Ultra Luminous X-ray sources ~one of the most curious objects in the universe~

Transcription

1 Ultra Luminous X-ray sources ~one of the most curious objects in the universe~ Shogo B. Kobayashi the University of Tokyo ULX 1

2 The discovery of the enigmatic sources pfabbiano & Trincheri 1987 X-ray observations of other galaxies with Einstein. Off nucleus X-ray sources with L X > erg/s >> L edd of neutron stars erg/s pwhat are they? Summation of X-ray binaries or/and Supernova Remnants? Some show variability; single and compact. Background AGN or foreground stars? They are resided in the observed galaxies. Namely, Ultra Luminous X-ray sources (ULXs; Makishima+00) count rate Energy (kev) ULX workshop@isas 2

3 An overview of ULXs pdefinition (e.g. Feng and Soria+11) Extragalactic and off nucleus point sources. L X > erg s -1 ~ L edd of 10 M BH. More than 400 are confirmed including candidate (Walton+11) IC 342 pcharacteristics L X = erg s -1, masses are poorly constrained. Favor high star forming rate region (e.g., arms of spiral galaxies). Some are binary system with high mass companions (~10-20 M ; e.g., Motch+14), but still their companions are poorly understood. pinterpretation L X >> L edd emissions from ~10 M BHs (Mineshige+07) or neutron stars (Bachetti+14)? L X L edd emissions from M BHs (Makishima+00)? 6 arc min X-2 X-1 Optical+X-ray ULX workshop@isas 3

4 Spectral types in ULX Show shifts in spectral shapes just like BHBs. pspectral states Types of spectrum (Gladstone+09). Broadened-Disk (BD) Hard Ultra Luminous (HUL) Soft Ultra Luminous (SUL) Well fitted with cool disk + cool & thick Comptonization. T in = kev T e = kev τ ~ 10 Spectra of ULXs in NGC1313 X-1 (HUL) XMM-Newton pn Can these spectral states be understood as extensions of ordinary BHBs? ULX workshop@isas 4

5 Comparing spectra with the BH binaries L/L edd ULXs??? Extremely lower cutoff energy Done, Gierlinski, Kubota, 2007 L/L edd ~ 0.3; Very High Cygnus X-1 L/L edd ~ 0.1; High Soft L/L edd < 0.01; Low Hard Non of them look similar to what we know in L/L edd < 1 regime L/L edd >> 1?? We poorly know what will happen in there ULX workshop@isas 5

6 Comparisib with high L/L edd sources Kobayashi & Done (in prep) Narrow Line Seyfert 1 AGN RX J L/L Edd ~ 10 ULX NGC1313 X-1 BH binary LMC X-3 (Disk dom.) L/L Edd ~ 0.8 BH binary XTE J (VHS) L/L Edd ~ 0.3 ULX workshop@isas 6

7 NGC 1313 X-1 vs PG M AGN = M L/L Edd ~ νfν ULXs are scaled to D 1244 = 211 Mpc L MM dot T in (M dot /M) 1/ Energy (kev) ULX workshop@isas 7

8 NGC 1313 X-1 vs PG νfν Flux of the disk 10 exceeds -4 that of AGN M ULX = 30 M ² T in becomes lower than that of AGN M AGN = M L/L Edd ~ L MM dot T in (M dot /M) 1/4 Simple scaling 10-3 from 10 other -2 high 10 Eddington -1 sources 1 do 10 not work Energy (kev) ULX workshop@isas 8

9 Super-critical accretion flow simulations Kawashima+12 Cool and thick outflow Hot emission region Optically and Geometrically thick accretion disk ULX 9

10 Spectral Variability (Holmberg IX X-1) Power-law ratio Ratio over 04/09/ factor ~3 change in L X Spectrum becomes more convex as the source shifts from HUL toward BD. > 1 kev band dominates the change in spectral shape. ULX workshop@isas 10

11 Spectral modeling direct-mcd+thc of MCD T e =2.7 kev T in =seed photon T bb y = (4kT e /m e c 2 )τ(1+τ/3) R raw flux MCD direct MCD THC (MCD) T(r) T in r R in BH ULX workshop@isas 11

12 Spectral modeling absorption(direct-mcd+thc(mcd)) (Makishima+08 Gladstone+09) Absorptions includes Our galaxy (fixed to observation) inter stellar abs. in Host galaxy Intrinsic absorption in ULX N H MCD R in BH ULX workshop@isas 12

13 Spectral analysis: HUL (Holmberg IX X-1) T e = 2.6±0.2keV T in = 0.23±0.02 kev R raw ~ 2300 km reduced χ 2 = 1.16 MCD+THC model successfully reproduced the spectrum; consistent with Gladstone+09 Requires cool MCD, and THC by a cool and thick (τ>10) corona. ULX workshop@isas 13

14 Spectral analysis: BD (Holmberg IX X-1) T in = 0.8±0.2 kev T e = kev N H = 0.4± cm -2 reduced χ 2 = 1.23 direct-mcd becomes weak and requires only THC(MCD). Consistent with Miyawaki+09(M82 X-2). ULX workshop@isas 14

15 Comparison of BD and HUL BD HUL T in =0.8 kev T e /T in = 2.5 T e =2.0 kev T e = 2.6 kev T in = 0.23 kev T e /T in = 11.3 Temperature ratio Q T e /T in HUL which has two distinct temperature has large Q, whereas the BD spectrum has smaller value. Q characterizes the spectral shape (Zhang+14 Kobayashi+16) ULX workshop@isas 15

