19 March

GRB 080319B was a gamma-ray burst (GRB) detected by the Swift satellite at 06:12 UTC on this day in 2008. The burst set a new record for the farthest object that was observable with the naked eye: it had a peak visual apparent magnitude of 5.8 and remained visible to human eyes for approximately 30 seconds. The magnitude was brighter than 9.0 for approximately 60 seconds.

The GRB’s red shift was measured to be 0.937, which means that the explosion occurred about 7.5 billion (7.5×109) years ago (the lookback time), and it took the light that long to reach Earth. This is roughly half the time since the Big Bang. The first scientific paper submitted on the event suggested that the GRB could have easily been seen to a red shift of 16 (essentially to the time in the universe when stars were just being formed, well into the age of reionization) from a sub-meter sized telescope equipped with near-infrared filters. The afterglow of the burst set a new record for the “most intrinsically bright object ever observed by humans in the universe”, 2.5 million times brighter than the brightest supernova to date, SN 2005ap.

Evidence suggests that the afterglow was particularly bright due to the gamma jet focusing exactly at the line of sight to Earth. This allowed an unprecedented examination of the jet structure, which appears to have consisted of a narrowly focused cone and a secondary wider one. If this is the norm for GRB jets, it follows that most GRB detections only capture the fainter wide cone, which means that most distant GRBs are too faint to detect with current telescopes. This would imply that GRBs are a far more common phenomenon than so far assumed. A record for the number of observed bursts with the same satellite on one day, four, was also set. This burst was named with the suffix B since it was the second burst detected that day. In fact, there were 5 GRBs detected in a 24-hour period, including GRB 080320.

Until this gamma-ray burst event, the Triangulum Galaxy, at a distance of about 2.9 million light years, was the most distant object visible to the naked eye. The galaxy remains the most distant permanent object viewable without aid.

It was soon suggested that this spectacle be named the Clarke Event, as it first reached Earth just hours before the death of Arthur C. Clarke, who was the 1956 Hugo Award winner for his 1955 science fiction short story “The Star”.