1. 1 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Ultra-Luminous X-ray Sources -- Past Observations, Current Status and Future with Astro-H -- 2013 年 7 月 26 日 @ 広島大学 水野 恒史 ( 広島大学 宇宙科学センタ ー ) February 24 th, 2014 @ HXI/SGD Workshop Tsunefumi Mizuno (Hiroshima Univ.)

2. 2 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Plan of the Talk Introduction of ULXs Past Observations –Summary of properties based on ASCA, Chandra, XMM and Suzaku observations Current Status and Future –Latest results by NuSTAR, Prospects with ASTRO-H Note: This talk places weight on work by Japanese scientists with ASCA/Suzaku. US/European scientists also have been doing excellent work with Chandra/XMM and obtained similar (i.e., consistent) results.

3. 3 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. What are ULXs? IC342 X-1 IC342 X-2 ASCA+DSS image of IC 342 (taken from TM’s PhD thesis)

4. 4 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Two Spectral States They exhibit, at least, two spectral states –PL-like state when L X is low –MCD-like state when L X is high One may interpret this as a soft-state/hard-state transition often seen in Galactic BHB, but the situation is not so simple (see following slides) IC342 X-2 L X =0.8x10 40 ->1.4x10 40 IC342 X-1 L X =1.9x10 40 ->0.6x10 40 Kubota+01 (D=4 Mpc assumed) (See also Okada+1998 for initial results on IC342 ULXs)

5. 5 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. MCD-like State: L X -T in Relation In the MCD-like state, the spectral variation primarily seen in high energy This results in not L X ∝ T in 4 relation (as seen in Galactic BHB), but L X ∝ T in 2 relation (as predicted in “Slim Disk”) High-flux: T in =1.87 keV, f bol =15.5x10 -12 Low-flkux: T in =1.42 keV, f bol =9.0x10 -12 (5.1 for L ∝ T 4 -relation) Mizuno+01 IC342 X-1 in 1993

6. 6 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. MCD-like State: Deviation from Standard Disk Slim Disk also predicts a shallower temperature profile (than that of standard disk) which actually has been seen in some ULXs NGC1313 X-2 in 2005 Mizuno+07 MCD-like state is not so common compared to PL-like state, hence the interpretation has been not conclusive yet

7. 7 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. PL-like State: Spectral Turnover (1) Detailed re-analysis of the PL state of IC342 X-1 reveals a spectral turnover in high-energy, presumably by Comptonization like what is seen from very high state in Galactic BHB Kubota+02 IC342 X-1 in 2000 when fitted with PL in 0.7-4 keV Such HE “turnover” are often seen in apparently PL-state from many ULXs (see next)

8. 8 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. PL-like State: Spectral Turnover (2) Such HE turnover is ubiquitous in apparently PL-state of ULXs Some ULXs show double-hump, supporting the Comptonization scenario Gladstone+09

9. 9 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. PL-like State: Luminosity Dependence IC342 X-1, Yoshida+13 PL-like state exhibits distinct features not seen in Galactic BHBs –spectral slope much flatter (index of ~1.5 vs. ~2.5) –spectral turnover at lower energy when source is bright (~ 5 keV vs. >=20 keV) One explanation of such a low-temperature, optically-thick corona is supercritical accretion flows (e.g. Kawashima+09) –  -kT e relation should be investigated and understood MCD-like state (1993) PL-like state (2000) (See also Vierdayanti+10 for earlier work on Ho XI X-1)

10. 10 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Tasks for ASTRO-H With ASTRO-H we can (and should) do the followings 1) convincingly confirm the presence or absence of the shallower temperature profile in MCD-like state (HXI) –sensitivity is OK (sources are bright). we just need to be lucky to observe this “rare” state 2) convincingly detect absorption features expected in high-PL state if they really exists (SXS) 3) measure or strongly constrain the spectral turnover in low-PL state to understand the emission mechanism (HXI) Hereafter let’s discuss items (2) and (3) with the latest results by Suzaku, XMM and NuSTAR

