TITLE: GCN CIRCULAR NUMBER: 21920 SUBJECT: LIGO/Virgo G298048: Effelsberg 100-m Radio Telescope observations of SSS17a DATE: 17/09/23 20:34:41 GMT FROM: Samaya Nissanke at Redboud U 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) using the position provided by Adams et al. (LVC GCN 21816). 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 Müller 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.