Revenge of the Magnetar

Reconnection events on the sun emit as much as 10³² ergs of energy. Flares from magnetars are about a million million times stronger, ~10⁴⁴ ergs, befitting their more intense magnetic fields.

"They're solar flares on steroids," quips Woods.

When the blast wave from SGR 1900+14 arrived on August 27th, 1998, it hit the night side of our planet - something flares from the sun never do - and scorched Earth's upper atmosphere. The radiation broke apart atoms and molecules into charged ions. Ions interact with radio signals, either absorbing or reflecting them, so radio listeners knew something had happened.

For instance, a registered nurse in Seattle was driving home from work at 2:00 a.m. listening to a local program on her car radio. The station faded - a blackout - and was moments later replaced by country music from Omaha, Nebraska. On the US east coast, where dawn was breaking at the time, hams chatting locally suddenly picked up voice transmissions from distant parts of Canada. Strange.

more Stanford University's network of VLF receivers registered a fadeout of 21.4 kHz signals on August 27, 1998, when the magnetar burst reached Earth. The shaded area denotes the part of our planet illuminated by the burst.

These propagation effects, so much like those experienced during ordinary solar flares, quickly subsided. No harm was done. Nevertheless, the event made a deep impression on astronomers. From halfway across the galaxy, SGR 1900+14 had "touched" our planet.

It happens more often than most people know. Since 1998, Earth has experienced "about 10 similar ionization events," says Umran Inan of Stanford University. "Five of them were caused by SGR 1900+14, and the rest from unknown sources."

Inan leads the Very Low Frequency (VLF) Research Group at Stanford University. He and his colleagues operate a network of low-frequency radio stations in North America and Antarctica. When Earth gets hit by ionizing radiation, the network records telltale changes in radio propagation. "We saw the blast from SGR 1900+14 in 1998 - it was very clear," he says.

"Many things can change the ionization of Earth's atmosphere," adds Inan. "Lightning can do it. So can sudden bursts of auroras at high latitudes." But these things cause local ionization. Solar flares, on the other hand, have global effects, ionizing the top of Earth's entire dayside atmosphere. Flares from magnetars can ionize the nightside, too. These signatures - nightside vs. dayside, global vs. local - help Inan identify the source of the ionization.

His "unknown sources" are probably magnetars not yet discovered by astronomers.