Xshooter A Wideband Spectrograph for GRBs

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X-shooter A Wideband Spectrograph for GRBs

• P. Goldoni, P. Filliatre
• On behalf of a larger collaboration

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Call for proposals for 2nd Generation
VLT Instruments (http//www.eso.org/instruments/v
lt2ndgenins.html)
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.
Specific targets rapid variation, unpredictable
point-like objects Output sky limited U to K
spectrum at R5000-10000 in one shot
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Main scientific goals of X-shooter

• Cosmic explosions
• GRB afterglows
• Supernovae
• High-z Universe
• Faint emission-line galaxies
• SFR(z)
• Tomography of the intergalactic medium
• Stellar physics
• Brown dwarfs

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X-shooter key points for GRBs

• High sensitivity (R21.5, 1h ? S/N10)
• U to K spectrum in one shot
• Sufficient resolution
• Can be operated quickly (5-15 mins after having
  the position)
• Sturdy design

? Very well designed for exploring GRBs
environment and line of sight up to high z
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Probing GRB environment
UVES spectrum of GRB 021004 Degraded to X-shooter
resolution (5000-10000)
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High-z GRBs with X-shooter
The brightest cosmic lighthouses visible up to z
16 Stars and Structure formation in the early
Universe Line of sight aborption
Lamb Reichart, 2000
Wavelength position of absorption lines and
Lyman-? forest as a function of redshift. To the
right X-shooter spectral range with respect to
UVES
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X-shooter spectrum of GRB 021004 at z8.5
Texp 2 hr, reionization at z7, 7 hours post
burst.
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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
Limiting magnitudes 1 hour exp., S/N10 per bin
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Project constraints and characteristics

• Very Fast realization ! (SWIFT launch 2004).
• Commisioning in 2007 and operation in 2008 are
  foreseen

• Automatic operations driven by robotic
  telescopes such as REM (Chile)

• First 2nd generation instrument to be operative
• but very tight budget

• More than half budget from member states

Consortium NL,D,I,F,ESO
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X-Shooter optical layout
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French contribution I Integral Field UnitAPC,
GEPI, APC
Realised by GEPI-Observatoire de Paris
(Girafe) DRS responsibility of APC
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X-shooter FOV OT positions with IFU
X-shooter FOV with IFU (1.8 x 4) is superposed
to the angular distribution of 20 OTs in their
galaxy.

• Extended obects
• Poor pointing
• Bad seeing

Bloom et al. 2002
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French contribution II the data reduction
software

• Goals
• A robust/quick DRS
• Go from raw data to ? flux calibrated spectrum
• Can be used at the mountain
• Can be used by scientists

Exemple the VIS arm
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Echelle spectrograph
What the detector look like in ideal world
What the detector look like in real world
Curved orders Tilted lines Variable
efficiency Overlapping orders
orders
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Conclusions

• X- shooter will be the first 2nd generation
  instrument operative at VLT
• It will be the most sensitive VLT single object
  spectrograph
• Fast Operations, high sensitivity, IFU allow to
  study very faint objects
• The main scientific aim will be the GRBs with the
  possibility of detecting the farthest sources at
  the reionization epoch or beyond