The 2023 outburst of RX J0440.9+4431/LS V +44 17

The Be X-ray Binary (BeXRB) RX J0440.9+4431/LS V +44 17 went from a regular type I outburst into its first giant type II outburst in 2023 January. This outburst was monitored with NuSTAR, INTEGRAL, NICER and Swift. NuSTAR observations were obtained both during the type I and II outbursts. Here we present a spectral analysis focusing on the NuSTAR data of the early type I outburst and compare its spectral and timing properties to the giant type II outburst that followed a few days later. We explore different spectral models and compare with the previously reported double-hump structure of the broadband spectrum. We further revisit the question of the presence of a cyclotron line in the context of different continuum models.