2026-04-13T06:40:00Zhttps://recercat.cat/oai/request

oai:recercat.cat:2117/3807262026-02-09T05:38:16Zcom_2072_1033col_2072_452950

The Neutron Star Population in M28: A Joint Chandra/GBT Look at Pulsar Paradise Vurgun, Eda Linares Alegret, Manuel Ransom, Scott Papitto, Alessandro Bogdanov, Slavko Bozzo, Enrico Rea, Nanda García Senz, Domingo Freire, Paulo Stairs, Ingrid Àrees temàtiques de la UPC::Física Neutron stars X-ray astronomy Estels de neutrons Astronomia de raigs X We present the results of a deep study of the neutron star (NS) population in the globular cluster M28 (NGC 6626), using the full 330 ks 2002–2015 ACIS data set from the Chandra X-ray Observatory and coordinated radio observations taken with the Green Bank Telescope (GBT) in 2015. We investigate the X-ray luminosity (LX), spectrum, and orbital modulation of the seven known compact binary millisecond pulsars in the cluster. We report two simultaneous detections of the redback PSR J1824-2452I (M28I) and its X-ray counterpart at LX = [8.3 ± 0.9] × 1031 erg s-1. We discover a double-peaked X-ray orbital flux modulation in M28I during its pulsar state, centered around pulsar inferior conjunction. We analyze the spectrum of the quiescent NS low-mass X-ray binary to constrain its mass and radius. Using both hydrogen and helium NS atmosphere models, we find an NS radius of R = 9.2–11.5 km and R = 13.0–17.5 km, respectively, for an NS mass of 1.4 M¿ (68% confidence ranges). We also search for long-term variability in the 46 brightest X-ray sources and report the discovery of six new variable low-luminosity X-ray sources in M28. Peer Reviewed Postprint (published version) 2022-12-01 Article https://iopscience.iop.org/article/10.3847/1538-4357/ac9ea0 http://creativecommons.org/licenses/by/4.0/ Open Access Attribution 4.0 International Institute of Physics (IOP)