|
April 21, 2000 -- Amateur astronomers from around the
world left their home-based observatories last week to attend
an unusual meeting -- the High-Energy Astrophysics Workshop for
Amateur Astronomers. Hosted by the NASA Marshall Space Flight
Center (MSFC) and the American Association of Variable Star Observers
(AAVSO), the workshop featured lectures by professional astronomers
who do cutting edge research on gamma ray bursts, magnetars,
and other high-energy phenomena.
Above: Group photo of attendees of the HEA Workshop taken
on the grounds of the U.S. Space and Rocket Center.
There's nothing strange about a meeting of scientists. Professional
astronomers hold them all the time to discuss their work. But
at this get-together the research scientists were talking to
amateur astronomers, to teach them about high-energy astrophysics
and to explain how they could become involved in the research,
too.
"This workshop was historic," said Dr. Gerald J. Fishman,
Chief Scientist for Gamma Ray Astronomy at MSFC and a principal
organizer for the workshop. "Some people think we are going
to send probes to the stars to study them, but that is science
fiction. Studying high-energy phenomena from earth with orbiting
and ground-based observatories is science fact; it's how we learn
about our universe. That's what these professionals do everyday.
The amateurs here are learning from the experts."
After three days of presentations and social interaction with
professional scientists, the amateurs -- themselves a dedicated
group of skilled observers -- returned home to continue their
own work and to share the wonders of high-energy astrophysics
with fellow amateurs, students, and the general public. Some of the participants will use
what they learned to begin their own research programs focusing
on high-energy objects like cosmic gamma-ray bursts and cataclysmic
variable stars.
The Brightest Explosions in the Universe
Gamma ray bursts (GRBs) were the highlight of the workshop. GRBs
are brief flashes of gamma rays, the most energetic component
of the electromagnetic spectrum. Because gamma rays cannot penetrate
the earth's atmosphere, astronomers must study them with orbiting
telescopes, such as NASA's Compton Gamma Ray Observatory (CGRO).
The Burst and Transient Source Experiment (BATSE) aboard CGRO
contains eight sensors that monitor the sky for GRBs.
 When
scientists first discovered GRBs in the 1960s, they thought these
mysterious flashes resided in our own galaxy, the Milky Way.
According to NASA astronomer Dr. Charles Meegan, however, data
from BATSE suggested the "stunning result" that GRBs
reside outside our galaxy.
Astronomers confirmed this in 1997 when BeppoSAX, an Italian-Dutch
satellite, detected the x-ray afterglow from a GRB. In fact,
GRB afterglows contain radiation that cascades down from gamma
rays through the x-ray, optical, and radio portions of the electromagnetic
spectrum. By measuring the redshift of ten GRB afterglows, scientists
have placed them between one-third and nine-tenths of the way
to the edge of the observable universe. That means the most distant
GRBs reside in galaxies that are over ten billion light years
from earth.
Those distances make the energy coming from GRBs hard to comprehend.
To put things into perspective, Dr. Meegan coined the term "megagal"
to represent one million times the luminosity of the entire Milky
Way galaxy. Amateurs were amazed to hear that GRBs have luminosities
ranging from 20 to 3000 megagals. According to Dr. Scott Barthelmy
of NASA's Goddard Space Flight Center (GSFC), a GRB 6,000 light
years away in the next spiral arm of the Milky Way would brighten
our night sky like the sun at high noon.
What Are Those Mysterious Objects?
Astronomers do not yet know what causes a GRB. Current theories
say GRBs might happen when binary neutron stars merge, when a
neutron star merges with a black hole, when a failed supernova
collapses to form a black hole, or when a white dwarf with an
extremely high magnetic field collapses. Whatever the GRB's source,
its optical afterglow probably results when extremely high energies
from the blast interact with the interstellar medium, the gasses
between stars.
 To test these theories, astronomers need
more observations of GRB afterglows. That is where amateur astronomers
join the hunt. The optical afterglow can fade from as bright
as 9th magnitude to 20th magnitude, a 25,000-fold decrease, in
just six hours. The rapid reaction required for optical observations
is difficult for professional telescopes, where operators set
observing schedules months in advance. To date, professionals
have observed the optical afterglow of only nineteen GRBs.
Above: In January 1999 astronomers used a robotic telescope
to capture these images of the visible light from a gamma ray
burst. The circled black dot is a fireball that briefly flared
during the explosion. Scientists were astonished to discover
how bright gamma ray bursts could be at optical wavelengths.
This one reached 9th magnitude, which means it would have been
visible in binoculars if anyone had been looking. [full
story]
Amateurs do not work under similar constraints. Warren B. Offutt,
for instance, operates W&B Observatory with his wife, Beverly,
in Cloudcraft, New Mexico. Offutt said, “If my observatory
is open and running, I can respond to a GRB in ten minutes. If
I'm in my house, I can open the observatory to respond in thirty
minutes.” After thirty minutes, the apparent magnitude of
the optical component should be between 14.0 and 16.6, within
reach of an 8-inch amateur telescope equipped with a CCD camera.
