TITLE:   GCN CIRCULAR
NUMBER:  37845
SUBJECT: EP241021a: 1.3m DFOT Optical observations
DATE:    24/10/23 11:12:06 GMT
FROM:    Amit Kumar Ror at ARIES <mitturor77894@gmail.com>

Amit K. Ror, Ansika Gupta, Tushar Tripathi, Shashi B. Pandey, Kuntal Mishra
(ARIES) report:


We observed the field of EP241021a detected by the Wide-field X-ray
Telescope on board the Einstein Probe mission (Einstein Probe team, Hu et
al. 2024, GCN 37834), with the 1.3m Devasthal Fast Optical Telescope
(DFOT), located at the Devasthal Observatory of the Aryabhatta Research
Institute of Observational Sciences (ARIES), India. The observations were
started on 2024-10-22 at 16:48:07 UT, i.e., ~ 1.49 days after the Einstein
Probe trigger. We have taken multiple frames with an exposure time of 300 s
in the R filter. The observations were taken in the bright moon phase. We
stacked the images after the alignment. We clearly detected optical
emission in our stacked image within the error box of the transient
position by Fu et al. 2024 (GCN 37840). We obtain the following preliminary
magnitude in the stacked image:


Date Start_UT T_start-T0 (days) Filter  Exp time (s)  Magnitude

=========================================================

2024-10-22 16:48:07     1.49     R     300s*12     21.62 +/- 0.10


Our detection is consistent with Gompertz et al. 2024, GCN 37835; Lipunov et
al. 2024, GCN 37839; Fu et al. 2024, GCN 37840; Fu et al. 2024, GCN 37842; Yang
et al. 2024, GCN 37843; and Li et al. 2024, GCN 37844


The magnitude is not corrected for the Galactic extinction in the direction
of the burst. Photometric calibration is performed using the standard stars
from the USNO-B1.0 catalogue. This circular may be cited.