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2024ApJ...960L..11L - Astrophys. J., 960, L11 (2024/January-2)

Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1.

LA MONACA F., DI MARCO A., POUTANEN J., BACHETTI M., MOTTA S.E., PAPITTO A., PILIA M., XIE F., BIANCHI S., BOBRIKOVA A., COSTA E., DENG W., GE M.-Y., ILLIANO G., JIA S.-M., KRAWCZYNSKI H., LAI E.V., LIU K., MASTROSERIO G., MULERI F., RANKIN J., SOFFITTA P., VELEDINA A., AMBROSINO F., DEL SANTO M., CHEN W., GARCIA J.A., KAARET P., RUSSELL T.D., WEI W.-H., ZHANG S.-N., ZUO C., ARZOUMANIAN Z., COCCHI M., GNARINI A., FARINELLI R., GENDREAU K., URSINI F., WEISSKOPF M.C., ZANE S., AGUDO I., ANTONELLI L.A., BALDINI L., BAUMGARTNER W.H., BELLAZZINI R., BONGIORNO S.D., BONINO R., BREZ A., BUCCIANTINI N., CAPITANIO F., CASTELLANO S., CAVAZZUTI E., CHEN C.-T., CIPRINI S., DE ROSA A., DEL MONTE E., DI GESU L., DI LALLA N., DONNARUMMA I., DOROSHENKO V., DOVCIAK M., EHLERT S.R., ENOTO T., EVANGELISTA Y., FABIANI S., FERRAZZOLI R., GUNJI S., HAYASHIDA K., HEYL J., IWAKIRI W., JORSTAD S.G., KARAS V., KISLAT F., KITAGUCHI T., KOLODZIEJCZAK J.J., LATRONICO L., LIODAKIS I., MALDERA S., MANFREDA A., MARIN F., MARINUCCI A., MARSCHER A.P., MARSHALL H.L., MASSARO F., MATT G., MITSUISHI I., MIZUNO T., NEGRO M., NG C.-Y., O'DELL S.L., OMODEI N., OPPEDISANO C., PAVLOV G.G., PEIRSON A.L., PERRI M., PESCE-ROLLINS M., PETRUCCI P.-O., POSSENTI A., PUCCETTI S., RAMSEY B.D., RATHEESH A., ROBERTS O.J., ROMANI R.W., SGRO C., SLANE P., SPANDRE G., SWARTZ D.A., TAMAGAWA T., TAVECCHIO F., TAVERNA R., TAWARA Y., TENNANT A.F., THOMAS N.E., TOMBESI F., TROIS A., TSYGANKOV S.S., TUROLLA R., VINK J., WU K. (The IXPE Collaboration)

Abstract (from CDS):

The Imaging X-ray Polarimetry Explorer measured with high significance the X-ray polarization of the brightest Z-source, Sco X-1, resulting in the nominal 2-8 keV energy band in a polarization degree of 1.0% ± 0.2% and a polarization angle of 8° ± 6° at a 90% confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broadband spectrum from soft to hard X-rays. The source has been observed mainly in its soft state, with short periods of flaring. We also observed low-frequency quasiperiodic oscillations. From a spectropolarimetric analysis, we associate a polarization to the accretion disk at <3.2% at 90% confidence level, compatible with expectations for an electron scattering dominated optically thick atmosphere at the Sco X-1 inclination of ∼44°; for the higher-energy Comptonized component, we obtain a polarization of 1.3% ± 0.4%, in agreement with expectations for a slab of Thomson optical depth of ∼7 and an electron temperature of ∼3 keV. A polarization rotation with respect to previous observations by OSO-8 and PolarLight, and also with respect to the radio-jet position angle, is observed. This result may indicate a variation of the polarization with the source state that can be related to relativistic precession or a change in the corona geometry with the accretion flow.

Journal keyword(s): Polarimetry - Spectropolarimetry - Neutron stars - Accretion - Stellar accretion disks - Low-mass x-ray binary stars - X-ray telescopes

Simbad objects: 13

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