Verification of the Swift UVOT Grism Flux Calibration (2013)ΒΆ

The verification has been split up by grism mode. The plots of the spectra below are showing wavelength offsets consistent with the determination of the anchor accuracy in 2014 which has been discussed elsewhere. The visible grism observations were mostly done without a lenticular filter, while the uv grism observations were mostly done using a lenticular filter.


The 2014 change from using an ad-hoc correction to a theoretically sound correction for the coincidence loss did not produce major changes, so the verification presented here is representative.

Some of the spectra displayed have flux levels inconsistent with the known flux. In the 2014 calibration of the effective area we found that nearly all these observations had problems related to field source spectra overlying the target or background.