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X-shooter II nd Generation VLT Spectrograph for GRBs. Paolo Goldoni, SAp/CEA-APC. Conseil Scientifique - APC 21/11/2003. 63%. Nombre de sursauts. N (> Φ). T 90 (s). Fluence Φ (cm -2 s -1 ). Lack of Weak Bursts w.r.t. uniform distribution in Euclidean space.

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X-shooter II nd Generation VLT Spectrograph for GRBs

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IInd Generation VLT Spectrograph for GRBs

Paolo Goldoni, SAp/CEA-APC

Conseil Scientifique - APC 21/11/2003



Nombre de sursauts

N (> Φ)

T90 (s)

Fluence Φ (cm-2 s-1)

Lack of Weak Bursts w.r.t. uniform distribution in Euclidean space

Duration distributionbimodal

63% ofbursts

last < 30 s


2704 burst

1967-1997 : The Long Wait


GRB 971214 Afterglow : 1.3-10 keV power law decline

TB+ 6,5 h

TB + 12 h

TB + 52 h

Optical Afterglow

Host Galaxies Redshift

~35 measured redshift

(0.16 <z < 4,5, <z>~1)

Cosmological sources

Most energetic (Γ ~100)

Emitted energy γ ~ 1050-1052 ergs

1997 : BEPPO-SAX, the counterparts


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

Evolutionof the GRB 03029/SN2003 spectrum,

from April1.13 UT (2.64 daysafter the burst)

toApril 8.13 UT (9.64days after the burst).The

early spectra consistof a power-law continuum

(F~ ν-0.9) withnarrow emission lines originatingfrom HII regionsin the host galaxyat a redshift ofz=0.168 taken after April 5show the development ofbroad peaks in thespectra characteristic

of asupernova.

From Stanek et al. 2003


GRB030329: Association with SN Ib

for long GRBs

From Stanek et al. 2003


Lorentz Factor > 100

1 Newly Formed BH surrounded by a torus










  • Int.
  • Shock
  • Rel.
  • Ejection

J. Paul


“Standard” model


State of the art(Zhang & Meszaros astro-ph/0311321)

(At least some) GRBs are the farthest stars we can observe

Open problems

Short Bursts ! No afterglow for T < 1 s

Structure of the jet ? Beaming ?

X-ray Flashes= GRB with lower peak energy

Less energetic GRBs ?

GRB at High Redshift ?

Are GRBs an effective SFR tracer ?


Discovery of Prompt Optical Emission of GRB 990123




Coups s-1 keV-1




Secondes après le déclenchement du sursaut

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 )


1999 : Prompt Optical Emission


mR = 15,3

Image NEAT 9 min aftertheburst



2002 : GRB021004

Optical Observations of the error box of GRB 021004

detectedand localizedwith HETE-2


Brightest Quasars vs. Brightest GRBs

Name V z

3C 273 ~12.86 0.158

PKS 2155-304 ~13.09 0.17

PG 1634+706 ~14.9 1.33

Name V z

990123 ~9 1.6

021004 ~15.3 2.3

021211 ~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


1) Very bright

2) Unperturbed Medium,

no proximity effect

3) Isotropic Distribution


1) Very Fast Transient

2) Small Number

SWIFT launch ~mid-2004

~150 localized afterglow/year !


“Call for proposals for 2nd Generation VLT

Instruments” (

R~ 104 wide-band visible-NIR high-throughput Spectrometer

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 mm) 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….

Goal of the instrument: Single object observations at the sky limit


Project Constraints and characteristics

Very Fast realization ! (SWIFT launch mid-2004).

Commisioning in 2006 and operation in 2007 are foreseen

Automatic operations driven by robotic telescopes at

Chili: REM (APC) and Tarot-2

First second generation instrument to be operative but

very tight budget

More than half budget from member states

Consortium NL,D,I,F,ESO


Main Scientific Topics for APC

GRB Afterglow, host galaxy, line-of-sight absorption

The brightest cosmic lighthouses visible up to

redshift  15 Stars and Structure formation in

The early Universe

Secondary Scientific Topics

1) Type Ia Supernovae

2) X-ray Binaries


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

Lamb & Reichart, 2000


X-shooter sensitivity

Sensitivity to a 30 kms-1 line (moderately strong IGM absorption line) as a function

of wavelength: X-shooter, FORS Giraffe and ISAAC


Afterglow Spectroscopy I : The Time evolution

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 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 to

observe 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


X-shooter spectrum of GRB 021004 at z=8.5

Texp = 2 hr, reionization at z=7, 7 hours post burst.


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 spectrophotometric

Accuracy over a wide spectral range of stellar and slightly extended


To map the spectral characteristics of extended objects

To reduce slit losses when operating with narrow spectrograph slits

To reach the limiting spectral resolution of the instrument or with

bad/variable seeing

To reduce the effect of pointing errors when the targets are invisible

in the acquisition system (or prompt response considerations preclude

the use of the acquisition CCD) and the coordinates are known to +/-1

arcsec accuracy


IFU advantage: X-shooter FOV & OT positions

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”.

Bloom et al. 2001


GRB 030329 and its host galaxy with HST

12-13 May Observations, V~22.7, M (Galaxy)~-16.5


APC Contribution

IFU and IFU Data Reduction Software

~15 % of total cost

PI F. Hammer, DRS PI: A. Claret

Science Team: P. Goldoni, H. Flores, P. Francois, Ph. Filliatre

Scientific return: Guaranteed time under discussion



X-shooter has been approved by ESO STC, it will be the first IInd generation instrument operative at VLT

It will be the most sensitive VLT single object spectrograph

The main scientific aim will be the GRBs with the possibility

of detecting the farthest sources at the reionization epoch or


APC/GEPI participation at ~15% guarantees

an interesting return