[vsnet-grb-info 28095] GRB 210610B: University of Siena Observatory optical photometry of the afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30198
SUBJECT: GRB 210610B: University of Siena Observatory optical photometry of the afterglow
DATE:    21/06/11 14:25:00 GMT
FROM:    Simone Leonini at Monarrenti Obs  <s.leonini at iol.it>

Alessandro Marchini, Andrea Lorini (University of Siena Observatory, Siena,
Italy), Simone Leonini (Montarrenti Observatory, Sovicille (SI), Italy),
Giacomo Bonnoli (IAA-CSIC, Granada, Spain) report:

We observed the field of GRB 210610B (Swift trigger 1054681, K.L. Page et al., GCN Circ. 30170) with the 0.3 m telescope  at University of Siena Observatory (Siena, Italy, K54). The GRB was extensively observed at all wavelengths, including optical photometry from many observatories (see e.g GCN Circulars 30173, 30174, 30175, 30176, 30177, 30178, 30180, 30181, 30185, 30187, 30188, 30190, 30191, 30193).

Our observations began under good weather conditions at 2021-06-10 20:37:53 UT (~0.75 h after GRB onset) with a series of 300s CCD exposures in the Rc filter, that were later added in groups of four for the photometry and further analysis.
The optical afterglow was clearly detected at a sky position in agreement with the UVOT astrometry reported in GCN Circ. 30170.
Our data cover continuously almost 6 hours of observations until the field set below the dome horizon. 

The preliminary Rc-band photometry was calibrated with stars from the APASS10 catalog (Henden et al., 2019) after conversion between the two photometric systems with the simple formula from Dymock & Miles (2009) for the CMC15 catalog: Rc=r’-0.22. Measurements are not corrected for galactic extinction. Reported uncertainties are statistical only.

The first and last measurements of our series are reported hereafter:

2021-06-10 h. 20:50 UT JD 2459376.368287, R = 16.83 ± 0.04
2021-06-11 h. 02:26 UT JD 2459376.601458, R = 17.52 ± 0.16

The evolution of the brightness is, within the limits of our precision, compatible with a single decay rate with index alpha=0.25 ± 0.04

Any enquiry on these observations can be addressed either to Alessandro Marchini (marchini at unisi.it) or to Giacomo Bonnoli (bonnoli at iaa.es). 

A brief description of our instrumental setup is available at the official webpage of the Astronomical Observatory of the University of Siena:
https://www.dsfta.unisi.it/en/research/labs/astronomical-observatory