I GW150914 and GW150914-GBM revisited

[Chronos]

The association between the LIGO detection of a black hole merger event and Fwemi detection of a short GRB appears to be unsettled based on this paper http://arxiv.org/abs/1602.07352, Fermi GBM signal contemporaneous with GW150914 - an unlikely association. The author points out the magnetic field strength required and unlikelihood of sufficient plasma in a binary black hole system to account for an EM signal of the power measured. While statistics claiming an association between the GRB and GW signal are impressive, the lack of a credible astrophysical mechanism to account for the GRB signal is not. The non-detection by other capable instruments [e.g., Swift, INTEGRAL, IceCube & ANTARES] is also unassuring.

 

[Jonathan Scott]

As with previous discussions on this subject, it seems clear that there is no obvious explanation for the GRB if GR is assumed to be correct right up to the level of black holes.

However, the author's conclusion that the GRB detection was therefore unrelated to the GW seems very one-sided.

I'm not aware of any direct evidence that GR is correct up to that level, so I would consider an alternative explanation to be that the objects were not black holes, although they were of comparable density, so the theory needs tweaking. Note that it has been previously suggested that polarization measurements suggest extremely strong magnetic field close to some quasars, which isn't easy to reconcile with black hole theory, and that's on a far larger scale than the assumed black holes in the GW case.

I can't think of any objective way of assessing the a-priori strength of the theory in this extreme case, and I must admit I've always had doubts about it myself, so in the absence of further information at presence the primary parameter in any discussions on this subject seems to be the author's level of confidence in standard GR black hole theory. I eagerly await further experimental results which may help to resolve this situation.