  The first JWST observations of TRAPPIST-1 c showed a secondary eclipse depth
of 421+/-94 ppm at 15 um, which is consistent with a bare rock surface or a
thin, O2-dominated, low CO2 atmosphere (Zieba et al. 2023). Here, we further
explore potential atmospheres for TRAPPIST-1 c by comparing the observed
secondary eclipse depth to synthetic spectra of a broader range of plausible
environments. To self-consistently incorporate the impact of photochemistry and
atmospheric composition on atmospheric thermal structure and predicted eclipse
depth, we use a two-column climate model coupled to a photochemical model, and
simulate O2-dominated, Venus-like, and steam atmospheres. We find that a
broader suite of plausible atmospheric compositions are also consistent with
the data. For lower pressure atmospheres (0.1 bar), our O2-CO2 atmospheres
produce eclipse depths within 1$\sigma$ of the data, consistent with the
modeling results of Zieba et al. (2023). However, for higher-pressure
atmospheres, our models produce different temperature-pressure profiles and are
less pessimistic, with 1-10 bar O2, 100 ppm CO2 models within 2.0-2.2$\sigma$
of the measured secondary eclipse depth, and up to 0.5% CO2 within 2.9$\sigma$.
Venus-like atmospheres are still unlikely. For thin O2 atmospheres of 0.1 bar
with a low abundance of CO2 ($\sim$100 ppm), up to 10% water vapor can be
present and still provide an eclipse depth within 1$\sigma$ of the data. We
compared the TRAPPIST-1 c data to modeled steam atmospheres of $\leq$ 3 bar,
which are 1.7-1.8$\sigma$ from the data and not conclusively ruled out. More
data will be required to discriminate between possible atmospheres, or to more
definitively support the bare rock hypothesis.
