DE MARTINO, DomitillaDomitillaDE MARTINOPAPITTO, ALESSANDROALESSANDROPAPITTOBELLONI, Tomaso Maria MelchiorreTomaso Maria MelchiorreBELLONIBURGAY, MARTAMARTABURGAYDe Ona Wilhelmi,EmmaDe Ona WilhelmiLi,JianLiPELLIZZONI, ALBERTO PAOLOALBERTO PAOLOPELLIZZONIPOSSENTI, ANDREAANDREAPOSSENTIREA,NandaREATORRES,D.F.TORRES2020-03-202020-03-2020150035-8711http://hdl.handle.net/20.500.12386/23452This work is based on observations obtained with XMM–Newton , an ESA science mission with instruments and contributions directly funded by ESA Member States, under programme 0729560. The authors wish to thank Dr. Norbert Schartel and the ESAC staff for their help in obtaining the XMM–Newton observation. The REM observations were obtained under programme DDT-REM:30901 and AOT-31:31002. The REM team is acknowledged for the support in the scheduling and data delivery. We acknowledge support from ASI/INAF I/037/12/0 and TMB from PRIN-INAF 2012-6. The Barcelona group acknowledges support from the grants AYA 2012-39303 and SGR 2014-1073. We are grateful to the anonymous referee, whose comments improved the clarity of this work.We present an analysis of X-ray, ultraviolet and optical/near-IR photometric data of the transitional millisecond pulsar binary XSS J12270-4859, obtained at different epochs after the transition to a rotation-powered radio pulsar state. The observations, while confirming the large-amplitude orbital modulation found in previous studies after the state change, also reveal an energy dependence of the amplitudes as well as variations on time-scale of months. The amplitude variations are anticorrelated in the X-ray and the UV/optical bands. The average X-ray spectrum is described by a power law with Γ index of 1.07(8) without requiring an additional thermal component. The power-law index Γ varies from ˜1.2 to ˜1.0 between superior and inferior conjunction of the neutron star. We interpret the observed X-ray behaviour in terms of synchrotron radiation emitted in an extended intrabinary shock, located between the pulsar and the donor star, which is eclipsed due to the companion orbital motion. The G5-type donor dominates the UV/optical and near-IR emission and is similarly found to be heated up to ˜6500 K as in the disc state. The analysis of optical light curves gives a binary inclination 46° ≲ i ≲ 65° and a mass ratio 0.11 ≲ q ≲ 0.26. The donor mass is found to be 0.15 ≲ M2 ≲ 0.36 M⊙ for a neutron star mass of 1.4 M⊙. The variations in the amplitude of the orbital modulation are interpreted in terms of small changes in the mass-flow rate from the donor star. The spectral energy distribution from radio to gamma-rays is composed by multiple contributions that are different from those observed during the accretion-powered state.STAMPAenArticle10.1093/mnras/stv21092-s2.0-85006994797000367997700079arXiv:1509.02765https://academic.oup.com/mnras/article/454/2/2190/28926832015MNRAS.454.2190DFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation