Surface brightness correction for compact extended sources observed by the AKARI Far-Infrared Surveyor in the slow-scan mode

摘要

Wepresentageneralsurfacebrightnesscorrectionmethodforcompactextendedsourcesimagedintheslow-scanpointedobservationmodeoftheFar-InfraredSurveyor(FIS)aboardtheAKARIinfraredastronomicalsatellite.OurmethodrecoverscorrectsurfacebrightnessdistributionmapsbyrescalingarchivedrawFISmapsusingthesurface-brightness-dependentinverseFISresponsefunction.Thefluxofatargetsourceisthenautomaticallycorrectedforasthesimplesumofsurfacebrightnesseswithintheadoptedcontourencirclingtheperimeterofthetarget(i.e.,contourphotometry).Thiscorrectionmethodiscontrastedwiththepreviousaperturephotometrymethodforpointsources,whichdirectlycorrectsforthetargetfluxwithaflux-dependentscalinglaw.Thenewsurfacebrightnesscorrectionschemeisapplicabletoobjectsofanyshapefromunresolvedpointsourcestoresolvedextendedobjects,aslongasthetargetisnotdeemeddiffuse,i.e.,thetotalextentofthetargetsourcedoesnotexceedtoomuchmorethanasingleFISscanwidthof10??.Thenewcorrectionmethodtakesadvantageofthewell-definedshape(i.e.,thescaleinvariance)ofthepointspreadfunction,whichenablesustoadoptapower-lawFISresponsefunction.WeanalyzethepointsourcephotometriccalibratordatausingtheFISAKARISlow-scanToolandconstraintheparametersoftheadoptedpower-lawFISresponsefunction.Weconcludethatthephotometricaccuracyofthenewcorrectionmethodisbetterthan10%errorbasedoncomparisonswiththeexpectedfluxesofthephotometriccalibrators,andthatresultingfluxeswithoutthepresentcorrectionmethodcanleadtoupto230%overestimatesordownto50%underestimates.