A Note on the Phase Law and Light Curve of Comet Tsuchinshan-ATLAS (C/2023 A3)

TL;DR

This paper analyzes the light curve of comet Tsuchinshan-ATLAS, revealing intrinsic brightness variations, a steep phase law, and ongoing activity surges related to fragmentation, with implications for understanding comet brightness behavior.

Contribution

It provides a detailed analysis of the comet's light curve and phase law, highlighting the intrinsic brightness and activity patterns during its observed period.

Findings

Intrinsic brightness was consistent in late March and early May.

The phase law is very steep, indicating strong phase angle effects.

The comet's activity surged again in May and June due to fragmentation.

Abstract

The light curve of comet Tsuchinshan-ATLAS peaked in mid-April 2024, which nearly coincided with a minimum phase angle of 2.9 deg. The question of a possible correlation between the two events has implications for the comet's overall performance. In this note I examine the light curve at times of equal phase angles to circumvent the effect and show that the comet was as bright intrinsically in late March as it was in early May. From a plot of the comet's magnitude at unit geocentric distance against the phase angle before and after its minimum on 18 April I derive a very steep phase law and a relatively flat, r^(-2.55) light curve failing to fit the recently reported magnitudes. After stalling in May and June, the comet's activity enters another surge (at a time of peak phase effect), as fragmentation continues.