Jochen Greiner - 1

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GROND an optical/NIR 7-channel
imager Capabilities for transient follow-up
Jochen Greiner Max-Planck Institut für
extraterrestrische Physik Garching, Germany
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GRB Afterglow and Light Curve
Afterglow emission at radio, optical, and NIR
wavelengths
12 hrs
2 hrs
48 hrs
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Quickly finding high-redshift GRBs

• Due to characteristic powerlaw spectrum of GRB
  Afterglow
• Derive redshifts from simultaneous photometry in
  7 filters.

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GRONDGRB Optical/NIR Detector
Imaging in 7 channels simultaneously
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GROND _at_ 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
d-twister
cryostat
GROND
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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 1K1K Arrays 4 E2V
  2K2K CCDs
• Field-of-view Visual 5.4x5.4
  (0.16/pixel) NIR 10x10
  (0.59/pixel)
• Dichroics tuned to minimize intrinsic
  polarization effects
• 2 shutters, i.e. gr and iz pairs of CCDs have
  same exposure
• Combined telescope and intrinsic mirror (K-band)
  dithering
• Sensitivity 4 min 1 hr gr 22.0
  mag 25.0 mag (AB) iz 21.5 mag 24.5 mag
  (AB) J/H/K 20/19.5/19 mag 23/22.5/22 mag (AB)

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Example of GROND sensitivity

• 7 filter bands cover Lyman-a for large z-range
  3ltzlt13
• GROND has proper z-band sensitivity to define
  drop-out for z8

Advantage of separate detector per filter can
add sensibilization for spectral band ?
GROND_at_2.2m detector/filter is 4x more sensitive
than FORS2 ? total efficiency only 4x less
than FORS2, not 16 (8.22/2.22)
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Photometric redshifts for GRBs
GRB 080913 at redshift 6.7
1st exposure starts T06 min T015 min XRT
position T035 min first SED (S of 3 OBs 16
min expo) T090 min VLT starts taking spectrum
with proper grism (5 mag fainter than 050904)
Greiner et al. 2009
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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 zirg
KHJ zirg
0.2-10 keV
GRB 080710
GRB 070802
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Seeing dust in SEDs
GRB 070802 first 2200 A bump at z2.45
Krühler et al. 2008
SED at 2000 sec after GRB
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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
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Chromatic flares
GRB 080129
GRB 081029
Nardini et al. 2012
Greiner et al. 2009
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Multi-filter light curves
SN 2009mg

Pulsar Fermi J1311-3430
WASP-4
Porb 93 min
Romani2012
Nikolov2012
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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
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Contemporaneous UV-NIR SEDs of blazars

• gt100 observed in 1 yr
• doubled of known BL Lac at zgt1.2
• High-z BL Lacs interesting for various
  applications, e.g. EBL studies

Rau et al. 2011.
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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
  kindsuse for GRBs is being reduced
• Presently contracted telescope access until 9/2016