Super-Giant Glitches and Quark Stars Sources of Gamma Ray Bursts

When a spinning-down neutron star undergoes a phase transition that produces quark matter in its core, a Super-Giant Glitch of the order\Delta\Omega =\Omega ? ? 0:3 occurs on time scales from 0.05 seconds to a few minutes. The energy released is about 10 5

Super-Giant Glitches and Quark Stars: Sources of Gamma Ray Bursts?McDonald Observatory and Astronomy Department, University of Texas, Austin, TX 78712; feng, xiebr@astro.as.utexas.edu

Feng Ma and Bingrong Xie

AbstractWhen a spinning-down neutron star undergoes a phase transition that produces quark matter in its core, a Super-Giant Glitch of the order= 0:3 occurs on time scales from 0.05 seconds to a few minutes. The energy released is about 1052 ergs and can account for Gamma Ray Bursts at cosmological distances. The estimated burst frequency, 10?6 per year per galaxy, is in very good agreement with observations. We also discuss the possibility of distinguishing these events from neutron star mergers by observing the di erent temporal behavior of gravitational waves.Subject headings: dense matter|elementary particles|

Various Equations of State (EOSs) predict di erent central densities for a 1:4M neutron stars, and some neutron stars may have central densities very close to cr . They can evolve from the initial situation with central density below the critical density to cr during the spin-down process. A phase transition occurring inside the star causes it to collapse, thus releasing gravitational energy in the form of a GRB. A sudden spin-up, much more dramatic than any pulsar glitches observed, then takes place, which we call\Super-Giant Glitch (SGG)".

2. Phase Transition and Super-Giant GlitchBaym and Chin (1976) studied the structure of a hybrid star, but they considered quark matter made of u and d quarks, which is stable only at densities higher than 10 0 and is unlikely to be reached in the center of neutron stars. Later, people found that the strange quark matter (made of approximately equal numbers of u; d and s quarks) has signi cantly lower energy than u; d quark matter at the same pressure (Farhi& Ja e 1984; Witten 1984). Witten even considered the possibility that strange quark matter is more stable than 56Fe and is the absolute ground state of nature. With the conjecture that strange quark matter is stable at zero pressure, some authors have studied the structure of strange stars (Alcock, Farhi& Olinto 1986a) and have even proposed a novel model which states that the GRB of 5 March 1979 was formed when a small lump of strange matter struck a rotating strange star (Alcock et al. 1986b). It was also proposed (Olesen& Madsen 1991) that a neutron star may burn into a strange star on time scales from 0.05 seconds to a few minutes. The time scales depend mainly on the time scale for the weak interaction and a di usion coe cient (see Olesen& Madsen 1991 for details), and does not rely on assuming whether strange quark matter is absolutely stable or not. However, the existence of pulsar glitches (Alpar 1987) seems to be strong evidence against the existence of strange stars at all and, hence, the mechanism of GRBs from strange stars (Kluzniak 1994). Whether or not strange quark matter can be absolutely stable depends on para

meters like the bag constant in the quark model and is unclear today, although it is believed that strange quark matter is more stable than u; d quark matter and may be 1

gamma rays:bursts|stars:neutron

1. IntroductionAlthough numerous explanations of Gamma Ray Bursts (GRBs) have been proposed, the exact nature of the GRB source, e.g., a neutron star binary merger (Paczynski 1986), a halo neutron star quake (Blaes, Blandford,& Madau 1990), or a\failed" supernova (Woosley 1993), remains hidden behind a relativistically expanding reball. Most observational consequences result from radiation processes (see Meszaros& Rees 1993 and Thompson 1994 for\generic" models for GRBs) and are independent of the birth details. Hence, when considering the possible sources of GRBs, the essential parameters are the time scale, the initial energy, the volume of the source, and most importantly, the birth rate of GRBs, which is about 10?6 per year per galaxy as indicated by observations (Piran 1992). Here we outline how a neutron star might change into a hybrid star, which has a quark core and a neutron star crust (e.g., Rosenhauer et al. 1992). That is, a spinning-down neutron star increases in central density towards the critical density ( cr 3 0, where 14 g cm?3 is the nuclear density) for 0 ' 2:8 10 phase transition from neutron matter to quark matter (see Rosenhauer et al. 1992 and references therein).

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