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When a Standard Candle FlickersThe Crab is the only bright steady source in the X-ray sky. The Crab consists of a pulsar wind nebula, a synchrotron nebula, and a cloud of expanding ejecta. On small scales, the Crab is extremely complex and turbulent. X-ray astronomers have often used the Crab as a standard candle to calibrate instruments, assuming its spectrum and overall flux remains constant over time. Four instruments (Fermi/GBM, RXTE/PCA, Swift/BAT, INTEGRAL/ISGRI) show a approx.5% (50 m Crab) decline in the Crab from 2008-2010. This decline appears to be larger with increasing energy and is not present in the pulsed flux, implying changes in the shock acceleration, electron population or magnetic field in the nebula. The Crab is known to be dynamic on small scales, so it is not too surprising that its total flux varies as well. Caution should be taken when using the Crab for in-orbit calibrations.
Document ID
20100042150
Acquisition Source
Marshall Space Flight Center
Document Type
Presentation
Authors
Wilson-Hodge, Colleen A. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Cherry, M. L. (Louisiana State Univ. New Orleans, LA, 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. (National Space Science and Technology Center Huntsville, AL, United States)
Case, G. L. (Louisiana State Univ. New Orleans, LA, 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)
Greiner, J.
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. Albuquerque, NM, United States)
Kouveliotou, C. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Kuulkers, E.
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. New Orleans, LA, United States)
Shaposhnikov, N.
Swartz, D. (Universities Space Research Association Huntsville, AL, United States)
von Kienlin, A.
Date Acquired
August 25, 2013
Publication Date
September 27, 2010
Subject Category
Astronomy
Report/Patent Number
M10-1075
Meeting Information
Meeting: 8th INTEGRAL Workshop: Restless Gamma-Ray Universe
Location: Dublin, Ireland
Country: Ireland
Start Date: September 27, 2010
End Date: September 30, 2010
Sponsors: European Space Agency
Distribution Limits
Public
Copyright
Public Use Permitted.

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