1. Ultraluminous X-ray sources (ULXs) are promising candidates for intermediate-mass black holes. Here we report about the Suzaku observation of two ULXs, X-1 and X-2, in NGC1313, both showed intensity-correlated spectral changes over a time span of 90 ks. The brighter source, X-1, exhibited the highest luminosity, 2.5 x 10 40 erg/s in 0.4-10 keV, ever recorded from this source. The intensity and spectral variations of X-1 are both ascribed to a strong power-law like component with a mild high energy curvature, while about 10 % of the flux is carried by a stable soft component which can be modeled by a cool disk emission. These properties suggest that the source was in the “very high state”, wherein the disk emission is strongly Comptonized and the optically-thick disk is truncated at a large radii or cooled off. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with the innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source becomes brighter. Hence X-2 is consistently interpreted to be in a slim disk state. These results suggest that the two ULXs have black hole masses of a few tens to a few hundreds solar masses. Suzaku Observation of Two Ultraluminous X-Ray Sources in NGC1313 Ultraluminous X-ray sources (ULXs): Abstract: Point-like X-ray sources with Lx>=3x10 39 erg/s Discovered by Einstein Observatory (Fabbiano 1989). Extensively studied by ASCA, XMM-Newton and Chandra (Makishima et al. 2000, Swartz et al. 2004, Stobbart et al. 2006) Promising candidate for intermediate-mass black holes. Key to understand spectral states of black holes. Study of spectral change is important T. Mizuno, H. Takahashi (Hiroshima Univ.), R. Miyawaki, K. Makishima (Tokyo Univ.), M. Miyamato (RIKEN/Tokyo Univ. of Science), K. Ebisawa (ISAS/JAXA), A. Kubota (RIKEN), Y. Ueda (Kyoto Univ.) and NGC1313 team NGC 1313 in X-rays: Observed by Suzaku on October 15 th net exposure 28ks (gross span of 90ks) Suzaku Observatoin of X-1 and X-2: XIS data of X-1: ( 「すざく」による NGC1313 中の大高度Ｘ線源の観測 ) 10 -2 10 -1 10 0 BHBBHB ULX? AGN 10 0 10 2 10 4 10 6 10 810 M82 IMBH? LLAGN L/LEL/LE NLSy1 M/M◎M/M◎ XIS0 (0.3-10 keV) X-1 X-2 SN1978K Cal sources 10′ 110100 Energy(keV) Low State Slim Disk High State Very High State Low State High State Very High State Slim Disk Nearby face-on Sb galaxy at D=3.7Mpc (Tully 1988) Hosts three X-ray luminous sources X-1 and X-2 have been extensively studied in X-rays (in 1993 and 1995 by ASCA, more than 15 times by XMM and 8 times by Chandra. Ideal target for ULXs study Highest luminosity ever reported (Lx~2.5 x 10 40 erg/s) Clear time variability by ~50 % (soften in brighter phase) fainter phase brighter phase XMM archival data 2004 June 5 2003 Dec 21, 2004 Jan 8 and 17 2000 Oct 17 and 2005 Feb 7 2003 Aug 23 (Miller et al. 2003; Feng & Kaaret 2006 ) Low-temp MCD Tin~0.2keV variable cutoff PL brighter phase fainter phase Stable cool disk + highly variable power-law with cutoff Similar to the very high state in Galactic BHB brighter phase fainter phase XIS data of X-2: Similar to ASCA/XMM spectra Clear time variability by ~50 % (soften in fainter phase) fainter phase brighter phase p-free disk model p=0.63, Rin=43 km MCD model Rin=96 km HXD-PIN Summary : ULXs are promising candidates for intermediate BHs. Missing link to connect stellar-mass BH and AGN a key to understand the BH radiation in a unified picture NGC1313 in X-rays host two ULXs which have been studied extensively by ASCA, Chandra and XMM-Newton Suzaku Observation of UGC1313 ULXs (X-1 and X-2) Intensity-correlated variability in 90ks for both ULXs X-1 (source closer to the nucleus)  highest flux ever reported (Lx~2.5 x 10 40 erg/s)  stable cool disk + variable power-law with cutoff  similar to the very high state in Galactic BHBs  M~200M sun to satisfy Eddington limit X-2 (off-nucleus source)  Single MCD for fainter phase and p-free model for brighter phase  common locus on a Ldisk-Tin diagram with ASCA data. Interpreted to be in the slim disk state. M~50M sun. See also Miyamoto et al. (this meeting) for XMM data of NGC1313 ULXs Data – NXB vs. CXB No significant detection of hard tail. Could constrain the spectral model with improved BG models (<=3% systematic errors) Stellar mass BHs 10 40 10 39 10 38 HR-diagram (Ldisk vs. Tin) for ULXs in high state/slim disk L (erg/s) L ∝ T 2 Advection Dominated Disk (Slim Disk) L ∝ T 4 Standard Disk M~200M sun is required to satisfy the Eddington limit Successful MCD fit to fainter phase data and p-free model fit to brighter phase data consistently interpreted to be in the slim disk state. XMM archival data 2003 Dec 21, 23, 2006 June5 and 2005 Feb 7 2003 Dec 25 2000 Oct 1, 2004 Jan 8, 16 and Nov 23 (Miller et al. 2003; Feng & Kaaret 2006 ) M~50M sun NGC1313 X-2 ULXs