Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A Gamma ray burst associated with LIGO GW event

  1. Feb 26, 2016 #1

    Jonathan Scott

    User Avatar
    Gold Member

    Quite unexpectedly, it seems that the Fermi Gamma-ray Burst Monitor spotted what appears to be a hard gamma-ray burst about 0.4s after the LIGO GW event, lasting about 1s: http://arxiv.org/abs/1602.03920

    This is not expected from a black hole merger (and as a black hole sceptic, I find it very interesting).

    There's also a new paper which suggests that perhaps this could be explained by the black hole merger occurring inside a star (which I find quite implausible, but which is generating a lot of news stories): http://arxiv.org/abs/1602.04735
     
  2. jcsd
  3. Feb 26, 2016 #2

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    Loeb's paper is indeed very interesting. The collapse of a massive star just before it coallesced with a companion black hole strikes me as a very odd coincidence - in fact a bit too coincidental for my tastes. It could imply a hitherto unsuspected mechanism for stellar collapse or merely be a nearby event unrelated to GW15091. We have ample cause to be alert to the risk of making unwarranted associations between two unrelated astrophysical events
     
  4. Feb 26, 2016 #3
    Potentially very silly question, but could the magnetic fields of the black holes generate something like this when the black holes merge?
     
  5. Feb 26, 2016 #4

    Jonathan Scott

    User Avatar
    Gold Member

    Black holes are not even supposed to be able to have magnetic fields (unlike neutron stars which can have extremely strong magnetic fields)!
     
  6. Feb 26, 2016 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Is that the sum total of what Loeb's considering? I got the impression that the core collapse of a single very rapidly rotating star could involve a brief stage during which there is an oblong or "dumb-bell" shape concentration of mass. NOT spherically symmetric. I didn't think coincidence needed to be involved. Let's look more closely at the loeb paper
     
  7. Feb 26, 2016 #6
  8. Feb 27, 2016 #7
    My bad, was certain I had read that rotating black holes would have a magnetic field, but I see now that they shed the magnetic field during the collapse.
     
  9. Feb 28, 2016 #8
    There is also a paper on the non-detection of neutrinos with ~1400 authors.
    "Within 500 s of the gravitational wave event, the number of neutrino candidates detected by IceCube and ANTARES were three and zero, respectively. This is consistent with the expected atmospheric background, and none of the neutrino candidates were directionally coincident with GW150914. We use this non-detection to constrain neutrino emission from the gravitational-wave event."​
    http://arxiv.org/abs/1602.05411
     
  10. Feb 28, 2016 #9
    I think the timing warrants an association, and I don't see how that is problematic as long as the relationship is only treated as a hypothesis until more evidence of the same originating event is available.

    I don't see the papers as anything more than "Hey, we saw this at (about) the same time" perhaps they are related. Exploring possible causal relationships between coincident events seems reasonable. Drawing conclusions is not yet reasonable.
     
  11. Feb 28, 2016 #10

    Jonathan Scott

    User Avatar
    Gold Member

    My reference to "hard gamma-ray burst" in my original post is slightly garbled as I hadn't noticed that the terminology is a bit confusing. It is correct to describe it as a "gamma-ray burst" and it is also described as a "short/hard burst", but I hadn't spotted that the "hardness" in the latter term is relative to the X-ray spectrum, not the gamma spectrum.

    The Fermi team paper (section 2.5 and figures 5 and 6) actually suggests that a plausible value for the energy spectrum peak is around 3.5MeV, and the distribution seems to go up at least to 10MeV. Even the highest bin, 38MeV-50MeV, shows an excess, although with little statistical significance.

    John Baez appeared to have initially read "above 50keV" as "about 50keV" but has now sorted that out.
     
  12. Feb 28, 2016 #11

    Jonathan Scott

    User Avatar
    Gold Member

    Note that the INTEGRAL team reckoned that they had ruled out any gamma ray activity around the time of the event down to a threshold which they considered would rule out the claim by the Fermi GBM team: http://arxiv.org/abs/1602.04180

    The Fermi GBM team however (see section 2.6 of their paper) argue that there are plausible reasons why INTEGRAL might have missed it.
     
