FromQuarkstoQuasars

Possible Gamma-ray Burst Detected in Andromeda (Updated)

Megan SmithMay 27th 2014

Yes, you read that correctly. Just a little over five hours ago, the Swift Gamma Ray Burst Telescope may have detected a close gamma ray burst (GRB). In the neighboring galaxy M31 (aka Andromeda), SWIFT observed a sudden emission of high-energy photons otherwise known as gamma rays. Still unconfirmed, this is the closest possible gamma ray discovery to date, at roughly 2.5 million light-years away.

The Swift Gamma Ray Burst Telescope is a space-based telescope equipped with a wide-field gamma ray detector (Burst Alert Telescope) that works by picking up incoming energy bursts. Two additional instruments focus on the source, sending data to ground based telescopes, prompting them to hone in on the source.

Gamma ray bursts or GRBs are divided into two categories, short SRBs and long SRBs. Short SRBs shoot out gamma rays at most, for only a couple of seconds, while long SRBs shoot out gamma rays for over two seconds. It may not seem like it, but these two categories are very different.

Short GRBS are formed when neutron stars (in a binary system) slam into one another. On the other hand, long GRBs are a result of massive stars going supernova. Stars end their lives in violent explosions, typically leaving behind remnants like neutron stars. However, when a very massive star dies and the remnant is a black hole, a GRB is emitted in the process.

Image depicting two colliding neutron stars resulting in short GRBs. Image Credit: NASA
Image depicting two colliding neutron stars resulting in short GRBs. Image Credit: NASA

We are only just beginning to understand gamma ray bursts and one in our own galactic neighborhood would be incredible. It is entirely possible that this is in fact not a GRB but a Ultraluminous X-ray Source (ULX) or even a 50 solar mass black hole devouring a meal rather quickly. ULXs are brighter than typical stars, but not as bright as galaxies; however, if this is a ULX then we should expect to observe x-rays for days to come rather than a few hours as with a GRB.

The event took place in a globular cluster within the Andromeda galaxy. Clusters like this one are a grouping of close,small, usually older stars in galactic halos. Since most of the stellar population in these clusters are not large enough to go supernova, astronomers are predicting this event is a short GRB. If that’s the case, it will have propelled spacetime ripples known as gravitational waves throughout the universe. Currently, the best detector for observing gravitational waves is not currently online. The US Laser Interferometer Gravitational-wave Observatory (LIGO) is right in the middle of a massive upgrade.

Whatever the source, this burst of energy has been travelling 2.5 million years to reach us. In cosmic terms, that is practically in our own back yard. Telescopes from all over the world will be aimed at this source in the coming days, hoping to observe the energy and record how it changes over time. Neutrino detectors, such as Antarctica’s IceCube detector should be able to record resulting neutrinos from a GRB this close.

Stay tuned as this story will be updated as new information and observations become available.

UPDATE:

As it turns out, SWIFT did not detect a gamma ray burst. Unfortunately, a bit of downtime in the telescope left researchers with an incomplete set of data, which resulted in a delay in the amount of time that it took to detect what was really going on. In short, the Swift telescope saw something that looked interesting, turned to focus in on the area, saw X-rays in the right area, reported home, triggered the report…and then the GSC servers went down. As such, astrophysicists were left with a tiny bit of preliminary data, and no way to update or confirm. It was all bad timing. As Once a full analysis was complete, our awesome, bright, “What was that?!” source was identified as less bright, and coming from a known object that produces X-rays.

Usually such false positives are weeded out and the public is never even aware of them because they (obviously) don’t get reported when Swift doesn’t find an afterglow. However, this time a false trigger coincidentally lined up with an actual X-ray source, and we didn’t have access to the data to re-analyze. As a result, astronomers had to work with only the Swift report.

It is an unfortunate occurrence, but such blunders and mishaps are common in science. Indeed, hypotheses, testing, errors, and corrections are the very essence of science. Phil Evans from the Swift team sums it up nicely:

Transient events are, by their nature, well, transient. Some are long lived, but others not. Indeed, this is why Swift exists, to enable us to respond very quickly to the detection of a GRB and gather X-ray, UV and optical data within minutes of the trigger. And Swift is programmed to send what it can of that data straight to the ground (limited bandwidth stops us from sending everything), and to alert the people on duty immediately.

The whole reason for this is to allow us to quickly make some statements about the object in question so people can decide whether to observe it with other facilities. This ability has led to many fascinating discoveries, such as the fact that short GRBs are caused by two neutron stars merging, the detection of a supernova shock breaking out of a star and the most distant star even seen by humans, to name just 3. But it’s tough. We have limited data, limited time and need to say something quick, while the object is still bright. People with access to large telescopes need to make a rapid decision, do they sink some of their limited observing time into this object? This is the challenge that we, as time-domain astronomers, face on a daily basis. Most of this is normally hidden from the world at large because of course we only publish and announce the final results from the cases where the correct decisions were made.

In this case, thanks to the power of social media, one of those cases where what proved to be the wrong decision has been brought into the public eye. You’ve been given a brief insight into the decisions and challenges we have to face daily. So while it’s a bit embarrassing to have to show you one of the times where we got it wrong, it’s also good to show you the reality of science. For every exciting news-worthy discovery, there’s a lot of hard graft, effort, false alarms, mistakes, excitement and disappointment. It’s what we live off. It’s science.

So it is unfortunate that it is not a GRB, but it is an important look into the problems and pitfalls of science. It is also a glimpse at what true science is all about–an acceptance of error and a determined moving forward.

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