Publications (2)0 Total impact
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Colleen A. Wilson-Hodge,
Michael L. Cherry,
Wayne H. Baumgartner,
Elif Beklen,
P. Narayana Bhat,
Michael S. Briggs,
Ascension Camero-Arranz,
Gary L. Case,
Vandiver Chaplin,
Valerie Connaughton, [......],
Lorenzo Natalucci,
William S. Paciesas,
Robert Preece,
James C. Rodi,
Nikolai Shaposhnikov, Gerald K. Skinner,
Doug Swartz,
Andreas von Kienlin,
Roland Diehl,
Xiao-Ling Zhang
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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.
10/2010; 43.
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Hans A. Krimm,
Scott D. Barthelmy,
Neil Gehrels,
Jack Tueller,
Wayne H. Baumgartner,
Jay R. Cummings,
Taka Sakamoto,
Edward E. Fenimore,
David M. Palmer,
Craig B. Markwardt, Gerald K. Skinner,
Michael Stamatikos
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ABSTRACT: The Swift Burst Alert Telescope (BAT) hard X-ray transient monitor tracks more than 700 galactic and extragalactic sources on time scales ranging from a single Swift pointing (approximately 20 minutes) to one day. The monitored sources include all objects from the Fermi LAT bright source list which are either identified or which have a 95% error confidence radius of less than eight arc minutes. We report on the detection statistics of these sources in the BAT monitor both before and after the launch of Fermi. Comment: 2009 Fermi Symposium; eConf Proceedings C091122
12/2009;
