TY - JOUR

T1 - Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1

AU - Bobrikova, Anna

AU - Forsblom, Sofia V.

AU - Di Marco, Alessandro

AU - La Monaca, Fabio

AU - Poutanen, Juri

AU - Ng, Mason

AU - Ravi, Swati

AU - Loktev, Vladislav

AU - Kajava, Jari J. E.

AU - Ursini, Francesco

AU - Veledina, Alexandra

AU - Rogantini, Daniele

AU - Salmi, Tuomo

AU - Bianchi, Stefano

AU - Capitanio, Fiamma

AU - Done, Chris

AU - Fabiani, Sergio

AU - Gnarini, Andrea

AU - Heyl, Jeremy

AU - Kaaret, Philip

AU - Matt, Giorgio

AU - Muleri, Fabio

AU - Nitindala, Anagha P.

AU - Rankin, John

AU - Weisskopf, Martin C.

AU - Agudo, Iván

AU - Antonelli, Lucio A.

AU - Bachetti, Matteo

AU - Baldini, Luca

AU - Baumgartner, Wayne H.

AU - Bellazzini, Ronaldo

AU - Bongiorno, Stephen D.

AU - Bonino, Raffaella

AU - Brez, Alessandro

AU - Bucciantini, Niccolò

AU - Castellano, Simone

AU - Cavazzuti, Elisabetta

AU - Chen, Chien-Ting

AU - Ciprini, Stefano

AU - Costa, Enrico

AU - De Rosa, Alessandra

AU - Del Monte, Ettore

AU - Di Gesu, Laura

AU - Di Lalla, Niccolò

AU - Donnarumma, Immacolata

AU - Doroshenko, Victor

AU - Dovčiak, Michal

AU - Ehlert, Steven R.

AU - Enoto, Teruaki

AU - Evangelista, Yuri

AU - Ferrazzoli, Riccardo

AU - García, Javier A.

AU - Gunji, Shuichi

AU - Hayashida, Kiyoshi

AU - Iwakiri, Wataru

AU - Jorstad, Svetlana G.

AU - Karas, Vladimir

AU - Kislat, Fabian

AU - Kitaguchi, Takao

AU - Kolodziejczak, Jeffery J.

AU - Krawczynski, Henric

AU - Latronico, Luca

AU - Liodakis, Ioannis

AU - Maldera, Simone

AU - Manfreda, Alberto

AU - Marin, Frédéric

AU - Marinucci, Andrea

AU - Marscher, Alan P.

AU - Marshall, Herman L.

AU - Massaro, Francesco

AU - Mitsuishi, Ikuyuki

AU - Mizuno, Tsunefumi

AU - Negro, Michela

AU - Ng, Chi-Yung

AU - O'Dell, Stephen L.

AU - Omodei, Nicola

AU - Oppedisano, Chiara

AU - Papitto, Alessandro

AU - Pavlov, George G.

AU - Peirson, Abel L.

AU - Perri, Matteo

AU - Pesce-Rollins, Melissa

AU - Petrucci, Pierre-Olivier

AU - Pilia, Maura

AU - Possenti, Andrea

AU - Puccetti, Simonetta

AU - Ramsey, Brian D.

AU - Ratheesh, Ajay

AU - Roberts, Oliver J.

AU - Romani, Roger W.

AU - Sgrò, Carmelo

AU - Slane, Patrick

AU - Soffitta, Paolo

AU - Spandre, Gloria

AU - Swartz, Douglas A.

AU - Tamagawa, Toru

AU - Tavecchio, Fabrizio

AU - Taverna, Roberto

AU - Tawara, Yuzuru

AU - Tennant, Allyn F.

AU - Thomas, Nicholas E.

AU - Tombesi, Francesco

AU - Trois, Alessio

AU - Tsygankov, Sergey S.

