{
  "bibcode": "2009GCN..9261....1K",
  "body": "T. Kruehler, J. Greiner and F. Olivares (all MPE Garching) report on behalf\nof the GROND team:\n\nWe obtained a second epoch of imaging of the field of GRB 090423 (Swift \ntrigger 350184, H. Krimm et al., GCN #9198), which started on 25 Apr. 2009 \nat 00:44 UT, 40.8 h after the trigger.\n\nIn the second epoch, the NIR afterglow (Tanvir et al. GCN #9202) is \nundetected in stacked images with a total integration time of 4800~s in \neach of J, H and K down to limiting AB magnitudes of J_AB > 22.7, H_AB > \n22.3 and K_AB > 21.6.\n\nTogether with the magnitudes reported in Olivares et al. (GCN #9215) this \nimplies a fading with a power law index faster than 1.2. This lower limit \non the temporal decay index is consistent with that found for the X-ray \nafterglow at a similar time interval (G. Stratta & M. Perri, GCN #9212).\n\nIn addition we report on a refined analysis of the GROND photo-z from \nOlivares et al. (GCN #9215). Using an improved photometric calibration and \nincluding the deep z' band upper limit from Perley et al. (GCN #9217) which \nis contemporaneous to our GROND imaging, we find a refined photometric \nredshift of 8.0+0.4-0.8 (90% confidence level). The error range is unlikely \nto improve due to the gap between the z' and J bands (for the negative \nerror), and the width of the J filter band (for the positive error).\n\nThis range covers the previous claims from photometric (GCNs #9213, #9215, \n#9217) and spectroscopic observations (GCNs #9219, #9222). The SED is well \ndescribed with a power law of index ~1. No signatures of intrinsic dust are \nevident with an upper limit of A_V < 0.5, assuming a SMC dust reddening \ntemplate.",
  "circularId": 9261,
  "createdOn": 1240771120000,
  "email": "kruehler@mpe.mpg.de",
  "subject": "GRB 090423: GROND second epoch imaging and refined SED",
  "submitter": "Thomas Kruehler at MPE/MPI  <kruehler@mpe.mpg.de>",
  "eventId": "GRB 090423"
}