X-Ray Astronomyy y

Black Holes & Neutron StarsStephen Eikenberry

11 January 2018

What are X-rays?What are X-rays?" X-rays are photons light (not "solid"X rays are photons light (not solid

particles)X h t l th (hi h )" X-rays are shorter wavelength (higher energy) than visible light photons

" Typical energies are 1 keV to 500 keV(Vs 1 5 eV to 3 eV for visible light)" (Vs. ~1.5 eV to ~3 eV for visible light)

" Typical wavelengths ~10Å to ~0.02Å

What makes X-rays?What makes X-rays?" Very HOT stuff produces X-rays viaVery HOT stuff produces X rays via

blackbody (thermal) radiation

What makes X-rays (II)y ( )" Electrical "collisions" between electrons and

t / l i ("b t hl " di ti )protons/nuclei ("bremstrahlung" radiation)

What makes X-rays (III)y ( )" Motion of relativistic (v~c) particles in a

ti fi ld (" h t " di ti )magnetic field ("synchrotron" radiation)

X-ray Binariesy" Star orbits a

compact objectcompact object (black hole or neutron star)neutron star)

" Gravity of CO pulls star matter offMatter orbits in" Matter orbits in accretion disk due to angular momentumangular momentum (like water in sink drain)drain)

X-ray Binaries - IIy" Friction transports

angular momentumangular momentum, allowing in-spiral of mattermatter

" Friction also heats matter to HIGHtempsp

" At T~108K, X-raysrays

Supernova remnantsp" Very energetic

particles fromparticles from supernova explosion

" Impact local interstellar medium "shock" frontX-ray" X-ray bremstrahlung

Pulsars" Rapidly rotating

neutron stars (more on this later)HUGE magnetic" HUGE magnetic fields (~1012 Gauss or higher)higher)

" Rotating magnet accelerates particles to v~c

" Relativistic particles in B-field in B-field synchrotron X-rays

Pulsar-powered supernova remnantsremnants

" Pulsar-acceleratedPulsar accelerated particles impact residual B-field ofresidual B-field of exploded star

" This gives more X-rays

" Crab Nebula SNR inner X-rayinner X ray synchrotron nebula

X-ray Burstersy" Matter accumulates

on surface ofon surface of neutron star

" More matter increases temp until thermonuclear flash occurs on NS surface

" Creates a "burst" of (mostly thermal) X(mostly thermal) X-rays

Summaryy" X-rays come from material in extreme

conditions (hot high velocity large magneticconditions (hot, high velocity, large magnetic fields)

" X-ray sources are often exotic systems: Black hole or neutron star binaries Black hole or neutron star binaries Supernova remnants

P l Pulsars Etc.

X-Ray Astronomy:P ti l M ttPractical Matters

How do we observe X-rays?How do we observe X-rays?" Not from the groundNot from the ground" Atmosphere absorbs X-

rays" Can do a mediocre job j

of observing hard X-rays from balloonsays o ba oo s

" All X-ray astronomy b t d f t llitbest done from satellites

How do we detect X-rays?How do we detect X-rays?" X-rays are very penetrating, but do stop givenX rays are very penetrating, but do stop given

enough materialX d t t t" X-ray detector types:

Scintillators Proportional counters CCDs CCDs Many others

X-ray scintillator detectorsy" Scintillators = crystal or

l ti hi h itplastic which emits a flash of light when hit b Xby X-rays

" Many similar to table ysaltVisible light detector" Visible light detector "reads" scintillator

" Brightness of flash gives energy of X-ray spectroscopy

X-ray scintillator detectors - IIy" Scintillators have good time resolution

(t i ll 1 )(typically ~ 1 s)" Mediocre spatial resolutionp

" Mediocre energy resolution (E/E ~ 10)" Very resistant to radiation damage in orbit

X-ray Proportional Countersy p" X-ray strikes detector,

ti i i ticreating an ionization "cloud" of electrons

" Grid of wires under voltage carries charge g gto amplifiersAmplitude of" Amplitude of electrical impulse gi es energ of X ragives energy of X-ray spectroscopy

X-ray proportional counters - IIy p p" Proportional counters have good time

l ti (t i ll 1 )resolution (typically ~ 1 s)" Good spatial resolutionp

" Mediocre energy resolution (E/E ~ 10)" Very resistent to radiation damage in orbit

" Slowly leak gas limited lifetime in orbitSlowly leak gas limited lifetime in orbit

X-ray CCDsy" X-ray strikes CCD pixel

and deposits chargeand deposits charge

" Ionization energy ~1 eV

" 1 keV X-ray ~1000 electrons

" Read noise ~10 e-, so we have strong signal

" Number of e- gives X-ray energyy gy

X-ray CCDs - IIy" CCDs have poor time resolution (typically a few

seconds) due to clocking timeseconds) due to clocking time" Excellent spatial resolution

" Excellent spectral resolution (E/E ~ 60)S ibl di i d i bi" Susceptible to radiation damage in orbit (electrons/protons damage semiconductor crystal structure)

" Good spectral/spatial properties make these theGood spectral/spatial properties make these the detectors of choice for many current missions.

