Pre-ALMA observations of GRBs in the mm/submm range
  GRBs generate an afterglow emission that can be detected from radio to X-rays
during days, or even weeks after the initial explosion. The peak of this
emission crosses the mm/submm range during the first hours to days, making
their study in this range crucial for constraining the models. Observations
have been limited until now due to the low sensitivity of the observatories in
this range. We present observations of 10 GRB afterglows obtained from APEX and
SMA, as well as the first detection of a GRB with ALMA, and put them into
context with all the observations that have been published until now in the
spectral range that will be covered by ALMA. The catalogue of mm/submm
observations collected here is the largest to date and is composed of 102 GRBs,
of which 88 had afterglow observations, whereas the rest are host galaxy
searches. With our programmes, we contributed with data of 11 GRBs and the
discovery of 2 submm counterparts. In total, the full sample, including data
from the literature, has 22 afterglow detections with redshift ranging from
0.168 to 8.2. GRBs have been detected in mm/submm wavelengths with peak
luminosities spanning 2.5 orders of magnitude, the most luminous reaching
10^33erg s^-1 Hz^-1. We observe a correlation between the X-ray brightness at
0.5 days and the mm/submm peak brightness. Finally we give a rough estimate of
the distribution of peak flux densities of GRB afterglows, based on the current
mm/submm sample. Observations in the mm/submm bands have been shown to be
crucial for our understanding of the physics of GRBs, but have until now been
limited by the sensitivity of the observatories. With the start of the
operations at ALMA, the sensitivity will be increased by more than an order of
magnitude. Our estimates predict that, once completed, ALMA will detect up to
98% of the afterglows if observed during the passage of the peak synchrotron
emission.
