X-ray pulsar GRO J1008$-$57 as an orthogonal rotator

S., Tsygankov, Sergey; Doroshenko, V. T.; Mushtukov, Alexander A.; Poutanen, Juri; Marco, Alessandro Di; Heyl, Jeremy; Monaca, Fabio La; Forsblom, Sofia V.; Malacaria, C.; Marshall, Herman L.; Suleimanov, V.; Svoboda, Jiřı́; Taverna, Roberto; Ursini, F.; Agudo, I.; Antonelli, L. A.; Bachetti, Matteo; Baldini, Luca; Baumgartner, W. H.; Bellazzini, R.; Bianchi, S.; Bongiorno, Stephen D.; Bonino, R.; Brez, A.; Bucciantini, N.; Capitanio, Fiamma; Castellano, Simone; Cavazzuti, E.; Chen, Chien-Ting; Ciprini, S.; Costa, E.; Rosa, A. De; Monte, E. Del; Gesu, Laura Di; Lalla, N. Di; Donnarumma, I.; Dovčiak, Michal; Ehlert, Steven R.; Enoto, T.; Evangelista, Y.; Fabiani, Sergio; Ferrazzoli, Riccardo; García, Javier Avilés; Gunji, Shuichi; Hayashida, Kentaro; Iwakiri, W.; Jorstad, Svetlana G.; Kaaret, Philip; Karas, Vladimír; Kislat, Fabian; Kitaguchi, Takao; Kolodziejczak, Jeffery J.; Krawczynski, H.; Latronico, L.; Liodakis, Ioannis; Maldera, S.; Manfreda, Alberto; Marin, Frédéric; Marinucci, Andrea; Marscher, A. P.; Massaro, F.; Matt, Giorgio; Mitsuishi, Ikuyuki; Mizuno, T.; Muleri, Fabio; Negro, Michela; Ng, Chi-Yung; O’Dell, Stephen L.; Omodei, N.; Oppedisano, C.; Papitto, A.; Pavlov, G. G.; Peirson, Abel L.; Perri, M.; Pesce-Rollins, Melissa; Petrucci, Pierre-Olivier; Pilia, M.; Possenti, A.; Puccetti, S.; Ramsey, Brian D.; Rankin, John; Ratheesh, Ajay; Roberts, O. J.; Romani, Roger W.; Sgrò, C.; Slane, Patrick; Soffitta, P.; Spandre, G.; Swartz, Douglas A.; Tamagawa, Toru; Tavecchio, F.; Tawara, Yuzuru; Tennant, Allyn F.; Thomas, N.; Tombesi, Francesco; Trois, A.; Turolla, R.; Vink, Jacco; Weisskopf, Martin C.; Wu, Kinwah; Xie, Fei; Zane, S.

doi:10.48550/arxiv.2302.06680

Cited by 4 publications

(9 citation statements)

References 36 publications

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Section: Observations and Analysismentioning

confidence: 56%

“…According to previous IXPE measurements, the RVM was always able to fit the data adequately (Doroshenko et al 2022;Marshall et al 2022;Tsygankov et al 2022Tsygankov et al , 2023. Here, based on the RVM, we are unsure if the intrinsic PF of the source is higher than those derived in other sources, but it is indeed lower than the theoretical prediction of 0.6-0.8 (Caiazzo & Heyl 2021), suggesting that the relatively low PFs measured in Her X-1 (Doroshenko et al 2022), Cen X-3 (Tsygankov et al 2022), 4U 1626−67 (Marshall et al 2022), and GRO J1008−57 (Tsygankov et al 2023) cannot be attributed to the sources not being in the supercritical state. One may consider other possibilities for relatively low polarizations as proposed by Doroshenko et al (2022) and Tsygankov et al (2022), including mode conversion due to vacuum resonance in the emitting plasma with a strong temperature gradient (Pavlov & Shibanov 1979;Lai & Ho 2002;Doroshenko et al 2022), the quasi-tangential effect occurred during radiation transfer (Wang & Lai 2009;Caiazzo & Heyl 2021), and reflection/scattering on the ambient surface or medium (Tsygankov et al 2022).…”

Section: Observations and Analysismentioning

confidence: 56%

“…if the bipolar field is the dominant component at that radius (Heyl & Shaviv 2000). In fact, the RVM model has been successfully used to model the phase dependent PA variation in several X-ray accreting pulsars (Doroshenko et al 2022;Tsygankov et al 2022Tsygankov et al , 2023. In addition to PF, the model contains the phase zeropoint φ 0 and 3 parameters for the pulsar geometry: inclination of the spin axis to the line of sight i p , magnetic obliquity θ, and the spin axis projected on the sky plane χ p (see Fig.…”

Section: Observations and Analysismentioning

confidence: 99%

“…It is uncertain whether the source is in the sub or supercritical state, as the cyclotron line energy does not vary as a function of luminosity (Bachhar et al 2022;Yang et al 2023); the Xray luminosity during detection also gives an ambiguous determination (Becker et al 2012;Mushtukov et al 2015). Later, a non-detection was obtained with an IXPE measurement of 4U 1626−67, a persistent ultracompact low-mass Xray pulsar, at a subcritical luminosity (Marshall et al 2022 around 0.1 with spin phase is seen in a transient Be/X-ray binary pulsar GRO J1008−57 during its subcritical outburst in late 2022 (Tsygankov et al 2023). Thus, it would be interesting to measure X-ray polarization from a source in a bona fide supercritical state, as a direct test to argue for or against this scenario.…”

