Analysis of SN 2023bch in NGC5784

The light curve was acquired with the following equipment:
-        LX850 @FD=8
-        QHY 268 M
-        Chroma R, G, B filter set

Each point consisted in 5 to 6 x 5mn exposures thru each filter.

The SN2023bch was imaged for light curve during the nights of 2, 4, 5, 6, 7, 11, 13, 15, 16, 19, 27 of February and 3 & 18 of March 2023.

The main difficulty with this SN is that it is superposed to the core of the galaxy.
The SN mag was obtained from the difference of flux in this region at various date with the flux measured on the 18 of March where the SN was supposed very faint.
In the points displayed below, the SN flux represent only 25% to less than 10% of the total flux.

The color calibration of the filters was performed in PI using APASS catalog with stars in the field of view. In particular, the B filter was calibrated using the APASS Blue channel and the APASS B-V index.

Note that the measurement at t=+17.5 days is the average of the 4 measurements on 11, 13, 15 and 16 of February.
The was necessary to improve the accuracy of this measurement point.

According to Purdue database, the supernova maximum occurred on January  the 27.
From our data at the maximum, the B mag = 15.3
At T max + 15 days, the B mag was recorded at 16.3.
The SN absolute magnitude of the maximum was estimated at Mmax(B) = -19.0, using the Phillips relationship (Wikipedia)  
The total reddening (due to both interstellar dust and NGC5784 dust), was estimated using the differences between B and V channels at:
-        tmax                           : where a pristine SN shows a B-V of 0.0
-        tmax + 15                   : where a pristine SN shows a B-V of 1.1
In our case these two values are consistent with near zero reddening.
Note that the NASA interstellar extinction calculator indicate values less than 0.1 mag for all R, V, B in this area of the sky. 

All this set the galaxy distance at 230 M Light-Years or 70 M parsecs. 

The error range was estimated from the individual image magnitude dispersion, and the fact that the SN mag was obtained as the difference between two flux measurements.
This compare reasonably well with available distance from scientific publications (see below).


For more details on the photometry procedure, please refer to the analysis of SN2021hiz : https://astrob.in/uz0ex5/0/