RAMBO. I. Project Introduction and First Results with uGMRT

Abstract Magnetic hot stars can emit both coherent and incoherent nonthermal radio emission. Understanding the nature of these emissions and their connection to stellar rotation and magnetic field characteristics remains incomplete. The RAdio Magnetospheres of B and O stars (RAMBO) project aims to address this gap by systematically detecting and characterizing gyrosynchrotron and cyclotron maser radio emission in rapidly rotating magnetic hot stars. Using the upgraded Giant Metrewave Radio Telescope, we present the first detection of radio emission from HD 55522 at 650 MHz, confirming it as a new radio-bright magnetic hot star. This supports the predictions of the Centrifugal Breakout model, furthering its application in understanding particle acceleration mechanisms in centrifugal magnetospheres of hot stars. Additionally, we report nondetections for four other targets, improving sensitivity limits by a factor of a few compared to previous observations. These findings demonstrate the potential of RAMBO to uncover the complexities of radio emission in massive stars and highlight the need for broader, multiwavelength observations to probe magnetospheric physics comprehensively. The sensitivity of the Square Kilometre Array will enable significant advancements.