Multiple-Component Analysis of the Time-Resolved Spectra of GRB041006: A Clue to the Nature of the Underlying Soft Component of GRBs

摘要

GRB041006wasdetectedbyHETE-2on2004October06.Thelightcurvesinfourdifferentenergybandsdisplaydifferentfeatures.Athigherenergybandsseveralpeaksareseeninthelightcurve,whileatlowerenergybandsasinglebroaderbumpdominates.Itisexpectedthatthesedifferentfeaturesaretheresultofamixtureofseveralcomponents,eachofwhichhasdifferentenergeticsandvariability.Weanalyzedthetime-resolvedspectra,whichwereresolvedintoseveralcomponents.Thesecomponentscanbeclassifiedintotwodistinctclasses.Oneisacomponentthathasanexponentialdecayof$$E_{ mp}$$withacharacteristictimescaleshorterthan$$sim;$$30s;itsspectrumiswellrepresentedbyabrokenpower-lawfunction,whichisfrequentlyobservedinmanypromptGRBemissions,soitshouldhaveaninternal-shockorigin.Anotherisacomponentwhose$$E_{ mp}$$isalmostunchangedwithacharacteristictimescalelongerthan$$sim;$$60s,andshowsaverysoftemissionandslowervariability.Thespectrumischaracterizedbyeitherabrokenpowerlaworablack-bodyspectrum.Byassumingthatthesoftcomponentisathermalemission,theradiationradiusisinitially$$4.4 imes10^{6}$$km,whichisatypicalradiusofabluesupergiant,anditsexpansionvelocityis$$2.4 imes10^{5}$$kms$$^{-1}$$inthesourceframe.