Fermi and Swift Observe Record-setting Gamma Ray Burst 107
symbolset writes "Phys.org shares a visual image of a 'shockingly bright' gamma ray burst observed April 27th, labelled GRB 130427A and subsequently observed by ground optical and radio telescopes. One gamma ray photon from the event measured 94 billion electron volts — three times the previous record. The burst lasted four hours and was observable for most of a day — another record. Typical duration of a gamma ray burst is from 10 milliseconds to a few minutes. Astronomers will now train optical telescopes on the spot searching for the supernova expected to have caused it — typically one is observed some few days after the burst. They expect to find one by the middle of May. The event occurred about 3.6 billion lightyears distant which is fairly close as gamma ray bursts go. Click on the GIF to view the actual burst."
Need expert opinion (Score:5, Interesting)
Re:Betelgeuse? (Score:5, Interesting)
This Gamma Ray Burst (GRB) was stronger than a typical GRB, and a typical GRB is much stronger than a typical supernova, at least in the beam. This paper [arxiv.org] considers the effects of a GRB at 2 kpc, or 6000 light years, or over 100 times further away than the 50 ly supernova limit. I don't know any details of the new GRB, but if it was as bright as they are implying, it could have been dangerous from the galactic center or beyond.
There is one asterisk here - a supernova will be dangerous for some time (possibly months), while a GRB lasts seconds. A GRB, even if it totally roasts one hemisphere of a planet, would miss the other side, while a SN could get both sides. There might be second order effects from the GRB (such as some sort of nuclear winter) that could cause havoc, but a single GRB just might not be able to totally sterilize a planet from 20,000 light years away. (The 50 ly supernova limit is not that firm, either). We don't know for sure in either case, and I for one would not like to find out.
Re:Need expert opinion (Score:2, Interesting)
Score 5; insightful?
All the GRBs we see are pointed right at us. They're highly directional; any GRBs that aren't pointed right at us we can't even detect.
Re:This may be important for quantum gravity (Score:5, Interesting)
No, although that was entertained (by some) in the fairly long history of these bursts.
In the early days (after GRB were detected by US satellites sent up to look for nuclear explosions) there were lots of theories, as we knew basically nothing about them. The consensus was that GRB were probably fairly close to us, in the galaxy (which kept the burst energy reasonable). The early satellites could only see the brightest bursts, so there weren't many bursts observed, and statistics were very poor, so you couldn't say much more. (At this time I remember some people proposing primordial black hole explanations.) One of the major goals of the Compton Space Telescope BATSE experiment was to be sensitive enough to GRB to be able to observe hundreds to thousands of them, with decent positions, enough data so that you should be able to see the Milky Way (the galactic disk) in the burst locations (i.e., that you would see more bursts along the Milky Way in the sky than in other directions). At the time, the consensus opinion was very strongly that BATSE would see the plane of the Milky Way in the aggregate burst positions, as they accumulated.
The experiment was flown and worked well and recorded an isotropic (random) distribution of bursts. (So much for conventional wisdom.) This meant that the bursts were either very far away (and thus very powerful) or very close (and thus relatively weak, weak enough that you could only see them up to a few light years, where everything is in the galactic disk, and thus can look random in direction, the way the brightest stars in the night sky appear more-or-less random in direction). I actually toyed around with an extraterrestrial intelligence explanation for close bursts at that time (the bursts would be some side effect of power generation or space travel, which would have implied that the ETIs were close and ubiquitous), but most people started thinking about extremely distant (to be random), and thus very powerful events. (IIRC, this was bad but not quite fatal for the primordial black hole explanation, as those bursts are strong enough that you would expect to see the galactic disk in the accumulated BATSE data, but maybe you could adjust things enough to get around that.)
This conundrum was resolved by the orbiting Swift telescope, which could not only see GRB, but could report a position back to Earth quickly enough to train an optical telescope on the spot within a few seconds. This was flown, and some GRBs were observed in the optical. (This also required some serious work on rapid response optical telescopes.) Swift + optical meant that we knew their positions very accurately, so the biggest telescopes could be used to see where, exactly, they were coming from (which turned out to be distant galaxies) and thus get a red shift, and thus a distance (the GRB of the OP is apparently at a red shift of 0.34). That, among other things, showed very clearly that these bursts could not be primordial black holes (or local ETI!), as those are much too weak to see bursting across cosmological distances.
Re:Need expert opinion (Score:4, Interesting)
IIUC, while any that we can detect are pointed in our direction, there's a lot of halo around the core of the emission. We generally pick things up from that halo, but the core would be a lot more intense. If it were pointed right at us, that would mean that the most intense portion of the beam was pointed at us. There isn't much spread, but the signal has been spreading out slowly for many light-years. (Hundreds? Thousands? Millions? Pick your incident to get your answer.) Even a laser spreads given that much distance. If there's no other reason, then there's bumpy space around stars, and variations in the galactic magnetic field.
So, yeah, unless they're very close we can't detect them unless they're pointed at us. But the directionality is sufficient that at sufficient distance there's a sufficient spread that most of the space where the signal can be detected is relatively weak compared to the central part of the beam.
OTOH, this is just "IIUC". I could be wrong. But I don't think so.