TITLE:   GCN CIRCULAR
NUMBER:  24485
SUBJECT: LIGO/Virgo S190510g: GRAWITA REM and Loiano optical observations
DATE:    19/05/11 15:55:17 GMT
FROM:    Aniello Grado at INAF-OAC  <aniello.grado@gmail.com>

P. D'Avanzo (INAF-OAB), E. Palazzi (INAF-OAS), G. Greco (Univ. Urbino), S.
Yang (INAF-OAPd), S. Campana (INAF-OAB), G. Stratta (INAF-OAS), A. Rossi
(INAF-OAS), Nicola Masetti (inaf-oas) and E. Brocato on behalf of GRAWITA
report:


We carried out further optical follow-up observations of the LIGO/Virgo GW
trigger S190509g (LVC, GCN Circ. 24442) with the 60-cm robotic telescope
REM located at the La Silla Observatory (Chile). The observations started
at 2019-05-11 at 00:49:48 UT, simultaneously in the g, r, i, z bands (the
REM NIR camera was not operational).
We observed the following galaxies within the 50% probability of the
updated skymap visible from La Silla:


RA(J2000) Dec(J2000) Dist(Mpc)
----------------------------------------------------
J055219-342051   05:52:19.00   -34:20:51.4   138.68
J055149-314446   05:51:49.92   -31:44:46.0   210.86
J054827-325838   05:48:27.60   -32:58:38.1   160.69
J060115-313225   06:01:15.09   -31:32:25.5   191.43
J055425-350235   05:54:25.29   -35:02:35.1   143.88
J055028-334429   05:50:28.73   -33:44:29.3   165.20
J055740-345601   05:57:40.71   -34:56:01.8   146.97
J055949-353200   05:59:49.81   -35:32:00.5   138.04

No clear counterpart for S190509g is found down to a typical 3sigma
magnitude of r > 19 (AB).

We also carried out optical follow-up of the possible transient we reported
in D'Avanzo et al. (GCN Circ. #24455) found in REM images at RA(J2000),
Dec(J2000) = 14:29:15.99, +09:41:12.3 with magnitude r = 17.3 (AB) on
2019-05-10 at 08:07:18 UT. Optical imaging follow-up observations of this
possible transient were carried out with the 1.5m Loiano telescope (Italy)
in the R band on 2019-05-10 at 20:44:08 UT (i.e. about 12.6 hours after the
REM detection reported in GCN Circ. #24455). In the Loiano images the
object is not detected down to a 3-sigma limiting magnitude of R > 20.3
(AB, calibrated against the SDSS). This non-detection is in agreement with
the findings reported by Zhu et al. (GCN Circ. #24479) and favor a fast
transient (like a stellar flare) interpretation for the nature of this
object, although the hypothesis of an image artifact cannot be completely
excluded.