GRB%20060614:

1

GRB 060614 a canonical fake short burst
L. Caito, M.G. Bernardini, C.L.
Bianco, M.G. Dainotti, R.
Guida, R. Ruffini.

3rd Stueckelberg Workshop
July 818, 2008 - Pescara
2
Scheme of the talk

• Characteristics and many peculiarities of GRB
  060614
• Theoretical interpretation of this source within
  the Fireshell scenario
• Results obtained and future hints of
  investigation

3
GRB 060614

• 2006 June 14 at 12.43.48 UT
• RAj2000 21l23 m27s
  
  
• DECj2000 -5302'02"
  
  
• Uncertainty 3'
• Most interesting issues
• The presence of both peculiarities of long
  bursts and peculiarities of short bursts
• The lack of any bright Ib/c supernova

(Mangano et
al., 2007)?
4
About GRB 060614... generalities

• Long burst T90(1025)s
  15/350 Kev
  
  (Barthelmy et al. 2006)?
• Low redshift Z0.125
  ( Price et al. 2006 )
• A short, hard and multi-peaked episode (5s)
  followed by a softer, prolonged emission (100s)
  (e.g. Della Valle 2006)?
• Strong hard to soft evolution in the first 400s
  of data
  
  (Mangano et al. 2006)?
• Standard XRT, Optical and UV afterglow detected
  until 4 ks after the trigger
  (Mangano et al. 2006)
• Light curves show some achromatic breaks
  at 29.7 4.4 ks in
  the optical and UV energy band
  at 36.6 2.4 ks in the X-ray energy
  bandat 104 ks from optical to X-Ray
  frequencies
  
  (Mangano et al. ,2007)?

5
About GRB 060614... energetics
UPPER LIMIT TO THE AVERAGE ENERGY E24
kev The peak energy decreased from 300 kev
during the initial group of peaks (20 of the
total fluence) to 8 kev during the BAT-XRT
overlap time ( about 80 s)




(Mangano et al., 2006)? Eiso2.5x1051 erg
more energetic than a short but less than a


typical long... Eiso,1p3.5x1050 erg
about one seventh of the total isotropic energy


released! F(2.170.04)x10-5 ergcm-2
F1p3.4x10-6 ergcm-2
?-Ray 15-150 kev


F2p1.9x10-5 ergcm-2

6
GRB 060614 is it a long...

• Duration
• Eiso intermediate value
• It fulfills all the empirical relations
  satisfied by long bursts
• 
  
  Eprest - Eiso correlation (Amati)?
• 
  E? - Eiso correlation
  (Ghirlanda)?
• 
  Lp, iso - Eprest c0rrelation
• It's close to its host galaxy

7
...or a short burst?

• Eiso intermediate value
• Moderate SSFR of the host galaxy
• 
  
  until 20 times less than
  RHost2Ms y-1 (L)-1
  long GRBs with SN !!!
  
  MvHost-15.5
• 
  (Fynbo et
  al., 2007)?
• 
  (Della Valle
  et al., 2007)?
• Spectral lags very small or absent
• (Plot for the Peak Luminosity vs Time Lags for
  many bursts GRB 060614 lies clearly in the
  region of the short GRBs. Gehrels et al.,
  2007)?

8
The lack of any bright Ib/c supernova
In the standard scenario long duration GRBs are
thought to be produced during the collapse of
massive stars. A broad-lined and luminous type
Ib/c core collapse SN should accompany these
GRBs. For nearby GRBs ( Z1) the SN emission
should be visible. Until now...
SN 1998bw / GRB 980425

SN 2003dh / GRB
030329 SN 2003lw / GRB 031203
SN 2006aj / GRB 060218

CONFIRM THIS ASSOCIATION,
UNTIL...

• GRB 060614 the first clear example of a nearby
  long burst
  without SN Ib/c emission observed!
• The SN-component should be about 80/100 times
  fainter than the archetypal SN 1998bw
• It would be strongly fainter than any Ic
  supernova not associated to GRBs ever observed
  Mvgt-13.5
  
  
  (Della Valle et al., 2006)
  

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The lack of any bright Ib/c supernovaA different
type of SN?

• Very low luminosity
• Low velocity of expansion
• ( 1.0 Kms-1)?

Type II SN
For the lack of broad undulations in a spectral
sample at ? between 4500 ? and 8000 ?
Due to the collapse of a massive star with a
burning energy so small that most of the 56Ni
fall back in the star. This system could give
rise to a black hole.
(Della Valle et al., 2006)?
10
The lack of any bright Ib/c supernovaOther
Hypothesis

• A chance superposition of a galaxy with the found
  redshift along the line of sight of the burst
  
  
  
  
  
  Probability
  5.6x10-6 (Gal Yam et al., 2006)
  
  
  
• Strong dust obscuration and extinction
  
  
  
  this possibility has been ruled out by
  multi-wavelength observations and spectroscopy of
  the host
  
  
• 
  
  
  
  
  
• 
  
  
• 
  

E(B-V)0.0216 mag NH2x1020 cm-2
- Detection of the early afterglow in the UV
energy band (Holland et al. 2006)? - No
significant reddening in the optical spectra of
the afterglow
(Fynbo et al., 2007)? (Della Valle et al., 2006)?
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The lack of any bright Ib/c supernovaa
possible origin

• Origin of the burst the merger of a Neutron Star
  and a massive White Dwarf
  (King et al., 2007)?
• In a binary system, a WD donor is subject to
  instability if it have mass
• Mwd0.66
  Macc
• Since Mwd cannot exceeds the Chandrasekar mass
• Macc1.4
  Ms
• It must be
• Macc2.1
  Ms

