7 research outputs found
An X-rays-to-radio investigation of the nuclear polarization from the radio-galaxy Centaurus A
Centaurus A is one of the closest radio galaxies to Earth. Its proximity allowed us to extensively study its active galactic nucleus but the core emission mechanism remains elusive because of local strong dust and gas obscuration. The capability of polarimetry to shave-off contaminating emission has been exploited without success in the near-infrared by previous studies but the very recent measurement of the 2â8 keV polarization by the Imaging X-ray Polarimetry Explorer (IXPE) brought the question back to the fore. To determine what is the prevalent photon generation mechanism to the multiwavelength emission from the core of Centaurus A, we retrieved from the archives the panchromatic polarization measurements of the central compact component. We built the total and polarized flux spectral energy distributions of the core and demonstrated that synchrotron self-Compton models nicely fit the polarized flux from the radio to the X-ray band. The linear polarization of the synchrotron continuum is perpendicular to the jet radio axis from the optical to the radio band, and parallel to it at higher energies. The observed smooth rotation of the polarization angle in the ultraviolet band is attributed to synchrotron emission from regions that are getting closer to the particle acceleration site, where the orientation of the jetâs magnetic fields become perpendicular to the jet axis. This phenomenon support the shock acceleration mechanism for particle acceleration in Centaurus A, in line with IXPE observations of several high-synchrotron peak blazars
An X-rays-to-radio investigation of the nuclear polarization from the radio-galaxy Centaurus A
Centaurus A is one of the closest radio-galaxies to Earth. Its proximity
allowed us to extensively study its active galactic nucleus but the core
emission mechanism remains elusive because of local strong dust and gas
obscuration. The capability of polarimetry to shave-off contaminating emission
has been exploited without success in the near-infrared by previous studies but
the very recent measurement of the 2 - 8 keV polarization by the Imaging X-ray
Polarimetry Explorer (IXPE) brought the question back to the fore. To determine
what is the prevalent photon generation mechanism to the multi-wavelength
emission from the core of Centaurus A, we retrieved from the archives the
panchromatic polarization measurements of the central compact component. We
built the total and polarized flux spectral energy distributions of the core
and demonstrated that synchrotron self-Compton models nicely fit the polarized
flux from the radio to the X-ray band. The linear polarization of the
synchrotron continuum is perpendicular to the jet radio axis from the optical
to the radio band, and parallel to it at higher energies. The observed smooth
rotation of the polarization angle in the ultraviolet band is attributed to
synchrotron emission from regions that are getting closer to the particle
acceleration site, where the orientation of the jet's magnetic fields become
perpendicular to the jet axis. This phenomenon support the shock acceleration
mechanism for particle acceleration in Centaurus A, in line with IXPE
observations of several high-synchrotron peak blazars.Comment: 10 pages, 6 figures, accepted for publication in MNRA
X-ray pulsar GRO J100857 as an orthogonal rotator
X-ray polarimetry is a unique way to probe geometrical configuration of
highly-magnetized accreting neutron stars (X-ray pulsars). GRO J100857 is
the first transient X-ray pulsar observed at two different flux levels by the
Imaging X-ray Polarimetry Explorer (IXPE) during its outburst in November 2022.