AU - Turolla, Roberto

AU - Vink, Jacco

AU - Wu, Kinwah

AU - Xie, Fei

AU - Zane, Silvia

PY - 2024/8/1

Y1 - 2024/8/1

N2 - Weakly magnetized neutron stars in X-ray binaries show a complex phenomenology with several spectral components that can be associated with the accretion disk, the boundary, and/or a spreading layer, a corona, and a wind. Spectroscopic information alone, however, is not enough to distinguish these components. The analysis of the timing data revealed that most of the variability, and in particular, kilohertz quasi-period oscillations, are associated with the high-energy component that corresponds to the boundary and/or spreading layer. Additional information about the nature of the spectral components, and in particular, about the geometry of the emission region, can be provided by X-ray polarimetry. One of the objects of the class, a bright, persistent, and rather peculiar galactic Type I X-ray burster GX 13+1, was observed with the Imaging X-ray Polarimetry Explorer (IXPE) and the XMM-Newton. Using the XMM-Newton data, we obtained the best-fit values for the continuum spectral parameters and detected strong absorption lines associated with the accretion disk wind. IXPE data showed the source to be significantly polarized in the 2-8 keV energy band, with an overall polarization degree (PD) of 1.4%±0.3% at a polarization angle (PA) of −2° ±6° (errors at the 68% confidence level). During the two-day long observation, we detected rotation of the PA by about 70° with the corresponding changes in the PD from 2% to nondetectable and then up to 5%. These variations in polarization properties are not accompanied by visible spectral state changes of the source. The energy-resolved polarimetric analysis showed a significant change in polarization, from being strongly dependent on energy at the beginning of the observation to being almost constant with energy in the later parts of the observation. As a possible interpretation, we suggest a constant polarization component, strong wind scattering, or a different polarization of the two main spectral components with an individually peculiar behavior. The rotation of the PA suggests a misalignment of the neutron star spin from the orbital axis.

AB - Weakly magnetized neutron stars in X-ray binaries show a complex phenomenology with several spectral components that can be associated with the accretion disk, the boundary, and/or a spreading layer, a corona, and a wind. Spectroscopic information alone, however, is not enough to distinguish these components. The analysis of the timing data revealed that most of the variability, and in particular, kilohertz quasi-period oscillations, are associated with the high-energy component that corresponds to the boundary and/or spreading layer. Additional information about the nature of the spectral components, and in particular, about the geometry of the emission region, can be provided by X-ray polarimetry. One of the objects of the class, a bright, persistent, and rather peculiar galactic Type I X-ray burster GX 13+1, was observed with the Imaging X-ray Polarimetry Explorer (IXPE) and the XMM-Newton. Using the XMM-Newton data, we obtained the best-fit values for the continuum spectral parameters and detected strong absorption lines associated with the accretion disk wind. IXPE data showed the source to be significantly polarized in the 2-8 keV energy band, with an overall polarization degree (PD) of 1.4%±0.3% at a polarization angle (PA) of −2° ±6° (errors at the 68% confidence level). During the two-day long observation, we detected rotation of the PA by about 70° with the corresponding changes in the PD from 2% to nondetectable and then up to 5%. These variations in polarization properties are not accompanied by visible spectral state changes of the source. The energy-resolved polarimetric analysis showed a significant change in polarization, from being strongly dependent on energy at the beginning of the observation to being almost constant with energy in the later parts of the observation. As a possible interpretation, we suggest a constant polarization component, strong wind scattering, or a different polarization of the two main spectral components with an individually peculiar behavior. The rotation of the PA suggests a misalignment of the neutron star spin from the orbital axis.

KW - accretion

KW - accretion disks

KW - polarization

KW - stars: neutron

KW - X-rays: binaries

KW - Astrophysics - High Energy Astrophysical Phenomena

U2 - 10.1051/0004-6361/202449318

DO - 10.1051/0004-6361/202449318

M3 - Article

VL - 688

JO - ASTRONOMY & ASTROPHYSICS

JF - ASTRONOMY & ASTROPHYSICS

SN - 0004-6361

M1 - A170

ER -