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X-shooter A Wideband Spectrograph for GRBs

X-shooter A Wideband Spectrograph for GRBs. P. Goldoni, P. Filliatre On behalf of a larger collaboration. “Call for proposals for 2nd Generation VLT Instruments” ( http://www.eso.org/instruments/vlt2ndgenins.html ). R~ 10 4 wide-band visible-NIR high-throughput Spectrometer.

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X-shooter A Wideband Spectrograph for GRBs

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  1. X-shooterA Wideband Spectrograph for GRBs P. Goldoni, P. Filliatre On behalf of a larger collaboration

  2. “Call for proposals for 2nd Generation VLT Instruments” (http://www.eso.org/instruments/vlt2ndgenins.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 R~5000-10000 in one shot

  3. 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

  4. X-shooter key points for GRBs • High sensitivity (R=21.5, 1h  S/N=10) • 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

  5. Probing GRB environment UVES spectrum of GRB 021004 Degraded to X-shooter resolution (5000-10000)

  6. 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

  7. X-shooter spectrum of GRB 021004 at z=8.5 Texp = 2 hr, reionization at z=7, 7 hours post burst.

  8. 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/N=10 per bin

  9. 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

  10. VIS arm UVB arm backbone 1st dichroic 2nd dichroic NIR arm X-Shooter optical layout

  11. French contribution I: Integral Field UnitAPC, GEPI, APC Realised by GEPI-Observatoire de Paris (Girafe): DRS responsibility of APC

  12. 100% 66% 66% 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

  13. 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

  14. the object lines Wavelength axis Space axis 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

  15. 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

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