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Title: When a Standard Candle Flickers
Type: Journal articleJournal article
Participant(s):
Forfatter:  Wilson-Hodge, Colleen A
Marshall Space Flight Center

Forfatter:  Cherry, Michael L
Louisiana State University, Dept. of Phys. & Astron

Forfatter:  Case, Gary L
Louisiana State University, Dept. of Phys. & Astron

Forfatter:  Baumgartner, Wayne H
Goddard Space Flight Center

Forfatter:  Beklen, Elif
Middle East Tech. University

Forfatter:  Bhat, P Narayana
University of Alabama in Huntsville

Forfatter:  Briggs, Michael S
University of Alabama in Huntsville

Forfatter:  Camero-Arranz, Ascension
Nat. Space Sci. & Technol. Center

Forfatter:  Chaplin, Vandiver
University of Alabama in Huntsville

Forfatter:  Connaughton, Valerie
University of Alabama in Huntsville

Forfatter:  Finger, Mark H
Universities Space Res. Assoc.

Forfatter:  Gehrels, Neil
Goddard Space Flight Center

Forfatter:  Greiner, Jochen
Max-Planck Inst. fur Extraterrestische Phys.

Forfatter:  Jahoda, Keith
Goddard Space Flight Center

Forfatter:  Jenke, Peter
Marshall Space Flight Center

Forfatter:  Kippen, R Marc
Los Alamos Nat. Lab.

Forfatter:  Kouveliotou, Chryssa
Marshall Space Flight Center

Forfatter:  Krimm, Hans A
Goddard Space Flight Center

Forfatter:  Kuulkers, Erik
Eur. Space Astron. Centre (ESAC)

Author:  Lund, Niels (Cwisno: 38305)
Technical University of Denmark
Email:

Forfatter:  Meegan, Charles A
Universities Space Res. Assoc.

Forfatter:  Natalucci, Lorenzo
INAF

Forfatter:  Paciesas, William S
University of Alabama in Huntsville

Forfatter:  Preece, Robert
University of Alabama in Huntsville

Forfatter:  Rodi, James C
Louisiana State University

Forfatter:  Shaposhnikov, Nikolai
Goddard Space Flight Center

Forfatter:  Skinner, Gerald K
Goddard Space Flight Center

Forfatter:  Swartz, Doug
Universities Space Res. Assoc.

Forfatter:  von Kienlin, Andreas
Max-Planck Inst. fur Extraterrestische Phys.

Forfatter:  Diehl, Roland
Max-Planck Inst. fur Extraterrestische Phys.

Forfatter:  Zhang, Xiao-Ling
Max-Planck Inst. fur Extraterrestische Phys.
Abstract: The Crab Nebula is the only hard X-ray source in the sky that is both bright enough and steady enough to be easily used as a standard candle. As a result, it has been used as a normalization standard by most X-ray/gamma-ray telescopes. Although small-scale variations in the nebula are well known, since the start of science operations of the Fermi Gamma-ray Burst Monitor (GBM) in 2008 August, a ~ 7% (70 mCrab) decline has been observed in the overall Crab Nebula flux in the 15-50 keV band, measured with the Earth occultation technique. This decline is independently confirmed in the ~ 15-50 keV band with three other instruments: the Swift Burst Alert Telescope ( Swift /BAT), the Rossi X-ray Timing Explorer Proportional Counter Array (RXTE /PCA), and the Imager on-Board the INTEGRAL Satellite (IBIS). A similar decline is also observed in the ~ 3-15 keV data from the RXTE /PCA and in the 50-100 keV band with GBM, Swift /BAT, and INTEGRAL /IBIS. The pulsed flux measured with RXTE /PCA since 1999 is consistent with the pulsar spin-down, indicating that the observed changes are nebular. Correlated variations in the Crab Nebula flux on a ~ 3 year timescale are also seen independently with the PCA, BAT, and IBIS from 2005 to 2008, with a flux minimum in 2007 April. As of 2010 August, the current flux has declined below the 2007 minimum.
Published: in journal: Astrophysical Journal Letters (ISSN: 2041-8213) (DOI: http://dx.doi.org/10.1088/2041-8205/727/2/L40), vol: 727, issue: 2, pages: L40, 2011
DOI:
See the publication in DTU Orbit See the publication in DTU Orbit

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