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Why Wait for the 4th of July?

Amateur Astronomers To Be Invited To Join Quest
For Fireworks Accompanying Gamma Ray Bursts

July 9, 1999: While many of us watched fireworks from the backyard this July 4, the cosmos offered up its own version of fireworks, as the Italian-Dutch Beppo-Sax satellite recorded gamma-ray burst GRB 990704. As soon as word of a bright gamma-ray burst reaches professional astronomers on the ground, telescopes across the globe began to search for an optical counterpart to the gigantic cosmic explosion. In the case of GRB 990704, observers at the Observatoire de la Cote d'Azur may have detected a 19th magnitude object at the position of the burst, but confirmation is still needed.

Right: Brian Lee of the University of Michigan removes dust covers from the four 200mm Canon telephoto lenses employed by ROTSE I. Credit: University of Michigan

Many scientists believe that the study of optical emission from the host galaxies of gamma-ray bursts may hold the key to understanding the origin of these high-energy explosions. And now, it's not just for the professionals. Capable amateur astronomers are being asked to help in the hunt for optical emission from gamma-ray bursts, and to provide follow-on observations of burst locations.

The possibility of professional-amateur cooperation in GRB investigations was the topic of a paper presented at the 111th annual meeting of the Astronomical Society of the Pacific (ASP), titled "Partners in Astronomy," held in Toronto July 1-7, 1999. The purpose of the meeting, held jointly with the American Association of Variable Star Observers (AAVSO) was to explore areas of research where amatuers and professionals might profitably collaborate.

Although gamma-ray bursts have been observed regularly by orbiting telescopes since the late 1960's, the first optical image of a burst-in-progress was obtained just a few months ago. Astronomers were astonished when the University of Michgan's Robotic Optical Transeint Search Experiment (ROTSE) photographed a bright, 8.9-magnitude object at the location of GRB 990123 while the burst was being observed in gamma-rays.


Above: A sequence of images (clipped from the centers of the frames) shows GRB 990123 brightening and then fading over a period of almost 10 hours. The brighter star at the bottom indicates that longer exposures were needed to capture the fading burst.

The acquisition of the images was not an accident. The Compton Gamma Ray Observatory data stream from space is continually monitored by a computer on the ground that can detect the presence of a burst in the data, compute a coarse sky-location, and transmit this information over the Internet. In the case of GRB990123, the ROTSE pictures were taken automatically with no human in the loop. Optical emission had been observed previously from GRBs, but always well after the burst's gamma-emission was no longer detectable.By this time, the optical brightness had faded to 20th magnitude or even fainter.

It is notable that ROTSE is not a super-sophisticated telescope, but uses four telephoto lenses originally designed for 35mm cameras. Each lens has its own CCD. A computer combines the four images into one and compares the scene with previous images to help locate the burst.

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What ROTSE saw in January immediately transformed the field of gamma-ray astronomy. The optical emission from GRB 990123 was so bright that it would have been visible through a pair of binoculars or a small amateur telescope - if the observer knew where to look. Astronomers have long known that gamma-ray bursts are bright at x-ray and gamma-ray wavelengths, but few if any would have guessed that they could be so brilliant visually.

Left: Close-up view of ROTSE I shows that the amateur need not buy an expensive telescope: ROTSE I uses four 200mm f/1.8 Canon telephoto lenses, each with a 2,048x2,048-pixel CCD camera. Credit: University of Michigan

"GRB 990123 was so bright that practically anyone could have seen it," noted John Horack, a gamma-ray astronomer at NASA/Marshall, and a co-author on the paper. "Many amateur astronomers have telescopes that can reach very faint magnitudes. Given what we known now about 990123 it seems possible that skilled amateurs, by monitoring GRB positions and searching for new counterparts, might be able to make an important contribution to gamma-ray burst research."

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Amateurs are often astonishingly skilled observers, and they maintain state-of-the art observatories complete with CCDs (charge-coupled devices), photometers, and other instruments that were once accessible only to professionals. One of the strengths of amateur astronomers is their ability to monitor positions and objects in the sky for long periods of time. Dedicated variable star observing is one example where amateurs have contributed  research-quality data to professionals for many years under the auspices of the AAVSO. Amateurs also make important contributions to searches for new comets, asteroids, and supernovae. 

The next frontier for amateur research may be gamma-ray bursts. Astronomers at NASA/Marshall are collaborating with the AAVSO and others to connect amateurs to the GRB Coordinates Network (GCN) pioneered by Scott Barthelmy at the NASA/Goddard  Space Flight Center.

The new program would be administered through the AAVSO and the NASA "Star Trails Society" as part of the NASA/Marshall "Partners in Discovery" program. Participating amateurs would receive rapid email notification when earth-orbiting gamma-ray observatories detect and localize a cosmic gamma-ray burst. Amateurs could then train their telescopes on the GRB coordinates and begin monitoring.

"It's likely that most amateurs won't catch the burst in progress," continued Horack, "but they might still make an important contribution through long term monitoring. One of the things that we'd expect from gamma-ray bursts that are located at the far corners of the Universe would be a 'gravitational lens' signature in at least a few of the bursts. We've been looking, but so far haven't seen such an event."

Right: ROTSE II emplys a larger telescope to take more detailed images of optical counterparts and other phenomena. Credit: University of Michigan

The basic idea behind gravitational lensing is that radiation from the burst is distorted and focused by the gravitational force of galaxies that lie between the Earth and the burst. If the geometry is just right, these galaxy-sized lenses create multiple paths that light can take from the burst to reach the Earth.  Some paths are longer than others, meaning that not all the radiation from the burst arrives at the same time. Therefore, the emission - including the optical - from lensed bursts could recur when  'after images' of the burst arrive weeks, months, or perhaps a few years later.

Web Links
GOTCHA! The Big One That Didn't Get Away describes how BATSE and ROTSE caught GRB 990123 in the act.
The Robotic Optical Transient Experiment (ROTSE) web site includes recent images and technical papers on how ROTSE works.
American Association of Variable Star Observers web site describes how amateur astronomers can contribute to professional astronomy.
Astronomical Society of the Pacific co-hosted the Partners in Astronomy meeting.
"These lenses in space are not simply a theory. Many gravitational lenses are known, including some observed by the Hubble Space Telescope.  

Studying the possibility of lensed GRBs is where amateurs may make a real contribution. Telescope time at professional facilities is extremely limited, and schedule constraints don't allow the sort of dedicated monitoring needed to look for secondary bursts.

The AAVSO will be holding a special conference on High-Energy Astronomy and the Amateur Astronomer," noted Janet Mattei, president of the AAVSO. The conference, to be held next spring, will help identify and formalize a variety of opportunities for amateur astronomers, including the field of gamma-ray bursts.

Right: The view to the east from ROTSE's perch at Los Alamos National Laboratory, N.M. As with any astronomical observations, clear, dark skies will be a great help in spotting GRB optical transients. Credit: University of Michigan

Any discoveries to be made by amateurs will require careful observing, and meticulous attention to detail. Optical emission from gamma-ray bursts quickly fades after the event to below 19th or 20th magnitude. Leif Robinson, editor of Sky & Telescope quipped, "That's duck soup for many CCD-equipped amateurs." The trick to catching 'the duck,' however, will lie not only in the techonology of observation, but will involve persistence, and a bit of luck as well.

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For more information, please contact:
Dr. John M. Horack , Director of Science Communications
Author: Dave Dooling
Curator: Linda Porter
NASA Official: Gregory S. Wilson