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GCN Circular 34020

LIGO/Virgo/KAGRA S230615az: GRANDMA observations of GOTO and GIT candidates
2023-06-19T10:22:54Z (a year ago)
Aleksandra Pyshna at Astronomical Observatory of Taras Shevchenko National University of Kyiv, Kyiv, Ukraine <>
R. Strausbaugh (UMN), O. Pyshna (AO TSNU of Kyiv), T. du Laz (CIT),
S. Pormente (OCA), A. Takey, A. Shokry, A. Fouad, M. Molham, A. Tawfeek
(NRIAG), S. Antier (OCA), M. Coughlin (UMN), P. Hello (IJCLAB),
S. Karpov, M. Prouza, M. Mašek, M. Blazek (FZU), A. Klotz (IRAP),
T. Pradier (Univ. Strasbourg), I. Tosta e Melo (UNICT), D. Turpin (CEA),
O.Burkhonov (UBAI), S.Ehgamberdiev (UBAI, NUUz), Y.Rajabov (UBAI),
T.Sadibekova (UBAI-CEA), Y.Tillayev (UBAI, NUUz), Xinglong ,
F. Guo (THU), X. F. Wang (THU), Y. Zhu (NAOC), J. Zhang (NAOC),
R. Inasaridze, R. Natsvlishvili, N. Kochiashvili, S. Beradze,
V.Aivazyan (AbAO), report on behalf of the GRANDMA collaboration:

The GRANDMA telescope network responded to the GOTO and GIT triggers
from LIGO/Virgo/KAGRA S230615az (Gompertz et al., GCN 33979, Kumar et al.,
GCN 33974, TNS 2023kvr).

The first observations started 20 hours after the reported detection
time from the sources candidates.

As time reference (T0), we choose:
for GOTO23hn 2023-06-15T21:27:14.688 UT (60110.89392 MJD)
for GOTO23hu 2023-06-15T21:35:15.936 UT (60110.89949 MJD)
for GIT230615aa 2023-06-15T18:30:26.928 UT (60110.77114 MJD)
for GIT230615ab 2023-06-15T18:53:10.838 UT (60110.78693 MJD)

In the following table we report a subset of the preliminary photometry
of our observations. Upper limits are reported as the faintest
source detected in frame; magnitudes and upper limits are reported
in the AB system.

T-T0 (day) |MJD   | Obser.   |Exposure| Filter | Mag +/- err  |Upp.Lim. (AB)
0.847|60111.74163|AbAO-T70|14x60s|R| - | > 20.6
0.956|60111.84993|KAO|7x120s|sdssr| 18.9 +/- 0.05 |     -
1.038|60111.93207|FRAM-CTA-N|28x120s|R| - |     > 18.7

T-T0 (day) |MJD   | Obser.   |Exposure| Filter | Mag +/- err  |Upp.Lim. (AB)
0.862|60111.76180|AbAO-T70|15×60s|R| - | > 20.9
0.984|60111.88393|FRAM-CTA-N|29x120s|R| - |     > 18.6

T-T0 (day) |MJD   | Obser.   |Exposure| Filter | Mag +/- err  |Upp.Lim. (AB)
0.939|60111.71026|UBAI-NT60|10x180s|R| - |     > 20.3
0.942|60111.72810|SNOVA|2x180s|C| - |     > 19.2
1.099|60111.87106|KAO|7x120s|sdssr| - |     > 20.3

T-T0 (day) |MJD   | Obser.   |Exposure| Filter | Mag +/- err  |Upp.Lim. (AB)
0.954|60111.72906|SNOVA|1x180s|C| - |     > 18.5
0.997|60111.78488|AbAO-T70|12×60s|R| - | > 21
1.037|60111.82444|KAO| 7x120s |sdssr| - |     > 21.3

KAO data has been calibrated with respect to the PS1 catalog.
FRAM-CTA-N data has been calibrated with respect to the APASS catalog.
Abastumani-T70 data has been calibrated with respect to the PS1 catalog.

This single detection of GOTO23hn indicates that the source is either flat
or increasing in brightness, but we note the difficulty of comparing
this narrow-band value to the original wide-band detection by GOTO.

GRANDMA is a worldwide coordinated telescope network
(  devoted to the observation of transients
in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS
497, 5518). Kilonova-Catcher (KNC) is the citizen science program of
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