Interpreting Flux from Broadband Photometry

TL;DR

This paper reviews methods for converting broadband photometry into flux for spectral energy distributions, emphasizing the importance of using spectra consistent with observations to improve accuracy, especially in UV wavelengths.

Contribution

It introduces improved techniques for transforming photometry into flux, advocating for spectral-based integration over traditional magnitude-to-flux conversions, applicable across various wavelengths.

Findings

Traditional magnitude-to-flux conversions can be inaccurate in UV.

Spectral-based flux integration yields more reliable results.

Recommendations improve bolometric luminosity calculations.

Abstract

We discuss the transformation of observed photometry into flux for the creation of spectral energy distributions and the computation of bolometric luminosities. We do this in the context of supernova studies, particularly as observed with the Swift spacecraft, but the concepts and techniques should be applicable to many other types of sources and wavelength regimes. Traditional methods of converting observed magnitudes to flux densities are not very accurate when applied to UV photometry. Common methods for extinction and the integration of pseudo-bolometric fluxes can also lead to inaccurate results. The sources of inaccuracy, though, also apply to other wavelengths. Because of the complicated nature of translating broad-band photometry into monochromatic flux densities, comparison between observed photometry and a spectroscopic model is best done by comparing in the natural units of the observations. We recommend that integrated flux measurements be made using a spectrum or spectral energy distribution which is consistent with the multi-band photometry rather than converting individual photometric measurements to flux densities, linearly interpolating between the points, and integrating. We also highlight some specific areas where the UV flux can be mischaracterized.