Space Grant Consortium - University of Wisconsin - Green Bay

Radio
 measurements
 of
 supernovae
 can
 create
 a
 detailed
 image
 of
 the
 front
 of
 the
 blast
wave
where
synchrotron
self‐absorption
and
free‐free
absorption
take
place
(Weiler
et
al.,
2002).
 
 By
 detecting
 the
 intensity
 and
 wavelength
 of
 the
 radio
 waves
 given
 off
 by
 a
supernova,
scientists
are
able
to
draw
conclusions
about
the
characteristics
of
the
CSM
of
the
star
such
as
if
it
was
uniform
or
clumpy
and
how
far
from
the
star
it
was
before
the
star
exploded
(see
Figure
1).
Radio
antennae
are
a
good
way
to
detect
photons
from
these
processes.

However,
one
of
the
 main
 disadvantages
 of
 radio
 antennae
 is
 that
 they
 have
 low
 resolving
 power.
 
 Radio
wavelengths
are
about
10 5 
times
larger
than
visible
light.

Therefore,
if
an
optical
and
radio
telescope
were
built
with
the
same
diameter,
the
radio
telescope
would
have
10 5 
times
less
resolving
 power.
 
 This
 means
 that
 some
 radio
 telescopes
 would
 have
 to
 be
 built
 on
 the
order
 of
 10‐100
 km
 to
 get
 the
 same
 resolving
 power
 as
 an
 optical
 telescope.
 
 Radio
astronomers
use
a
technique
called
interferometry
to
rectify
this
problem.

If
two
“normal”
sized
radio
antennae
were
placed
a
few
kilometers
apart
and
their
received
signals
were
synchronized,
the
separate
dishes
could
act
like
a
single
dish
and
give
an
image
of
a
thin
strip
 of
 the
 sky.
 
 If
 many
 antennae
 were
 placed
 near
 each
 other,
 and
 each
 of
 them
synchronized
their
image
with
each
of
the
other
ones,
then
one
could
create
a
clear
image
of
the
sky.
The
Very
Large
Array
(VLA) 4 
is
a
collection
of
27
radio
antennae,
each
about
25
meters
in
diameter,
 which
 monitors
 various
 celestial
 phenomena
 such
 as
 quasars,
 supernovae
 and
gamma
 ray
 bursts.
 Normally,
 in
 order
 to
 study
 celestial
 bodies
 at
 a
 great
 distance
 with
acceptable
image
clarity,
a
huge
dish
must
be
used.

However,
the
VLA
fixes
this
problem
by
having
 groups
 of
 satellites
 take
 images
 together
 in
 different
 configurations.
 
 In
 the
 A
configuration,
all
of
the
antenna
are
spread
out
with
each
arm
at
21km.

This
simulates
a
single
radio
dish
that
is
36
km
in
diameter.

The
size
of
the
array
decreases
slowly
with
the
B
and
C
configurations
until
it
is
finally
in
the
D
configuration
where
all
of
the
antennae
are
placed
within
0.6km
of
the
center.

When
the
antenna
are
in
the
A
configuration,
the
radio
array
has
the
most
magnification
and
can
pick
up
the
greatest
amount
of
detail.

When
the
size
of
the
array
shrinks,
scientists
can
study
the
overall
structure
of
the
celestial
object.
The
Weiler
et
al.
(2002)
parameterized
model
is
based
on
six
parameters
that
describe
the
properties
of
the
observed
radio
emissions.

The
basis
for
these
parameters
comes
from
the
work
 of
 Chevalier
 (1990)
 on
 the
 interactions
 of
 the
 CSM
 with
 a
 supernova
 blast
 wave.
These
parameters
can
provide
many
details
about
the
CSM.

The
features
the
parameters
represent
are
shown
in
Figure
1.
4 The VLA of the National Radio Astronomy Observatory is Operated by Associated Universities, Inc. under a
cooperative agreement with the National Science Foundation
21