Magnetars are the most strongly magnetized neutron stars, and one of the most promising targets for X-ray polarimetric measurements. We present here the first Imaging X-ray Polarimetry Explorer observation of the magnetar 1RXS J170849.0-400910, jointly analyzed with a new Swift observation and archival NICER data. The total (energy- and phase-integrated) emission in the 2-8 keV energy range is linerarly polarized, at a ∼35% level. The phase-averaged polarization signal shows a marked increase with energy, ranging from ∼20% at 2-3 keV up to ∼80% at 6-8 keV, while the polarization angle remains constant. This indicates that radiation is mostly polarized in a single direction. The spectrum is well reproduced by a combination of either two thermal (blackbody) components or a blackbody and a power law. Both the polarization degree and angle also show a variation with the spin phase, and the former is almost anticorrelated with the source counts in the 2-8 and 2-4 keV bands. We discuss the possible implications and interpretations, based on a joint analysis of the spectral, polarization, and pulsation properties of the source. A scenario in which the surface temperature is not homogeneous, with a hotter cap covered by a gaseous atmosphere and a warmer region in a condensed state, provides a satisfactory description of both the phase- and energy-dependent spectro-polarimetric data. The (comparatively) small size of the two emitting regions, required to explain the observed pulsations, does not allow to reach a robust conclusion about the presence of vacuum birefringence effects.

A Strong X-Ray Polarization Signal from the Magnetar 1RXS J170849.0-400910

Bonino R.;Massaro F.;
2023-01-01

Abstract

Magnetars are the most strongly magnetized neutron stars, and one of the most promising targets for X-ray polarimetric measurements. We present here the first Imaging X-ray Polarimetry Explorer observation of the magnetar 1RXS J170849.0-400910, jointly analyzed with a new Swift observation and archival NICER data. The total (energy- and phase-integrated) emission in the 2-8 keV energy range is linerarly polarized, at a ∼35% level. The phase-averaged polarization signal shows a marked increase with energy, ranging from ∼20% at 2-3 keV up to ∼80% at 6-8 keV, while the polarization angle remains constant. This indicates that radiation is mostly polarized in a single direction. The spectrum is well reproduced by a combination of either two thermal (blackbody) components or a blackbody and a power law. Both the polarization degree and angle also show a variation with the spin phase, and the former is almost anticorrelated with the source counts in the 2-8 and 2-4 keV bands. We discuss the possible implications and interpretations, based on a joint analysis of the spectral, polarization, and pulsation properties of the source. A scenario in which the surface temperature is not homogeneous, with a hotter cap covered by a gaseous atmosphere and a warmer region in a condensed state, provides a satisfactory description of both the phase- and energy-dependent spectro-polarimetric data. The (comparatively) small size of the two emitting regions, required to explain the observed pulsations, does not allow to reach a robust conclusion about the presence of vacuum birefringence effects.
2023
944
2
1
12
https://arxiv.org/abs/2301.12919
Zane S.; Taverna R.; Gonzalez-Caniulef D.; Muleri F.; Turolla R.; Heyl J.; Uchiyama K.; Ng M.; Tamagawa T.; Caiazzo I.; Di Lalla N.; Marshall H.L.; Ba...espandi
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/2000072
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 13
  • ???jsp.display-item.citation.isi??? 8
social impact