A Comprehensive Study of Short Bursts from SGR1806$-$20 and SGR1900$+$14 Detected by HETE-2

[摘要] Temporalandspectralstudiesofshortbursts($$lesssim$$afewhundredmilliseconds)arepresentedforthesoftgammarepeaters(SGRs)1806$$-$$20and1900$$+$$14usingtheHETE-2samples.Infiveyearsfrom2001to2005,HETE-2localized50burstsfromSGR1806$$-$$20and5burstsfromSGR1900$$+$$14.Thecumulativenumber–intensitydistributionofSGR1806$$-$$20intheactiveyear2004iswelldescribedbyapower-lawmodelwithanindexof$$-$$1.1$$pm$$0.6.Itisconsistentwithpreviousstudies,butburstdatatakeninotheryearsclearlygiveasteeperdistribution.Thismaysuggestthatmoreenergeticburstscouldoccurmorefrequentlyinperiodsofgreateractivity.Fromthedata,thespectralevolutionduringburstswithatimescaleof$$gtrsim$$20 msdoesnotseemtobecommonintheHETE-2sample.Thespectraofallshortburstsarewellreproducedbyatwoblackbodyfunctionwithtemperaturesof$$sim4$$and$$sim11$$keV.FromatiminganalysistotheSGR1806$$-$$20data,atimelagof2.2$$pm$$0.4 msisfoundbetweenthe30–100 keVand2–10 keVradiationbands.Thismayimply(1)averyrapidspectralsofteningandenergyreinjection,(2)diffused(elongated)emissionplasmaalongthemagneticfieldlinesinpseudo-equilibriumwithmulti-temperatures,or(3)aseparate(locatedat$$lesssim$$700 Km)emissionregionofasoftercomponent(say,$$sim$$4 keV),whichcouldbereprocessedX-raysbyhigherenergy($$gtrsim$$11 keV)photonsfromanemissionregionnearthestellarsurface.

[学科分类] 天文学(综合)

[关键词] "gamma rays: general";"pulsars: individual(SGR 1806–20;SGR 1900+–X-rays: stars"