High Energy Astronomy

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Module 21 Solar Activity its Effects on Earth
Activity 2 High-Energy Astronomy
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Summary

• In this Activity, you will learn about how the
  Suns weather affects the Earth, and how the
  high-energy electromagnetic radiation from the
  Sun is monitored by astronomers on Earth. In
  particular, we will look at
• the active Sun and Earths upper atmosphere and
  climate
• high-energy processes in space
• detecting UV radiation - the IUE, EUVE
• detecting X-ray radiation - ROSAT, AXAF
• detecting ?-ray radiation- GRO COMTEL and
• solar Connections - RHESSI X-ray imager and
  TIMED ultraviolet
  imager.

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Time 0 Sun produces burst of cosmic rays
The Active Sun the Earth
During its active periods, the Sun emits solar
cosmic rays. Those which reach Earth are mostly
protons that is, hydrogen atoms with no
electrons (H). The highest-energy particles
arrive about 30 minutes after the flares maximum
is seen on Earth, as the light reaches us before
the particles can.
Time 8 minutes Light from burst reaches Earth
Time about 1/2 hr First (fastest) particles
arrive
Time about 1 hrParticle flux at Earth is
heaviest
About one hour after the flares maximum, the
number of particles reaches its peak.
This radiation is very dangerous for astronauts,
but on Earth we are shielded from it by the
atmosphere.
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Auroras (Northern Southern Lights)
When these particles approach Earth, they begin
to experience Earths magnetic field and some
become trapped. As the field is stronger near
the poles (the clue is that the B field lines are
close together) more particles are trapped
there. Since moving charged particles create a
magnetic field of their own, Earths magnetic
field is distorted.
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Atmospheric havoc
A big solar flare can lead to heating of the
outer layers of Earths atmosphere, and it
expands slightly. The cosmic rays also affect
short-wave radio transmissions. Satellites will
tend to lose altitude they may even re-enter the
atmosphere and burn up.
Thats cause the Sunstransmission is
sodynamic!
This radio transmissionis full of static...
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The Earths Climate
Lots of sunspots higher T on Earth

• Over the last few hundred years there have been
  two periods of very few sunspots
• The Maunder Minimum (MM), 1645 to 1715, and
• The Little Maunder Minimum (LMM), from about
  1800 to 1830.
• During these periods, the temperatures in Europe
  were exceptionally low (especially during the
  Maunder Minimum).

Earths temperatures
Few sunspots low T on Earth
No. of sunspots
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Scandinavia
Greenland
Canada
The Sun Makes History
From 800-1000AD, Erik the Red, his son Lief and
others made numerous trips from Scandinavia to
Greenland (so named by the entrepreneurial Erik
to make it more attractive to potential
settlers), with landings in northern Canada and
perhaps even further south in the USA.
Several Norse settlements flourished in Greenland
until about 1200 AD, when they began to decline
by 1500 they were all abandoned.
One major factor was the weather there was a
Little Ice Age, and like so many colonists (even
today) the Norse failed to learn from the locals
(most probably Inuit) how to adapt. When the
Norse couldnt cope with the increasingly cold,
bitter weather, they returned to Europe. If it
wasnt for the Sun, the Norse would probably have
colonised America 500 years before Columbus
landed!
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Carbon-dating
Carbon-dating is not the process of going to the
movies with a lump of coal, graphite or
diamond! For some time people have worked out the
age of rocks, tombs, and so on by finding out how
much carbon-14 there is in them. The older the
item, the less carbon-14 there is (because it
decays). Carbon-14 dating is sensitive to the
rate at which 14C is produced in the atmosphere
by cosmic rays.
Using carbon-dating, we can tell that there was
very low solar activity in the MM and LMM, but
also between 1410 and 1530, and before that, 1280
to 1340. These periods were known to be unusually
cool as the Norse found out, to their
chagrin.
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Solar luminosity
Solar luminosity is usually very stable, and
varies only by about 0.1. However the
temperatures during the Maunder minimum tell us
that the luminosity must have fallen by about
0.5. Would this be enough to cause a Little Ice
Age? Were not sure there are many other
competing factors which can lower Earths surface
temperature. For example, volcanoes and huge
meteor impacts can fill the air with
energy-absorbing dust, so the Earth will cool
down.
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• High-Energy Processes in Space

