Ultracompact x ray binaries ucxbs
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Ultracompact X-ray binaries (UCXBs). Nelemans & Jonker, 2006 Bildsten & Deloye, 2004 Belczynski & Taam, 2003 http://online.kitp.ucsb.edu/online/ultra_c03/ etc. Introduction. UCXBs. Why study UCBs? strong GR sources

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Ultracompact X-ray binaries (UCXBs)

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Ultracompact X-ray binaries(UCXBs)

Nelemans & Jonker, 2006

Bildsten & Deloye, 2004

Belczynski & Taam, 2003

http://online.kitp.ucsb.edu/online/ultra_c03/

etc.


Introduction


UCXBs

Why study UCBs?

  • strong GR sources

  • Unique astro labs (compact object, short period variability and peculiar chemical composition).

  • Test of binary evolution theory, in particular the CE phase.


UCXBs

  • Persistent, hard and bright X-ray sources

    • Lx ~ 1036 – 1039 erg s-1

    • ~108 yr above 1036 erg s-1

  • NS accretor and low mass degenerate companion

  • Periods < 1 hour

Artist’s conception of NS accreting from a WD


Pulse frequency as a function of orbital phase (XTE J1751 -305) Markwardt et al. 2002


Mass functions of three X-ray MSPs in UCXBs

  • 1751 -305: 1.28×10-6 M_sun, 42min, 2.3ms

  • 0929 -314: 2.7×10-7 M_sun, 44min, 5.4ms

  • 1807 -294: 1.6×10-7 M_sun (smallest mass function among all stellar binaries), 40min, 5.25ms


An indirect evidence for UCXBs

Van Paradijs & McClintock,

1994


Ne/O/C emission lines-- another fingerprint of UCXBs?

X-ray spectra

4U 1626 -67

an oxygen/neon rich accretion disc

(Schulz et al., 2001)


Optical spectral


4U 0614 +09,

Carbon-oxygen accretion disc


Open questions:


Cold/Hot white dwarf model (Deloye & Bildsten, 2003)


UCXBs as bright X-ray sources in elliptical galaxies? (Bildsten & Deloye, 2004)


Origin?

  • Dynamical or primordial?

Origin 1: exchange interaction

Red-white binary enters from right

green enters from left

chaos ensues eventually ejecting white


Origin 2: RG NS collision

  • RG NS collisions

    • If RG is massive CE phase can cause inspiral

    • Otherwise RG envelope is ejected leaving an eccentric WD-NS binary

      • Subsequent gravitational radiation causes inspiral


Origin 3:

  • Descendants of primordial binaries

Belczynski & Taam


Formation channels

UCXB


Galactic SFR ~ 1-3 /yr (Blitz 1997) or 1~10 /yr (Gilmore 2001).

Uncertainties:

X-ray duty cycle for transients, 33

CE evolution (α×λ=0.1), 20

IMF (independent secondary), 10

478*100/33/20/10=7

Calibration


Thanks for your patience!


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