主要内容:
这里的标准烛光指的是用来校准仪器的，不是计算距离的。
精彩摘抄:
文章信息:
- · arXiv e-print (arXiv:1010.2679)
- · References in the Article
- · Also-Read Articles (Reads History)
- ·
- · Translate This Page
| Title: |
| When A Standard Candle Flickers |
| Authors: |
| Wilson-Hodge, Colleen A.; Cherry, Michael L.; Baumgartner, Wayne H.; Beklen, Elif; Narayana Bhat, P.;Briggs, Michael S.; Camero-Arranz, Ascension; Case, Gary L.; Chaplin, Vandiver; Connaughton, Valerie; Finger, Mark H.;Gehrels, Neil; Greiner, Jochen; Jahoda, Keith; Jenke, Peter; Kippen, R. Marc; Kouveliotou, Chryssa; Krimm, Hans A.;Kuulkers, Erik; Meegan, Charles A.; Natalucci, Lorenzo; Paciesas, William S.; Preece, Robert; Rodi, James C.;Shaposhnikov, Nikolai; Skinner, Gerald K.; Swartz, Doug; von Kienlin, Andreas |
| Publication: |
| eprint arXiv:1010.2679 |
| Publication Date: |
| 10/2010 |
| Origin: |
| ARXIV |
| Keywords: |
| Astrophysics - High Energy Astrophysical Phenomena |
| Comment: |
| 22 pages, 5 figures; Submitted to Astrophysical Journal Letters |
| Bibliographic Code: |
| 2010arXiv1010.2679W |
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 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 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 INTEGRAL Joint European Monitor (JEM-X) and in the 50 - 100 keV band with GBM and INTEGRAL/IBIS. Observations from 100 to 500 keV with GBM suggest that the decline may be larger at higher energies. 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.
没有评论:
发表评论