Context. PSR J1023+0038 is the first millisecond pulsar that was ever observed as an optical and UV pulsar. So far, it is the only optical transitional millisecond pulsar. The rotation- and accretion-powered emission mechanisms hardly individually explain the observed characteristics of optical pulsations. A synergistic model, combining these standard emission processes, was proposed to explain the origin of the X-ray/UV/optical pulsations.Aims. We study the phase lag between the pulses in the optical and X-ray bands to gain insight into the physical mechanisms that cause it.Methods. We performed a detailed timing analysis of simultaneous or quasi-simultaneous observations in the X-ray band, acquired with the XMM-Newton and NICER satellites, and in the optical band, with the fast photometers SiFAP2 (mounted at the 3.6 m Telescopio Nazionale Galileo) and Aqueye+ (mounted at the 1.8 m Copernicus Telescope). We estimated the time lag of the optical pulsation with respect to that in the X-rays by modeling the folded pulse profiles with two harmonic components.Results. Optical pulses lag the X-ray pulses by similar to 150 mu s in observations acquired with instruments (NICER and Aqueye+) whose absolute timing uncertainty is much smaller than the measured lag. We also show that the phase lag between optical and X-ray pulsations lies in a limited range of values, delta phi is an element of(0 - 0.15), which is maintained over timescales of about five years. This indicates that both pulsations originate from the same region, and it supports the hypothesis of a common emission mechanism. Our results are interpreted in the shock-driven mini pulsar nebula scenario. This scenario suggests that optical and X-ray pulses are produced by synchrotron emission from the shock that formed within a few light cylinder radii away (similar to 100 km) from the pulsar, where its striped wind encounters the accretion disk inflow.
Investigating the origin of optical and X-ray pulsations of the transitional millisecond pulsar PSR J1023+0038 / Illiano, G.; Papitto, A.; Ambrosino, F.; Miraval Zanon, A.; Coti Zelati, F.; Stella, L.; Zampieri, L.; Burtovoi, A.; Campana, S.; Casella, P.; Cecconi, M.; de Martino, D.; Fiori, M.; Ghedina, A.; Gonzales, M.; Hernandez Diaz, M.; Israel, G. L.; Leone, F.; Naletto, G.; Perez Ventura, H.; Riverol, C.; Riverol, L.; Torres, D. F.; Turchetta, M.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - ELETTRONICO. - 669:(2023), pp. A26.0-A26.0. [10.1051/0004-6361/202244637]
Investigating the origin of optical and X-ray pulsations of the transitional millisecond pulsar PSR J1023+0038
Burtovoi, A.;
2023
Abstract
Context. PSR J1023+0038 is the first millisecond pulsar that was ever observed as an optical and UV pulsar. So far, it is the only optical transitional millisecond pulsar. The rotation- and accretion-powered emission mechanisms hardly individually explain the observed characteristics of optical pulsations. A synergistic model, combining these standard emission processes, was proposed to explain the origin of the X-ray/UV/optical pulsations.Aims. We study the phase lag between the pulses in the optical and X-ray bands to gain insight into the physical mechanisms that cause it.Methods. We performed a detailed timing analysis of simultaneous or quasi-simultaneous observations in the X-ray band, acquired with the XMM-Newton and NICER satellites, and in the optical band, with the fast photometers SiFAP2 (mounted at the 3.6 m Telescopio Nazionale Galileo) and Aqueye+ (mounted at the 1.8 m Copernicus Telescope). We estimated the time lag of the optical pulsation with respect to that in the X-rays by modeling the folded pulse profiles with two harmonic components.Results. Optical pulses lag the X-ray pulses by similar to 150 mu s in observations acquired with instruments (NICER and Aqueye+) whose absolute timing uncertainty is much smaller than the measured lag. We also show that the phase lag between optical and X-ray pulsations lies in a limited range of values, delta phi is an element of(0 - 0.15), which is maintained over timescales of about five years. This indicates that both pulsations originate from the same region, and it supports the hypothesis of a common emission mechanism. Our results are interpreted in the shock-driven mini pulsar nebula scenario. This scenario suggests that optical and X-ray pulses are produced by synchrotron emission from the shock that formed within a few light cylinder radii away (similar to 100 km) from the pulsar, where its striped wind encounters the accretion disk inflow.
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