Probing the central engine of long gamma-ray bursts and hypernovae with gravitational waves and neutrinos

📝 Abstract

There are the two common candidates as the viable energy source for the central engine of long gamma-ray bursts (GRBs) and hypernovae (HNe), neutrino annihilation and magnetic fields. We investigate gravitational wave (GW) emission accompanied by these two mechanisms. Especially, we focus on GW signals produced by neutrinos from a hyper-accreting disk around a massive black hole. We show that neutrino-induced GWs are detectable for $\sim $1 Mpc events by LISA and $\sim$ 100 Mpc by DECIGO/BBO, if the central engine is powered by neutrinos. The GW signals depend on the viewing angle and they are anti-correlated with neutrino ones. But, simultaneous neutrino detections are also expected, and helpful for diagnosing the explosion mechanism when later electromagnetic observations enable us to identify the source. GW and neutrino observations are potentially useful for probing choked jets that do not produce prompt emission, as well as successful jets. Even in non-detection cases, observations of GWs and neutrinos could lead to profitable implications for the central engine of GRBs and HNe.

💡 Analysis

There are the two common candidates as the viable energy source for the central engine of long gamma-ray bursts (GRBs) and hypernovae (HNe), neutrino annihilation and magnetic fields. We investigate gravitational wave (GW) emission accompanied by these two mechanisms. Especially, we focus on GW signals produced by neutrinos from a hyper-accreting disk around a massive black hole. We show that neutrino-induced GWs are detectable for $\sim $1 Mpc events by LISA and $\sim$ 100 Mpc by DECIGO/BBO, if the central engine is powered by neutrinos. The GW signals depend on the viewing angle and they are anti-correlated with neutrino ones. But, simultaneous neutrino detections are also expected, and helpful for diagnosing the explosion mechanism when later electromagnetic observations enable us to identify the source. GW and neutrino observations are potentially useful for probing choked jets that do not produce prompt emission, as well as successful jets. Even in non-detection cases, observations of GWs and neutrinos could lead to profitable implications for the central engine of GRBs and HNe.

📄 Content

arXiv:0906.3833v2 [astro-ph.HE] 3 Dec 2009 Probing the central engine of long gamma-ray bursts and hypernovae with gravitational waves and neutrinos Yudai Suwa∗ Department of Physics, School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan and Max-Planck-Institut f¨ur Astrophysik, Karl-Schwarzshild-Str. 1, D-85741 Garching, Germany Kohta Murase† Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto, 606-8502, Japan (Dated: November 1, 2018) There are the two common candidates as the viable energy source for the central engine of long gamma-ray bursts (GRBs) and hypernovae (HNe), neutrino annihilation and magnetic fields. We investigate gravitational wave (GW) emission accompanied by these two mechanisms. Especially, we focus on GW signals produced by neutrinos from a hyper-accreting disk around a massive black hole. We show that neutrino-induced GWs are detectable for ∼1 Mpc events by LISA and ∼100 Mpc by DECIGO/BBO, if the central engine is powered by neutrinos. The GW signals depend on the viewing angle and they are anti-correlated with neutrino ones. But, simultaneous neutrino detections are also expected, and helpful for diagnosing the explosion mechanism when later electromagnetic observations enable us to identify the source. GW and neutrino observations are potentially useful for probing choked jets that do not produce prompt emission, as well as successful jets. Even in non-detection cases, observations of GWs and neutrinos could lead to profitable implications for the central engine of GRBs and HNe. PACS numbers: 04.30.-w, 14.60.Lm, 98.70.Rz I. INTRODUCTION Gamma-ray bursts (GRBs) are the most luminous explosions in the universe. The production of GRBs is believed to require that only the small amount of matter is accelerated up to ultrarelativistic speeds and collimated as a jet [1, 2]. The duration of GRBs ranges from ∼10−3 s to ∼103 s, with a roughly bimodal distribution of long GRBs of T >∼2 s and short GRBs of T <∼2 s. The geometrically corrected gamma-ray energy of long GRBs is typically Eγ ∼1050−52 ergs [3, 4] (see also [5]), which is much smaller than the isotropic gamma-ray energy Eiso γ ∼1052−54 ergs. The requirements for the energy budget and time scales suggest that long GRBs involve the formation of a black hole (BH) (e.g., [6]) or magnetars via a catastrophic stellar collapse event. The discovery of supernovae (SNe) associated with GRBs brought us the more direct evidence that GRBs result from a small fraction of massive stars that undergo a catastrophic energy release event towards the end of their evolution [7, 8]. Interestingly, some of the SNe associated with GRBs (e.g., GRB 980425, GRB 060218) showed evidence for broad lines indicating high-velocity ejecta with inferred explosion energy of Ekin ∼1052 ergs (e.g., [9]), and those energetic SNe are often called hypernovae (HNe). The central engine of both GRBs and HNe has to supply such an enormous explosion energy (for reviews, e.g., [10]). For the class of long GRBs, the commonly discussed candidates are massive stars whose core collapses to a black hole, either directly or after a brief accretion episode, possibly in the course of merging with a companion. This collapsar scenario is one of the most widely believed scenarios to explain the huge release of energy in GRBs and HNe [6, 11, 12]. In this scenario, the collapsed iron core of a massive star forms a temporary disk around a few solar mass BH and accretes at a high rate (∼0.1 −10 M⊙s−1), which is believed to produce a powerful jet leading to a GRB. The duration of the burst in this scenario can be related to the fall-back time of matter to form a disk or the accretion time of the disk. Possibly, HNe that are brighten by nickel could also be explained by a disk wind, which is subrelativistic with a speed comparable to the escape velocity of the inner disk [12]. Provided a disk and BH form, the greatest uncertainty in the collapsar scenario is the mechanism for converting the disk binding energy or BH rotation energy into directed relativistic outflows. So far, two general mechanisms ∗suwa@utap.phys.s.u-tokyo.ac.jp †kmurase@yukawa.kyoto-u.ac.jp 2 have been proposed: neutrino annihilation and magnetohydrodynamical (MHD) mechanisms in various kinds. In the former case, neutrino pairs are generated in the hot disk and impact one another with the largest angles along the rotational axis and deposit some fraction of the accretion energy [13, 14, 15, 16, 17, 18, 19]. It should be noted that the efficiency of energy deposition is no greater than ∼1% of the total neutrino emission [20], so that the required neutrino energy is Eν ∼1053−54 ergs in order to achieve the jet energy of Ej ∼1052 ergs (which should be larger than the gamma-ray radiation energy). One important property of this dense, hot accretion flow is that the density is so high that cooling of the flow is dominated by neutrinos. This accretion fl

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