Lets quickly revise what we have studied about
electromagnetic radiation, cosmic rays and the
Earths atmosphere.
To begin with, the visible spectrum (which we
call light) is only a very small part of the
whole electromagnetic spectrum.
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Visibleregion
Click herefor info onnm, GHz etc.
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Photons of different wavelengths can penetrate
the Earths atmosphere to different depths.
Visible
Ground level
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That means that on the surface of the Earth we
can do a good job of detecting visible light and
the higher-energy radio waves, but not much else.
The good news is that we dont get zapped by
X-rays, scorched by the infra-red, or fried in
the ultraviolet.
Visible
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Rockets to the rescue
Visible
These are observed from space, using rockets and
satellites
Enough of these radiations get through that we
can also use upper-atmosphere stuff balloons,
and telescopes on high, dry mountains and in
Antarctica
Ground level
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From now on, when it is relevant, we are going to
use this bar to showyou in which part of the
spectrum the various instruments are working.
Ultraviolet and X-ray astronomy detects high
energy processes such as emissions from solar
flares and from pulsars accreting (collecting)
material from a stellar companion. There arent
any pulsars in the Solar System, so we dont
study them here they are covered in Exploring
Stars and the Milky Way.
Extremely energetic cosmic events produce Gamma
Ray Bursts - the origin of which is still not
decided - possibly black holes colliding and
merging!
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High-energy processes in the Sun are best studied
using ultraviolet or X-ray detectors.
Were now going to examine some of the techniques
and instruments used in detecting high-energy
photons, most particularly from the Sun (because
its the nearest star, and because it affects us
so much here on Earth and in our space
activities).
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This image shows X-ray emission from active
regions on the Sun. Humans cant see X-rays, so
representative colour has been used to show their
energy and intensity.
X-ray images of active regions are much more
informative than visible light images, because
the high-energy processes which emit X-rays are
concentrated over and within active regions.
On the other hand, the lower-energy processes
which emit visible light are spread out over the
entire photosphere. We see sunspots, but not much
else.
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IUE - The International Ultraviolet Explorer
The IUE was launched in 1978 to provide a space
telescope for ultraviolet astronomy. IUE was a
collaborative project between NASA, ESA and the
British SRC agencies.
IUEs estimated lifetime was 3 to 5 years.
Amazingly, it continued to perform long after
that. After 18 years, 8 months and 4 days it was
finally shut down, having made over 100,000
observations of comets, planets, stars, novae,
supernovae, galaxies, and quasars. Bravo, IUE!
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IUE was placed in geosynchronous orbit that is,
it stayed over the same spot on the Earth by
orbiting once per day.
The really beautiful thing about the IUE was that
it could look at very small ranges of ultraviolet
radiation, making lots of measurements close
together. In fact, it could make 11,000 separate
measurements as it scanned the ultraviolet
band. For more information, visit the Internet
sitehttp//www.esa.int/science/iue
Lovely fine detail
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EUVE - the Extreme Ultraviolet Explorer
EUVE - the Extreme Ultraviolet Explorer
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Launched in June 1992, the EUVE observes at
wavelengths between 7 and 76 nm, exploring
astronomical spectra right up in the high energy
UV, near the X-ray band.

• It carries two sets of instruments
• The first set consists of three scanning
  telescopes, clustered together and aligned to
  point in the same direction, to carry out an
  all-sky survey of extreme ultraviolet sources.
• The second set is the Deep Survey/Spectrometer
  Telescope, which combines a telescope to image
  very distant sources and a spectrometer to
  analyse radiation by wavelength.