X-ray Telescopesy p" Telescopes focus light onto detectors" Hard to focus X-rays (they go through things

like metal)

" Why? ~ 1 ÅS i b l 1 Å li" Spacing between metal atoms ~1 Å slip through the "cracks"

" General principle: good mirrors must be smooth on size scales <<smooth on size scales

X-ray Telescopes - IIy p" Grazing incidence

tilt mirror so thattilt mirror so that projected distance between atoms is <<1between atoms is <<1 Å

" This only allows weak focusing of X-rays g y(small angle change per bounce)p )

" Use multiple bounces to focus onto detectorto focus onto detector

X-ray Telescopes - IIIy p" Tilt gives very small

projected area ofprojected area of mirror (small collecting area)collecting area)

" Multiple nested mirrors greatly increases collecting gareaXMM uses 58 nested" XMM uses 58 nested mirrors, for example

X-ray Observationsy" Telescopes + detectors combine to provide:

X-ray images X-ray spectra X-ray time series

Gamma-Ray Astronomyy y

Black Holes & Neutron StarsStephen Eikenberry

11 January 2018

Following slides from Markus Böttcher (OhioU) -mostlymostly

The Gamma Ray Skyy yThe Electromagnetic Spectrum

Gamma Rays:

Wavelength Eph ≥ 100 keV ≥ 1019 Hz

Frequency

≥ 10 Hz ≤ 0.1 nm

The Atmosphere is

Need satellites to

High flying air

Atmosphere is opaque to

gamma-raysNeed satellites to observe planes or

satellites

g y

The Sky in Different Wavelength Bands

Radio Wavesi ibl li hRadio WavesInfraredVisible light

X-rays-rays

The Gamma-Ray Sky3C279 ( )Plane of the Milky Way 3C279 (quasar)e o e y W y

(diffuse emission)Geminga (pulsar)

Crab (SNR)

PSR 1951+32 (pulsar)

(SNR)

PKS 0528+134 EGRET, E > 100 MeV

(p )Vela (pulsar) (quasar)3C454.3 (quasar)

More than half of all gamma-ray sources are still unidentified!

The Problem of Identifying -ray Sources

EGRET error contours

Pulsar

Black Hole XBlack Hole X-Ray Binary

What’s the source ofWhat s the source of the -ray emission?

Need more information (b db d e t ;(broadband spectrum;

variability)

The Detection of Gamma Rays from SpaceGamma Rays are deeply penetrating and do not

ionize material (hardly at all!)

→ Need to convert the -ray’s energy to kinetic energy of an electron, and detect / gy ,

track the electron

Interactions of gamma-rays with matter

1 Ph l i Ab i (E 300 k V)1. Photoelectric Absorption (E ≤ 300 keV)

hthr = ion

abs ~ 3 ~ -3 abs

Interactions of gamma-rays with matter (cont.)

= 6 65x10-25 cm2

2. Compton Scattering (300 keV ≤ E ≤ 8 MeV)

T 6.65x10 cm

C

hKN≈ 511 keV

3. Electron-Positron Pair Production (E ≥ 8 MeV)

hKN 511 keV→

pe+ e-

p→

hthr= 2 mec2 (1 + me/mp) ≈ 1022 keV

Problems for the Detection of Gamma Rays from Space

1) Low number fluxes

Typical fluxes of the brightest -ray sources in the sky:

FE ~ 10-2 – 10-3 -rays cm-2 s-1 MeV-1

2) High background from cosmic rays

Background of high-energy particles (protons and electrons) constantly irradiating the detector) y g

Problems for the Detection of Gamma Rays from Space (cont )Rays from Space (cont.)

=> Need long integration times to measure a significant signal

Sensitivity limit for detection of a source at a confidence level of n (i.e., an excess of n times the standard deviation of the

background -ray flux dFB/dE):

Fmin = n √ (dFB/dE) E Aeff (E, ) Tobs

whereeff ( ) obs

lid l hi h fl i i i i = solid angle over which -ray flux is impinging on the detector

A ff = effective detector area = A*cos*PdAeff effective detector area A cos PdetTobs = Integration (observing) time

Problems for the Detection of Gamma Rays from Space (cont )Rays from Space (cont.)