11. 11 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Absorption Lines by ASTRO-H SXS In supercritical accretion scenario, absorption features are expected => task for A-H SXS However …. Simulation by Shidatsu (Kyoto Univ.) SXS/SXI, 150 ks IC342 X-1, high-PL state He-like/H-like Fe absorption (EW=30 eV) detected by 99.9%, velocity shift determined to within 250 km/s

12. 12 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Constraints on Line Features Strong constraints on emission/absorption line features for Ho IX X-1 by Suzaku Ho IX X-1 by Suzaku (500 ks) Both emission and absorption line restricted to EW<=30 eV in Fe-K band, lower than what is seen in Galactic BHB GRS 1915+105 NB the line features are geometry dependent, hence A-H SXS observation is still valuable Walton+13

13. 13 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Spectral Turnover by ASTRO-H HXI Spectral turnover not well constrained for low-PL state ASTRO-H HXI can constrain kT e up to ~20 keV IC342 X-1 in High/Low PL states (Yoshida+13) HXI sensitivity for continuum (rather conservatively assumed to be 10 -7 p/s/cm 2 /keV)

14. 14 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Spectral Turnover seen by NuSTAR Spectral turnover not well constrained for low-PL state NuSTAR starts to detect turnover and additional component Unfolded IC342 X-1 spectrum by XMM/NuSTAR clear detection of spectral turnover above 10 keV from low-PL state Also detect a “hint” of additional HE component, e.g., high-temp corona Commonly-seen in ULXs by NuSTAR (Ho IX X-1, NGC1313 X-1, Circinus X-5) =>their “investigation” is the task for A-H HXI RANA+14

15. 15 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Summary ULXs = sources with L X >=10 39 erg/s, requiring M BH =10-1000 M sun or  =1-100 They exhibit two spectral states, MCD-like state in high-L and PL-like state in low-L –not historical high/low states, but could be due to slim disk and Comptonization, respectively ASTRO-H will (should) reveal their nature –absorption line feature by SXS –shallower temperature profile, turnover and additional component (found by NuSTAR) by HXI Thank you for your Attention

16. 16 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Reference Colbert & Mushotzky 1999, ApJ 519, 89 Fabbiano 1989, ARA&A 27, 87 Gradstone+09, MNRAS 397, 1836 Kawashima+09, PASJ 61, 769 Kokubun+12, proc. SPIE 7732, 773215 Kubota+01, ApJL 547, 119 Kubota+02, MNRAS 337, L11 Mineshige+94, ApJ 426, 308 Mizuno+01, ApJ 554, 1282 Mizuno+07, PASJ 59, S257 Okada+1998, PASJ 50, 25 RANA+14, arXiv:1401.4637 Walton+13, ApJL 773, 9 Vierdayanti+10, MNRAS 403, 1206 Yoshida+13, PASJ 65, 48

17. 17 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Backup Slides

18. 18 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. PL-like State: Luminosity Dependence Ho IX X-1, Vierdayanti+10 PL-like state exhibits distinct features not seen in Galactic BHBs –spectral slope much flatter (index of ~1.5 vs. ~2.5) –spectral turnover at lower energy when source is bright (~ 5 keV vs. >=20 keV) One explanation of such a low-temperature, optically-thick corona is supercritical accretion flows (e.g. Kawashima+09) –  -kT e relation should be investigated and understood

19. 19 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. Supercritical Accretion Flow Kawashima+09 Supercritical accretion flow is expected to produce outflow which Compton-upscatter soft photons, as low-temperature, optically- thick corona when source is bright

20. 20 2014-02_HXISGDWS_ULXs.ppt T. Mizuno et al. HXI Sensitivity Kokubun+12, proc. SPIE f<=10 -7 p/s/cm 2 /keV above 10 keV