ASCA Observations of Two Ultraluminous IRAS Galaxies: IRAS 15307+3252 and IRAS 20460+1925

摘要

WereportonASCAobservationsoftwoultraluminousfar-infraredgalaxies,IRAS15307+3252andIRAS20460+1925.AnX-rayfluxof1.53?—10a?’12ergcma?’2sa?’1inthe2a€“10keVbandwasdetectedfromIRAS20460+1925.Thecontinuousspectrumiswellrepresentedbyapowerlawwithaphotonindexof1.99+0.18a?’0.15andexcessphotoelectricabsorptionbyacolumnof(2.6+0.29a?’0.32?—1022cma?’2intherestframe.ThespectrumalsoshowsanironKemissionlinewithanequivalentwidthof260+145a?’137eVandacentroidenergyof6.36?±0.08keVintherestframe.ThesespectralpropertiesareconsistentwiththoseofSeyfert-2galaxies,althoughtheintrinsic2a€“10keVX-rayluminosity(correctedforabsorption)of1.20?—1044ergsa?’1ishighandclosetothatofquasars.NoX-raysweredetectedfromIRAS15307+3252,andtheupperlimittotheX-rayfluxis7.2?—10a?’14ergcma?’2sa?’1inthe2a€“10keVband.However,theupperlimitontheratiooftheX-rayfluxtothefar-infraredfluxisnotinconsistentwithasourcecontainingahighlyobscuredquasar.