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Many brown dwarfs are on ultra-short period and tidally-locked orbits aroundwhite dwarf hosts. Because of these small orbital separations, the brown dwarfsare irradiated at levels similar to hot Jupiters. Yet, they are easier toobserve than hot Jupiters because white dwarfs are fainter than main-sequencestars at near-infrared wavelengths. Irradiated brown dwarfs are, therefore,ideal hot Jupiter analogs for studying the atmospheric response under strongirradiation and fast rotation. We present the 1.1--1.67$\rm \mu m$spectroscopic phase curve of the irradiated brown dwarf (SDSS1411-B) in theSDSS J141126.20+200911.1 brown-dwarf white-dwarf binary with the near-infraredG141 grism of Hubble Space Telescope Wide Field Camera 3. SDSS1411-B is a$50~\rm M_{\rm Jup}$ brown dwarf with an irradiation temperature of 1300K andhas an orbital period of 2.02864 hours. Our best-fit model suggests aphase-curve amplitude of 1.4$\%$ and places an upper limit of 11 degrees forthe phase offset from the secondary eclipse. After fitting the white-dwarfspectrum, we extract the phase-resolved brown-dwarf emission spectra. We reporta highly wavelength-dependent day-night spectral variation, with the water-bandflux variation of about $360\pm70\% $ and a comparatively small J-band fluxvariation of $37\pm2\%$. By combining the atmospheric modeling results and theday-night brightness-temperature variations, we derive a pressure-dependenttemperature contrast. We discuss the difference in the spectral features ofSDSS1411-B and hot Jupiter WASP-43b, and the lower-than-predicted day-nighttemperature contrast of J4111-BD. Our study provides the high-precisionobservational constraints on the atmospheric structures of an irradiated browndwarf at different orbital phases.

Mapping the pressure-dependent day-night temperature contrast of a strongly irradiated atmosphere with HST spectroscopic phase curve