Quasars, Pulsars, Gamma-Ray Bursts! Oh, my!

Collapsars, magnetars, X-ray pulsars, γ-ray pulsars,millisecond radio pulsars...

Giacconi et al. (1962)

Rocket carried 3 Geiger counters to225km - one counter failed (#1).Windows of counters pointed 55° fromthe axis of the rocket (i.e. the Zenith).Windows made of mica covered withlampblack.Rocket rotated at 2.0 rps, 350 s above80km.

The Data

The Results

They argued that the source was locatedabout 10° above the horizon bycomparing the absorption through the airand the mica assuming monochromaticsource.

What Did the Aerobee See?

Fig. 2 superimposedon the HEAO all-skysurvey.The object known asSco X-1 is thebrightest in the X-raysky at an azimuthangle of 210° alongthe G.T. axis.

What about the scruff at 60°?

The detection at 60°albeit not as dramaticas the 210° result isalso associated withan LMXB, Cygnus X-2.What is the flux ofCygnus X-2 comparedwith Sco X-1?

Cygnus X-2 3 1

The Answer:

Sco X-1: 14000 µJy (LMXB)Cyg X-1: 235-1320 µJy (HMXB)Cyg X-2: 450 µJy (LMXB)Cyg X-1: 90-430 µJy (HMXB)BTW:

What were they looking for from the moon?What became of American Science andEngineering?

LMXBs and HMXBs

Low-mass X-ray BinariesLow mass main sequence star or white dwarfin orbit with a neutron star or black holeRoche lobe overflow driven by gravitationalradiation

High-mass X-ray BinariesHigh mass main sequence star in orbit with aneutron star or black holeWind accretor or Roche lobe overflow

LMXBs

LMXB Properties

Long-lasting system - GR drives the evolutionNS/BH can accrete much of the donor’s mass

The donor might be disrupted completely.The neutron star gains lots of angular momentum.Magnetic field of the neutron star gets “buried.”

The faint donor is tidally distorted.Orbit is circularized and tidally locked.Accretion rate does not depend on orbital phase.It is hard to see the changing aspect of the donor inthe glare of the accretion disk.

Result: MSP with WD or alone.

HMXBs

HMXB Properties

Short-lived system - stellar evolutionNS/BH accretes little of the donor’s mass

The donor may evolve normally.Magnetic field of the neutron star preserved.

The bright donor may only be minimallydistorted.

Orbit may be elliptical.Accretion rate may depend on orbital phase.

Result: BH/NS with BH/NS/WD or alone.

Binary Stellar Evolution

When mass moves from one star to the other,the orbit changes. Need to remember Kepler’sLaws!

Second Law: Ω a2 M1M2/(M1+M2) = LThird Law: Ω2a3= G (M1+M2)2nd + 3rd:

a =GM2

1M2

2

L2M

LMXBs and HMXBs

In an LMXB, the donor is less massivethan the neutron star, so the orbit willwiden ending the mass transfer, unless Lis not conserved or the donor expands asit loses mass.In an HMXB, the donor is more massivethan the neutron star, so the orbit willshrink increasing the mass transfer.

Roche Lobe

The force pulling a particle toward the centre ofthe star equals the force pulling it away.

With some algebra you find that,

where f = UGLY.

mF = à

r2GM1 +

(aàr)2GM2 à Ω2 a

M

M2à rð ñ

mF =

a2GMf

ar,

M

M1

ð ñ

Tidal Circularization

A topical analogy tounderstand how thisworks is aerobraking.Raising the tidesdissipates orbital energyas friction in the star.Because the energy isremoved at periastron,the apastron movesinward.

Quasars - Active Galaxies

The nuclear activity of galaxies spans awide spectrum ranging from normalgalaxies through Seyfert galaxies andradio galaxies to quasars and QSOs.QSO - quasi-stellar objectQuasar - quasi-stellar radio sourceThe term QSO has fallen out of use.The key surprise about 3C 273 and 3C48 was of course their distance.Luminosity of about 1047 erg/s from asmall region -- you’ll estimate theirmasses in the problem set. 3C 273 in B/R/J (DSS/2MASS)

and at 1.4 GHz (VLA NVSS)

Hewish et al. (1968)

Built a large multibeamantenna to look atscintillation of quasarradiation through theinterplanetary plasma.

SensitiveHigh time resolutionLow frequency

What did they observe?

“Bits of scruff thatappeared at the samesidereal time each day”The pulses arrive slightlylater at lower frequencies.Used the expectedfrequency drift due to theEarth’s motion todetermine the position ofthe source on the sky.The position did notchange over the year.

The pulse frequency isconstant except for theEarth’s Doppler shift.Suggested that it waspulsation of a whitedwarf or neutron star.

Light through Plasmas

A plasma is a fluid in which the charged particles arefree to move (there are currents).

Taking the time derivative of (1) and putting into thecurl of (2),

Let’s assume that no net charge develops so the firstterm vanishes.

∇ âB =c4ùJ +

c1∂t∂E ∇ âE +

c1∂t∂B = 0

∇ â (∇ âE) +c24ù

∂t∂J+

c21∂t2∂2E = 0

∇ â (∇ â E) = ∇(∇ á E)à∇2E

Now the currents

A current is a charge times a velocity,

where we have assumed that v<<c.Combining the last few equations gives,

Let and substitute

J = neev and Jç = neevç , mevç = eE

à∇2E +c24ù

me

nee2E +c21∂t2∂2E = 0

k2E +c2

ω2

pE à ω2E = 0 with

E = E0ei(kxàωt)

ω2p = me

4ùnee2

Dispersion Measure (1)

EM radiation travelling through a plasmahas the dispersion relation:

So, the pulse travels faster at higherfrequencies,

ω2 = ω2p + c2k2 so vg = dk

dω = c2ωk = c 1 à

ω2

ω2

p

r

d÷dt =t =

vg

L socL

÷3 1àω2

ω2

p

ò ó3/2

÷2p

Dispersion Measure (2)

We can also use a integrated quantity,

The dispersion constant is

and the dispersion measure is

t2 à t1 = mc2ùe2(ωà2

2à ωà2

1)R0

d nedl

D = (t2 à t1)/(÷à2

2à ÷à2

1)

DM (cmà3pc) = 2.410 â 10à16D (Hz)

Why is it important?

The paper has outlinedmany of the techniquesused in pulsar astronomytoday:

DM distancesPulse countingDoppler positioningThe name “pulsar” forpulsating star (this endedup being the wrong model)

How did they do it?The key was that they werelooking for scintillation, sothey

Looked at low frequencieswhere pulsars are brightest.Used a fast time constant,multiple frequencies and lagcables to see the time shiftsinduced by scintillation.Sensitivity - pulsars onaverage aren’t that bright.

Klebesadel et al.

Four Vela satellites inEarth orbit observedseveral bursts of gamma-rays.Could use timing of theburst arrival to determinethe location on the skyand extra-terrestrialorigin.

Locating GRBs

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