mercredi 24 février 2016

Taking (some) fun out of {go fast} scientific [reports]

Wet blanket policy...
Disclaimer: this first paragraph is just cheap entertaining and self-deprecating of the blogger, no offence to any real scientist of course!
The playful science popularizer Bob Burstard is looking for a freshsucker to swindle. Looking off in the distance, Bob sees a happy-go-lucky science enthusiast Alice Arxivpecker, minding the recent discovery of gravitational waves (GW) while whistling through internet. The cunning Burstard quickly types a draft report and polishes a catchy headline, causing Alice to web surf directly through his front page. He then tries to show her his theory to explain the Gamma-Ray Burst serendipitously detected 0.4 seconds after the GW event...

Then comes some serious information.

... on a Gamma ray burst associated with GW150914

The Fermi/GBM team reported a possible hard X-ray transient on 2015-09-14 at 09:50:45.8 UTC, about 0.4 s after the reported LIGO/Virgo burst trigger time, and lasting for about one second (Blackburn et al. 2015; Connaughton, V. et al 2016). The light travel time can introduce a time difference between INTEGRAL and Fermi detections of up to ±0.5 s, depending on the source position within the LVC error region. We do not observe any excess within a -0.5 s to +0.5 s window around the Fermi/GBM trigger (Figure 1), and set a 3-sigma upper limit of 1.5×10-7erg cm-2 in one second, assuming a typical short hard GRB, characterized by Band model with parameters α = −0.5, β = −2.5, Epeak = 1000 keV. A substantial part of the candidate event in the GBM comes from the high-energy BGO detector, above 100 keV (Blackburn et al. 2015), where the Fermi/GBM effective area is about a factor 30-40 smaller than that of the INTEGRAL/SPI-ACS... Finally, we stress that to compare the GBM and SPI-ACS sensitivities, it is inappropriate to use a soft spectral model as in the computation of our early flux upper limits (Ferrigno et al. 2015), since the spectral properties of the GBM candidate are very different.
V. Savchenko et al., (Submitted on 12 Feb 2016)

... a search of the INTEGRAL-ACS data revealed a detection rate of only 55% of GBM-detected weak short GRBs (Briggs et al., in preparation). We do not consider, therefore, the non-detection of GW150914-GBM by INTEGRAL-ACS, a sufficient reason to reject our candidate
V. Connaughton, et al. 
(Submitted on 11 Feb 2016 (v1), last revised 16 Feb 2016 (this version, v3))

... and the first evidence for nearly neutral black holes?
I have shown that for black hole - black hole (BH-BH) mergers, if at least one of the BHs carry even a small amount of charge Q, the inspiral process generates a loop circuit, which induces a magnetic dipole. The system behaves like a giant pulsar with an increasing wind power. If q can be as large as ∼ (10-5 − 10-4), the magnetospheric wind right before the coalescence would make a short-duration GRB. The GRB is expected to be delayed with respect to the GW chirp signal. The putative short GRB signal associated with GW 150914 (Connaughton et al. 2016) can be well interpreted with this theory. 
The nearly isotropic nature of this wind pulse suggests that every BH-BH merger could be associated with a short electromagnetic transient if Q is not strictly zero. The question is whether q can be large enough to make it observable. Given the large event rate of BH-BH mergers revealed by the detection of GW 150914 (Abbott et al. 2016b), the non-detection of very bright short GRBs already suggests that for the majority of BHs, q cannot significantly exceed 10-5. This is consistent with the general expectation that BHs are essentially not charged. Pessimistically, the weak short GRB signal detected by the Fermi/GBM team ... is a chance coincidence and non-physical. If so, the upper limit of a signal (Savchenko et al. 2016) would constrain q to be below a few 10-5 .
Bing Zhang (UNLV)
(Submitted on 15 Feb 2016 (v1), last revised 16 Feb 2016 (this version, v2))

//update February 26 2016
The physical constraints required by the association of the Fermi GBM signal contemporaneous with GW150914 - radiative power of 1049 erg.s-1 , and corresponding magnetic fields on the black hole of the order of 1012 Gauss - are astrophysically highly implausible. Combined with the relatively high random probability of coincidence of 0.22 percents, we conclude that the electromagnetic signal is likely unrelated to the BH merger. 
... requiring that the magnetic field is produced by electric charge on one of the black holes (Zhang 2016) would imply a charge Q = GM√(LEM)c5/2 = 5×1016 coulombs. This horrific amount of electric charge would have produced the electric field near the horizon E = √(LEM)c3/2/(GM)=2×1012 in cgs units (statvolts per centimeter), amounting to nearly 5% of the quantum Schwinger field EQ = me2c3/(e).
Maxim Lyutikov (Purdue University)
(Submitted on 23 Feb 2016)

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Cher-ère lecteur-trice, le blogueur espère que ce billet vous a sinon interessé-e du moins interpellé-e donc, si le coeur vous en dit, osez partager avec les autres internautes comme moi vos commentaires éclairés !
Dear reader, the blogger hopes you have been interested by his post or have noticed something (ir)relevant, then if you are in the mood, do not hesitate to share with other internauts like me your enlightened opinion !