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X-shooterIInd Generation VLT Spectrograph for GRBs
Paolo Goldoni, SAp/CEA-APC
Conseil Scientifique - APC 21/11/2003
1967-1997 : The Long Wait
BATSE2704 burst
Lack of Weak Bursts w.r.t. uniform distribution
in Euclidean space
Fluence Φ (cm-2 s-1)
N (
> Φ
)
Duration distribution bimodal
63% of burstslast < 30 s
T90 (s)
Nom
bre
de s
ursa
uts 63%
Optical Afterglow
TB+ 6,5 h TB + 12 h TB + 52 h
GRB 971214 Afterglow : 1.3-10 keV power law decline
1997 : BEPPO-SAX, the counterparts
Host Galaxies Redshift~ 35 measured redshift(0.16 <z < 4,5, <z>~1)
Cosmological sourcesMost energetic (Γ ~100)
Emitted energy γ ~ 1050-1052 ergs
http://www.mpe.mpg.de/~jcg/grbgen.html
Afterglow lightcurves:Breaks, Bumps, Wiggles and the emergency of a SN
Wijers et al. 1997
Harrison et al. 1999
Berger et al. 2003
GRB 030329: the appearance of SN2003dh
Evolution of the GRB 03029/SN 2003 spectrum,from April 1.13 UT (2.64 days after the burst)to April 8.13 UT (9.64 days after the burst). Theearly spectra consist of a power-law continuum
(F ~ ν -0.9) with narrow emission lines originating from
H II regions in the host galaxy at a redshift of z=0.168 taken after April 5 show the development of broad peaks in the spectra characteristicof a supernova.
From Stanek et al. 2003
J. Paul 7
“Standard” model
1
1 Newly Formed BH surrounded by a torus
4 Ext. shock
4
3 Int.Shock
3
Lorentz Factor >
100
2
2 Rel. Ejection
5
5Reverse
shock
Open problems
X-ray Flashes= GRB with lower peak energyLess energetic GRBs ? GRB at High Redshift ?
Short Bursts ! No afterglow for T < 1 s
Are GRBs an effective SFR tracer ?
Structure of the jet ? Beaming ?
(At least some) GRBs are the farthest stars we can observe
State of the art (Zhang & Meszaros astro-ph/0311321)
1999 : Prompt Optical Emission
1 2 3
Discovery of Prompt Optical Emission of GRB 99012331 2
Secondes après le déclenchement du sursaut
Cou
ps s
-1 k
eV-1
Prompt Emission is not limited to γ-ray domain, GRB 990123 emitted in optical an isotropic
equivalent energy of ~ 1049 ergs (mV ~ 9 in image 2 )
ROTSE-1
2002 : GRB021004Optical Observations of the error box of GRB 021004
detected and localized with HETE-2
Image NEAT 9 min after the burst
mR = 15,3
Image DPOSS(20/8/1990)
Name V z3C 273 ~12.86 0.158 PKS 2155-304 ~13.09 0.17PG 1634+706 ~14.9 1.33
Brightest Quasars vs. Brightest GRBs
Name V z990123 ~9 1.6 021004 ~15.3 2.3021211 ~18.2 1.01
Brightest GRBs can be used as new cosmological probes !
IGM study in several line of sights with unprecedented brightness
GRBs as cosmological probe
Pros1) Very bright2) Unperturbed Medium, no proximity effect3) Isotropic Distribution
Cons1) Very Fast Transient2) Small Number
SWIFT launch ~mid-2004
~150 localized afterglow/year !
“Call for proposals for 2nd Generation VLTInstruments” (http://www.eso.org/instruments/vlt2ndgenins.html)
The main goal is to get maximum detectivity on stellar or small emission-line objects,while covering the largest possible wavelength range (ideally 0.32 to 2.4 m) in a single observation, presumably leading to a multiple arm ("x-shooter") system. A particularly important requirement is the ability to get spectrographic data on unpredictable/fast varying objects like supernova explosions or gamma ray burst optical counterparts, for the latter if possible in a matter of minutes….
