NASA NTRS · 20120001447
When a Standard Candle Flickers: Crab Nebula Variations in Hard X-rays
Abstract
In 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.
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Wilson-Hodge, Colleen A., Cherry, M. L., Case, G. L., Baumgartner, W. H., Beklen, E., Bhat, P. N., Briggs, M. S., Camero-Arranz, A., Chaplin, V., Connaughton, V., Finger, M. H., Gehrels, N., Greiner, J., Jahoda, K., Jenke, P., Kippen, R. M., Kouveliotou, C., Krimm, H. A., Kuulkers, E., Lund, N., Meegan, C. A., Natalucci, L., Paciesas, W. S., Preece, R., Rodi, J. C.. 2011-09-07. When a Standard Candle Flickers: Crab Nebula Variations in Hard X-rays. https://ntrs.nasa.gov/citations/20120001447
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