Did NASA probe detect a KILLER GAMMA-RAY burst in Andromeda?

'40 solar masses of antimatter went FOOM' we're told

Updated Sky watchers are rapidly turning their instruments in the direction of Andromeda, after NASA's Swift spacecraft spotted what looks like a deadly gamma-ray burst spotted at 9:21 PM UMT, May 27.

That's got astrophysicists excited, because Andromeda is our nearest galactic neighbour, which means the data collection from the event will be rich pickings that could stretch all the way to gravitational waves.

See below for an update on this developing story.

Since Andromeda – M31 to its familiars – is 2.5 million light-years distant, humans' long-gone predecessors were fooling around with the first stone tools when the event actually took place.

Nature notes that if the burst was caused by colliding neutron stars, gravitational wave observations could be the result.

Sadly the world's most sensitive gravitational wave instrument, America's Laser Interferometer Gravitational-wave Observatory (LIGO) is offline for a US$200 million upgrade and can't be deployed for this event.

The first job the world of astrophysics has will be to analyse the data collected by NASA's Swift spacecraft, which was the first to spot the event (gamma ray bursts, GRBs, are Swift's mission, after all), and match it up with other observations. That will determine whether what's just wiped out any nearby lifeforms in its path is a GRB or an Ultra-luminous X-Ray Object.

The reason for doubt is that while it's close, the M31 event is pretty small as GRBs go. That makes some astronomers think the UXRO option is more likely. Even if that were so, its proximity would yield exciting science.

A third possibility noted by Australian astronomer Katie Mack on her @Astrokatie Twitter account is a neutron star in a binary system eating its partner:

Another possibility: outburst from a low-mass x-ray binary (LMXB), where a black hole or neutron star is eating its companion star. #GRBm31

— Katie Mack (@AstroKatie) May 28, 2014

Preliminary estimates of put the source of the event at about 500 solar masses, making it the biggest “nearby” explosion we've been able to detect.

Whatever it was, our solar system was slightly off-axis for the event, which science-fiction author Charlie Stross tweeted was a good thing for us, here on Earth, because it means we're not in the way of the killer burst:

It’s a GRB. 500 solar masses. Prob a pair-production supernova. About 40 solar masses of antimatter went FOOM. Good thing we’re off-axis!

— Charlie Stross (@cstross) May 27, 2014

Which was followed by:

If we were on-axis to a super-Eddington GRB event in M31, right now, we would be puking our guts out, dying of radiation sickness. Eek.

— Charlie Stross (@cstross) May 27, 2014

Ouch.

Science Alert quotes Swinburne University of Technology astronomer Dr Alan Duffy as saying that the burst would “potentially be visible in gravitational waves, a key prediction of Einstein, ending a long quest to detect these ripples in space time”.

As io9 explains, the burst was first spotted by Swift's BAT – Burst Alert Telescope – which works out the position of a detected burst to within 3 acrminutes. Swift then swings around to get a more accurate fix, between 20 and 70 arcseconds, before its X-Ray telescope narrows that to 3 arcseconds so that the instrument's UV/optical telescope gets an even finer fix.

Watch #GRBm31 on Twitter for the unfolding story. ®

Updated to add

After publication, NASA reanalysed the data from its probe (initial findings mirrored here) and concluded "we do not believe this source to be [an] outburst. Instead, it was a serendipitous constant source". In other words, it wasn't a gamma-ray burst as first thought.

Thanks @swift_phil for setting us all straight on "#GRBm31/#ULXm31" even though it TOTALLY SPOILED OUR DAY. http://t.co/aOWAvxMkdN

— Katie Mack (@AstroKatie) May 28, 2014