The gamma-ray burst GRB 130427A erupted on April 27th with record-setting power. That made it an easy target for two of NASA's orbiting observatories, major ground-based telescopes, and even one lucky backyard observer. It reached visual magnitude 7.4.
Over the past four decades, orbiting observatories have recorded thousands of gamma-ray bursts (GRBs) coming from the depths of space. The lion's share of those have been snared by NASA's Swift, launched in 2004; and Fermi Gamma-ray Space Telescope, launched in 2008.
But one that erupted at 7:47 Universal Time on April 27th turned out to be a record-setting blast. "We have waited a long time for a gamma-ray burst this shockingly, eye-wateringly bright," notes Julie McEnery, Fermi's project scientist, in a NASA press release. One of the blast's gamma rays had an energy at least 35 billion times that of a visible-light photon.
Moreover, this GRB, designated 130427A, lasted for hours — easily long enough for numerous ground-based telescopes to swing around to watch at visible-light and infrared wavelengths. Its location, in northeastern Leo, was right ascension 11h 32m 33s, declination +27° 41′ 56″.
Not many GRBs become bright enough in visible light to be within range of amateur observers. But this one was, and it caught the attention of Patrick Wiggins, who just happened to be awake — and imaging the night sky with his 14-inch telescope in Tooele, Utah. Wiggins was in the middle of snack break when notice arrived about Swift's detection. "I figured I was too late to catch anything, but I was currently working a spot on the sky just a few degrees from the predicted location," Wiggins told me via email, "so I slewed over and made a quick 60-second exposure."
There, clearly evident in the middle of his image, was a 13th-magnitude dot — too bright to be a GRB, Wiggins thought. So he slewed over a bit and took another image — and there it was again. He kept recording throughout the night, finally shutting down as dawn approached. At right are one of his images (made hazy by strong moonlight) and the light curve he derived. "It was my first GRB detection," exults Wiggins. "That it happened on my birthday made it even more special to me."
And that was just the afterglow. Three RAPTOR all-sky monitors recorded an optical counterpart at magnitude 7.4, 50 seconds before the Swift satellite trigger. Within a minute the optical glow was fainter than magnitude 10. Several other robotic telescopes were pointing to the spot within minutes; they caught the afterglow at about 11th magnitude. This compares to the visible-light record holder GRB 080319B, which reached magnitude 5.3 in 2008.
Gamma-ray bursts are typically short or long. Astronomers think that the latter type, which usually last no longer than a minute or so, herald the death of a supermassive star. The collapse of the star's core triggers jets of relativistic matter so powerful that they bore outward through the star and into the surrounding space. Interactions with shells of gas previously shed by the dying star creates dazzling outbursts of radiation — the most luminous explosions known.
GRB 130427A appeared so bright because it was relatively nearby, "just" 3.6 billion light-years away. This proximity ranks among the 5% closest GRBs recorded to date, and it gives observers hope that they'll be able to spot the star's shattered remains in the days and weeks ahead.
Ironically, gamma-ray scientists from around the world had just wrapped up a weeklong meeting to discuss their latest findings when the brilliant blast appeared.