Ultracompact X-ray binaries(UCXBs)

Nelemans & Jonker, 2006

Bildsten & Deloye, 2004

Belczynski & Taam, 2003

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

etc.

Introduction

Ultracompact binaries(UCBs) Porb<1hr,

cannot reside a H-rich star

AM CVn systems( 16 + 2 )

See Nelemans, 2005 for reviewastro-ph/ 0409676

UCXBs( 12 + 4 )

UCXBs

Why study UCBs?

1. strong GR sources

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

3. 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 3 3 3sin

( , )( ) 2

S XX S X

X S

M i PKf M M

M M G

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

4U 1626 -67an oxygen/neon rich accretion disc

(Schulz et al., 2001)

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

X-ray spectra

Optical spectral

4U 0614 +09,Carbon-oxygen accretion disc

Open questions:

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

3 3 3sin( , )

( ) 2S X

X S XX S

M i PKf M M

M M G

UCXBs as bright X-ray sources in elliptical galaxies?

(Bildsten & Deloye, 2004)

Origin?

• Dynamical or primordial?

Red-white binary enters from right

green enters from left

chaos ensues eventually ejecting white

Origin 1: exchange interaction

Origin 2: RG NS collision

• RG NS collisions– If RG is massive CE phase can cause inspiral – Otherwise RG envelope is ejected leaving an ecce

ntric 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, 33CE evolution (α× λ=0.1), 20 IMF (independent secondary), 10

478*100/33/20/10=7

MM

Calibration

Thanks for your patience!