TITLE:   GCN CIRCULAR
NUMBER:  21914
SUBJECT: LIGO/Virgo G298048: SRT observations of SSS17a in NGC 4993
DATE:    17/09/22 19:06:44 GMT
FROM:    Enzo Brocato at INAF-OA Roma  <enzo.brocato@oa-roma.inaf.it>

Giambattista Aresu, Matteo Bachetti, Franco Buffa, Marta Burgay, Marco 
Buttu, Teresa Caria, Ettore Carretti, Paola Castangia, Giuseppe Carboni, 
Silvia Casu, Raimondo Concu, Alessandro Corongiu, Gianluigi Deiana, 
Elise Egron, Antonietta Fara, Francesco Gaudiomonte, Vincenzo Gusai, 
Adelaide Ladu, Sara Loru, Silvia Leurini, Lino Marongiu, Andrea Melis, 
Pino Melis, Carlo Migoni, Sabrina Milia, Alessandro Navarrini, Andrea 
Orlati, Pierluigi Ortu, Stefano Palmas, Alberto Pellizzoni, Delphine 
Perrodin, Maura Pilia, Tonino Pisanu, Sergio Poppi, Andrea Possenti, 
Andrea Saba, Giampaolo Serra, Mauro Serrau, Gabriele Surcis, Alessio 
Trois, Valentina Vacca, Gian Paolo Vargiu - all from INAF Osservatorio 
Astronomico di Cagliari
Viviana Casasola - INAF Osservatorio Astrofisico di Arcetri
Giancarlo Ghirlanda - INAF Osservatorio Astronomico di Brera
Simona Righini, Matteo Stagni - INAF Istituto di Radioastronomia di Bologna
on behalf of GRAvitational Wave Inaf TeAm (GRAWITA) report:.

Following the VLA detection of a radio source (Mooley et al., LVC GCN 
21814; Corsi et al., LVC GCN 21815) coincident with the optical 
transient SSS17a/DLT17ck (Coulter et al. LVC GCN 21529; Allam et al., 
LVC GCN 21530; Yang et al., LVC GCN 21531), the possible counterpart of 
G298048 (LVC, LVC GCN 21505) in NGC 4993, we carried out observations of 
the field with the Sardinia Radio Telescope at 7.2 GHz (central 
frequency, with a bandwidth of 680 MHz). Observations were conducted on 
the days 2017-09-07, 2017-09-08, 2017-09-09, and 2017-09-19, for a total 
of approximately 18 hours of on-the-fly mapping over the entire 
region and about 8 minutes of on-source time. The target was observed at 
low elevations (<27 degrees) and the weather conditions were suboptimal 
for a large fraction of the observing time.

Data were taken to image a field of 0.3x0.3 deg^2 centred on the position
of the source that was reported to be detected with the VLA on 2017-09-03.
Calibration and analysis were conducted following two different
approaches:

- according to the procedures described in Egron et al. (2017,MNRAS, 470, 1329), we did
not detect any source and find an upper limit for a steady source at the
position of the target of 1.5 mJy (1 sigma) and a global rms of the image
of 0.9 mJy/beam (1 sigma);

- by using the map-making software described in Carretti et al. (2010, MNRAS, 405, 1670), 
 we did not detect any source at that position, at an upper limit of
0.5 mJy rms (1 sigma) as computed for a steady source.

According to the condition of each single observation, we find an upper
limit ranging between at most 1 and 3 mJy for each observing session. At
present a refinement of the analysis is ongoing and observations at
subsequent epochs and at higher frequencies are planned.

-- 
Enzo Brocato
INAF - Osservatorio Astronomico di Roma
Via di Frascati 33,  
I-00040 Monteporzio Catone, Italy
Phone:  +39 0694286438 Fax: +39 06 9447243
skype: enzo.brocato
URL: SpoT Group Homepage: www.oa-teramo.inaf.it/SPoT