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confidence: 99%

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A Significant Detection of X-ray Polarization in Sco X-1 with PolarLight and Constraints on the Corona Geometry

Long

Feng

et al. 2022

ApJL

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We report the detection of X-ray polarization in the neutron-star low-mass X-ray binary Scorpius (Sco) X-1 with PolarLight. The result is energy-dependent, with a nondetection in 3–4 keV but a 4σ detection in 4–8 keV; it is also flux-dependent in the 4–8 keV band, with a nondetection when the source displays low fluxes but a 5σ detection during high fluxes, in which case we obtain a polarization fraction of 0.043 ± 0.008 and a polarization angle of 52.°6 ± 5.°4. This confirms a previous marginal detection with OSO-8 in the 1970s and marks Sco X-1 as the second astrophysical source with a significant polarization measurement in the keV band. The measured polarization angle is in line with the jet orientation of the source on the sky plane (54°), which is supposedly the symmetry axis of the system. Combining previous spectral analysis, our measurements suggest that an optically thin corona is located in the transition layer under the highest accretion rates, and disfavor the extended accretion disk corona model.

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Section: Observations and Analysismentioning

confidence: 56%

Section: Observations and Analysismentioning

confidence: 56%

Section: Observations and Analysismentioning

confidence: 99%

mentioning

confidence: 99%

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A Significant Detection of X-ray Polarization in Sco X-1 with PolarLight and Constraints on the Corona Geometry

Long

Feng

et al. 2022

ApJL

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“…Later, a nondetection was obtained with an IXPE measurement of 4U 1626−67, a persistent ultracompact lowmass X-ray pulsar, at a subcritical luminosity (Marshall et al 2022). Recently, a similar polarization signature with PF varying around 0.1 with spin phase is seen in a transient Be/Xray binary pulsar GRO J1008−57 during its subcritical outburst in late 2022 (Tsygankov et al 2023). 12 Thus, it would be interesting to measure X-ray polarization from a source in a bona fide supercritical state, as a direct test to argue for or against this scenario.…”

Section: Introductionmentioning

confidence: 91%

X-Ray Polarimetry of the Accreting Pulsar 1A 0535+262 in the Supercritical State with PolarLight

Long

Feng

Hong

et al. 2023

ApJ

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The X-ray pulsar 1A 0535+262 exhibited a giant outburst in 2020, offering us a unique opportunity for X-ray polarimetry of an accreting pulsar in the supercritical state. Measurement with PolarLight yielded a nondetection in 3–8 keV; the 99% upper limit of the polarization fraction (PF) is found to be 0.34 averaged over spin phases, or 0.51 based on the rotating vector model. No useful constraint can be placed with phase-resolved polarimetry. These upper limits are lower than a previous theoretical prediction of 0.6–0.8, but consistent with those found in other accreting pulsars, like Her X-1, Cen X-3, 4U 1626−67, and GRO J1008−57, which were in the subcritical state, or at least not confidently in the supercritical state, during the polarization measurements. Our results suggest that the relatively low PF seen in accreting pulsars cannot be attributed to the source not being in the supercritical state, but could be a general feature.

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Determination of X-ray pulsar geometry with IXPE polarimetry

et al. 2022

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We report on IXPE observations of the Be-transient X-ray pulsar LS V +44 17/RX J0440.9+4431 at two luminosity levels during the giant outburst in January-February 2023. Considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in superand sub-critical states with significantly different emission region geometry, associated with the presence of accretion columns and hot spots, respectively. We focus here on the pulse-phase resolved polarimetric analysis and find that the observed dependencies of the polarization degree and polarization angle (PA) on pulse phase are indeed drastically different for the two observations. The observed differences, if interpreted within the framework of the rotating vector model (RVM), imply dramatic variations of the spin axis inclination and the position angle and the magnetic colatitude by tens of degrees within just a few days separating the observations. We suggest that the apparent changes in the observed PA phase dependence are predominantly related to the presence of a polarized unpulsed component in addition to the polarized radiation associated with the pulsar itself. We show that the observed PA phase dependence in both observations can then be explained with a single set of RVM parameters defining the pulsar's geometry. We also suggest that the additional polarized component is likely produced by scattering of the pulsar radiation off the equatorial disk wind.

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X-ray pulsar GRO J1008$-$57 as an orthogonal rotator

Cited by 4 publications

References 36 publications

A Significant Detection of X-ray Polarization in Sco X-1 with PolarLight and Constraints on the Corona Geometry

A Significant Detection of X-ray Polarization in Sco X-1 with PolarLight and Constraints on the Corona Geometry

X-Ray Polarimetry of the Accreting Pulsar 1A 0535+262 in the Supercritical State with PolarLight

Determination of X-ray pulsar geometry with IXPE polarimetry

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