1169101
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485 citations
Résumé:

Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gamma-ray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.

Ref HAL: in2p3-00377212_v1
Ref Arxiv: 0903.1602
DOI: 10.1088/0004-637X/695/1/L72
Ref. & Cit.: NASA ADS
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35 citations
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Radio pulsar PSR J1028-5819 was recently discovered in a high-frequency search (at 3.1 GHz)in the error circle of the EGRET source 3EG J1027-5817. The spin-down power of this young pulsar is great enough to make it very likely the counterpart for the EGRET source. We report here the discovery of gamma-ray pulsations from PSR J1028-5819 in early observations by the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope. The gamma-ray light curve shows two sharp peaks having phase separation of 0.460 +- 0.004, trailing the very narrow radio pulse by 0.200 +- 0.003 in phase, very similar to that of other known $\gamma$-ray pulsars. The measured gamma-ray flux gives an efficiency for the pulsar of 10-20% (for outer magnetosphere beam models). No evidence of a surrounding pulsar wind nebula is seen in the current Fermi data but limits on associated emission are weak because the source lies in a crowded region with high background emission. However, the improved angular resolution afforded by the LAT enables the disentanglement of the previous COS-B and EGRET source detections into at least two distinct sources, one of which is now identified as PSR J1028-5819.

Ref HAL: hal-00430362_v1
Ref Arxiv: 0810.2555
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In this communication devoted to the prompt emission of GRBs, we claim thatsome important parameters associated to the magnetic field, such as its indexprofile, the index of its turbulence spectrum and its level of irregularities,will be measurable with GLAST. In particular the law relating the peak energyEpeak with the total energy E (like Amati's law) constrains the turbulencespectrum index and, among all existing theories of MHD turbulence, iscompatible with the Kolmogorov scaling only. Thus, these data will allow a muchbetter determination of the performances of GRBs as particle accelerators. Thisopens the possibility to characterize both electron and proton accelerationmore seriously. We discuss the possible generation of UHECRs and of itssignature through GeV-TeV synchrotron emission.

Commentaires: Edited by Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia.

Ref HAL: hal-00339110_v1
Ref Arxiv: 0810.3562
DOI: 10.1126/science.1165572
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86 citations
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Energetic young pulsars and expanding blast waves (supernova remnants, SNRs) are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 ms, a period derivative of 3.614 x 10-13 s s-1 . Its characteristic age of 104 years is comparable to that estimated for the SNR. It is conjectured that most unidentified Galactic gamma ray sources associated with star-forming regions and SNRs are such young pulsars.

Commentaires: 18 pages, 3 figures + supplemental material, published in Science Express, October 16, 2008, Contact authors: G. Kanbach, K. Wood, M. Ziegler

Ref HAL: in2p3-00013575_v1
Ref Arxiv: astro-ph/0106210
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To date, only three objects have been firmly established as very high-energy gamma-ray sources in the Northern sky: the Crab nebula, which is a plerion, and the two blazars Markarian 501 and Markarian 421. This paper reviews the most striking results obtained for these sources by the CAT atmospheric Cherenkov imaging telescope.

Ref HAL: in2p3-00087398_v1
Ref Arxiv: astro-ph/0109286
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To date, only two extragalactic objects have been firmly established as very high-energy gamma-ray sources in the Northern sky: these are the two blazars Markarian 501 and Markarian 421. This paper reviews the most striking results obtained from these sources by the CAT atmospheric Cherenkov imaging telescope, with a particular emphasis on the 1999-2000 and 2000-2001 observation campaigns of Markarian 421.

Commentaires: 4 pages, 5 figures, to appear in Proc. of the SF2A conference "Semaine de l'Astrophysique Francaise", May 28 - June 1st, 2001 (Lyon, France) - GAM

Ref HAL: in2p3-00113422_v1
Ref Arxiv: astro-ph/0608247
DOI: 10.1051/0004-6361:20065884
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14 citations
Résumé:

We have measured the gamma-ray fluxes of the blazars Mrk 421 and Mrk 501 in the energy range between 50 and 350 GeV (1.2 to 8.3 x 10^25 Hz). The detector, called CELESTE, used first 40, then 53 heliostats of the former solar facility "Themis" in the French Pyrenees to collect Cherenkov light generated in atmospheric particle cascades. The signal from Mrk 421 is often strong. We compare its flux with previously published multi-wavelength studies and infer that we are straddling the high energy peak of the spectral energy distribution. The signal from Mrk 501 in 2000 was weak (3.4 sigma). We obtain an upper limit on the flux from 1ES 1426+428 of less than half that of the Crab flux near 100 GeV. The data analysis and understanding of systematic biases have improved compared to previous work, increasing the detector's sensitivity.

Commentaires: 15 pages, 14 figures, accepted by A&A (July 2006) August 19 -- corrected error in author list