Last month's AstroAlert test went very well, and I'd like to share with all participants what we found out. We are gratified to see the enthusiasm and dedication with which so many of you responded.
To recap, our test message was sent out on Friday, February 14, 2003, at 1:05 p.m. EST (that is, 18:05 Universal Time). It began as follows:
This Sky & Telescope AstroAlert is being issued [as a test] in support of the SuperNova Early Warning System (SNEWS). We seek your assistance in pinpointing the location of a possible supernova explosion. Neutrino detectors give the target’s approximate coordinates (equinox 2000.0) in the constellation Boötes, as follows:
|Right ascension:||13h 38m|
Please check this region of the sky as soon as possible using your naked eyes, binoculars, a telescope, or a camera. You are looking for a starlike point of light...
In all, we received 83 responses via our online report form and several more by direct e-mail. Some respondents, in their eagerness, rushed to send us a negative report after stepping outdoors and looking up at the daytime sky! But the replies really began to roll in late Friday night and early Saturday morning, after people had had a chance to check out the target area in Boötes and Virgo for themselves. Unfortunately, many of you described nearly impossible observing conditions (a snowstorm under way, an overcast sky, or cirrus illuminated by glare from the nearly full Moon). Those who could see the stars were typically braving frigid temperatures.
As a few people astutely guessed, we had in mind that people might be able to "discover" the asteroid Vesta. On February 16th it was situated well inside the specified 13° radius from the center of our target region, near right ascension 13h 02m, declination +4.6° (equinox 2000.0), in the constellation Virgo. Since Vesta was about magnitude 6.7 and near a stationary point in its retrograde loop among the stars, it met some of the criteria expected of a supernova candidate. It was a starlike point, not obviously moving, and not shown on any printed star atlas or prior photograph of the region.
What follows is a summary of how people met our challenge.
GEOGRAPHICAL DISTRIBUTION. We truly had a global response. For while the United States was heavily represented (including Hawaii and Alaska), we also heard from observers in Greece, Finland, Turkey, Sweden, Canada, Brazil, France, the Netherlands, Germany, England, Ireland, Italy, Australia — even the Isle of Man!
MESSAGE TRAVEL TIME. One of our goals was to learn how quickly the AstroAlert would reach local servers after bouncing around the Internet. Thanks to the 35 people who carefully dissected their message headers to extract this information, we now know that this travel time ranged from 8 to 136 minutes, the average being 55 minutes. Interestingly enough, there was no obvious correlation between this interval and a person's distance from the Sky & Telescope offices. A few people in Europe received the message much sooner than did those in our neighboring states of New Hampshire and Connecticut.
HOW SOON WAS IT READ? A dozen or so respondents happened to be sitting right at their computers when the message arrived. Another person was away from his desk, but he received notification on his mobile phone when it came in. Some 70 percent of the respondents actually saw the message within 8 hours of the time we sent it.
SEARCH STRATEGIES. Our test message said nothing about the expected magnitude of the "supernova," so those who had clear skies usually began by checking the target area with the naked eye, then switching to binoculars. This was probably a wise choice, given the large area of sky to be covered. One observer used an 82-mm refractor and several used Schmidt-Cassegrains in the 0.25- to 0.4-meter range. But while these observers could see considerably fainter stars than those using binoculars, they could not examine as wide a field efficiently.
TIME SPENT IN SEARCH. Many (actually, most) respondents sadly had overcast skies during the February 14-18 period of our test. What's more, many who could see stars had to contend with a very bright Moon, cirrus, and extremely cold temperatures. Yet we do appreciate the valiant efforts made under less-than-pleasant conditions. Sixteen of you conducted careful, systematic searches in the vicinity of the target, devoting between 10 and 120 minutes each. The average time spent was 42 minutes.
Among those who reported finding no unusual object, the reason was generally that too small an area of sky had been examined. This was a particular problem for those using telescopes rather than binoculars.
Of the 16 who conducted extended searches, six people did realize that we had Vesta in mind. In some cases they were using software that alerted them to the presence of Vesta, either before they started their search or while they were checking what they found. A few observers simply knew that Vesta had to be in the vicinity, but they avoided plotting its exact location, preferring to see if they could find it themselves in the sky. One who succeeded (using 8 × 56 binoculars) swept the sky in a widening spiral from the target location we gave, comparing the star fields to those shown in the Cambridge Star Atlas and Millennium Star Atlas.
Another person adopted what — in hindsight, at least — appears to have been the best strategy of all. He took a series of unguided, 8-second exposures of the region with a Nikon CP4500 Coolpix camera. This gave him a set of digital images to examine without having to wait for film processing. His images showed stars as faint as magnitude 7.5, and he found that real stars and starlike objects were easy to tell from "hot pixels." A hot pixel usually had a specific color (red, green, or blue) and appeared repeatedly at the same place in the frame.
Kate Scholberg (SNEWS) and Rick Fienberg and I (Sky & Telescope) sincerely thank all of you who joined in this first test of the nearby-supernova AstroAlert. Most of you had to cope with miserable observing conditions, and we are impressed at your spirit of participation.
We'll conduct more tests from time to time. In each case they will be clearly identified as tests. Keep in mind, however, that there could be a real neutrino detection — and an AstroAlert announcing it — at any time. This could come tonight, next week, or two years from now. That's when the skills we are honing will really pay off in helping to identify the next galactic supernova on the rise.
Sky & Telescope