GCN Circular 21920

M. Kramer, A. Kraus, R. Eatough (MPI fuer Radioastronomie)

The 100-m Effelsberg telescope of the MPIfR  observed the location of SSS17a 
(Coulter et al. 2017, LVC GCN 21529
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 ) using the position provided by Adams et al.
(LVC GCN 21816
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 ). Observations were conducted at 5, 15 and 32 GHz; none of them
detected a counterpart.

Observations at 32 GHz were performed at 10/9/2017 at UT 13:35 with the 100m telescope under moderate weather 
conditions using its secondary focus 9mm multi-beam receiver. In total, six maps were performed
on the position of SSS17a. Data analysis was done with the MPIfR���s software packages 
���Toolbox��� and ���Nod3��� (see M��ller et al., 2017). First, some weather effects were removed by 
subtracting the maps of one of the ���Off���-Horns from the ���On���-Horn. After some additional
baseline adjustment, the data was averaged and calibrated in Jy. Calibration parameters 
were determined by a similar observation of 3C286. The rms of the final map was 30 mJy 
(due to imperfect weather conditions and low elevation). Efforts are ongoing to
improve those limits.

Observations at C-band were also conducted at 10/9/2017 13:10 UT.  No source was detected and limits do not
improve on previous reports (e.g. Paragi et al., LVC CGN 21763; Alexander et al., LVC CGN 21851).

At a central frequency of 14.6 GHz, we used a cryogenically cooled
receiver (summed polarisations for 128 spectral channels, across a
bandwidth of 500 MHz, and with a data sampling interval of ��� 65 us) on
15/9/2017 (MJD 58011.537210648) for approximately 4025 seconds. Data
have been dedispersed in the range 0 to 50 000 pc cm���3 and analysed
for periodic signals and transient burst like events (e.g. FRBs) using
single pulse search tools in the presto software package
(http://www.cv.nrao.edu/ sransom/presto/).

For a 10-sigma detection threshold, we achieve the following limits to
periodic signals: 76 uJy and 52 uJy for duty cycles of 10% and 5%,
respectively. Note that at this frequency, weather effects can
decrease the sensitivity by at least a factor of two. More accurate
flux calibration using a noise diode and reference source is on-going.

At this observing frequency our transient search has revealed signals
that cannot yet be easily distinguished from terrrestrial radio
interference. Sensitivity limits for transients depend upon the
unknown intrinsic pulse width and pulse broadening factors, however
for a single pulse of width 1,3,5 and 10 ms, and DM of 1000 pc cm���3
(smearing at the central frequecny channel = 10.414 us), we find
6-sigma flux density limits of 0.32, 0.19, 0.15 and 0.10 Jy
respectively.