Is GRB050509b a genuine short?

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Is GRB050509b a genuine short?

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

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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

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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

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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'.

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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.

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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
• B1.6 x 10-3
• ? 1 (/cm3)?
• R 1 x 10-11
• E1.48x1048erg

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• 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.

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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 gt 3 x 1015 cm
• ?
• 0.9 x 10-2 ( /cm3)
  r lt 3 x 1015 cm
• R 6 x 10-6
• E 3.2 x 1049 erg
  EP-GRB 2.1 x 1049

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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.

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• 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).

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• 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

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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.