The process is more likely with a neutron star
accretor!
12
The lack of any bright Ib/c supernovaa possible
origin

• For its characteristics lengthscale and amount
  of energies involved, the unstable merger of a
  massive WD and a NS can produce long GRBs without
  accompanying supernova (King et al.,
  2007)?
• 
  

GRB 060614!
and also GRB 060505 presents similar
peculiarities... (T904s, Z0.09...NO SN
observed!)?
13
Data analysis of GRB 060614

• We realized a detailed analysis of the
  observational data in
• 15-150 keV energy band, corresponding to the
  Gamma-Ray Peak of the Afterglow. Data from
  the Burst Alert Telescope (BAT) on the Swift
  satellite
• 
  
• 0.3-10 keV energy band, the X-Ray Afterglow.
  Data from the X-Ray Telescope (XRT) on the
  Swift satellite
• We plan to analyze also the Optical emission
  of the source.

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Theoretical interpretationBrief reminder of the
model

• The explosion of a canonical GRB consists
  of two different processes
• the emission of a flash of relativistic photons
  when the optically thick fireshell reaches the
  transparency condition. This is the Proper GRB
  (P-GRB)
• 
  
• the strongly hard to soft emission of energy
  due to the inelastic collision of the optically
  thin fireshell of baryonic matter with the Circum
  Burst Medium (CBM). This is the Afterglow phase
  
  
  ( Ruffini et al., 2001b, 2007a )?

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Theoretical interpretationBrief reminder of the
model

• In this scenario, GRB o6o614 is naturally
  interpreted as a canonical GRB

The long, softer Gamma-Ray tail is the Peak of
the Afterglow
The first hard emission is the P-GRB
(Mangano et al., 2007)?
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Theoretical interpretationBrief reminder of the
model

• Both short and long GRBs originate from the
  gravitational collapse to a black hole.
  
  (Ruffini et
  al., 2001b)
  
  
• CANONICAL BURSTS LONG BURSTS

GENUINE SHORT BURSTS
Blt10-5, P-GRB is dominant
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Theoretical interpretation Brief
reminder of the model
Two free parameters describe completely the
energetics and dynamics of the phenomenon Etote
it's the total energy of
the plasma BMbc2/Etote it represents
the contribution of
the baryonic matter to the total
amount of
energy. It
oscillates between 10-5 and 10-2
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Theoretical interpretation
Brief reminder of the model

• We assume the hypothesis of the interaction of
  the expanding fireshell with the CBM to give
  rise of the
• total multi wavelength emission (Afterglow).
• This interaction takes place with fully inelastic
  collisions.
• 
  
  in the
  distribution of the peak luminosities
  have
  a fundamental role
• The variation of density of CBM, ncbm
• The variation of the ratio between the effective
  area of emission and the total area of the shell
  in expansion
  
  
  
  R Aeff/Atot
  

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Theoretical interpretation
Brief reminder of the model

• The emission from the baryonic matter shell is
  isotropic.
• in the first approximation, we assume a
  modeling of spherical shell for the distribution
  of CBM thin shell around the fireshell...
  
  
• we can consider just the radial coordinate of the
  expansion.
  ( Ruffini et al.,
  2002)
• 
  
• With these assumptions, our theoretical fitting
  curves are in good agreement with
  the observational data.

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The fit of the observed luminosity 15-150 keV
energy band
Etote 2.94x1051 erg
B2.8x10-3
EP-GRB 1.15x1050 erg ?Trans346 (the fit starts
after the P-GRB)
ncbm 4.45x10-4 partcm-3
R1.72x10-8 very low
density... ...did GRB 060614 explode
in a galactic halo?
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The fit of the observed luminosityThe role of
the very low density
The total energy of the peak of the Afterglow is
larger than the one of the P-GRB of about one
order of magnitude
Eiso,1p1.15x1050 erg P-GRB Eiso2.83x1051
erg Afterglow

The morphology of the light curve manifests
an inverse trend...
...an high, hard P-GRB and a much lower afterglow
emission!
This is due to the very low
density of the CBM!!!

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The fit of the observed luminosityGRB 060614 a
fake short burst

• GRB 060614 is an example of fake short burst
• the Afterglow is dominant although a peculiar
  low density of the environment produces an hard
  initial spikelike emission and a deflated tail
• (See Bernardini et al., 2007 on the very similar
  case of GRB 970228)?

LONG BURSTS 10-5 lt B lt 10-2 Afterglow
is dominant
FAKE SHORT BUSTS 10-5 lt B lt
10-2 Afterglow is dominant but they manifest an
hard P-GRB emission
GENUINE SHORT BURSTS B lt
10-5 P-GRB is dominant
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The fit of the observed luminosity 0.3-10 keV
energy band
Making R to variate and ncbm to be constant
Etote 2.94x1051 erg
B2.8x10-3
EP-GRB 1.15x1050 erg ?Trans346
ncbm 4.70x10-6 partcm-3
R1.27x10-2
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Density vs radius, R vs radius
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Final Remarks

• The peculiar source GRB 060614 finds a natural
  interpretation in
  our canonical GRB scenario two sharply different
  components in the phenomenon, the P-GRB and the
  Afterglow
• GRB 060614 is a fake short burst
• the high value of the peak luminosity of the
  P-GRB compared with the lower afterglow one
  (although the opposite behavior of the
  corresponding total energies) is a consequence of
  the very low density of the environment
• Our results are consistent with the merging of a
  Neutron Star and a White Dwarf in a galactic
  halo. We are still working on this issue, as
  well as on the interpretation of the optical
  emission observed
•