Even after four hours, the expected magnitude is between 16.6
and 19.7.
How will amateurs know when and where to observe GRBs? Dr. Barthelmy
runs the GRB Coordinates Network (GCN) from NASA/Goddard in Greenbelt,
Maryland. When an orbiting telescope observes a burst, it notifies
GCN, which in turn notifies astronomers around the world, including
the almost twenty professional telescopes that participate in
the search for afterglows.
Working with Dr. Barthelmy, Aaron Price of AAVSO's Gamma Ray
Burst Network, is setting up Network members to receive alerts
from GCN. AAVSO's GRB Network contains sixty-four amateurs, quadrupling
the number of telescopes looking for GRB afterglows. Dr. Mario
Matto, a cardiologist and amateur astronomer who is one of three
chairpersons for the AAVSO Network stressed, however, that more
observers are needed, especially from the Southern Hemisphere.
Eyes on the Night Sky
When AAVSO receives a GRB alert, it will notify members of
the GRB Network, usually by pager or e-mail. Because pagers are
best for rapid response times, AAVSO will supply pagers to network
members without one. To make responses worthwhile, individual
members can customize the alerts they receive based on the GRB's
location, the size of the error box in which the GRB resides,
the time of day, day of the week, and any other criteria that
members recommend. AAVSO's director Janet Mattei hopes to create
star charts with error boxes to help team members locate the
GRBs.
GRB Alerts
Gamma rays cannot penetrate the earth's atmosphere, so astronomers
must receive GRB alerts from orbiting space telescopes. The Compton
Gamma Ray Observatory, which NASA will decommission later this
year for safety reasons, is the only satellite that currently
provides immediate coordinates for GRBs. BeppoSAX and the Rossi
XTE use x-ray afterglows to provide coordinates within a few
hours.
Upcoming missions, including HETE-2 (2000), INTEGRAL (2001),
and Swift (2003), will speed response times up again. HETE-2
and INTEGRAL will immediately provide coordinates for 30 GRBs
each year. Swift, which is being built by GSFC along with Pennsylvania
State University and others, will immediately provide coordinates
for 300 GRBs each year. With the imminent and sorely disappointing
loss of Compton, astronomers eagerly await the launch of these
new gamma ray telescopes.
CONTACT
Amateur astronomers and others who want to join AAVSO's Gamma
Ray Burst Network or other observing programs should visit AAVSO's
website at www.aavso.org. |
Once alerted, amateur astronomers will race to their
telescopes to commence observations. “The earlier the better,”
according to astronomer Arne A. Hendon. Dr. Hendon recommended
that during the first hour after a GRB, amateurs should begin
with 10-20 second CCD exposures and end with one-minute exposures.
Exposures from one to six hours after the GRB should be five
minutes long.
Professionals and amateurs agreed that amateurs must use standard
Johnson filters (preferably R- & V-band) when observing GRBs.
According to Dr. Matto, “the data are essentially useless
without filtered observations.” Dr. Mattei said the organization
is seriously considering buying filter packages for network members
to standardize observations.
As amateurs provide optical data, professionals will use it to
test their models of what causes GRBs. Professionals want to
explore how the optical component is related to the initial gamma
ray outburst. Color information in the optical range will help
determine whether GRBs radiate like a beam in one direction,
or isotropically in all directions. That will affect calculations
of their energies and occurrence rates. In the end, professionals
hope to determine the source of GRBs and their role in the evolving
universe.
High-Energy Astrophysics in the Milky Way
Amateurs attending the workshop learned that GRBs are not
their only opportunity to contribute to high-energy astrophysics.
Dr. Mattei gave an inspiring presentation about amateur contributions
to professional research on cataclysmic variable stars (CVs).
A CV typically is a binary system that contains a white dwarf
that steals matter from its companion through an accretion disk.
During outbursts, CVs radiate energy in the x-ray, extreme ultraviolet,
and ultraviolet regions of the electromagnetic spectrum.
By monitoring CVs optically, amateurs alert professionals about
outbursts, allowing the professionals to turn their orbiting
telescopes onto the stars at just the right moment. By observing
CVs during outbursts, amateurs provide data to test theories
about the cause of outbursts and how accretion disks work. Dr.
Mattei said that since the 1970s, amateurs have helped sixteen
observatory spacecraft with high-energy CV research.
The fun does not end there either. Amateurs can make valuable
observations of other variable stars such as BL Lac objects and
certain low mass x-ray binaries. High-energy astrophysics is
an exciting field of research with no end in sight.
As said by Giancarlo Favero, an amateur astronomer and workshop
participant from Padova, Italy, “Astronomy lasts a lifetime.” |
Join our growing
list of subscribers - sign
up for our express news delivery and you will receive
a mail message every time we post a new story!!!
Headlines