Spectral transition of ultraluminous X-ray source, NGC 2403 SRC3

1. Spectral transition of ultraluminous X-ray source, NGC 2403 SRC3 N. Isobe (RIKEN, Suzaku Help Desk) and Suzaku SWG team of NGC 2403 K. Makishima (RIKEN/U. Tokyo), M. Kawaharada, A. Senda (RIKEN), H. Takahashi, T. Mizuno (Hirishima U.), R. Miyawaki (U. Tokyo), T. Yoshida (Tokyo Univ of Schience), R. Mushotzky (GSFC/NASA) 8 Years of Science with Chandra

2. Ultraluminous X-ray Sources (ULXs) • X-ray point sources with a luminosity of L >> 1039 ergs s-1, frequently found in nearby normal galaxies (Fabbiano et al. 1989) • Promising candidate of intermediate mass black holes with a mass of M >> 10 M◎, (M◎ is the solar mass). (e.g. Makishima et al. 2000) • Two spectral states (e.g., Kubota et al. 2001) • Multi-color disk (MCD) and Power Law (PL) • Important sources to study black holes at high accretion rate. 8 Years of Science with Chandra

3. Suzaku • 5th Japanese X-ray observatory, launched in June 2005 (Mitsuda et al. 2007) • Two instruments • X-ray Imaging Spectrometer (XIS) • 3 FI and 1 BI CCDs • 0.2 – 12 keV • Hard X-ray Detector (HXD) • PIN : 10 – 70 keV • GSO : 40 – 600 keV • Advantages • Low and stable background • Good energy resolution • High sensitivity • Wide energy band • Results on ULXs • NGC 1313 (Mizuno et al, 2007) • Suzaku J1305-4931 (Isobe et al. 2008) Suzaku XIS HXD @ Terada (Saitama U.) 8 Years of Science with Chandra

4. NGC 2403 • Spiral galaxy (SABcd) at a distance of 3.2 ± 0.4 Mpc (Freedman & Madore 1988) • Several bright X-ray sources, including ULX. (Fabianno & Trinchieri 1987) • Suzaku observation on March 16th, 2006 during SWG phase • ASCA observation in 1997 (Kotoku et al.,1999) • Discovery of a supernova SN2004dj motivated a series of Chandra, XMM-Newton observations SRC5 SRC3 4 arcmin = 3.7 kpc Suzaku XIS image (0.5 – 10 keV) Optical image (DSS) 8 Years of Science with Chandra

5. Suzaku Spectrum of SRC3 • Suzaku XIS spectrum of NGC 2403 SRC 3 • is successfully described with multi-temperature black body emission from accretion disk (Multi-color disk model; MCD). • Tin = 1.09 ± 0.03 keV • Rin = 116.9 + 5.9 – 5.5 km • Lbol = 1.75 x 1039 ergs s-1 • is not fitted with a PL model. MCD XIS 0+2+3 (FI) XIS 1 (BI) MCD(c2 = 296.5/334 ) PL (c2 = 585.3 / 334) 8 Years of Science with Chandra

6. SRC3 SRC5 Relation between Lbol and Tin (Kotoku et al. 2000, Makishima et al. 2000, Isobe et al. 2007 and reference therein) 8 Years of Science with Chandra

7. Spectral transition of SRC3 • Only the Chandra data obtained in December, 2004 showed the PL-like spectrum. • G = 2.37 ± 0.07 • The X-ray flux of the observation is slightly smaller than the Suzaku observation by 15 %. • Spectral transition between the MCD-like and the PL-like states is • Frequently observed in Galactic black holes. • Observed in some well-studied ULXs. (e.g. Kubota et al. 2001) Suzaku (2006 May) MCD Chandra (2004 Aug.) MCD Chandra (2004 Dec.) PL Newton (2004 Sep.) MCD Chandra (2004 Aug.) Chandra (2004 Dec.) Newton (2004 Sep.) Ratio to the best-fit MCD model to Suzaku data 8 Years of Science with Chandra

8. Slim disk state (MCD-like) Very high state (PL-like) High/Soft state (MCD) Low/Hard state (PL) 100 1 10 Energy [keV] Spectral states of black holes Lbol / LEdd Spectral transition of NGC 2403 SRC 3 Slim disk state ⇔ Very high state 1 2< G < 3 0.1 G < 2 Suzaku XIS Chandra/Newton 0.01 8 Years of Science with Chandra (e.g. Kubota et al. 2004)

9. Slim disk scenario for SRC 3 Standard disk (in MCD) • Radial temperature profile • T ∝ r -0.75 Slim disk • Advection and/or photon trapping become important. ⇒ Flat profile (Watarai et al. 2000) • T ∝ r –p with 0.5 < p < 0.75 (p-free disk model; Mineshige et al. 1994, Vierdayanti et al. 2006) Summary of p-free disk fitting MCD : p = 0.75 (Standard disk) Limit in Slim disk state p = 0.5 8 Years of Science with Chandra

10. Summary • We examined the spectral variation of the ULX, NGC 2403, in nearly 10 years, using ASCA, Suzaku, Chandra and XMM-Newton. • NGC 2403 SRC3 showed the MCD-like spectra, except for one Chandra observation. • Tin = 1.09 ± 0.03 keV • Rin = 116.9 + 5.9 – 5.5 km (in the Suzaku Observation) • Lbol = 1.75 x 1039 ergs s-1 • We found the transition to the PL-like spectrum in the Chandra observation, conducted on December 2004, with the flux about 10 % lower than the other observations. • G = 2.37 ± 0.07 • The spectral transition of NGC 2403 SRC 3 can be naturally explained to be a transition between Very High state (PL-like) and slim disk state (MCD-like). 8 Years of Science with Chandra

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12. Chandra image 8 Years of Science with Chandra

13. Spectral transition of SRC 3 PL Chandra ACIS S5 MCD (c2 = 194.8/123) PL (c2 = 110.7/123) 8 Years of Science with Chandra