the transient universe: ay 250 spring 2007 existing transient surveys: high energy ii: x-ray...

The Transient Universe: AY 250 Spring 2007

Existing Transient Surveys:High Energy II:X-ray Binaries

Geoff Bower


Discovery of X-ray Stars

Giacconi et al 1962


Aerobee Rocket

• Designed by James van Allen

• Aerojet booster• Bumblebee second stage

• Maximum altitude of 225 km

• Above 80 km for 350 seconds

• Traveled for 120 km


New Detectors

• Geiger counters

• Greater collecting area

• Anti-coincidence shields

• 50-100 times more sensitive than solar X-ray experiments


Two Discoveries

• Sco X-1• No optical counterpart

known– Eventually 13th mag Lx ~ 10^3 Lopt

• Radio counterparts expected

• X-ray background detected

• Earth origin?


Two Sources Discovered

Giacconi et al 1964


More Sources Found

Rossi 1967

•SNR•Nearby AGN•Galactic sources


Characterizing Sco X-1

• Some variability– X-ray– Optical

• 1000 x energy in X-rays than any other band

• Thermal spectrum 50 x 10^6 K

• Atomic lines in optical

• No clear understanding in early days


Pulsations & Occultations

Schreier et al 1972

~ 4 Seconds R < 10^9 cm


Binary Model

Mx ~ 1 MsunM* ~ 17 – 46 Msun


Neutron Star & Black Hole Binaries

• Periodic Fluctuations• Bursts of X-ray

emission following accretion

• Masses exceeding 3 Msun


LMXB & HMXB

• Low mass companion (< 10 Msun)

• Star overfills its Roche lobe

• Lifetime – 10^7 – 10^9 y

• High mass companion

• Stellar wind drives mass accretion

• Lifetimes < 10^7 y

Only hundreds in the entire galaxyDozens known


Galactic Distribution

O LMXB* HMXBGrimm et al 2002


Galactic Distribution


Luminosity Distributions


Super-Eddington Accretors


GRS 1915+105

• Discovered in gamma-rays but strong X-ray source

• LMXB– 15 M_sun BH– K giant companion

Fender & Belloni 2004


Variability on Wide Range of Time Scales

RXTEASM


Coupling Between Hardness, Temperature, and Radius


Well Defined X-ray States

Markward et al 1999

Hard

Soft

Cool, distant disk Hot, close disk


Photon Index

Tem

pera

ture


Superluminal Motion


Coupled Radio/X-ray Activity


Comparison to AGN

• Tau ~ M^-1/2• Jet Quenching at 1 -

10% L_EDD

Triangles: XRBSquares: AGN


Chandra Observations of the Galactic Center

Muno et al 2002

1 Msec2300 sources< 10 multi-wavelength counterparts


Foreground Separation


Galactic X-ray Sources


GC Transients


Overabundance of Transients in Central Parsec

Radius Transients Stellar Mass Transient Rate

1 pc 4 2 X 10^6 M_sun

20

20 pc 3 3 x 10^7 1


Two Explanations for Transient Overdensity

• LMXBs

• Dynamical friction drives compact objects to GC

• Three-body interactions produces LMXB

• HMXB

Ghez et al 2006


One LMXB Known

X-ray eclipsesPorquet et al 2005

Double-lobe radio sourceBower et al 2005

the transient universe: ay 250 spring 2007 existing transient surveys: high energy ii: x-ray...

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