TITLE:   GCN CIRCULAR
NUMBER:  9322
SUBJECT: GRB 090423: 250 GHz upper limit for a z=8.2 GRB with MAMBO-2 at the IRAM 30m
DATE:    09/05/04 18:21:20 GMT
FROM:    Dominik A. Riechers at Caltech  <dr@caltech.edu>

D. A. Riechers (Caltech), F. Walter (MPIA Heidelberg), F. Bertoldi
(AIfA Bonn), C. L. Carilli (NRAO), P. Cox (IRAM), C. Kramer (IRAM),
D. Riquelme (IRAM) report:

"We used the Max-Planck-Millimeter Bolometer (MAMBO-2) array at the
IRAM 30-m telescope to observe the field of view toward the host
galaxy of GRB 090423 (GCN 9198) at redshift z=8.2 (GCN 9219), RA
09:55:33.19, Dec +18:08:57.7 (J2000) at 250 GHz. Observations were
carried out for 4.5 hr on 2009 April 25, centered at UT 18.5.  We
obtained a non-detection of

    S_nu(250 GHz,1.20 mm) = 0.23 +/- 0.32 mJy

(1 sigma error), i.e. a 3 sigma upper flux density limit of 0.96 mJy
on the GRB afterglow and the dust continuum in the host galaxy at 1.2
mm (rest-frame 130 um). Together with the 3 mm observations carried
out at the Plateau de Bure Interferometer (GCN 9273), this indicates a
flat spectral slope at millimeter wavelengths. The 117-element MAMBO-2
bolometer detectors cover 210-290 GHz (half power). The bolometers
have a FWHM beam size of 10.7 arcsec, at a pixel spacing of 20
arcsec. Observations were carried out in ON-OFF observing mode under
good weather conditions, with low sky noise and opactities of
tau=0.1-0.26 (derived from skydips). Calibrations were performed on
CW-LEO.

We acknowledge the excellent support of the staff at IRAM. IRAM is
supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). This
message may be cited."