The accretion/ejection link in the neutron star X-ray binary 4U 1820-30 I: a boundary layer-jet coupling?
The accretion flow/jet correlation in neutron star (NS) low-mass X-ray binaries (LMXBs) is far less understood when compared to black hole (BH) LMXBs. In this paper we will present the results of a dense multiwavelength observational campaign on the NS LMXB 4U 1820-30, including X-ray (NICER, NuSTAR...
| Autores: | , , , , , , , , , , , , , , , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2023 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/348909 |
| Acceso en línea: | http://hdl.handle.net/10261/348909 |
| Access Level: | acceso abierto |
| Palabra clave: | Accretion Accretion discs Stars: neutron X-rays: binaries X-rays: individual: 4U 1820-30 ISM: jets and outflows |
| Sumario: | The accretion flow/jet correlation in neutron star (NS) low-mass X-ray binaries (LMXBs) is far less understood when compared to black hole (BH) LMXBs. In this paper we will present the results of a dense multiwavelength observational campaign on the NS LMXB 4U 1820-30, including X-ray (NICER, NuSTAR, and AstroSat) and quasi-simultaneous radio (ATCA) observations in 2022. 4U 1820-30 shows a peculiar 170 d super-orbital accretion modulation, during which the system evolves between ‘modes’ of high and low X-ray flux. During our monitoring, the source did not show any transition to a full hard state. X-ray spectra were well described using a disc blackbody, a Comptonization spectrum along with a Fe K emission line at ∼6.6 keV. Our results show that the observed X-ray flux modulation is almost entirely produced by changes in the size of the region providing seed photons for the Comptonization spectrum. This region is large (∼15 km) in the high mode and likely coincides with the whole boundary layer, while it shrinks significantly (≲10 km) in low mode. The electron temperature of the corona and the observed rms variability in the hard X-rays also exhibit a slight increase in low mode. As the source moves from high to low mode, the radio emission due to the jet becomes ∼5 fainter. These radio changes appear not to be strongly connected to the hard-to-soft transitions as in BH systems, while they seem to be connected mostly to variations observed in the boundary layer. |
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