Low-mass X-ray binary (LMXB) outbursts are often first detected by X-ray all-sky monitors like MAXI or Swift/BAT. Only after the detection of new outbursts by these instruments can observations with more sensitive multi-wavelength telescopes be triggered. This causes a gap in the coverage of the rising parts of the outbursts, limiting our knowledge of their early stages. Here we introduce the "X-ray Binary New Early Warning System (XB-NEWS)", which aims to detect and announce new LMXB outbursts within days of their first optical rise. This results in triggering multi-wavelength campaigns during the very early stages of outbursts and understanding their origin. As a demonstration of the project, we further present the results of a comprehensive multi-wavelength campaign of the neutron star LMXB MAXI J1807+132 during its 2023 outburst which was triggered by XB-NEWS. Observations were made with several ground and space-based observatories spanning radio to X-ray wavebands. We are able to characterize the broadband (optical and X-ray) spectral and timing properties during different stages of the outburst and uncover a few peculiar features in the phenomenology. We detect a delay of nearly 5 days in the rise of X-rays compared to the optical rise suggesting involvement of viscous timescales from a truncated accretion disk. As the source transitions to different canonical states, we trace the evolution of the accretion disk and corona. A large radius of the last stable orbit, suggests the possibility of the source harboring a stronger-than-usual magnetic field, albeit without any pulsations. In the intermediate and hard state during the outburst we detect signatures of synchrotron emission from a jet that extends well into the optical wavelengths. The end of the main outburst marks the beginning of several re-flares which display a complex behavior, of unknown origin, with high variability but low hardness.
09.10.2024
Speaker: Dr. Sandeep Rout, New York University in Abu Dhabi
The seminar will be held in aula IB09 at IAPS-INAF in the Area di Ricerca di Tor Vergata (ARTOV).
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