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Register a new userIron line afterglows: general constraints
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Authors
Gabriele Ghisellini
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The discovery of a powerful and transient iron line feature in the X-ray afterglow spectra of gamma-ray bursts would be a major breakthrough for understanding the nature of their progenitors, strongly suggesting the presence of a large, iron rich, mass in the vicinity of the burst event. Model-independent limits to the size and the mass of the the iron line emitting region are derived and discussed. We also discuss how these results can be used to constrain the amount of beaming or anisotropy of the burst emission.
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We discuss how a powerful iron line emission can be produced if ~1-5 iron rich solar masses are concentrated in the close vicinity of the burst. Recombination, thermal and fluorescent reflection are discussed. We find that recombination suffers the high Compton temperature of the plasma while the other two scenarios are not mutually exclusive and could account for the claimed iron line detected in two afterglows.
We consider a temporal response of relativistically broadened line spectrum of iron from black hole accretion irradiated by an X-ray echo under strong gravity. The physical condition of accreting gas is numerically calculated in the context of general relativistic hydrodynamics under steady-state, axisymmetry in Kerr geometry. With the onset of a point-like X-ray flare of a short finite duration just above the accretion surface, the gas is assumed to be ionized to produce a neutral iron fluorescent line. Using a fully relativistic ray-tracing approach, the response of line photons due to the X-ray illumination is traced as a function of time and energy for different source configurations around sw and Kerr black holes. Our calculations show that the X-ray echo on the accretion surface clearly imprints a characteristic time-variability in the line spectral features depending on those parameters. Simulated line profiles, aimed for the future microcalorimeter missions of large collecting area such as {it Athena}/X-IFU for typical radio-quiet Seyfert galaxies, are presented to demonstrate that state-of-the-art new observations could differentiate various source parameters by such an X-ray tomographic line reverberation.
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We present an extensive study of non-minimal flavour violation in the squark sector in the framework of the Minimal Supersymmetric Standard Model. We investigate the effects of multiple non-vanishing flavour-violating elements in the squark mass matrices by means of a Markov Chain Monte Carlo scanning technique and identify parameter combinations that are favoured by both current data and theoretical constraints. We then detail the resulting distributions of the flavour-conserving and flavour-violating model parameters. Based on this analysis, we propose a set of benchmark scenarios relevant for future studies of non-minimal flavour violation in the Minimal Supersymmetric Standard Model.
We forecast the reionization history constraints, inferred from Lyman-alpha damping wing absorption features, for a future sample of $sim 20$ $z geq 6$ gamma-ray burst (GRB) afterglows. We describe each afterglow spectrum by a three-parameter model. First, L characterizes the size of the ionized region (the bubble size) around a GRB host halo. Second, $langle{x_{rm HI}rangle}$ is the volume-averaged neutral fraction outside of the ionized bubble around the GRB, which is approximated as spatially uniform. Finally, $N_{mathrm{HI}}$ denotes the column-density of a local damped Lyman-alpha absorber (DLA) associated with the GRB host galaxy. The size distribution of ionized regions is extracted from a numerical simulation of reionization, and evolves strongly across the Epoch of Reionization (EoR). The model DLA column densities follow the empirical distribution determined from current GRB afterglow spectra. We use a Fisher matrix formalism to forecast the $langle{x_{rm HI}(z)rangle}$ constraints that can be obtained from follow-up spectroscopy of afterglows with SNR = 20 per R=3,000 resolution element at the continuum. We find that the neutral fraction may be determined to better than 10-15% (1-$sigma$) accuracy from this data across multiple independent redshift bins at $z sim 6-10$, spanning much of the EoR, although the precision degrades somewhat near the end of reionization. A more futuristic survey with $80$ GRB afterglows at $z geq 6$ can improve the precision here by a factor of $2$ and extend measurements out to $z sim 14$. We further discuss how these constraints may be combined with estimates of the escape fraction of ionizing photons, derived from the DLA column density distribution towards GRBs extracted at slightly lower redshift. This combination will help in testing whether we have an accurate census of the sources that reionized the universe.
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