The Swift space telescope, launched in November, has seen its first gamma-ray bursts (GRBs) - the massive cosmic explosions it was built to study.
The telescope detected its first burst on 17 December, only a few days after its instruments were switched on.
On 19 December, the US space agency satellite caught three more.
GRBs are the most powerful explosions in the Universe, releasing more than one hundred billion times the energy our Sun emits in a year.
Swift orbits Earth in wait for a burst to come into its field of view.
Following a detection, the satellite veers round to point its X-ray telescope (XRT) and UV/Optical telescopes toward the blast.
Testing phase
Because the telescope is currently undergoing tests, scientists were not able to interrupt operations to chase the first few bursts.
But on 23 December, the telescope spotted a long GRB that lasted about two minutes and turned to observe it. The XRT obtained an accurate position, spectrum and decay light curve for its afterglow.
"We haven't quite got to the point yet where we're routinely cranking out bursts. That should happen in a couple of weeks," said senior Swift scientist Professor David Burrows of Penn State University, US.
When the satellite is fully operational, it will be able to turn to view the source within about a minute of detecting a cosmic blast.
"Speed is crucial, because clues to what caused the burst may disappear quickly," said Professor Alan Wells, leader of the UK's University of Leicester's XRT team.
"In the past, it has taken hours to view the afterglow with a high-quality telescope. Now we'll be on the scene within minutes."
Professor Burrows said that apart from a circuit problem with the thermal control on the XRT, the satellite was performing very well.
The mission aims to understand what GRBs are. Scientists know there are two types of burst which could be caused by entirely different types of event.
In one scenario, bursts occur when a star collapses in on itself, giving birth to a black hole.
Another possibility could be that bursts come from the collision between two neutron stars.
"If some bursts are coming from very old neutron stars, these may have drifted out of the galaxies, so we will see them coming from areas of blank sky. That's the kind of thing we want to try to study," Professor Burrows told the BBC News website.
The team has released the first image taken by Swift, of the Cassiopeia A supernova remnant. This object is the relic of a gigantic stellar explosion that was seen to occur in about 1680.
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