September 26, 2004Lucy Fortson - Extreme Astronomy Short Course Multiwavelength astronomy is extreme...

September 26, 2004

Lucy Fortson - Extreme Astronomy Short Course

Multiwavelength astronomy Multiwavelength astronomy is is extreme astronomy!extreme astronomy!

OUTLINEo Importance of Multiwavelength Astronomyo Some Basicso A Picture of our Universeo How Images are Madeo How Photons are Made

• In particular, Gamma Rayso Image isn’t Everything

• Spectral and Time domain informationo The Blazar Example

September 26, 2004Lucy Fortson Extreme Astronomy Short Course

Importance of Multiwavelength astronomyImportance of Multiwavelength astronomy

No astrophysical object emits photons at a single wavelength.

Some objects have many photon producing and changing mechanisms going on at once

o Need multiwavelength astronomy to piece together whole picture

Because we can’t always see all wavelengths, we use other wavelengths to detect objects.


What does the em-spectrum tell us?What does the em-spectrum tell us?

Transports energy Electric and magnetic fields oscillate: that’s the “wave” Moves at speed of light, 3 x 108 m/s Wavelength, frequency, energy all related Type of radiation (usually) depends on

energy/temperature of object

Putting it into perspective


Atmospheric effectsAtmospheric effects

Only visible, most radio and some infra-red gets through air!

To see Gamma-ray, X-ray, UV and some IR, need to get above atmosphere.

o Can indirectly “see” gamma-rays from ground through airshowers.


A Picture of our universeA Picture of our universe

There’s a lot happening in the photon universe - in spite of Dark Matter and Dark Energy

From the objects in our Solar System to the furthest quasar and even the Big Bang itself, photons are emitted, scattered, absorbed and otherwise mangled on their way to us.

Let’s take a brief tour…

Sun

Earth

Moon

IPM

Heliosphere

ISM

Solarwind

Nebula

Supernova

StellarBHGCBH

AGN

GRBIGM

Photons

Planets

MagField

Galaxy

Moon

Radio

Infra-red

X-rayX-ray

Visible

UV

Visible

Radio

X-rayEUV

IR

Sun

Saturn

Jupiter

X-ray

Visible

Infrared

Radio

Interplanetary Medium• Dust• Gas• Magnetic Fields• Cosmic Rays

visible

Open cluster:Pleiades - M45at 380 ly

radio

ultra violetnear IR

x-ray

Planetary NebulaDumbbell - M27at 1250 ly

Radio

Far IR

visible

near IR

x-ray

Emission Nebula(M17 - Omega Nebula)

5000 light years awayin Sagittarius

x-ray

near IR

radio

mid-IR

far IR

Visible

Radio

UV

X-ray

Radio, Visible, X-ray

Gamma-ray

Crab NebulaM1 - 6300 lyin Taurus

low x-ray

ultraviolet

gamma-raygamma sourcesx-ray

infrared

short radio

visible

Multi-wavelengthMilkyway

long radio

radio

ultraviolet

x-ray

mid-IR

visible

Andromeda GalaxyM31 - 2.9 mil ly

Centaurus A10 mil ly

Mid IR

X-Ray

UV

Vis: Ground

Radio Gamma Ray

Near IR

Vis: Hubble


More than just a pretty pictureMore than just a pretty picture

An “image” is made up of pixels containing number of photons received by a detectoro depends on sensitive range of detectoro may be combinations of two or three

“filters”o color is usually artificially determined

Hubble site example Comparing images of an object in

different wavelengths can tell us about the many processes going on.


The peculiar Centaurus A The peculiar Centaurus A

This peculiar galaxy resulted from merging an elliptical and spiral galaxy

Colors tell us:o blue - new starso red - old starso black - dust lanes


Timelapse images of Supernova 1987aTimelapse images of Supernova 1987a

Comparing visible, x-ray and radio shows radical changes.

Supernova blast wave reaches surrounding material

X-ray, radio images show where real hotspots are:

o radio confirms high energy electrons in mag field

o x-ray indicates temperatures of blast millions of degrees


A little isn’t enoughA little isn’t enough

In some cases, images are made because that is what is expected.

Each “new” wavelength goes thru phase of low statistics and/or low resolution.

TeV gamma ray astronomy has come of age with new detectors - useful images! SNR RXJ1713

Crab Nebula

HESS images


Image isn’t everythingImage isn’t everything

Images only tell part of the storyo After all, x-ray and gamma-ray astronomy has told us

lots before we got to the point where we could make an “image”.

Plot parameters of photons to understand the information behind the image:

o intensity versus energy (spectrum)o intensity versus time (light curve)

But to understand all this - we need to know how photons are made!


How photons are made or modifiedHow photons are made or modified

Thermal Radiation Nuclear, atomic or molecular

excitationso (absorption, emission lines)

Acceleration or de-acceleration of charged particles

Elementary particle decay Scattering (gain or lose energy)


Thermal radiationThermal radiation

Anything above absolute zero emits EM radiation

o Stars, gas, planets, YOU!

“Blackbody Radiation”

o The hotter an object the higher the intensity

o The hotter an object the higher frequency the peak emission.


