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تسجيل مستخدم جديدThe Connection between Gamma-Ray Bursts and Extremely Metal-Poor Stars as Nucleosynthetic Probes of the Early Universe
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The connection between the long GRBs and Type Ic Supernovae (SNe) has revealed the interesting diversity: (i) GRB-SNe, (ii) Non-GRB Hypernovae (HNe), (iii) X-Ray Flash (XRF)-SNe, and (iv) Non-SN GRBs (or dark HNe). We show that nucleosynthetic properties found in the above diversity are connected to the variation of the abundance patterns of extremely-metal-poor (EMP) stars, such as the excess of C, Co, Zn relative to Fe. We explain such a connection in a unified manner as nucleosynthesis of hyper-aspherical (jet-induced) explosions Pop III core-collapse SNe. We show that (1) the explosions with large energy deposition rate, $dot{E}_{rm dep}$, are observed as GRB-HNe and their yields can explain the abundances of normal EMP stars, and (2) the explosions with small $dot{E}_{rm dep}$ are observed as GRBs without bright SNe and can be responsible for the formation of the C-rich EMP (CEMP) and the hyper metal-poor (HMP) stars. We thus propose that GRB-HNe and the Non-SN GRBs (dark HNe) belong to a continuous series of BH-forming stellar deaths with the relativistic jets of different $dot{E}_{rm dep}$.
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Long-duration gamma-ray bursts (GRBs) are thought to be connected to luminous and energetic supernovae (SNe), called hypernovae (HNe), resulting from the black-hole (BH) forming collapse of massive stars. For recent nearby GRBs~060505 and 060614, how
ever, the expected SNe have not been detected. The upper limits to the SN brightness are about 100 times fainter than GRB-associated HNe (GRB-HNe), corresponding to the upper limits to the ejected $^{56}$Ni masses of $M({rm ^{56}Ni})sim 10^{-3}M_odot$. SNe with a small amount of $^{56}$Ni ejection are observed as faint Type II SNe. HNe and faint SNe are thought to be responsible for the formation of extremely metal-poor (EMP) stars. In this Letter, a relativistic jet-induced BH forming explosion of the 40 $M_odot$ star is investigated and hydrodynamic and nucleosynthetic models are presented. These models can explain both GRB-HNe and GRBs without bright SNe in a unified manner. Their connection to EMP stars is also discussed. We suggest that GRBs without bright SNe are likely to synthesize $Mnisim 10^{-4}$ to $10^{-3}M_odot$ or $sim 10^{-6}M_odot$.
We review recent results on the high-redshift universe and the cosmic evolution obtained using Gamma Ray Bursts (GRBs) as tracers of high-redshift galaxies. Most of the results come from photometric and spectroscopic observations of GRB host galaxies
once the afterglow has faded away but also from the analysis of the GRB afterglow line of sight as revealed by absorptions in their optical spectrum.
After the Big Bang nucleosynthesis, the first heavy element enrichment in the Universe was made by a supernova (SN) explosion of a population (Pop) III star (Pop III SN). The abundance ratios of elements produced from Pop III SNe are recorded in abun
dance patterns of extremely metal-poor (EMP) stars. The observations of the increasing number of EMP stars have made it possible to statistically constrain the explosion properties of Pop III SNe. We present Pop III SN models whose nucleosynthesis yields well-reproduce individually the abundance patterns of 48 such metal-poor stars as [Fe/H] $mathrel{rlap{lower 4pt hbox{$sim$}}raise 1pt hbox {$<$}}-3.5$. We then derive relations between the abundance ratios of EMP stars and certain explosion properties of Pop III SNe: the higher [(C+N)/Fe] and [(C+N)/Mg] ratios correspond to the smaller ejected Fe mass and the larger compact remnant mass, respectively. Using these relations, the distributions of the abundance ratios of EMP stars are converted to those of the explosion properties of Pop III SNe. Such distributions are compared with those of the explosion properties of present day SNe: The distribution of the ejected Fe mass of Pop III SNe has the same peak as that of the resent day SNe but shows an extended tail down to $sim10^{-2}-10^{-5}M_odot$, and the distribution of the mass of the compact remnant of Pop III SNe is as wide as that of the present day stellar-mass black holes. Our results demonstrate the importance of large samples of EMP stars obtained by ongoing and future EMP star surveys and subsequent high-dispersion spectroscopic observations in clarifying the nature of Pop III SNe in the early Universe.
The nature of the first massive stars may be inferred by investigating the origin of the extremely metal-poor (EMP) stars, likely formed from the ejecta of one or a few previous massive stars. We investigate the rotational properties of early massive
stars by comparing the abundance patterns of EMP stars with rotating massive stellar models. Low metallicity 20 $M_{odot}$ stellar models with initial rotation rates between 0 and $70~%$ of the critical velocity are computed. Explosions with strong fallback are assumed. The ejected material is considered to fit individually the abundance patterns of 272 EMP stars with $-4<$ [Fe/H] $<-3$. With increasing initial rotation, the [C/H], [N/H], [O/H], [Na/H], [Mg/H] and [Al/H] ratios in the massive star ejecta are gradually increased. Among the 272 EMP stars considered, $sim 40-50~%$ are consistent with our models. About $60 - 70~%$ of the CEMP star sample is reproduced against $sim 20 - 30~%$ for the C-normal EMP star sample. The CEMP stars are preferentially reproduced with a material coming from mid to fast rotating massive stars. The velocity distribution derived from the best massive star models increases from no rotation to fast rotation. The maximum is reached for massive stars having initial equatorial velocities of $sim 550 - 640$ km~s$^{-1}$. Although subject to significant uncertainties, these results suggest that the rotational mixing operating in between the H-burning shell and the He-burning core of early massive stars played an important role in the early chemical enrichment of the Universe. The comparison of the velocity distribution derived from the best massive star models with velocity distributions of nearby OB stars suggests a greater amount of massive fast rotators in the early Universe. This may have important consequences for reionization or integrated light from high redshift galaxies.
The origin of carbon-enhanced metal-poor (CEMP) stars plays a key role in characterising the formation and evolution of the first stars and the Galaxy since the extremely-poor (EMP) stars with [Fe/H] leq -2.5 share the common features of carbon enhan
cement in their surface chemical compositions. The origin of these stars is not yet established due to the controversy of the origin of CEMP stars without the enhancement of s-process element abundances, i.e., so called CEMP-no stars. In this paper, we elaborate the s-process nucleosynthesis in the EMP AGB stars and explore the origin of CEMP stars. We find that the efficiency of the s-process is controlled by O rather than Fe at [Fe/H] lesssim -2. We demonstrate that the relative abundances of Sr, Ba, Pb to C are explained in terms of the wind accretion from AGB stars in binary systems.
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