Spectral Variation of Hard X-Ray Emission from the Crab Nebula with the Suzaku Hard X-Ray Detector

摘要

TheCrabNebulaisoneofthebrightestandmoststablesourcesintheX-raysky.Year-scalefluxvariationfromtheobjectwasrecentlyrevealedinthehardX-raybandbyfoursatellites.Thismarkedthefirstdetectionofyear-scalevariabilityfrompulsarwindnebulaeinthehardX-rayband.TheCrabNebulahasbeenobservedatleastonceayearforcalibrationpurposeswiththeSuzakuHardX-rayDetector(HXD)sinceitslaunchin2005.Inordertoinvestigatepossiblespectralchangesaswellasfluxvariation,archivaldataoftheHXDwereanalyzed.Thefluxvariationreportedbyotherinstrumentswasconfirmedinthe25a€“100keVbandbytheHXDatafewpercentlevel,butfluxabove100keVdidnotfollowthetrendinvariationbelow100keV.ThehardnessratiosproducedutilizingthePINandGSOsensorsinstalledintheHXDexhibitsignificantscattering,therebyindicatingspectralvariationsinthehardX-rayband.Thespectralchangeswerequantifiedbyspectralfittingwithabrokenpower-lawmodel.Thedifferencebetweenthetwophotonindexesofthebrokenpower-lawmodelinharderandsofterenergybandsisintherangeof$$$$2.54.Takingintoaccountafluxvariationof6.3%andaspectralvariationtime-scaleofafewdays,multicomponentsofthebrokenpower-law-shapedsynchrotronemissionwithdifferentcoolingtimesaresuggested.