Emission and absorption effectsEmission and absorption effects

A spectrum may be modified by medium it passes through

Thermal spectrum of Sun from photosphere is modified:

o by its chemical elements to produce absorption lines

o by the corona (hot plasma) to produce emission lines


Extreme effects from extreme astronomyExtreme effects from extreme astronomy

The high energy world invades the imagination

o The Hulk created by gamma rays

o Fantastic Four gain powers by exposure to cosmic rays


How Gamma-rays are madeHow Gamma-rays are made

Gamma-rays are emitted through four basic processes:

o Transitions between nuclear energy levels (line emission)

o Annihilation of particles with antiparticles (line emission)

o Decays of elementary particles (broad band emission)

• neutral pion decay is major player in gamma ray astronomy

o Acceleration of charged particles• Bremsstrahlung - field around nucleus• Synchrotron - static magnetic field• Compton scattering - EM field of photon


High Energy emission mechanisms (1)High Energy emission mechanisms (1)

Bremsstrahlung - “breaking radiation”o Radiation is emitted when charged particles

accelerate in the field of an ion


high energy emission mechanisms (2)high energy emission mechanisms (2)

Synchrotron - “ magnetic spin radiation”o Caused by a relativistic electron as it spirals around a

magnetic field lineo Non-relativistic version is called cyclotron radiation


high energy emission mechanisms (3)high energy emission mechanisms (3)

Compton Scattering - “rebound radiation”o A high-energy photon hits a low-energy electron. The

photon loses energy, and the electron gains some.o Inverse Compton Scattering: A low-energy photon hits a

relativistic electron. The photon gains energy, becoming an X- or gamma-ray.


The spectral keysThe spectral keys

Supernova remnant Cas A observed in gamma rays o What emission mechanism is at work?

Dotted lineo neutral pion decay

Dashed lineo Bremsstrahlung and Compton, B=1.6 mG

Solid lineo Brem + Compton, B=1 mG


Time domainTime domain

Multiwavelength light curves of seven pulsars seen in HE gammas

o measure intensity versus timeo pulsars repeat, so build up peaks


The multiwavelength story of AG(N)The multiwavelength story of AG(N)

Active galaxies have very high luminosities

o large amount of star formation

o accretion driven jets

Multiwavelength analysis helps figure out which is which:

o Arp 220 versus Centaurus A


Active Galactic NucleiActive Galactic Nuclei

• Giant elliptical galaxies• Black hole at center• Relativistic jets, accretion power

(3c219 courtesy NRAO/HST)


Active galaxy’s Shocking blobsActive galaxy’s Shocking blobs

Jets of M87 o knots of material

ejected out of central core propagate down the jet

o seen side on What happens when

jet is aimed at Earth? Blazar!

o beamed gamma ray and x-ray emission


blazar Light Curvesblazar Light Curves

Building up data from different wavelengths over timeo variability seen on

minutes, days, years

o correlations in flares between wavelengths


Mrk 501 spectral energy distributionMrk 501 spectral energy distribution

Correlation in variability between synchrotron and g-ray emission naturally explained by IC:

o Same population of electrons produce both components.

-Ray measurements provide separate constraint on electron energy, breaks degeneracies.


Blazar Emission MechanismsBlazar Emission Mechanisms

Current paradigm:Synchrotron Self ComptonExternal ComptonProton Induced CascadesProton Synchrotron

Energetics, mechanism for jet formation and collimation, nature of the plasma, and particle acceleration mechanisms are still poorly understood

(Buckley, Science, 1998)


AGNs: The Central Engine?AGNs: The Central Engine?

More than phenomenological understanding of radiative processes

VHE -rays provide probes of strong gravity close to the central engine


SummarySummary

Multiwavelength astronomy is relatively newo radio since 1950’s, x-ray, gamma-ray since 1970’s

Just learning the best ways to utilize MWL as tool

o coordination amongst different astronomy cultures• targets of opportunity

o merging data archives from different groupso time-domain (building lightcurves) is resource

intensive MWL is extreme because it pulls together all

the information we have on different objects:MWL WILL DOMINATE THE FUTURE OF

ASTRONOMY

Image Resources for Multiwavelength Astronomy Presentation

• Tour of the Universe Images

o Cool Cosmos website with FABU LOU S detailed info:http://coolcosmos.ipac.caltech.edu

o Hubble site with all of its usual help:http://hubblesite.org http://hubblesite.org/sci.d.tech/behind_the_pictures/m eaning_of_ color/filters.shtm l

o Astronomy Picture of the Day website:http://antwrp.gsfc.nasa.gov/apod/ap020920.html

o Great Explorations in M ath and Science website:http://www.lhsgems.org/IUtour.html

• Electrom agnetic Spectrum , Emission Mechanism so GLAST experiment EPO webpage:

http://glast.sonoma.edu/resources/presentations.html

September 26, 2004Lucy Fortson - Extreme Astronomy Short Course Multiwavelength astronomy is extreme...

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Transcript of September 26, 2004Lucy Fortson - Extreme Astronomy Short Course Multiwavelength astronomy is extreme...