The Signature of the Blandford-Znajek Mechanism in GRB Light Curves

Abstract

In 1977, Blandford and Znajek showed how the spin energy of a rotating black hole may be extracted electromagnetically through a magnetic field that threads the black hole horizon. A characteristic feature of this mechanism is that, under certain fairly general conditions, the energy loss rate decays exponentially. We looked precisely for such behavior in the X-ray light curves of Long and Ultra Long duration Gamma-Ray Bursts (GRBs) observed with the XRT instrument on board the Swift satellite, and found that almost 30% of XRT light curves show an exponential decay before they reach the afterglow plateau. A similar behavior (Fast Rise Exponential Decay-FRED) was observed in γ-rays with the BATSE instrument aboard the CGRO satellite. We consider both of these findings as the signature of the Blandford-Znajek mechanism in action in the central engine of GRBs.

Thermomagnetic Ettingshausen-Nernst effect in tachocline, magnetic reconnection phenomenon in lower layers, axion mechanism of solar luminosity variations, coronal heating problem solution and mechanism of ADM variations around BH

“…The formal physics of this idea almost completely coincides with the well-known idea of (Komissarov, 2009) and (Beskin, 2010), but, surprisingly, it describes not only the BZ-like effect (see e.g. (Pan et al, 2017;Contopoulos et al, 2017) and Refs. therein), but also the thermomagnetic EN effect (see Fig.…”

“…So, on the one hand, the duration of a GRB depends closely on the magnetic flux accumulated on the event horizon, and on the other hand, that is actually why we observe a clear exponential decay in the fraction of GRB events (see (Contopoulos et al, 2017)). And vice versa, in order to restore the Meissner effect, it is necessary to include the non-chaotic variations of the magnetic field, and thereby to push out the external magnetic field with the help of a current (see e.g.…”

“…Hence, we understand that the BZ effect excludes the external magnetic field of the Meissner effect near the horizon, since, unlike the Meissner effect, it changes the shape of the magnetic field and thereby reveals a mechanism, how the spin energy of a rotating BH may be extracted electromagnetically through the magnetic field that threads the BH horizon (see e.g. (Nathanail and Contopoulos, 2014;Penna, 2014a,b;Contopoulos et al, 2017)). Therefore, the chaotic variations of the flux always penetrate into the thin film (see e.g.…”

“…28b on the right). It is very important that the BZ effect also shows that it is possible to hold this magnetic flux for the duration of the GRB even without accretion onto the BH (see the original Penrose process of (Penrose and Floyd, 1971), (Contopoulos, 1984) and the analogous one of (Contopoulos et al, 2017)).…”

Collapsing supra-massive magnetars: FRBs, the repeating FRB121102 and GRBs

“…When a magnetar with polar B field ∼ 10 14 − 10 15 G collapses to form a BH, can an ambient plasma threaded with magnetic field ∼ 10 12 G be maintained near the EH? (In the context of GRB modeling, Contopoulos et al (2017) find that B ∼ 10 4 G can hover near the horizon.) (b) Accretion of plasma by itself cannot generate such high B since the Eddington limit for the magnetic field is,…”