GROND an optical/NIR 7-channel imager: Capabilities for transient follow-up Jochen Greiner Max-Planck Institut für extraterrestrische Physik Garching, Germany

GRB Afterglow and Light Curve Afterglow emission at radio, optical, and NIR wavelengths ~2 hrs ~12 hrs ~48 hrs

Quickly finding high-redshift GRBs Due to characteristic powerlaw spectrum of GRB Afterglow: Derive redshifts from simultaneous photometry in 7 filters.

GROND=GRB Optical/NIR Detector Imaging in 7 channels simultaneously K J H g r i z

GROND @ 2.2m MPI telescope (La Silla) History: First light: Apr 30, 2007 First GRB: May 21, 2007 Photometric calibration: Jul 2007 Routine observations: since Sep 2007 fastest response time: 2 min H K J Electronics M3 cryostat δ-twister cryostat GROND

GROND: General Design 7 bands: Sloan g’, r’, i’, z’ and J, H, K One detector for one filter band (no movable filters!) 3 HAWAII 1K*1K Arrays + 4 E2V 2K*2K CCDs Field-of-view: Visual: 5.4´x5.4´ (0.16´´/pixel) NIR: 10´x10´ (0.59´´/pixel) Dichroics tuned to minimize intrinsic polarization effects 2 shutters, i.e. g’r’ and i’z’ pairs of CCDs have same exposure Combined telescope and intrinsic mirror (K-band) dithering Sensitivity: 4 min 1 hr g’r’ 22.0 mag 25.0 mag (AB) i’z’ 21.5 mag 24.5 mag (AB) J/H/K 20/19.5/19 mag 23/22.5/22 mag (AB)

Example of GROND sensitivity 7 filter bands cover Lyman-α for large z-range: 3<z<13 GROND has proper z-band sensitivity to define drop-out for z~8 Advantage of separate detector per filter: can add sensibilization for spectral band:  GROND@2.2m detector/filter is 4x more sensitive than FORS2  total efficiency only 4x less than FORS2, not 16 (8.22/2.22)

Photometric redshifts for GRBs GRB 080913 at redshift 6.7 1st exposure starts T0+6 min T0+15 min: XRT position T0+35 min: first SED (Σ of 3 OBs = 16 min expo) T0+90 min: VLT starts taking spectrum with proper grism (5 mag fainter than 050904) Greiner et al. 2009

Combined GROND-Swift/XRT SEDs Some GRB afterglow SEDs extend from 240 nm to 10 keV with single power law; most with slope break of 0.5 in both cases: sensitive to extinction AV and/or Ly-break Greiner et al. 2011 KHJ z’i’r’g’ KHJ z’i’r’g’ 0.2-10 keV GRB 080710 GRB 070802

Seeing dust in SEDs GRB 070802: first 2200 A bump at z=2.45 Krühler et al. 2008 SED at 2000 sec after GRB

SEDs every minute GRB 071031 First image: 4 min after GRB onset, ~80 sec after trigger 1st night: 6 hrs continuous exposure; 350 data points ß-evolution (instead of one for all AG) Krühler et al. 2008

Chromatic flares GRB 080129 GRB 081029 Nardini et al. 2012 Greiner et al. 2009

Multi-filter light curves SN 2009mg Multi-filter light curves Pulsar Fermi J1311-3430 WASP-4 Porb = 93 min Romani+2012 Nikolov+2012

Recognize ‘thermal’ transients With 7 filter bands you always get an SED Transient classification according to SED: allows to distinguish other types of transients, e.g. accretion-disk dominated galactic transients “GRB” 100331A  likely galactic transient

Contemporaneous UV-NIR SEDs of blazars >100 observed in 1 yr doubled # of known BL Lac at z>1.2 High-z BL Lacs interesting for various “applications”, e.g. EBL studies Rau et al. 2011.

Transient follow-up GROND is built for rapid (min), automatic response Simultaneous 7-filter broad-band coverage is helpful for identification Particularly advantageous for color changes along with intensity changes GROND science goals include transients of all kinds; use for GRBs is being reduced Presently contracted telescope access until 9/2016