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We present the discovery of two small planets transiting HD 93963A(TOI-1797), a G0\,V star (M$_*$=1.109\,$\pm$\,0.043\,M$_\odot$,R$_*$=1.043\,$\pm$\,0.009\,R$_\odot$) in a visual binary system. We combinedTESS and CHEOPS space-borne photometry with data from MuSCAT 2, `Alopeke,PHARO, TRES, FIES, and SOPHIE. We validated and spectroscopically confirmed theouter transiting planet HD 93963 Ac, a sub-Neptune with an orbital period ofP$_c \approx$ 3.65 d, reported as a TESS object of interest (TOI) shortly afterthe release of Sector 22 data. HD 93963 Ac has a mass of M$_c = 19.2 \pm 4.1$M$_{\oplus}$ and a radius of R$_c = 3.228 \pm 0.059$ R$_{\oplus}$, implying amean density of $\rho_c=3.1\pm0.7$ gcm$^{-3}$. The inner object, HD 93963 Ab,is a validated 1.04 d ultra-short period (USP) transiting super-Earth that wediscovered in the TESS light curve and that was not listed as a TOI, owing tothe low significance of its signal (TESS signal-to-noise ratio $\approx$ 6.7,TESS $+$ CHEOPS combined transit depth D$_b=141.5 \pm 8.5$ ppm). We intensivelymonitored the star with CHEOPS by performing nine transit observations toconfirm the presence of the inner planet and validate the system. HD 93963 Abis the first small (R$_b = 1.35 \pm 0.042$ R$_{\oplus}$) USP planet discoveredand validated by TESS and CHEOPS. Unlike planet c, HD 93963 Ab is notsignificantly detected in our radial velocities (M$_b = 7.8 \pm 3.2$M$_{\oplus}$). We also discovered a linear trend in our Doppler measurements,suggesting the possible presence of a long-period outer planet. With a V-bandmagnitude of 9.2, HD 93963 A is among the brightest stars known to host a USPplanet, making it one of the most favourable targets for precise massmeasurement via Doppler spectroscopy and an important laboratory to testformation, evolution, and migration models of planetary systems hostingultra-short period planets.

The HD 93963 A transiting system: A 1.04d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS