The next MEPCO is coming ... to Bulgaria, in early August, 1999!
For details on this astronomical conference just before the total solar eclipse click here!

Strong Soft Gamma Burst like Sunshine for Earth's Ionosphere We tend to think that the distant Universe doesn't affect our planet much - only the Sun and the occasional crashing asteroid do. But on August 27th, 1998, things were different. On that day a mighty shower of gamma rays arrived in the solar system from a distant neutron star, the soft gamma repeater SGR 1900+14. And when this 'soft gamma burst' (soft being only relative to the ordinary gamma ray bursts with the higher photon energy) hit the ionosphere of the night side of the Earth, it had an ionizing effect as strong as the Sun! "It was as if night was briefly turned into day in the ionosphere," says Umran Inan, professor of electrical engineering at Stanford Univ. and head of a research group that observed the atmospheric disturbance. The ionosphere is the portion of the atmosphere between 60 to 80 kilometers in altitude that plays an important role in radio communications. So it is quite likely that the range of high-powered radio stations, which usually reach much farther at night due to lower ionospheric activity levels, was suddenly reduced to their lower, daytime ranges during the burst's five-minute duration. Stanford's Very Low Frequency Research Group operates a string of stations in North America that use VLF radio transmissions to monitor changes in the ionosphere, a region that is above the range of weather balloons and below that of satellites. Normally, the researchers use the network, called the Holographic Array for Ionospheric Lightning research (HAIL), to study the effects that localized phenomena like lightning have on the ionosphere. But they were perfectly positioned to measure the impact of the extra-solar energy pulse. During the five minutes that the gamma- and X-ray radiation impinged on Earth's upper atmosphere, the researchers found that the level of ionization or electrical activity in the ionosphere, which is normally quiescent at night, suddenly flared to daytime levels. The scientists saw the effect clearly in stations monitoring the ionosphere over the western United States, which were included in the area illuminated by the burst, but not over the eastern part of the country, which was in shadow. They also saw evidence of a 5.16-second pulsation that corresponds with the X-ray star's previously established rotation rate, indicating that the ionization in Earth's atmosphere varied in accordance with the pulsations of the gamma-ray burst. There was also an radio "afterglow" of the Aug. 27th burst, which is seen as additional evidence that neutron stars with extremely strong magnetic fields ("magnetars") are behind the Soft Gamma Repeater phenomenon. (Partially dapted from a Stanford News Release of Sept.29, 1998)

An MSFC News Release and lots of background from of Sept. 29, 1998 on the ionospheric effect, as well as Stanford and NASA Releases. NSF and NRAO News Releases on the radio observations. JPL Release about the burst itself BBC and CNN stories on the ionospheric effect ABCNEWS story on the radio observations. Very Low Frequency Research Group and Inan's homepage More on SGR 1900+14: A paper on the discovery of the neutron star associated with SGR 1900+14 and a related Science News article. More on the magnetar hypothesis: A tutorial by R. Duncan and Magnetars.com.

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