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When a Standard Candle Flickers: Crab Nebula Variations in Hard X-raysIn the first two years of science operations of the Fermi Gamma-ray Burst Monitor (GBM) since August 2008, a ~7% (70 mcrab) decline was 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 four other instruments: Swift/BAT, the RXTE/PCA, INTEGRAL/IBIS, and INTEGRAL/SPI. 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, INTEGRAL/IBIS, and INTEGRAL/SPI. 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, IBIS, and SPI from 2005 to 2008, with a flux minimum in April 2007. As of April 2011, the Crab nebula flux has stopped declining and may be beginning to increase. We will present updated results on our multi-instrument study of long-term Crab nebula variations.
Document ID
20120001447
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Wilson-Hodge, Colleen A. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Cherry, M. L. (Louisiana State Univ. LA, United States)
Case, G. L. (Louisiana State Univ. LA, United States)
Baumgartner, W. H. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Beklen, E. (Middle East Technical Univ. Ankara, Turkey)
Bhat, P. N. (Alabama Univ. Huntsville, AL, United States)
Briggs, M. S. (Alabama Univ. Huntsville, AL, United States)
Camero-Arranz, A. (Universities Space Research Association Huntsville, AL, United States)
Chaplin, V. (Alabama Univ. Huntsville, AL, United States)
Connaughton, V. (Alabama Univ. Huntsville, AL, United States)
Finger, M. H. (Universities Space Research Association Huntsville, AL, United States)
Gehrels, N. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Greiner, J. (Max-Planck-Inst. fuer Extraterrestrische Physik Germany)
Jahoda, K. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Jenke, P. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Kippen, R. M. (Los Alamos National Lab. NM, United States)
Kouveliotou, C. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Krimm, H. A. (Universities Space Research Association Greenbelt, MD, United States)
Kuulkers, E. (INTEGRAL Science Data Center for Astrophysics Versoix, Switzerland)
Lund, N. (Danish National Space Center Denmark)
Meegan, C. A. (Universities Space Research Association Huntsville, AL, United States)
Natalucci, L. (Istituto di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Rome, Italy)
Paciesas, W. S. (Alabama Univ. Huntsville, AL, United States)
Preece, R. (Alabama Univ. Huntsville, AL, United States)
Rodi, J. C. (Louisiana State Univ. LA, United States)
Date Acquired
August 25, 2013
Publication Date
September 7, 2011
Subject Category
Astronomy
Report/Patent Number
M11-0563
Meeting Information
Meeting: 2011 meeting of the High Energy Astrophysics Division of the American Astronomical Society
Location: Providence, RI
Country: United States
Start Date: September 7, 2011
End Date: September 10, 2011
Sponsors: American Astronomical Society
Distribution Limits
Public
Copyright
Public Use Permitted.

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