AstroNote 2024-108

Simultaneous multi-band (uvgriz) photometric observations of AT 2024ggi (ATLAS24fsk) (AstroNotes 2024-100, Srivastav et al., 2024-101, Killestein et al., 2024-102, Chen et al., 2024-103, Hoogendam et al., 2024-104, Zhai et al., 2024-105, Yang et al., 2024-107, Pérez-Fournon et al.) field were performed under moderate sky conditions (seeing ~1.3”) starting from 14:57 UT, 2024-04-11 (~11.6 hr after the ATLAS discovery, AstroNotes 2024-100). The observations were acquired using the Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University at Lijiang Observatory (IAU code: 044) of Yunnan Astronomical Observatories, Chinese Academy of Sciences. As the source was at a lower altitude, the observations began with 50 cm twin telescopes (g, r, i, z bands), and later, 1.6m was also utilized. The pre-processing and preliminary photometry of the images were done with automatic data reduction and photometry pipeline developed for the Mephisto. Here, we note that the Mephisto filter system (u, v, g, r, I, and z) mean transmission wavelengths are 345, 385, 530, 630, 837, and 945 nm, and the effective band widths are 38, 37, 79, 102, 109 and 71 nm.

SourceURL:file:///home/brajesh/Documents/Circular-SN2024ggi.docx

The preliminary photometric magnitudes of initial frames are below:

u = 16.12 +/- 0.02,

v = 16.07 +/- 0.01,

g = 16.04 +/- 0.01,

r = 15.94 +/- 0.01,

i = 16.12 +/- 0.02,

z = 16.13 +/- 0.02 mag.

The expected Galactic foreground extinction and the host contamination have not been removed from the estimated magnitudes. Further analysis is in progress, and monitoring will be continued in the upcoming nights.

Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.