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Suzaku Observation of Two Ultraluminous X-Ray Sources

in NGC1313

December 7, 2006 @ Suzaku 2006 Conference

T. Mizuno, R. Miyawaki, K. Ebisawa, A. Kubota,M. Miyamoto, L. Winter, Y. Ueda, N. Isobe, K. Makishima

and the NGC1313 team

mizuno@hepl.hiroshima-u.ac.jp

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Ultraluminous X-ray sources (ULXs)Ultraluminous X-ray sources (ULXs)

•X-ray sources with Lx>=3x1039 erg/s : Ledd>20Msun

•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)•Often associated with regions of start formation.•Show variability by a factor of ~5.•Two spectral states: PL and MCD (La Paroal et al. 2001, Kubota et al. 2001)

•Promising candidate for intermediate-mass black holes (IMBHs).•Key to understand the black hole radiation in high accretion rate. Study of spectral change is important

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Four Spectral States of Galactic BHBsFour Spectral States of Galactic BHBs

1 10 100Energy(keV)

Low State

Slim Disk

High State

Very High State

Low State

High State

Very High State

Slim Disk

PL with thermal cutoff

PL

Opt. thick disk

PL with cutoff(disk photon

Comptonization)

Opt. thick cool/truncated disk

Opt. thick high-temp disk

High Luminosity

Low Luminosity

McClintock & Remillard 2006Kubota & Makishima 2004

ULXs are important to verify the unified picutre of BH radiation

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Suzaku observation of NGC1313Suzaku observation of NGC1313

XIS0 (0.3-10 keV)

X-1

X-2Cal sources

7′

•Nearby face-on Sb galaxy at d=3.7Mpc •Hosts three X-ray luminous sources•X-1 and X-2 have been extensively studied in X-rays (twice by ASCA, more than 15 times by XMM and 8 times by Chandra.

•Ideal target for ULXs study•Observed on 2005 October 15 for 90 ks (net exposure ~30 ks)

SN1978K

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Time-averaged Spectra of X-1/X-2Time-averaged Spectra of X-1/X-2

X-1

X-2

XIS0 (0.3-10 keV)

X-1

X-2

Crab Ratio (arbitrary)

Energy (keV) 101

Lx=2.5 x 1040 erg/sPL-like with HE cutoff

Lx=6 x 1039 erg/sMCD-like convex spectrum

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X-2: Light Curve/SpectraX-2: Light Curve/Spectra

HF phaseLF phase

Lx=6 x 1039 erg/s

XIS(FI) Light Curve

XMM archival data2003/12/21,12/23, 2005/2/7,2006/6/52003/12/252000/10/17, 2004/1/8, 1/16 and 1/23

HFLF

(Miller et al. 2003; Feng & Kaaret 2006)

Unfolded Spectra

MCD-type with Tin=1.2-1.6 keV

PL-type (~2.2)

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Spectral Variability of X-2Spectral Variability of X-2•Intensity change by ~50%•Spectral change: hardens as the source gets brighter

•HF phase: p-free •(Tin=1.86 keV, p=0.63, =151/143)

•HF phase: MCD •(Tin=1.50 keV, 1Rin=80 km, 2/=172/144)

•LF phase: MCD •(Tin=1.24 keV, Rin=100 km, 2/=72/76)

Suzaku BI spectra

X2 is inSlim Disk State

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X-1: Light Curve/SpectraX-1: Light Curve/Spectra

HF phase

LF phase

Lx=2.5 x 1040 erg/s

XMM archival data2004/6/52003/12/21, 2004/1/8 and 1/172000/10/17 and 2005/2/7 Oct 172003/8/23

HFLF

(Miller et al. 2003; Feng & Kaaret 2006)

Suzaku data:PL-type with HE cutoff

most of XMM data:PL-type with =1.7-2.4

Highest Luminosity ever observed (2.5 x 1040 erg/s)

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Spectral Variability of X-1Spectral Variability of X-1•Spectrum changes above 1keV•Opposite to X-2: softens as the source gets brighter

•p-free fit:HF phase: Tin=2.1 keV, p=0.60, 2/=243/219LF phase: Tin=2.7 keV, p=0.51, 2/=84/95

Contradict to Slim Disk prediction

•p-free fit:HF phase: Tin=2.1 keV, p=0.60, /=243/219LF phase: Tin=2.7 keV, p=0.51, 2/=84/95

•MCD+cutoffPL fit:HF phase: =0.9, Ec=3.4 keV, 2/=240/218LF phase: =1.6, Ec=6.0 keV, 2/=83/94

•Variable cutoff PL:dominate the spectrumcomptonization

•Stable coold disk (Rin=4000 km, Tin=0.2 keV):

disk truncated (or cooled) due to comptonization

Likely to be in theVery High State

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Note on BH massNote on BH mass

•X-2 is interpreted to be in Slim Disk State Lx is close to Ledd

Medd~50Msun

•X-1 is likely to be in the Very High StateLx <=Ledd

M>=200Msun

Even if a super-Eddington condition by a factor of 3 is allowed, M>=70Msun is required.

ULXs in NGC1313 are IMBH

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SummarySummary

•ULXs are promising candidates of IMBH.•Spectral change is a key to understand ULXs/BH radiation

•Suzaku found intensity-correlated spectral changes from two ULXs in NGC1313 and strengthened the analogy to BHBs•X-1 and X-2 are interpreted to be in the Very High State dominated by Comptonization and the Slim Disk State shining close to the Eddingtion limit, respectively.•M>=50Msun -> IMBH

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BackUp SlidesBackUp Slides

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HR-diagram of BHB/ULXsHR-diagram of BHB/ULXs

Stellar mass BHs

1040

1039

1038

L(erg/s)

L T∝ 2

Advection Dominated Disk(Slim Disk)

L T∝ 4

Standard Disk

NGC1313 X-2

ULXs

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Spectral Variability of X-2Spectral Variability of X-2•Intensity change by ~50%•Spectral change: hardens as the source gets brighter

•HF phase: p-free Tin=1.86 keV, p=0.63, =151/143

•HF phase: MCD Tin=1.50 keV, 1Rin=80 km, 2/=172/144

•LF phase: MCD (p=0.75) Tin=1.24 keV, Rin=100 km, 2/=72/76

•Employ a p-free disk model to examine a disk temperature profile

Standard disk (MCD): p=0.75Slim disk: p=0.75-->0.5 (Watarai et al. 2001)

prrTrT inin /

Suzaku BI spectra

X2 is inSlim Disk State