GRB080319B:
a high resolution spectroscopic view
Valerio D’Elia
(INAF – OAR)
&
F. Fiore, F. Nicastro (Rome),
R. Perna (Colorado), Y. Krongold (Mexico),
E.Meurs, L.Norci (Dublin)
+ MISTICI group (Rome/Milan)
Nanjing - China
June, 24th - 2008
OUTLINE
• GRB080319B wih UVES
• Absorbing systems (main + intervening)
• Main system gas separation in components
• Fine structure absorbing features
• Fine structure line variability
• Conclusions and perspectives
OBSERVATION LOG
19 March 2008, 06:12:49 UT: the brightest GRB ever (z=0.937)
• Observed before, during and after the GRB worldwide
• R=5 at about 20 s and H=4.2 at about 50 s from the GRB: naked eye GRB!
UVES observations began just 8m30s after the GRB (fastest response and
higest S/N ever)
Two RRM and one ToO observations of the event (8.5m, 2h and 3h time delay)
Obs.
UT
Time from
burst (s)
RRM1
06:21:26
517
600
3050
2
B+R
12 13
RRM2
08:06:42
6833
1800
7  12
1+2
B+R
16 17
ToO
09:07:22
10482
1200
58
1+2
B+R
16 17
Exp. (s)
S/N
Dich. Arms Rmag
Circumburst
environment
Intergalactic matter
GRB explosion
site
Host gas
far away
To
Earth
ABSORBING SYSTEMS
2)
#1
1) Intervening
3)
5)
4)
Main system
#2
#4
#3
Unidentified
lines
z
= 0.76
z=0.937
0.71
0.53
0.57
Fe II
Fe II
?
Fe II
FeMn
II II Cr II
Mg I
Mg II
Mg I
Ni II
?
Mg II
?
Fe II Mg II
Mg I Mg II
MAIN SYSTEM GAS SEPARATION IN COMPONENTS
Six components clearly identified
MAIN SYSTEM GAS SEPARATION IN COMPONENTS
Although some lines are saturated, we have so many transitions
that the six components fit results to be very robust
MAIN SYSTEM GAS SEPARATION IN COMPONENTS
VI V
IV
III
II
I
Component I shows strong Mg II absorption but no evidence of
Mg I: this is possibly the closest component to the GRB
FINE STRUCTURE FEATURES
The gross structure of an atom is due to the principal quantum number
n, giving the main electron shells of atoms. However, electron shells
exhibit fine structure, and levels are split due to spin-orbit
coupling (the
energy difference
between the
electron spin
being parallel or
First fine structure
antiparallel to
excited level
the electron's orbital
moment).
Fine structure splitting
FINE STRUCTURE FEATURES
How to populate fine structure excited levels:
1. Collisional processes:
Incoming
e-
J=2
J=1
J=0
n
(O I)
2. Radiative processes:
2a. Indirect UV pumping
Incident UV
radiation
n+1
2b. Direct IR pumping
Incident IR
radiation
Radiative
de-excitation
STRONG
VARIABILITY
Selection
rule: J=0,±1
EXPECTED!
Photoexcitation
(Si II, C II)
n
J=1/2
J=3/2
J=5/2
J=3/2
J=1/2
J=7/2
(Fe II)
n
J=9/2
FINE STRUCTURE LINE VARIABILITY
Fine structure lines nearly
disappear
in less than 2 hours
(less than 1h rest frame at
z=0.937)!
Ground state lines remain
constant (slight increment
compatible with the
decreasing of the excited
levels)
The strongest fine structure line variation
ever found
(optical depth reduced by a factor of 4 – 20)
Fe II*
2396
Fe II
2374
FINE STRUCTURE LINE VARIABILITY
Fine structure of component III and IV drops faster than that of component I
Possible explanation:
Component I experiences
higher fluxes for longer
times, i.e., is the closest
component to the GRB.
In addition, component I can
receive contribution from
collisional excitation (hints of
a higher temperatures)
FINE STRUCTURE LINE VARIABILITY
The ratio between the fine structure and ground levels are linked to the UV
flux experienced by the GRB
Using GRB080319B
lightcurve and spectral
energy distribution, we can
compute the UV luminosity
of the GRB and thus the
distance of the absorber in a
steady-state approximation.
Component I
Components
III/IV
This yields
d = 18-34 kpc:
outside the host galaxy!
Prochaska et al. 2006
Diffuse emission elongated
south of the AG
Two faint clumps at 1.5’’ and 3’’
 12 and 24 kpc at z=0.937
Tanvir et al. 2008
CONCLUSIONS
GRB080319B at z = 0.937 is the brightest GRB ever and the
brightest and fastest-observed UVES GRB ever: 8.5 mins after
the trigger and S/N = 50
• At least five different absorption systems identified, (main system at the GRB
redshift + 4 intervening), between z = 0.937 and z = 0.5
• The main system can be resolved into six components, constituted by
different shells of gas absorbing the radiation at different distances from the
GRB
• The strongest fine structure line variation ever found in a GRB (optical depth
reduced by a factor of 4 – 20 in less than 1 hour rest frame), withnesses UV
pumping as excitation mechanism. d=18-34 kpc, well outside the host galaxy!
• Time-dependent photoexitation models are under construction. Preliminary
results confirm that the distance from the GRB is greater than 1 kpc