  13. Feb 28, 2016 #12
    One wonders if there are other events caught by the GBM team and missed by the INTEGRAL team.

    When one observer "sees" and event and another observer fails to "see" an event, I tend to lean toward a genuine observation unless there is a documented history of spurious reports.
     
  14. Feb 28, 2016 #13

    Jonathan Scott

    User Avatar
    Gold Member

    See last paragraph of section 2.6 of the Fermi team paper:
     
  15. Feb 28, 2016 #14
    That seems like an important point. Thanks for the post.
     
  16. Feb 28, 2016 #15
    Do a fast acceleration of any celestial bodies( black holes) produce gravitational waves?
     
  17. Feb 28, 2016 #16

    Jonathan Scott

    User Avatar
    Gold Member

    Fast acceleration of a massive body cannot occur in isolation, as that would violate conservation laws. Gravitational waves are typically produced by changes in configuration of systems involving two masses, such as when they are orbiting rapidly around each other, and are only detectable in extreme cases, such as merging black holes. However, that is not the topic of this thread, so please take any further discussion elsewhere.
     
  18. Feb 28, 2016 #17

    Ken G

    User Avatar
    Gold Member

    I wonder about two things:
    1) Why on Earth would anyone expect a neutrino event to be detected when the electromagnetic detection is so marginal? Don't we barely see neutrinos from nearby supernovae that can be seen optically with low grade telescopes?
    2) The gravitational wave detection was a bit marginal-- a 5 sigma detection. The gamma-ray detection was also a bit marginal-- also 5 sigma! What kind of spectacular coincidence is that? Two totally different kinds of detectors, seeing different aspects of the same event, both registering 5 sigma detections. I'm pretty sure a Bayesian analysis of the relative probability of that, and a non-detection, would show that the non-detection of gamma rays is the more likely conclusion.

    Basically, both my points are about how strange I find it that people are not analyzing the joint probabilities of these various detections, they almost seem to expect that marginal detections with one instrument should be associated with marginal detections with another. That is certainly not the normal state of affairs.
     
  19. Feb 28, 2016 #18

    Jonathan Scott

    User Avatar
    Gold Member

    If the original hypothesis about a black hole collision was correct, no detectable neutrinos or electromagnetic effects were expected. The observations were therefore to check for any surprises, and the Fermi GBM result was a surprise.

    The gravitational wave detection was not at all marginal (confidence level of 99.99994%) and was far stronger statistically than the gamma-ray detection (for which they estimated a "false alarm" probability of about 0.22%), so I don't understand the rest of your post.
     
  20. Feb 28, 2016 #19
    Is it possible the accretion disks would have electromagnetic fields which interacted (Two become one?) to spout gamma rays?

    Some potential questions:
    • How would "riding" the gravity waves have affected their timing?
    • How would rapidly rotating (near C) atomic particles in two different orbits "collide"? It would seem they would leak synchrotron type radiation until they achieved a single stable orbit around the conglomerate black hole. But gravity waves might disrupt this, as might "ringing" deformations in the new hole.
    • Why wouldn't there be neutrinos in the accretion disk merger?
    • Why the 0.4 second delay?
    My knowledge of the physics and the math are lacking, so I ask as a duffer.

    I agree with Dr. Courtney that this is just a weak hypothesis lacking more data.

    There were likely lots of energetic events going on nearby the collapse, but expecting any of them to be visible at this distance might be unreasonable.
     
  21. Feb 28, 2016 #20

    Ken G

    User Avatar
    Gold Member

    Both detections are reported as 5 sigma detections. Ponder the likelihood of that.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Gamma ray burst associated with LIGO GW event
  1. WR104 Gamma Ray Burst (Replies: 1)

  2. Gamma Ray Bursts (Replies: 5)

  3. Gamma Ray Bursts (Replies: 7)

Loading...