GRB080319B: a high resolution spectroscopic view Valerio D’Elia (INAF – OAR) & F. Fiore, F....
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Transcript of GRB080319B: a high resolution spectroscopic view Valerio D’Elia (INAF – OAR) & F. Fiore, F....
GRB080319B: GRB080319B: a high resolution spectroscopic viewa 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)
June, 24th - 2008Nanjing - China
• GRB080319B wih UVES
• Absorbing systems (main + intervening)
• Main system gas separation in components
• Fine structure absorbing features
• Fine structure line variability
• Conclusions and perspectives
OUTLINE
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)
Exp. (s) S/N Dich. Arms Rmag
RRM1 06:21:26 517 600 3050 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
GRB explosion site
Circumburstenvironment
To Earth
Host gasfar away
Intergalactic matter
ABSORBING SYSTEMS
Fe II
Cr IIMg I
Ni II
1) Main system z=0.9372) Intervening #1z = 0.76
Fe II
Mg II
3) Intervening #2z = 0.71
Fe II
Mg II Mg I
5) Intervening #4z = 0.53
Fe II
Mg II Mg IMn II
4) Intervening #3z = 0.57
Fe II
Mg II
Unidentified lines
?
??
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
Component I shows strong Mg II absorption but no evidence of Mg I: this is possibly the closest component to the GRB
IIIIIIIVVVI
MAIN SYSTEM GAS SEPARATION IN COMPONENTS
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
antiparallel to
the electron's orbital
moment).
Fine structure splitting
First fine structure excited level
FINE STRUCTURE FEATURES
How to populate fine structure excited levels:
1. Collisional processes:
2. Radiative processes:
n
n + 1
Photoexcitation
Radiative de-excitation
Incident UV radiation
J=1/2
J=3/2
2a. Indirect UV pumping
J=9/2
J=7/2
J=5/2
J=3/2
J=1/2
2b. Direct IR pumping
Incident IR radiation
Selectionrule: J=0,±1
(Si II, C II) (Fe II)
Incominge-
(O I)J=0
J=1
J=2
n
n
STRONG VARIABILITY EXPECTED!
Fine structure lines nearly disappear
in less than 2 hours (less than 1h rest frame at
z=0.937)!
FINE STRUCTURE LINE VARIABILITY
Fe II 2374
Fe II* 2396
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)
Fine structure of component III and IV drops faster than that of component I
FINE STRUCTURE LINE VARIABILITY
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)
The ratio between the fine structure and ground levels are linked to the UV flux experienced by the GRB
FINE STRUCTURE LINE VARIABILITY
Component I
Components III/IV
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.
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