Upper Limits of Iron Line Flux in X-Ray Afterglow of Two Gamma-Ray Bursts with ASCA

[摘要] TheironemissionlineintheX-rayafterglowspectraofaGamma-RayBurstisthoughttobeakeytounderstandingtheenvironmentofprogenitors.AlthoughtwoindependentobservationswithBeppoSAXandASCAreportedstrongred-shiftedironemissionline,thestatisticalsignificanceofthesedetectionswasnotveryhigh.FurtherobservationswereexpectedandtwomoreGRBs,GRB990123andGRB990704,wereobservedwiththeX-raysatelliteASCAin1999.Thespectraofthesetwoafterglowscanbeexplainedbyasimplepower-lawmodelwithexcessabsorption,butwithoutanyironemission-linefeature.The90%upperlimitfortheironlinefluxisaslowasFFe=3.3×10−6photonscm−2s−1,orlessthan∼100eVinequivalentwidth(EW).Thisupperlimitisanorder-of-magnitudesmallerthantheprevioustwodetectionsof1–3keVinEW.

[学科分类] 天文学(综合)

[关键词] "gamma-ray burst: general";hypernovae;"line: formation";"stars: neutron"