WHEN A STANDARD CANDLE FLICKERS

Journal Article · Tue Feb 01 04:00:00 EST 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/727/2/L40· OSTI ID:21560521

Wilson-Hodge, Colleen A; Jenke, Peter; Kouveliotou, Chryssa ^[1]; Cherry, Michael L; Case, Gary L ^[2]; Baumgartner, Wayne H; Krimm, Hans A ^[3]; Beklen, Elif ^[4]; Bhat, P Narayana; Briggs, Michael S; Chaplin, Vandiver; Connaughton, Valerie ^[5]; Camero-Arranz, Ascension ^[6]; Finger, Mark H ^[7]; Gehrels, Neil; Jahoda, Keith ^[8]; Greiner, Jochen ^[9]; Kippen, R Marc ^[10]; Kuulkers, Erik ^[11]; Lund, Niels ^[12]

---

1. VP 62 Space Science Office, NASA Marshall Space Flight Center, Huntsville, AL 35812 (United States)
2. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States)
3. CRESST/NASA GSFC, Astrophysics Science Division, Greenbelt, MD 20771 (United States)
4. Physics Department, Middle East Technical University, 06531 Ankara (Turkey)
5. University of Alabama in Huntsville, Huntsville, AL 35899 (United States)
6. National Space Science and Technology Center, Huntsville, AL 35805 (United States)
7. Universities Space Research Association, Huntsville, AL 35805 (United States)
8. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD 20771 (United States)
9. Max-Planck Institut fuer Extraterrestische Physik, 85748 Garching (Germany)
10. Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
11. ISOC, ESA, European Space Astronomy Centre (ESAC), P.O. Box 78, 28691 Villanueva de la Canada (Madrid) (Spain)
12. Danish National Space Center, Technical University of Denmark, Juliane Maries Vej 30, 2100 Copenhagen (Denmark)

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 2008 August, a {approx}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 {approx}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 Imager on-Board the INTEGRAL Satellite (IBIS). A similar decline is also observed in the {approx}3-15 keV data from the RXTE/PCA and in the 50-100 keV band with GBM, Swift/BAT, and INTEGRAL/IBIS. 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 {approx}3 year timescale are also seen independently with the PCA, BAT, and IBIS from 2005 to 2008, with a flux minimum in 2007 April. As of 2010 August, the current flux has declined below the 2007 minimum.

• OSTI ID: 21560521
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 727; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMIC GAMMA BURSTS
COSMIC RADIATION
COSMIC RADIO SOURCES
CRAB NEBULA
ELECTROMAGNETIC RADIATION
HARD X RADIATION
IONIZING RADIATIONS
MEASURING INSTRUMENTS
NEBULAE
PRIMARY COSMIC RADIATION
PROPORTIONAL COUNTERS
PULSARS
RADIATION DETECTORS
RADIATION SOURCES
RADIATIONS
SUPERNOVA REMNANTS
X RADIATION
X-RAY SOURCES