  We present four new secondary eclipse observations for the ultrahot Jupiter
WASP-121b acquired using the Hubble Space Telescope Wide Field Camera 3. The
eclipse depth is measured to a median precision of 60ppm across 28
spectroscopic channels spanning the 1.12-1.64 micron wavelength range. This is
a considerable improvement to the 90ppm precision we achieved previously for a
single eclipse observation using the same observing setup. Combining these data
with those reported at other wavelengths, a blackbody spectrum for WASP-121b is
ruled out at >6-sigma confidence and we confirm the interpretation of previous
retrieval analyses that found the data is best explained by a dayside thermal
inversion. The updated spectrum clearly resolves the water emission band at
1.3-1.6 micron, with higher signal-to-noise than before. It also fails to
reproduce a bump in the spectrum at 1.25 micron derived from the first eclipse
observation, which had tentatively been attributed to VO emission. We conclude
the latter was either a statistical fluctuation or a systematic artefact
specific to the first eclipse dataset.
