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

GRB030329: Association with SN Ib

for long GRBs

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

X-shooter Science Case: Faint Object Spectroscopy

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

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 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