Observations of compact binariesusing XMM-Newton

Gavin Ramsay

What is a compact binary?

Two stars orbiting around each other on timescales less than ~few hrsOne star a white dwarf the other a starsimilar to the Sun but less massive

How compact are they?

The Sun!

A compact binary with 2hr orbital period

Characteristics depend on the magneticfield of the white dwarf

B<10^4G

B~10^6G

B>10^7G

XMM-Newton

XMM-MSSL polar survey

Surprise was that so many were inlow accretion states: ~half of the systems

A survey of 40 strongly magnetic binary systems

Not there!Important input for population synthesis models

Ramsay et al (2004)

EP Dra - an eclipsing polar

EP Dra - accretion dip and eclipse

Ramsay et al (2004)

The X-ray spectra of polars

Long been the subject of greatcontroversy. Standard model suggestsL_soft/Lhard~1/2

Survey suggests that most polars showX-ray spectrum consistent to that predictedby standard model. However….

Ramsay & Cropper (2004)

EU UMa - shows very little hard X-ray flux

Some systems, however, showemission properties not predicted by the standard accretion model. One proposalis that dense blobs of materialare present in the accretionflow which do not generatehard X-rays. Not clear why some systems have blobs whileothers do not. Not related tomagnetic field strength.

Ramsay et al (2004)

B<10^4G

B~10^6G

B>10^7G

XMM-Newton observations of Intermediate Polars

FO Aqr: P_spin=20.9min, Porb=4.9hrs

Evans et al (2004)

FO Aqr: X-ray spectrum

Huge absorption dip due accretion ‘curtain’

Evans et al (2004)

B<10^4G

B~10^6G

B>10^7G

Disc accreting binaries

YZ Cnc: Porb~2.1hrs

Hakala et al (2004)

YZ Cnc: X-ray spectrum

Hakala et al (2004)

Evidence for jets?

Model with no-blue shift Model with blue shift of1200km/s

Hakala et al (2004)

ULTRA-compact binary: Porb<10min

Jupiter

Ultra-compactbinary

RX J1914+24: Porb 569 sec (9.5min)

Ramsay et al (2005)

Models fall into accretion and non-accreting model.

Accreting models predict it wouldspin down over time.

Non-accreting model suggests it would spin-up over time (the electricstar model).

RX J1914+24: spinning up

Ramsay et al (2005)

Spining up at a rate of 6.6x10^-12s/s

Ramsay et al (2005)

What is the electric star model?

Sounds far fetched - but!….

We know it operates on Jupiter

RX J1914+24: X-ray spectrum

Very odd!Ramsay et al (2005)

Both ultra-compacts have been discoveredin X-rays. Search for more!

Programme to search for ultra-compactsystems in XMM-Newton and Chandraarchives.

Have yet to find one but have discoveredlots of flare stars!

Trenholme, Ramsay & Foley (2004)