Soft X-ray extended emissions of short gamma-ray bursts as electromagnetic counterparts of compact binary mergers: Possible origin and detectability

Takashi Nakamura, Kazumi Kashiyama, Daisuke Nakauchi, Yudai Suwa, Takanori Sakamoto, Nobuyuki Kawai

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18 Citations (Scopus)

Abstract

We investigate the possible origin of extended emissions (EEs) of short gamma-ray bursts with an isotropic energy of ∼1050-51 erg and a duration of a few 10 s to ∼100 s, based on a compact binary (neutron star (NS)-NS or NS-black hole (BH)) merger scenario. We analyze the evolution of magnetized neutrino-dominated accretion disks of mass ∼0.1 M around BHs formed after the mergers and estimate the power of relativistic outflows via the Blandford-Znajek (BZ) process. We show that a rotation energy of the BH up to ≳ 1052 erg can be extracted with an observed timescale of ≳ 30(1 + z) s with a relatively small disk viscosity parameter of α < 0.01. Such a BZ power dissipates by clashing with non-relativistic pre-ejected matter of mass M ∼ 10-(2-4) M , and forms a mildly relativistic fireball. We show that the dissipative photospheric emissions from such fireballs are likely in the soft X-ray band (1-10 keV) for M ∼ 10-2 M , possibly in NS-NS mergers, and in the BAT band (15-150 keV) for M ∼ 10-4 M , possibly in NS-BH mergers. In the former case, such soft EEs can provide a good chance of ∼6 yr-1 (ΔΩsoftEE/4π) (script RGW/40 yr-1) for simultaneous detections of the gravitational waves with a ∼0small letter o with dot below.1 angular resolution by soft X-ray survey facilities like the Wide-Field MAXI. Here, ΔΩsoftEE is the beaming factor of the soft EEs and script RGW is the NS-NS merger rate detectable by the advanced LIGO, the advanced Virgo, and KAGRA.

Original languageEnglish
Article number13
JournalAstrophysical Journal
Volume796
Issue number1
DOIs
Publication statusPublished - 2014 Nov 20

Keywords

  • X-rays: bursts
  • accretion, accretion disks
  • gamma-ray burst: general

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