It was expected that the EUVE would have to be
terminated in 1996, but it has been so
successful that the mission ran until December
31, 2001, despite NASA funding constraints. EUVE
re-entered the Earths atmosphere in late January
2002. For more information, visit the Internet
site http//ssl.berkeley.edu/euve/
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Detecting X-ray radiation
Well now take a look at the Roentgen Satellite,
known as ROSAT for short. ROSAT is an X-ray
observatory that is, it was built to observe and
record radiation in the X-ray region of the
spectrum.
ROSAT was developed cooperatively by Germany, the
US and the UK.
ROSAT was launched in 1990, with an expected
operational lifetime of 3 years but lasted well
beyond its anticipated lifetime. (These
designers are better than they think!) The
mission ended November 1999. For more
information, visit the Internet site
http//xte.gsfc.nasa.gov/docs/rosat/rosgof.html
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Chandra (formerly known as AXAF)
The Chandra X-ray Observatory, named after the
famous Indian-American astrophysicist and Nobel
laurate Subrahmanyan Chandrasekhar, was launched
in July 1999. It is now operating in its
final, eccentric orbit which takes it one-third
of the way to the Moon at apogee. This is
necessary for an X-ray telescope because it
needs to operate well out of the Earths
atmosphere and Van Allen Belts. However it also
means that the observatory cannot be serviced in
case of a malfunction.
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The Chandra X-ray Observatory being launched in
July 1999 aboard the Shuttle Columbia
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Chandras special features
Chandra improves on existing astronomical
observation in the X-ray region in its spatial
resolution which is an order of magnitude finer
(0.5 arcsec on axis) than previously achieved.
An order of magnitude is a factor of ten that
means that Chandra can see things in about ten
times as much detail than previous X-ray missions.
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Chandra was also designed to have very good
energy sensitivity from 0.1 to 10 keV, with high
spectral resolution observations over most of
this range.
However as Chandra passed through the Earths
radiation belts in its highly elliptical orbit in
the first months of the mission, it was found to
be focussing not only X-rays, but also protons
electrons from those radiation belts onto its
detector chips. The chips are now being protected
as Chandra passes through the radiation belts,
but in the meantime degradation of its energy
resolution chips has meant that Chandras energy
resolution capabilities have dropped by a factor
of 4, which may limit the scientific capabilities
of the telescope.
For more information, visit the Chandra Internet
site
http//chandra.harvard.edu/
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Detecting ?-ray radiation
We cannot focus ?-rays but can obtain some
positional information by tracking them through
more than one detector. Its a bit like the way
we locate things using parallax while one
measurement gives you almost no information
except a direction and an apparent size (in
parsecs), two measurements give you such details
as the distance to the object and its real size
(in kilometres, for instance). And if you make
more measurements, you can be more confident
about the results as their accuracy will increase.
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CGRO
The Arthur Holly Compton Gamma Ray Observatory
was launched in April 1991.
Arthur Holly Compton was a researcher who made
great progress in his studies of gamma rays and
how to detect them.
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CGRO contained several instruments, including
COMPTEL - The Imaging Compton Telescope
COMPTEL consisted of two detector arrays, 1.5 m
apart, each containing a scintillator. A
scintillator acted basically as an amplifier
Every time one gamma ray enters a scintillator,
many gamma rays come out the other end.
The mission ended June 2000.
For more information about CGRO, visit

http//cossc.gsfc.nasa.gov/
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Sun-Earth Connection
NASAs Sun-Earth Connection program aims to
Understand the Sun, Heliosphere and Planetary
Environments as a Single Connected System
Currently 14 missions support the research
program, including RHESSI, IMAGE and TIMED, and
there are another 12 missions in development or
under study. For more information,
visithttp//sec.gsfc.nasa.gov/
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• Sun-Earth Connection focuses on
• the Suns atmosphere and flares

• the Suns magnetic field

• the Earths upper atmosphere

• the Earths magnetic field and

• the coupling among them.

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RHESSI Imaging solar flares
The Reuven Ramaty High-Energy Solar
Spectroscopic Imager (RHESSI) was launched on Feb
2002 with the aim of studying particle
acceleration and explosive energy release in
solar flares.
RHESSI combines high-resolution imaging in X-rays
and gamma rays with high-resolution spectroscopy
to pinpoint the location and dynamics of
high-energy processes. For a mission update,
visit the website http//hesperia.gsfc.nasa.gov/h
essi/
Dr. Ramaty was a pioneer in the fields of solar
physics and high energy astrophysics, and one of
the founding members of the HESSI team.
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IMAGE
The Imager for Magnetopause-to-Aurora Global
Exploration (IMAGE) spacecraft was launched in
March 2000.
It the first satellite dedicated to imaging the
Earths magnetosphere. The main goal of IMAGE is
to determine the shape of the magnetosphere and
how it changes in response to interplanetary
disturbances. Its instruments can detect
energetic neutral atom, observe extreme and far
ultraviolet, and conduct radio sounding imaging.
For more information, visit http//pluto.space.sw
ri.edu/IMAGE/
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TIMED
The Thermosphere, Ionosphere, Mesosphere
Energetics and Dynamics (TIMED) mission uses
remote sensing and imaging to help space
scientists to understand the flow of energy
through the complex transition region between
space and the Earth.
TIMED was successfully lunched on 7 December
2001, and is studying the Earths mesosphere and
ionosphere. It has completed its initial 2 year
orbital mission and is now in the extended
mission phase.
For mission updates, visit http//www.timed.jhuap
l.edu/
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Solar Probe
NASAs Solar Probe will obtain the first in-situ
measurements from within in the Suns corona.
The mission objectives are to understand what
heats the solar corona and how the solar wind is
accelerated.
The mission is currently under study and its
proposed launch date is August 2012. For mission
updates, visit http//solarprobe.gsfc.nasa.gov/
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Summary

