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...
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.
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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.
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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.
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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!
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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)
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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.
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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.
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
Time domainTime domain
Multiwavelength light curves of seven pulsars seen in HE gammas
o measure intensity versus timeo pulsars repeat, so build up peaks
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
Active Galactic NucleiActive Galactic Nuclei
• Giant elliptical galaxies• Black hole at center• Relativistic jets, accretion power
(3c219 courtesy NRAO/HST)
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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.
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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)
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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
September 26, 2004Lucy Fortson Extreme Astronomy Short Course
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