=> Problem, in particular for variable sources: , p

Low duty cycle: Source signal may extend onlysignal may extend only over a small fraction of the integration time!

M d fl iMeasured flux is only an average over the integration

Integration time

gtime.

Measured flux

Problems for the Detection of Gamma Rays from Space (cont.)

3) Collimation / Source Localization

G hi hl iGamma-rays are highly penetrating Can not be focused, e.g., by mirrors or lenses!

Solutions:

A) Passive Collimation

Shi ld D f di i f h k dShield Detector from most directions of the sky, except a narrow cone;

virtually no directional information about sources D

Shie

ld Shield

virtually no directional information about sources within the cone (typically ~ few o).

Detector

Collimation / Source Localization (cont.)

B) Orientation Effects

A is proportionalAeff is proportional to cos

BATSE (Burst and

Detector

BATSE (Burst and Transient Source Experiment) on the C G R ShieldCompton Gamma-Ray Observatory

Collimation / Source Localization (cont.) Fl

ux( )C) Occultation Techniques

F

Fsource

For example: Earth Occultation Technique

t

Source

Collimation / Source Localization (cont.)

D) Coded Masks

C d d k tCoded mask casts a shadow pattern on the detector, whichthe detector, which can be unfolded to

calculate the distribution of

sources in the field of viewof view.

DDetector

Collimation / Source Localization (cont.)

E) Tracking the trajectory of secondary particles

For example: In pair Anti-Coincidence For example: In pair conversion telescopes

Scintillation Dome

p

Trajectory of

Pair conversion layers + closely

spaced spark secondary

electron/positron pair is tracked by imaging e+ e-

p pchambers

Widely spaced sparkis tracked by imaging (optical readout) or

spark chamber

Widely spaced spark chambers; Time-of-flight coincidence

systemptechnique

system

Detection Techniquesq

1) Scintillation Techniques) q

Gamma-ray produces electron-hole pair;

recombination produces a (often UV) photon;

registered with optical readout

2) S lid St t D t t2) Solid State Detectors

Gamma-ray produces multiple electron-hole pairs i d d i din doped semiconductors;

recombination produces an optical photon;

registered with optical readout

Detection Techniques (cont.)q ( )3) Compton Telescopes

For -rays with energies of ~ 1 – 10 MeV, direct scintillation or solid state detection becomes inefficient. Photons interact with matter mainly

through Compton scattering

EHave the -ray undergo Compton scattering

event in an upper detector layer (1);

determine direction of motion and energy of the down-scattered photon in a second, lower

detector layer (2).

E’ =E

1 + (E

y ( )

L1

E’1 + (Emec– cos

Need to also measure energy and direction of the recoil electron in layer 1 to uniquely

determine -ray direction. L2

Detection Techniques (cont.)q ( )

4) Spark Chambers4) Spark Chambers

Gamma-ray produces electron-positron pair;Gamma ray produces electron positron pair;

pair trajectory is traced by spark chamber technique

5) Drift Chambers5) Drift Chambers

Gamma-ray produces electron-positron pair;

pair trajectory is traced by drift chamber technique

Detection Techniques (cont.)q ( )6) Imaging Atmospheric Cherenkov Telescopes

High-energy -rays (GeV – TeV energies) produce air showers in the atmosphereproduce air showers in the atmosphere.

Relativistic particles with energy Photons ElectroRelativistic particles with energy

Ethr = mec2 (n/√n2 – 1 – 1)

Photons ElectroPositrons

(n = index of refraction)

produce nano-second flashes ofproduce nano second flashes of Cherenkov radiation.

Imaging the shape and extent of Cherenkov light pattern gives energy and arrival direction of primary -ray.

Detection Techniques (cont.)q ( )7) Secondary particle detector arrays; wave

front samplingfront sampling

High-energy -rays (GeV – TeV energies) produce air showers in the Photons Electro

atmosphere.Photons Electro

Positrons

Measure the time evolution of the wave front of secondary particles y p

(electrons and positrons) to determine primary -ray’s energy (E > 1 – 10

T V) d di iTeV) and direction.

Gamma-Ray yTelescopesp

Brief History of Gamma Ray Astronomy2008 F i (GLAST) All k it i f th M V G V k 3 h

2004 Swift: Dedicated -ray burst mission: prompt X-ray/optical follow-up;

2008 Fermi (GLAST): All-sky monitoring of the MeV – GeV sky every 3 hr with sensitivity a factor of > 10 better than EGRET.

