ALMA observations of the gamma-ray binary system PSR B1259-63/LS 2883 during the 2024 periastron passage

We present observations of the gamma-ray binary PSR B1259-63/LS 2883 with the Atacama Large Millimeter/submillimeter Array (ALMA) at Bands 3 (97 GHz), 6 (233 GHz), and 7 (343 GHz). PSR B1259-63/LS 2883 consists of a pulsar in a highly eccentric orbit around a massive companion star, with the pulsar passing through the circumstellar disk near periastron. Our new data were obtained over several epochs, ranging from -61 to +29 days from the periastron passage in 2024. We report an increase in flux in all bands near the periastron. The significant change in Band 3 flux suggests synchrotron emission from the interaction between the pulsar wind and the stellar wind or disk. The Band 6 flux shows an increase around periastron and a transition from thermal emission from the circumstellar disk to synchrotron emission. The Band 7 observation +24 days after periastron shows a brightening, suggesting that the pulsar's passage through the disk does not result in its immediate destruction. We discuss the implications of these results for the interaction between the pulsar wind and the circumstellar disk, such as the possible disk expansion after periastron.
Comment: Accepted for publication in ApJ Letters