X-RAYX-RAY BINARIESBINARIES

M.C. RAMADEVIM.C. RAMADEVI

ISRO Satellite CentreISRO Satellite Centre

Bangalore.Bangalore.YAM Jan, 2007

Discovery of X-ray Binaries HistoricdiscoveryofabrightXraysourceScoX1in1962byRiccardoGiacconiandteam;first extra-solar X-ray detectionDetectedduringarocketflightwhichwaslauchedtolookforXraysfromMoonThesourcewasextremelybrightinXrays.Anopticalstarof13thmagnitudewasfoundatthislocation

Giacconi et al., 1962Sco X-1

Xraybackground

TRIGGERED

X-RAY

ASTRONOMY

Was Quite Intriguing...

Later in 1970, the first X-ray satellite, UHURU, discovered another

X-ray source Cen X-3Found to have PULSATIONS in X-rays; 4.84 sec

Only a neutron star can produce such pulsationsContinuous monitoring showed slight variation in the pulse periodThese variations - recognised as due to DOPPLER SHIFT; the star is moving in an ORBIT.X-rays found to disappear for 11 hours in every 2.09 days; ECLIPSES

Ahhhh.. ECLIPSING BINARY SYSTEM !!!!

Here we go THIS IS A BINARY SYSTEM WITH NEUTRON STAR AND A COMPANION STAR (OPTICAL COUNTERPART): X-RAY BINARY

time

time

counts

counts

Special class of binaries which emit predominantly in X-rays

The Most luminous galactic X-ray sources

Lx ~ 10 36 to 10 38 ergs/s

Consist of a compact object and a companion star orbiting about a common centre of mass.

The compact object can be a white dwarf (cataclysmic variables), a neutron star or a black hole.

Companion star can be a normal star or a white dwarf.

What are X-ray Binaries?

X-ray emission

Compact star accretes matter from the companion star The gravitational potential energy of the in-falling matter is converted to kinetic energy eventually giving rise to radiation

Gravitational potential energy

(accreted matter swirls in)

Kinetic energy

(friction between layers)

(viscous heating)

Heat (T ~ 10 7 K)

Radiation (X-rays, UV)

What could possibly give rise to such high X-ray luminosities ?

GRAVITY

Start off with Binary Stars:2 stars, gravitationally bound to each other in an orbit, about a common centre of mass

How are X-ray Binaries formed?

Accretion from stellar wind Accretion through Roche lobe outflow

Two mechanisms of mass transfer in a binary system

Accretion from stellar wind Accretion through Roche lobe outflow

High-Mass X-ray Binaries (HMXB)

Low-Mass X-ray Binaries (LMXB)

LMXB:

Mass of the companion star ~ few solar masses.Usually NS systems accreting mass from the wind of companion, a Be star.

Classification of X-ray Binaries

Observations from X-ray binaries

Spectra suggests different emission processesDifferent spectral statesHigh/Soft StateVery High StateHard State

X-ray binaries are observed as transient sources which suddenly brighten up in X-rays by a factor of 100 to 1000

Light Curve has different profilesPulsations Type I bursts Type II bursts EclipsesPersistent outbursts

X-ray Pulsars - PulsationsAccretion onto a magnetized Neutron Star

Accretion powered Pulsars

B ~ 1012 G

Cen X-3, observed by UHURU; 4.8 sec (Giacconi et. al., 1971)

THIS IS NOT OBSERVED IN BLACK HOLE SYSTEMS

Accretion onto weakly magnetised NS or WD

X-ray bursts

(1735-444)15 s

X-ray bursts H burning

X-ray Superbursts He burning

Thermonuclear explosion on the surface of a WD or NS (Type I Bursts)

Type I Bursts

Unstable, explosive burning in bursts (release over short time)

Burst energythermonuclear(from the surface ofNS or WD)

Persistent fluxgravitational energy(from the accretion disk)

Observation of thermonuclear energy

THIS IS NOT OBSERVED IN BLACK HOLES, since they dont have a surface.

Type II Bursts

120 days

Transient outburstsLikely to originate due to instabilities in the accretion diskObserved in both NS and BH systems

Accretion onto black holes

There is no hard surface. How can we detect it?Will there be any radiation from the infalling matter??

Yes, from the accretion disk around a BH

Black Hole X-Ray Binaries

Strong X-ray sources

Rapidly, erratically variable (with flickering on time scales of less than a second)

Sometimes: Quasi-periodic oscillations (QPOs)Sometimes: Radio-emitting jets

Accretion disks around black holes

Variabilities observed in Black Holes

Understanding AccretionEvolution of the accretion disk

. m

X-ray Properties Radio Properties

disk

disk

corona

corona

corona

Spectra suggests different emission processes

Soft state

Hard state

Example An outburst observed in 4U 1543-47

June-August 2002, 2-10 keV LC

Spectral and temporal

analysis is required

to understand accretion

Spectral-Temporal

States:

VHS:

HSS:

LHS:

(Remillard & McClintock, 2004; Park et al 2004)

Why study X-ray Binaries?To understand accretion:

Accretion - known to power the most luminous objects in the Universe.

Understanding accretion around the compact objects like the neutron star and the stellar mass black holes can help understand accretion around supermassive black holes which form the heart of Active Galactic Nuclei, Quasars etc.

Accretion is everywhere: be it the formation of stars or planetary systems or galaxies.

Also to understand behavior of matter very close to the event horizon of a black hole where General Theory of Relativity is applicable, Black Hole X-ray Binaries are good candidates.

X-ray Binaries form good laboratories for these studies.

Evolved picture of a Low-Mass X-ray binary: accretion through Roche-lobe overflow

ASTROSAT

Indias first multi-wavelength ASTROnomy SATellite

INDIAS FIRST DEDICATED SATELLITE FOR ASTRONOMYUV/Optical 130-6000 nm), Soft X-rays (0.2 - 10 keV) , Hard X-rays (10 150 keV)

Thank You

LMXB

For NS, there is emission from boundary layer where disk meets NS and surface of NS (for a less magnetized NS). Optical emission arises from outer disk, companion star, and X-rays reprocessed by disk or companion.For BH, X-ray emission is from disk.

HMXB

Mostly the compact object is a neutron star, in eccentric orbit around the companionX-rays transients occur when the neutron star accretes matter from the wind of the companion star (Be star)No prominent disks emission

Be star

Neutron star

Binary Orbit

Compact star mass = M1 MNormal star mass = M2 M

Binary separation = a, mass ratio q = M2/M1

+CM MM 12

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221

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cm )1(105.3 3/23/13/1110

hrPqMa +=

Geometry

Observed phenomenology depends on viewing angle.

Typical X-ray bursts:

1036-1038 erg/s duration 10 s 100s recurrence: hours-days regular or irregular

Frequent and very brightphenomenon !

(stars 1033-1035 erg/s)

Discovery

First X-ray pulsar: Cen X-3 (Giacconi et al. 1971) with UHURU

First X-ray burst: 3U 1820-30 (Grindlay et al. 1976) with ANS

Today:~50

Today:~40

Total ~230 X-ray binaries known

T~ 5s

10 s

X-Ray Pulsar Cen X-3

Pulses are modulated at orbital period of 2.09 days

Formation of Accretion disk around the compact object