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Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
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2014 (English)In: ASTROPHYSICAL JOURNAL LETTERS, ISSN 2041-8205, Vol. 782, no 2, L14- p.Article in journal (Refereed) Published
Abstract [en]

Using data from the Fermi Large Area Telescope (LAT), we report the first clear gamma-ray measurement of a delay between flares from the gravitationally lensed images of a blazar. The delay was detected in B0218+357, a known double-image lensed system, during a period of enhanced gamma-ray activity with peak fluxes consistently observed to reach >20-50x its previous average flux. An auto-correlation function analysis identified a delay in the gamma-ray data of 11.46 +/- 0.16 days (1 sigma) that is similar to 1 day greater than previous radio measurements. Considering that it is beyond the capabilities of the LAT to spatially resolve the two images, we nevertheless decomposed individual sequences of superposing gamma-ray flares/delayed emissions. In three such similar to 8-10 day-long sequences within a similar to 4 month span, considering confusion due to overlapping flaring emission and flux measurement uncertainties, we found flux ratios consistent with similar to 1, thus systematically smaller than those from radio observations. During the first, best-defined flare, the delayed emission was detailed with a Fermi pointing, and we observed flux doubling timescales of similar to 3-6 hr implying as well extremely compact gamma-ray emitting regions.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014. Vol. 782, no 2, L14- p.
Keyword [en]
galaxies: active, gamma rays: galaxies, gravitational lensing: strong, quasars: individual (B0218+357)
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-101735DOI: 10.1088/2041-8205/782/2/L14ISI: 000331153000001OAI: diva2:705672


Funding agencies:

Royal Swedish Academy Crafoord Foundation;  Italian Ministry of Education, University and Research (MIUR) FIRB-2012-RBFR12PM1F 

Available from: 2014-03-17 Created: 2014-03-14 Last updated: 2014-03-17Bibliographically approved

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Larsson, Stefan
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Department of AstronomyThe Oskar Klein Centre for Cosmo Particle Physics (OKC)Department of Physics
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