X-RAY X-RAY BINARIES BINARIES M.C. RAMADEVI M.C. RAMADEVI ISRO Satellite Centre ISRO Satellite Centre Bangalore. Bangalore. YAM – Jan, 2007
Sep 16, 2015
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
a
221
32 )(4 :law sKepler' PMMMGa +=pi
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