R~ 104 wide-band visible-NIR high-throughput Spectrometer
Goal of the instrument: Single object observations at the sky limit
Consortium NL,D,I,F,ESO
Project Constraints and characteristics
Very Fast realization ! (SWIFT launch mid-2004).Commisioning in 2006 and operation in 2007 are foreseen
More than half budget from member states
First second generation instrument to be operative but very tight budget
Automatic operations driven by robotic telescopes atChili: REM (APC) and Tarot-2
GRB Afterglow, host galaxy, line-of-sight absorption
1) Type Ia Supernovae
2) X-ray Binaries
Main Scientific Topics for APC
The brightest cosmic lighthouses visible up toredshift 15 Stars and Structure formation inThe early Universe
Secondary Scientific Topics
Lamb & Reichart, 2000
X- shooter Spectral range and maximum redshift
Wavelength position of absorption lines and Lyman-α forest as a function of redshift. To the right X-shooter spectral range with respect to UVES
X-shooter sensitivity
Sensitivity to a 30 kms-1 line (moderately strong IGM absorption line) as a functionof wavelength: X-shooter, FORS Giraffe and ISAAC
Afterglow lightcurve (R~13.6 after 5 minutes, R~18 after 1 day).Arrows mark the ‘cooling’ and ‘injection’ breaks. The vertical line mark the jet break.
Afterglow Spectroscopy I : The Time evolution
Afterglow Spectroscopy II : The spectral break
Afterglow spectra at 4 different epochs along with X-shooter spectral range
Cosmological Lyman-α absorption
4 z > 5.8 quasars (Becker et al. 2001). X-shooter wil be able toobserve all this band with 1 exposure
GRB spectra, where are the lines ?
GRB021004 (z=2.23) spectrum taken with NOT R~19.0,importance of a WIDE spectral range
APC Contribution: Integral Field Unit Fed. APC: GEPI-Meudon, SAp
1 spectrum for every micro lens: PSF sampling and ~ 1 magnitude gain w.r.t. slit spectrograph
Realised by GEPI-Observatoire de Paris (Girafe):DRS responsibility of SAp
Why an IFU
To perform (mini) area spectroscopy for higher spectrophotometricAccuracy over a wide spectral range of stellar and slightly extendedtargets
To map the spectral characteristics of extended objects
To reduce slit losses when operating with narrow spectrograph slitsTo reach the limiting spectral resolution of the instrument or withbad/variable seeing
To reduce the effect of pointing errors when the targets are invisiblein the acquisition system (or prompt response considerations precludethe use of the acquisition CCD) and the coordinates are known to +/-1arcsec accuracy
IFU advantage: X-shooter FOV & OT positions
Bloom et al. 2001
X-shooter FOV with IFU (1.6” x 3.2”) is superposed to the angular distribution of 20 OTs in their galaxy. 1 pixel is 0.2” x 0.2”.
http://www-int.stsci.edu/~fruchter/GRB/030329/
GRB 030329 and its host galaxy with HST
12-13 May Observations, V~22.7, M (Galaxy)~-16.5
X-Shooter Planning
Phase A Phase B Phase C Phase D
Nov 2003 Avr 2004 Apr 2005 Apr 2006
Apr 2004 Apr 2005 Apr 2006 Jul 2007
6 months 12 months 12 months 16 months
APC Contribution
IFU and IFU Data Reduction Software
PI F. Hammer, DRS PI: A. Claret
Science Team: P. Goldoni, H. Flores, P. Francois, Ph. Filliatre
Scientific return: Guaranteed time under discussion
~15 % of total cost
Conclusions
X-shooter has been approved by ESO STC, it will be the first IInd generation instrument operative at VLT
APC/GEPI participation at ~15% guaranteesan interesting return
It will be the most sensitive VLT single object spectrograph
The main scientific aim will be the GRBs with the possibilityof detecting the farthest sources at the reionization epoch orbeyond