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In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope
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2012 (English)In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 35, no 6, 346-353 p.Article in journal (Refereed) Published
Abstract [en]

The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between similar to 6 and similar to 13 GeV with an estimated uncertainty of similar to 2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.

Place, publisher, year, edition, pages
2012. Vol. 35, no 6, 346-353 p.
Keyword [en]
Cosmic-rays, Geomagnetic cutoff, Absolute energy scale, Fermi Large Area Telescope
National Category
Physical Sciences Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-76771DOI: 10.1016/j.astropartphys.2011.10.007ISI: 000300760800007OAI: diva2:527118
141Available from: 2012-05-16 Created: 2012-05-16 Last updated: 2012-05-16Bibliographically approved

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Axelsson, MagnusZimmer, Stephan
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