2002 INTEGRAL: Major advances in high-resolution imaging and spectroscopy of Galactic -ray sources

arcsecond localization of GRBs

1991 CGRO: First all-sky survey of the -ray sky; major discoveries in all

1997 BeppoSAX: First high-precision localization of -ray bursts; cosmological origin of GRBs established

1987 Whipple (ACT): First credible detection of a TeV source (Crab Nebula)1989 SIGMA: First high-resolution images (13’) in hard X-rays / soft -raysareas of -ray astronomy; -ray astronomy becomes an integral part of astronomy

1975 COS B: First detailed ra map of the Milk Wa ith 24 point1979 HEAO-3: Discovery of radioactive 26Al emission in the Milky Way1981 SMM: Studies of solar flare -ray emission; 56Co-lines from SN 1987A

1968 OSO-3: Discovery of > 100 MeV -ray emission from the Milky Way1972 SAS-2: First high-energy -ray images; discovery of Geminga pulsar1975 COS-B: First detailed -ray map of the Milky Way with 24 point sources

1961 EXPLORER-II: First detection of high-energy -rays from space1967 VELA satelllites: Discovery of -ray bursts (not published until 1973)1968 OSO 3: Discovery of > 100 MeV ray emission from the Milky Way

1) The Compton Gamma Ray Observatory (CGRO)

(1991 – 2000)

Oriented Scintillation-Spectrometer Experiment (OSSE): ~ 0 1 10 MeV

Compton Telescope (COMPTEL): ~ 1 30 M V(OSSE): ~ 0.1 – 10 MeV – 30 MeV

Energetic Gamma-Ray Experiment Telescope (EGRET): pair

conversion telescope,

~ 20 MeV – 30 GeV

Burst and Transient Source Experiment (BATSE):p ( )

0.015 – 110 MeV

2) The International Gamma-Ray Astrophysics L b t (INTEGRAL)Laboratory (INTEGRAL)

Launched 2002Launched 2002

Two -ray telescopes:

Imager on Board the INTEGRAL Satellite (IBIS), optimized for high ( ) p g

spatial resolution;

Spectrometer on INTEGRAL (SPI), p ( ),optimized for high spectral

resolution.

E 20 k V 8 M VEnergy range: ~ 20 keV – 8 MeV

Both use coded-mask technique for imaging.

3) AGILE(A i l G I i i LE )(Astro-rivelatore Gamma a Immagini LEggero)

Italian gamma-ray satellite mission;

Similar technology and capabilities as

launched April 23, 2007

EGRET, intended to bridge the gap between EGRET and Fermi (GLAST)

Two instruments:

Gamma RayGamma-Ray Imaging Detector

(GRID): SuperAGILE:( )

30 MeV – 50 GeV

p

18 – 60 keV

4) The Fermi Gamma-Ray Space Telescope (formerly: Gamma Ray Large Area Space Telescope (GLAST)

Launched June 11, 2008Si il t h l EGRET ( iSimilar technology as EGRET (pair

conversion), but much improved sensitivity, large field of view (~ sensitivity, large field of view ( sr), and slightly extended energy range (~ 20 MeV – 300 GeV).

Will operate in constant slewing mode to survey the sky for flaring high energ raflaring high-energy -ray

sources:

O f ll k 3 hOne full-sky scan every 3 hr.

Fermi

i iTwo main science instruments:

• LAT (Large Area• LAT (Large Area Telescope)

GBM (GLAST• GBM (GLAST Burst Monitor)

The Large Area Telescope (LAT)Pair Conversion Telescope

Quantity LAT EGRETQ yEnergy Range 20 MeV – 300 GeV 20 MeV – 30 GeV

Peak Effective Area > 8000 cm2 1500 cm2

Field of View > 2 sr 0.5 sr

Angular Resolution < 3.5o (at 100 MeV) 5.8o (at 100 MeV)< 0.15o (at > 10 GeV)

Point Source Sensitivity < 6*10-9 cm-2 s-1 10-7 cm-2 s-1

The LATAll Sky MapThe LATAll-Sky Map

The GLAST Burst Monitor (GBM)All-sky Monitor optimized to

detect X-ray / soft -ray flashesflashes

(~ 8 keV – 30 MeV)

Source localization to < 15o

5) Atmospheric Cherenkov Telescopes

Experiment Technique Ethr (TeV) Location

Whipple IACT 0 25 Arizona USAWhipple IACT 0.25 Arizona, USAHEGRA-IACT IACT array 0.50 Canary Islands

CANGAROO-II IACT 0.1 Woomera, AustraliaHEGRA-AIROBICC Wavefront

sampling15 Canary Islands

Themistocle Wavefront 3 Themis, Francesampling

STACEE Solar Tower ACT 0.05 Albuquerque, NM, USA

HESS IACT array 0 04 Gamsberg NamibiaHESS IACT array 0.04 Gamsberg, NamibiaMAGIC IACT 0.01 Canary Islands

VERITAS IACT array 0.05 Arizona, USA