The polarization properties were found to be independent of the source
luminosity, with the polarization degree varying between non-detection to about
15% over the pulse phase. Fitting the phase-resolved spectro-polarimetric data
with the rotating vector model allowed us to estimate the pulsar inclination
(130 deg, which is in good agreement with the orbital inclination), the
position angle (75 deg) of the pulsar spin axis, and the magnetic obliquity (74
deg). This makes GRO J100857 the first confidently identified X-ray pulsar
as a nearly orthogonal rotator. The results are discussed in the context of the
neutron star atmosphere models and theories of pulsars' axis alignment.Comment: 11 pages, 7 figures, submitted to A&A. arXiv admin note: text overlap
with arXiv:2209.0244
An X-rays-to-radio investigation of the nuclear polarization from the radio-galaxy Centaurus A
International audienceCentaurus A is one of the closest radio-galaxies to Earth. Its proximity allowed us to extensively study its active galactic nucleus but the core emission mechanism remains elusive because of local strong dust and gas obscuration. The capability of polarimetry to shave-off contaminating emission has been exploited without success in the near-infrared by previous studies but the very recent measurement of the 2 - 8 keV polarization by the Imaging X-ray Polarimetry Explorer (IXPE) brought the question back to the fore. To determine what is the prevalent photon generation mechanism to the multi-wavelength emission from the core of Centaurus A, we retrieved from the archives the panchromatic polarization measurements of the central compact component. We built the total and polarized flux spectral energy distributions of the core and demonstrated that synchrotron self-Compton models nicely fit the polarized flux from the radio to the X-ray band. The linear polarization of the synchrotron continuum is perpendicular to the jet radio axis from the optical to the radio band, and parallel to it at higher energies. The observed smooth rotation of the polarization angle in the ultraviolet band is attributed to synchrotron emission from regions that are getting closer to the particle acceleration site, where the orientation of the jet's magnetic fields become perpendicular to the jet axis. This phenomenon support the shock acceleration mechanism for particle acceleration in Centaurus A, in line with IXPE observations of several high-synchrotron peak blazars
An X-rays-to-radio investigation of the nuclear polarization from the radio-galaxy Centaurus A
International audienceCentaurus A is one of the closest radio-galaxies to Earth. Its proximity allowed us to extensively study its active galactic nucleus but the core emission mechanism remains elusive because of local strong dust and gas obscuration. The capability of polarimetry to shave-off contaminating emission has been exploited without success in the near-infrared by previous studies but the very recent measurement of the 2 - 8 keV polarization by the Imaging X-ray Polarimetry Explorer (IXPE) brought the question back to the fore. To determine what is the prevalent photon generation mechanism to the multi-wavelength emission from the core of Centaurus A, we retrieved from the archives the panchromatic polarization measurements of the central compact component. We built the total and polarized flux spectral energy distributions of the core and demonstrated that synchrotron self-Compton models nicely fit the polarized flux from the radio to the X-ray band. The linear polarization of the synchrotron continuum is perpendicular to the jet radio axis from the optical to the radio band, and parallel to it at higher energies. The observed smooth rotation of the polarization angle in the ultraviolet band is attributed to synchrotron emission from regions that are getting closer to the particle acceleration site, where the orientation of the jet's magnetic fields become perpendicular to the jet axis. This phenomenon support the shock acceleration mechanism for particle acceleration in Centaurus A, in line with IXPE observations of several high-synchrotron peak blazars
The detection of polarized X-ray emission from the magnetar 1E 2259+586
International audienceWe report on IXPE, NICER, and XMM-Newton observations of the magnetar 1E 2259+586. We find that the source is significantly polarized at about or above 20 per cent for all phases except for the secondary peak where it is more weakly polarized. The polarization degree is strongest during the primary minimum which is also the phase where an absorption feature has been identified previously. The polarization angle of the photons are consistent with a rotating vector model with a mode switch between the primary minimum and the rest of the rotation of the neutron star. We propose a scenario in which the emission at the source is weakly polarized (as in a condensed surface) and, as the radiation passes through a plasma arch, resonant cyclotron scattering off of protons produces the observed polarized radiation. This confirms the magnetar nature of the source with a surface field greater than about 1015 G
Detection of X-Ray Polarization from the Blazar 1ES 1959+650 with the Imaging X-Ray Polarimetry Explorer
Observations of linear polarization in the 2â8 keV energy range with the Imaging X-ray Polarimetry Explorer (IXPE) explore the magnetic field geometry and dynamics of the regions generating nonthermal radiation in relativistic jets of blazars. These jets, particularly in blazars whose spectral energy distribution peaks at X-ray energies, emit X-rays via synchrotron radiation from high-energy particles within the jet. IXPE observations of the X-ray-selected BL Lacâtype blazar 1ES 1959+650 on 2022 May 3â4 showed a significant linear polarization degree of Î _x = 8.0% ± 2.3% at an electric-vector position angle Ï _x = 123° ± 8°. However, on 2022 June 9â12, only an upper limit of Î _x †5.1% could be derived (at the 99% confidence level). The degree of optical polarization at that time, Î _O ⌠5%, is comparable to the X-ray measurement. We investigate possible scenarios for these findings, including temporal and geometrical depolarization effects. Unlike some other X-ray-selected BL Lac objects, there is no significant chromatic dependence of the measured polarization in 1ES 1959+650, and its low X-ray polarization may be attributed to turbulence in the jet flow with dynamical timescales shorter than 1 day