To Power the X-Ray Plateaus of Gamma-Ray Bursts through Larger Amplitude Electromagnetic Waves

Abstract

The origin of the gamma-ray burst (GRB) X-ray plateau, especially the internal plateau, is still unclear, but it could be related to a GRB’s magnetar central engine. It is generally believed that the spin-down power of the magnetar is injected into forward external shock; however, we propose here that most of the power will be dissipated behind the GRB jet through a larger amplitude electromagnetic wave. Based on this proposal, the relevant physical conditions and observational implications are analyzed and discussed, and various kinds of X-ray light curves could be reproduced. Although the chromatic multiband afterglow in the standard external afterglow fireball model is still a matter of debate, we can naturally explain this feature through this proposal, i.e., the electrons generating the X-ray plateau and emitting the optical afterglow are accelerated by different mechanisms. It is emphasized that both the GRB jet and the spin-down wind should have significant observational consequences in the magnetar scenario, and should be focused equally in GRB physics.

Evidence of X-ray plateaus driven by the magnetar spindown winds in gamma-ray burst afterglows

“…The millisecond magnetars (e.g., Usov 1992;Duncan & Thompson 1992;Dai & Lu 1998a,b;Zhang & Mészáros 2001;Bucciantini et al 2007;Metzger et al 2011;Du 2020) and black hole (BH) hyperaccretion (e.g., Popham et al 1999;Narayan et al 2001;Kohri et al 2005;Gu et al 2006;Liu et al 2007;Kawanaka et al 2013;Hou et al 2014) are two main candidates of GRB central engines. For the recent reviews see Liu et al (2017) and Zhang (2018).…”

“…Their typical decay index is predicted to be ∼ 1.2, but the observations are in the range of 0 − 1.5 under the different circumstances and conditions (e.g., Sari et al 1998;Zhang et al 2006). However, the spindown winds might not be injected into GRB jets, but dissipated behind GRB jets to power Xray plateaus in the GRB magnetar model (Du 2020). In this scenario, the indices of the decays after plateaus are ≥ 2 (Zhang & Mészáros 2001).…”

“…For the hypermassive magnetar, the very short life leads that the spindown winds can not accu-mulate enough energy to produce observable features (Rosswog et al 2000). For the supramassive magnetar case, as discussed in Du (2020), it (with life time 100 s) has enough time to power the energetic spindown winds to generate the X-ray plateau followed by a steeper decay (with decay index > 3). This phenomenon is called internal X-ray plateaus, which is understood as the collapse of a supramassive magnetar into a BH after the magnetar spindown (e.g., Troja et al 2007;Rowlinson et al 2010;Chen et al 2017;Hou et al 2018).…”

Statistical analyses on the energies of X-ray plateaus and flares in gamma-ray bursts

“…It is widely believed that they originate from massive collapsars (e.g., Woosley 1993;MacFadyen & Woosley 1999) and binary compact object mergers (e.g., Paczyński 1986;Eichler et al 1989;Narayan et al 1992). Currently, GRB central engines are still uncertain, but there are two leading models, i.e., the stellar-mass black hole (BH) hyperaccretion model (e.g., Woosley 1993;Popham et al 1999;Narayan et al 2001;Yi et al 2017;Liu et al 2018Liu et al , 2019 and for a review see Liu et al (2017) and the model of a rapidly rotating neutron star (NS) with a strong magnetic field of ∼ 10 15 G, et al 2007;Dainotti et al 2008Dainotti et al , 2010Dainotti et al , 2011aDainotti et al , 2013aDainotti et al , 2016Du 2020) and for a review see Dainotti & Del Vecchio (2017). A similar shallow decay also occurs in the optical light curves (e.g., Si et al 2018;Dainotti et al 2020) and Fermi -LAT GRBs (e.g., Dainotti et al 2021).…”

“…LGRBs and SGRBs are approximately several hundred and several thousand seconds, respectively. Generally, the extra energy injections from the spin-down of a millisecond magnetar (e.g., Dai & Lu 1998a,b;Zhang & Mészáros 2001;Rowlinson et al 2010;Bucciantini et al 2012;Gompertz et al 2013;Du 2020) or a supramassive fast-rotating quark star (e.g., Hou et al 2018;Ouyed et al 2020) are expected to explain the plateaus. Other models on the jet modes, such as the two-component ejecta (e.g., Toma et al 2006;Yamazaki 2009), jets with microphysical factor evolutions (e.g., Ioka et al 2006;Panaitescu et al 2006) or bulk Lorentz factor distributions (e.g., Uhm & Beloborodov 2007), delayed deceleration jets (e.g., Duffell & Mac-Fadyen 2015), and off-axis jets (e.g., Beniamini et al 2020), have been proposed.…”