Accretion Disk Spectra of the Ultra luminous X ray Sou - PDF document

Accretion Disk Spectra of the Ultra-luminous X-ray Sources in Nearby Spiral Galaxies and Galactic superluminal jet sourcesKen EbisawaKubota, T. Mizuno, K. Watarai Ultraluminous X-ray Sources (ULX)•Discovered with Einstein in nearby spiral Galaxies (e.g., Fabbiano1988) •10 keV)~1039erg s-Too bright for X-ray binaries, too dim for AGNMost sources are located off-center of the Galaxy (Colbert and Mushotzky1999) •�100 M¤not to exceed the Eddington Characteristics of ULX•Significant time variation (Source1 in IC342; Okada et al. 1998)•Compact object in nature Characteristics of ULX•low transition? (Source1 and 2 in IC342; Kubota et al. 2001)•Orbital modulation (?) from Source 2 (Sugihoet al. 2001) , from a ULX in Circinusgalaxy (Bauer et al. 2001)•Similar to Galactic black hole candidates “hot disk”problem in ULX and superluminal jet sources•ULX energy spectra–Thermal spectrum, like standard optically thick accretion disk (no advection, T) µDisk temperature too highfor given luminosity and mass, assuming Schwarzschild black hole (= 3 R(Okada et al. 1998; Makishima et al. 2000)Same problem in Galactic superluminal jet sources GRS1915+105 and GRO J1655-40 (Zhang, Cui and Chen 1997) M=1.8 M¤L= 0.4 LM=9 M¤L= 12 L M=100 M¤L= L M= 7 M¤L= 0.1 Lhot disk”problem in ULX and superluminal jet sourcesEither too large mass accretion rates(superluminosity) or too small massrequiredDisk color temperature for Schwarzschild black holeT~ 1.3/1.7) (M1/4 ( •Too hotaccretion disks in ULX and superluminal jet sources•To explain the observation, you need either too large massaccretionrate or too small mass, as long as standard diskaround Schwarzschild black holeis assumed Schwarzschild disk best- M=1.8 M¤L= 0.4 LM=9.4 M¤L= 11 L M=100 M¤L= L M= 7 M¤L= 0.1 L •Makishima et al. (2000) M=const, L OK with standard model Too small mass Too large mass accretion rate How to explain the “accretion disk?•Standard accretion disk around Kerr black hole may explain the hard disk spectra (Zhang, Cui and Chen 1997; Makishima et al. 2000)–= 3 R(Schwarzschild) à0.5 R(extreme Kerr)higher disk temperature possible Laorand PiranTransfer function”for a=0.998 available with xspecKerr diskScwarzschild Inclined Kerr disk is brighter in high energies •When the disk is face-on, the Kerr disk spectrum is not very different from the Schwarzschild case•Hard emission from innermost parts is enhanced for inclined Kerr disks (Doppler boosts)•edge on Kerr disk has very harder spectrum Kerr disk Schwarzschild disk Application of Kerr disk spectra•GRO J1655-–, d=3.2 kpc=1.7 fixed–M=16 M¤with a=0.998 (extremely Kerr)–M=7 M¤suggests a=0.68 to 0.88 (Gielinskiet al. 2001)Inclined Kerr disk model works to solve too-small mass problem–450 Hz QPO (Strohmayer2001) supports a standard disk around a spinning black hole (and Kluzniak Application of Kerr disk spectra•IC342 Source 1–on Kerr disk (d=4Mpc, TM=29 M¤and L=14 LNot much different from Schwarzschild case–on (i= 80°) Kerr disk (a=0.998)M= 355 M¤and L=0.9 Lproblem may be solved only ifthe disk is highly inclined•Still unreasonably large mass required–Kerr disk model is not plausiblefor ULX,because disk inclination should be random Slim disk (optically thick ADAF disk) –Emerges when L~ LOptically thick and geometrically thickdisk ~ 1, ln) ~10 for slim diskàcan be ~ 10 L Abramowiczet al. (1995) Unstable Slim disk (advection dominated) Slim disk Standard diskSoft state. From recent study of Galactic black hole candidates•Standard optically thick disk –Gravitational energy release ®T( r)µr -= const., LDisk instability–Energy release ®Disk compotonizationOptically thick ADAF disk –Energy release ®T( r)µr - T increaseM increase. T increaseM increase. Optically thick ADAF disk (slim disk) Wataraiet al. (2001)Lsaturates at high Tin(due to advection)IC342 spectral change explained well Strong disk comptonizationIC342 source 1, Schwarzschild disk with M=100 M¤, L=L(Tin = 0.6 keVPut comptonizingcorona with y=(4kT~0.5 ®soft photons comptonizedand appear in higher energy band•observed hard spectrum can be explained Slim disk model for ULX•Fitting ASCA IC342 Source 1 spectrum with Watraislim disk model (face-on, T= 1.7, pseudo-Newtonian potential)–M=23 M~ 6 LSlim disk model fit successful with reasonable mass and disk luminosity! SummaryStandard and near edge-on accretion diskaround Kerr black holecan explain the hard spectra of Galactic superluminal jet sources –Apparently hard spectra are due to relativistic effects•luminosity and hard spectra of ULXsmay be explained bySlim diskaround a few tens of Mblack hole –Such heavy black holes likely in massive star forming region