16 Q and the spectral shape 10-4 Power-law ratio Q reflects changes in the spectral shape. A shift from the HUL to the BD can be expressed as a change from Q 10 to Q~5. ULX workshop@isas 16

17 Q and the spectral shape Holmberg IX X-1 HUL BD ULX 17

18 Q and the spectral shape IC 342 X-1 HUL BD ULX 18

19 Q and the spectral shape NGC 1313 X-1 HUL BD ULX 19

20 Q and the spectral shape NGC 1313 X-1 HUL SUL BD ULX 20

21 Q and the spectral shape Holmberg II X-1 HUL SUL ULX 21

22 Q and the spectral shape M33 X-8 BD ULX 22

23 Q and the spectral shape 3 spectral shapes can be discriminated, not only by its apparent shape, but also quantitatively in the L vs Q plane. ULX workshop@isas 23

24 Comparison of transition luminosities HUL SUL BD ULX 24

25 Comparison of transition luminosities 3 ULX workshop@isas 25

26 Comparison of transition luminosities 3 15 ULX workshop@isas 26

27 Comparison of transition luminosities The transition luminosity (L c ) scatters among the ULX sample Assuming that L c indicates a particular L X /L edd, then their mass should also have similar range. e.g., if we assume the smallest as 10M, the maximum reaches100m. ULX workshop@isas 27

28 Local spectral structures (again Hol IX X-1) 10-4 Power-law ratio The poor variability in < 1 kev suggests N H is unchanged. The actual fit results give roughly stable N H. N H < cm -2 with Galactic component subtracted. ULX workshop@isas 28

29 Local spectral structures: photoelectric absorption N H is rather stable in ULXs, e.g., NGC1313 X-1 constant within ±30%. The minimum is ~10 20 cm -2, most of them are ~ cm -2. Even one with the maximum value, it is < cm -2. ULX workshop@isas 29

30 Local spectral structures: Fe Kαlines (Hol IX X-1) 99% c.l. Stacked all the XMM-Newton EPIC-PN data. Searched for any kind of narrow (σ=10 ev) Fe Kα features. No features were required, < 30 ev upper limit in equivalent width. ULX 30

31 Local spectral structures: Fe Kαlines (others) The line search analysis was done with other two high flux ULXs No features were required as well, and only limits were obtained. IC 342 X-1: -30 ev < EW < 60 ev NGC 1313 X-1: -20 < EW < 40 ev ULX 31

32 N H vs EW of Fe Kαlines pcomparison with the Galactic high mass X-ray binaries (HMXBs) Due to stellar wind, N H ~10 24 cm -2 and strong Fe Kα reprocessing features are seen in HMXBs. Derived N H and EW of Fe Kα lines are much smaller in ULXs. The matters that can produce features are poor around ULXs. pfully ionized due to large L X? ξ=l/nr 2 is constant if we assume stellar wind accretions. In super critical accretion flows, full ionization is difficult to be achieved due to the low emmissivity. ULXs are difficult to be considered as wind fed HMXB systems. Roche-lobe over flows? or other possible accretion mechanisms? ULX workshop@isas 32

33 A possible system that can explain ULXs prequired conditions for the accretion system High mass accretion rate to afford erg s -1. The masses have an order of magnitude distribution. Matters that do not account for X-ray emissions are poor. pbondi-hoyle accretion onto BHs L bond nm BH2 v -3. L~10 40 erg s -1 if 100M BH enters an n~100 cm -3 region with v=1 km s -1 (Mii and Totani+01, Nakamura+16). N H ~ cm -2 for ~few pc gas cloud. Do not require companions that produces the spectral features. The density of surrounding gas is much smaller than the stellar winds (expected EW ~ few ev). Dense gas region n ~100 cm -3 v r B = 2GM BH /v 2 M BH ULX workshop@isas 33

34 The new discovery: ULX pulsar (M82 X-2) Bachetti+14 on pulse off pulse spectrum Brightman+16 kt cut ~ kev L 3-50 kev ~ erg s -1 Cut-off energy is slightly higher than those of ULXs (kt cut =7 kev). Can be categorized as a ULX, but may be a different population? At least, some of them truly require L X >> L edd emission. ULX workshop@isas 34

35 More ULX Pulsars in 2016! NGC5907 X-1 NGC7793 P13 best P = sec best P = sec Blind-search analysis on XMM-Newton and NuSTAR archival data were conducted (Israel+16) Two more ULXs were newly found to be pulsars. ULX workshop@isas 35

36 New ULX Pulsar; NGC7793 P-13 : SWIFT * : XMM Israel+16 Israel+16 Stronger pulsed fraction at higher energy band. Transient source. Propeller effect (Bachetti+14)? X-ray spectrum is similar to ordinary ULXs, but slightly harder (Pintore+17)? Suited science for NuSTAR or future hard X-ray missions XMM-Newton Motch+14 ULX workshop@isas 36

37 Summary Some new results are obtained in resent few years. Their low-energy rollover and featureless continuum spectra are distinct from what we expect from the ordinary Galactic (HM) X- ray Binaries. They can be possibly explained as emissions from isolated M BHs accreting via Bondi-Hoyle accretions. However, at least a few of them are pulsating neutron stars with super-critical accretion flows. Their spectral mechanisms and discrimination from other type of ULXs are still open questions. Please enjoy the work shop! ULX workshop@isas 37