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					Is GRB050509b a genuine short?

        Gustavo de Barros,
       Maria Grazia Bernardini,
        Carlo Luciano bianco,
           Roberto Guida,
            Remo Ruffini.
Characteristics
---------------------------------------------------------------




This GRB is important
because is the first short
GRB with observed
afterglow

- Z = 0.2248

- duration of BAT data:
40 ms
                                                                  fig. from Nature,Vol 437, 851
         Short scale + afterglow
         --------------------------------------------------------------------------------------------------



Gehrels et al. (2005) say that the data observed by
BAT are typical of a short burst.

But there are also
(after 100s from BAT
data) observations
from XRT.

So, how classify this
GRB?

                                                                                fig. from Nature,Vol 437, 851
               Fireshell model
               ------------------------------------------------------------------




 In the fireshell model canonicals GRBs have two
important emission phases:

1- when the plasma reaches the moment of
transparency (decouple of photons) there is the
emission we call 'proper-GRB' (P-GRB).

2- After this, the fireshell (formed now mainly by
barions) reaches the CBM (circumburst medium) and
emits energy by inelastic collisions. This emission is
called 'afterglow'.
            What about 050509b?
            -----------------------------------------------------------------------------------------------



We analysed GRB050509b to see it's
classification. It could be:
 a fake short;


   just a long with an observed P-GRB (almost
called 'precursor' in the literature)
   a genuine short.
                      First Analysis
                     ------------------------------------------------------------



In the first analisys we identifyed the prompt emission
(data from BAT) with the P-GRB. In this case these data
would be the 'short part' of the GRB and the XRT-data
the long part.
The parameters are:

   B=1.6 x 10-3
   ρ = 1 (#/cm3)‫‏‬
   R = 1 x 10-11
   E=1.48x1048erg
The first analisys show us that this GRB is a long one
because almost 80% of the total energy is emmitted in the
afterglow. The point of view (in literature) that this is a 'short'
with afterglow, is nothing more then our canonical picture for
GRBs. The first part is the P-GRB which is 'short' in time,
accompained by the afterglow.
                   Second analysis
                   ------------------------------------------------------------------------

  In the second analisys we want to see if is possible to
do a fit in which the GRB will be a genuine short. To do
this we identifyed the data from BAT (prompt emission)
with the peak of the afterglow. The parameters are:

   B = 1.1 x 10-4

              0.9 ( #/cm3)                                           ;           r > 3 x 1015 cm
   ρ=
            0.9 x 10-2 ( #/cm3)                                      ;           r < 3 x 1015 cm

   R = 6 x 10-6

   E = 3.2 x 1049 erg                                                    EP-GRB = 2.1 x 1049
                Second analysis
               -----------------------------------------------------------------------

In the second analysis all the observed data are from the
emission of the afterglow. The P-GRB is
too hard to be
observed, we
expect a peak
emission for it,
about 850 kev.
Since the above
threshold for
BAT is 350 kev,
it wasn't
observed.
The second analisys says that this GRB would be a genuine
short. Because it has 65% of the total energy emmitted in the
P-GRB. But it is important to note that we cannot see the
'short' characteristic of it. The short timescale data observed
by BAT are part of the 'long' domain of the GRB (the
afterglow).
                    The B parameter
                  ---------------------------------------------------------------




1o analysis: black line - B = 1.6 x 10-3. Long GRB



2o analysis:
yellow line
B = 1.1 x 10-4.
Genuine short GRB
                 Conclusions
                 -----------------------------------------------------




 This GRB may be a genuine short one, but has
also the possibility to be long.

 We expect hard emission in the begining phases
(850 kev in this case).

We need data also in this range to remove
ambiguity (in possible newer sources), and to
constraint the parameters of the model.

 We hope that Glast satellite will help us to solve
these problems.

				
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posted:6/24/2012
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