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When a standard candle flickers
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Gehrels, Neil Greiner, Jochen Bhat, P. Narayana Cherry, Michael L. Case, Gary L. Wilson-Hodge, Colleen A. Preece, Robert Kippen, R. Marc Rodi, James C. Baumgartner, Wayne H. Chaplin, Vandiver Connaughton, Valerie Finger, Mark H. Jahoda, Keith Jenke, Peter Paciesas, William S. Meegan, Charles A. Kuulkers, Erik Kouveliotou, Chryssa Briggs, Michael S. Camero-Arranz, Ascension Natalucci, Lorenzo Krimm, Hans A. Lund Sr., Niels |
| Copyright Year | 2011 |
| Description | 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 August 2008 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 INTErnational Gamma-Ray Astrophysics Laboratory Imager on Board INTEGRAL (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 change in 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 April 2007. As of August 2010, the current flux has declined below the 2007 minimum. |
| File Size | 612539 |
| Page Count | 7 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_20110014630 |
| Archival Resource Key | ark:/13960/t6qz7746v |
| Language | English |
| Publisher Date | 2011-01-01 |
| Access Restriction | Open |
| Subject Keyword | Astrophysics Swift Observatory Beklen Elif Gamma Ray Telescopes Crab Nebula Proportional Counters X Ray Timing Explorer Occultation Gamma Ray Bursts X Ray Sources Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