• We have seen that there is some evidence that
  Earths weather can respond to major variations
  in the Suns activity, and that this also affects
  radio transmissions.
• High-energy radiation is also a hazard to
  astronauts.
• On Earth, we can detect and study visible light
  and some radio waves with reasonable success, but
  for the higher-energy photons it is necessary to
  use detectors in orbit in the upper atmosphere or
  in space.
• Some of these detectors, working in the X-ray,
  ultraviolet and gamma ray bands, were discussed.

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Image Credits
X-Ray Sun ISAS, Yohkoh Project, SXT
Grouphttp//antwrp.gsfc.nasa.gov/apod/image/9812/
solsticesun_sxt.jpg Sunspots National Solar
Observatoryhttp//antwrp.gsfc.nasa.gov/apod/image
/9701/sunspot_nso.jpg Aurora overhead, in
Alaskahttp//antwrp.gsfc.nasa.gov/apod/image/9811
/aurora2_jc_big.jpg The International Ultraviolet
Explorer http//antwrp.gsfc.nasa.gov/apod/image/iu
e_logo.gif The Extreme Ultraviolet
Explorer http//w3.cea.berkeley.edu/image/papers/s
ci_archive_pubs_papers_539_539_f3.gif ROSAT
satellite http//heasarc.gsfc.nasa.gov/Images/rosa
t/rosat_sat.html AXAF http//hea-www.harvard.edu/a
sc/gifs/AXAF-smaller2.gif Arthur Holly Compton
Gamma Ray Observatory http//erbscobe.gsfc.nasa.go
v/groviewt.gif Chandra X-ray Observatory Launch
in the Shuttle Columbia http//chandra.harvard.edu
/
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Image Credits
RHESSI - NASA http//hesperia.gsfc.nasa.gov/hessi/
images/hessi1a.jpg Solar Probe -
NASA http//solarprobe.gsfc.nasa.gov/sp_relative2h
uman.jpg IMAGE - NASA http//image.gsfc.nasa.gov/i
mage/image_logo.jpg TIMED - NASA http//stp.gsfc.n
asa.gov/missions/timed/images/timed.2.jpg
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Now return to the Module home page, and read more
about the Sun, weather and instrumentation in the
Textbook Readings.
Hit the Esc key (escape) to return to the Module
21 Home Page
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Conversion
The table below may assist you when converting
between photon frequency, wavelength and energy.
Region Wavelength Frequency Energy hard gamma 1
x 10-9 nm 3x1026 Hz 1.2 x 1012 eV gamma 1 x 10-6
nm 3x1023 Hz 1.2 GeV gamma/X-ray 0.001 nm 3x1019
Hz 12 MeV X-ray 1 nm 3x1017 Hz 120
keV X-ray/UV 10 nm 3x1016 Hz 12 keV UV 100
nm 3x1015 Hz 1.2 keV visible (blue) 400
nm 7.5x1017 Hz 3.1 eV visible (red) 700
nm 4.3x1017 Hz 1.8 eV IR 10000 nm 3x1013 Hz
0.12 eV MW 1 cm 30 GHz 1.2 x 10-4
eV MW/radio 10 cm 3 GHz 1.2 x 10-5
eV radio 100 m 3 MHz 1.2 x 10-8 eV radio 100
km 3 kHz 1.2 x 10-11 eV
Please see the next slide for explanations of nm,
eV etc.
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Explanations
The formulae that were used to make the
conversions in the table are
nm nanometer The prefix nano- means 10-9, so a
nanometer is 0.000000001 metre. Hz hertz Hertz
is the unit given to frequency of a waveform, in
cycles per second. GHz gigahertz The prefix
giga- means 109 , so a GHz is a billion cycles
per second. MHz megahertz Mega- means 106, so
a MHz is a million cycles per second. eV
electron-volts The electron-volt is a unit of
energy it is the energy involved in moving an
electron through a potential difference of 1
volt. 1 eV 1.60 x 10-19 J ( joules), where 1 J
is (roughly) the energy youd expend if you
lifted a mass of 1 kg to a place 10 cm higher.
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Return to the Activity
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