Ultra Luminous X-ray sources ~one of the most curious objects in the universe~ Shogo B. Kobayashi the University of Tokyo ULX workshop@isas 1
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 > 10 40 erg/s >> L edd of neutron stars 10 38 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
An overview of ULXs pdefinition (e.g. Feng and Soria+11) Extragalactic and off nucleus point sources. L X > 10 39 erg s -1 ~ L edd of 10 M BH. More than 400 are confirmed including candidate (Walton+11) IC 342 pcharacteristics L X = 10 39-41 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 100-1000 M BHs (Makishima+00)? 6 arc min X-2 X-1 Optical+X-ray ULX workshop@isas 3
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 = 0.2-0.5 kev T e = 1.5-3.0 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
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
Comparisib with high L/L edd sources Kobayashi & Done (in prep) Narrow Line Seyfert 1 AGN RX J0439-45 L/L Edd ~ 10 ULX NGC1313 X-1 BH binary LMC X-3 (Disk dom.) L/L Edd ~ 0.8 BH binary XTE J1550-564 (VHS) L/L Edd ~ 0.3 ULX workshop@isas 6
NGC 1313 X-1 vs PG 1244+026 1 1 1 10-1 M AGN = 4 10 6 M L/L Edd ~ 10 2 10-2 νfν 3 10-3 4 10-4 5 10-5 ULXs are scaled to D 1244 = 211 Mpc 6 10-6 10-7 7 10-8 L MM dot T in (M dot /M) 1/4 8 10-3 10-2 10-1 1 10 Energy (kev) ULX workshop@isas 7
NGC 1313 X-1 vs PG 1244+026 1 νfν 10-1 10-2 10-3 10 20 Flux of the disk 10 exceeds -4 that of AGN. 10-5 4 M ULX = 30 M ² T in becomes lower than that of AGN. 10-6 M AGN = 4 10 6 M L/L Edd ~ 10 10-7 10-8 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
Super-critical accretion flow simulations Kawashima+12 Cool and thick outflow Hot emission region Optically and Geometrically thick accretion disk ULX workshop@isas 9
Spectral Variability (Holmberg IX X-1) Power-law ratio Ratio over 04/09/26 10-3 10-2 1 2 5 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
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 -0.75 R in BH ULX workshop@isas 11
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
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
Spectral analysis: BD (Holmberg IX X-1) T in = 0.8±0.2 kev T e = 2.0 +0.3-0.1 kev N H = 0.4±0.2 10 21 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
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
Q and the spectral shape 10-4 Power-law ratio 10-3 10-2 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
Q and the spectral shape Holmberg IX X-1 HUL BD ULX workshop@isas 17
Q and the spectral shape IC 342 X-1 HUL BD ULX workshop@isas 18
Q and the spectral shape NGC 1313 X-1 HUL BD ULX workshop@isas 19
Q and the spectral shape NGC 1313 X-1 HUL SUL BD ULX workshop@isas 20
Q and the spectral shape Holmberg II X-1 HUL SUL ULX workshop@isas 21
Q and the spectral shape M33 X-8 BD ULX workshop@isas 22
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
Comparison of transition luminosities HUL SUL BD ULX workshop@isas 24
Comparison of transition luminosities 3 ULX workshop@isas 25
Comparison of transition luminosities 3 15 ULX workshop@isas 26
Comparison of transition luminosities 3 20 6 8 15 5 6 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
Local spectral structures (again Hol IX X-1) 10-4 Power-law ratio 10-3 10-2 The poor variability in < 1 kev suggests N H is unchanged. The actual fit results give roughly stable N H. N H < 1.8 10 21 cm -2 with Galactic component subtracted. ULX workshop@isas 28
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 ~3 10 21 cm -2. Even one with the maximum value, it is < 8 10 21 cm -2. ULX workshop@isas 29
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 workshop@isas 30
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 workshop@isas 31
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
A possible system that can explain ULXs prequired conditions for the accretion system High mass accretion rate to afford 10 40 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 ~ 10 21 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
The new discovery: ULX pulsar (M82 X-2) Bachetti+14 on pulse off pulse spectrum Brightman+16 kt cut ~ 14 +5-3 kev L 3-50 kev ~ 7.5 10 39 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
More ULX Pulsars in 2016! NGC5907 X-1 NGC7793 P13 best P = 1.1372873 sec best P = 0.4183890 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
New ULX Pulsar; NGC7793 P-13 : SWIFT * : XMM 2013 2014 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. 2013 2014 XMM-Newton Motch+14 ULX workshop@isas 36
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 100-1000 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