SIDOLI, LaraLaraSIDOLIPostnov, K.K.PostnovTiengo, A.A.TiengoEsposito, P.P.EspositoSGUERA, VITOVITOSGUERAPAIZIS, ADAMANTIAADAMANTIAPAIZISRodriguez Castillo, G. A.G. A.Rodriguez Castillo2022-02-172022-02-1720200004-6361http://hdl.handle.net/20.500.12386/31411We report on the results of a NuSTAR observation of the Supergiant Fast X-ray Transient pulsar IGRJ11215-5952 during the peak of its outburst in June 2017. IGRJ11215-5952 is the only SFXT undergoing strictly periodic outbursts, every 165 days. NuSTAR caught several X-ray flares, spanning a dynamic range of 100, and detected X-ray pulsations at 187.0 s, consistent with previous measurements. The spectrum from the whole observation is well described by an absorbed power-law (with a photon index of 1.4) modified, above 7 keV, by a cutoff with an e-folding energy of 24 keV. A weak emission line is present at 6.4 keV, consistent with Kalpha emission from cold iron in the supergiant wind. The time-averaged flux is 1.5E-10 erg/cm2/s (3-78 keV, corrected for the absorption), translating into an average luminosity of about 9E35 erg/s (1-100 keV, assuming a distance of 6.5 kpc). The NuSTAR observation allowed us to perform the most sensitive search for cyclotron resonant scattering features in the hard X-ray spectrum, resulting in no significant detection in any of the different spectral extractions adopted (time-averaged, temporally-selected, spin-phase-resolved and intensity-selected spectra). The pulse profile showed an evolution with both the energy (3-12 keV energy range compared with 12-78 keV band) and the X-ray flux: a double peaked profile was evident at higher fluxes (and in both energy bands), while a single peaked, sinusoidal profile was present at the lowest intensity state achieved within the NuSTAR observations (in both energy bands). The intensity-selected analysis allowed us to observe an anti-correlation of the pulsed fraction with the X-ray luminosity. The pulse profile evolution can be explained by X-ray photon scattering in the accreting matter above magnetic poles of a neutron star at the quasi-spherical settling accretion stage.STAMPAenArticle10.1051/0004-6361/2020380782-s2.0-85089197249WOS:000541950100001http://arxiv.org/abs/2004.10452v1https://www.aanda.org/articles/aa/full_html/2020/06/aa38078-20/aa38078-20.html2020A&A...638A..71SFIS/05 - ASTRONOMIA E ASTROFISICA