If one of the former distances were correct, Kothes says, "the minimum energy you need for the synchrotron nebula to be produced is higher than the energy the pulsar has released since its birth." In contrast, the new distance means the nebula is emitting no more energy than the pulsar can provide. As he reports in work to appear in Astronomy & Astrophysics, he's convinced 3C 58 marks the site of the 1181 blast.
If 3C 58 is as close as Kothes thinks, then the 1181 blast was even more of a wimp than astronomers believed. At his proposed distance, the 1181 explosion was roughly a fifth as luminous as the 1987 supernova in the Large Magellanic Cloud, a nearby galaxy, that also emitted less light than the norm. Kothes suggests the two blasts were similar. He estimates the progenitor of 3C 58 began life as a blue star of spectral type O that was 20 to 30 times more massive than the sun.
Of course, if the nebula doesn't mark the blast site, all bets about the progenitor are off. Is the mystery solved?
Not so fast, says Dartmouth College astronomer Robert Fesen. He thinks 3C 58 may be thousands of years old—which means it didn't arise in a blast just 832 years ago. The problem, Fesen says, is that the nebula is large and expanding slowly, which suggests it has been expanding for a long time. But a link to the 1181 supernova means 3C 58 is younger than the Crab Nebula—born in 1054—even though it is larger than the Crab Nebula and is expanding at half the Crab’s speed. Kothes counters that 3C 58's expansion has likely slowed greatly in recent centuries, but Fesen is dubious.
Is 3C 58 really the remnant of the 1181 supernova? "I don't know," Fesen says. "It's in the right spot. There's nothing else in that area. We've looked. If it wasn't 3C 58, then what the heck did the people see in 1181?" Yet the nebula seems too old, he says. "I've puzzled over this for many, many years," Fesen says. "It's a mystery."