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

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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.”

Web LinksHigh-Energy Astrophysics for Everybody -- Science@NASA headline

Amateurs Catch a Gamma Ray Burst -- Science@NASA headline

Sign-up for the AAVSO Gamma-ray Burst Network -- although this page says there is a Dec. 1, 1999 deadline, you can still register!

American Association of Variable Star Observers