Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: X-Ray Spectroscopy of Gamma-Ray Bursts   Observational evidence of iron absorption and emission lines in X-ray spectra
of Gamma-Ray Bursts is quite compelling. I will briefly review the results,
summarize different models and describe the connection with massive progenitors
in star-forming regions implied by these results. This link is also supported
by measurements of the X-ray absorbing gas in several GRB's, with column
density consistent with that of Giant Molecular Clouds harbouring
star-formation in our Galaxy, as well as by evidences gathered in other
wavelengths. However, the volume density inferred by the fireball-jet model is
much lower than typical of a GMC, and I will confront this with the alternative
explanation of fireball expansion in a high dense medium, outlining the
problems that both models have at present. Finally I will briefly summarize
some results on dark GRB's, and describe the prospects of high resolution X-ray
spectroscopy in getting closer to the central environment of GRB, and far in
the Early Universe by using GRB as beacons to probe star and galaxy formation.

19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an