Fields In Active Galactic Nuclei Research Articles

An X-ray high-frequency quasi-periodic oscillation in NGC 1365

This study presents the detection of a high-frequency quasi-periodic oscillation (QPO) in the Seyfert galaxy NGC 1365 based on observational data obtained by XMM-Newton in January 2004. Utilizing the weighted wavelet Z-transform (WWZ) and Lomb-Scargle periodogram (LSP) methods, a QPO signal is identified at a frequency of 2.19 × 10−4 Hz (4566 s), with a confidence level of 3.6σ. The signal is notably absent in the lower 0.2–1.0 keV energy band, with the primary contribution emerging from the 2.0–10.0 keV band, where the confidence level reaches 3.9σ. Spectral analysis shows that there are multiple absorption and emission lines in the high-energy band (> 6 keV). The correlation between the QPO frequency (fQPO) and the mass of the central black hole (MBH) of NGC 1365 aligns with the established logarithmic trend observed across black holes, indicating the QPO is of high frequency. This discovery provides new clues for studying the generation mechanism of QPOs in Seyfert galaxies, which helps us understand the accretion process around supermassive black holes and the characteristics of strong gravitational fields in active galactic nuclei.

RadioAstron space VLBI imaging of polarized radio emission in the high-redshift quasar 0642+449 at 1.6 GHz

Polarization of radio emission in extragalactic jets at a sub-milliarcsecond angular resolution holds important clues for understanding the structure of the magnetic field in the inner regions of the jets and in close vicinity of the supermassive black holes in the centers of active galaxies. Space VLBI observations provide a unique tool for polarimetric imaging at a sub-milliarcsecond angular resolution and studying the properties of magnetic field in active galactic nuclei on scales of less than 10^4 gravitational radii. A space VLBI observation of high-redshift quasar TXS 0642+449 (OH 471), made at a wavelength of 18 cm (frequency of 1.6 GHz) as part of the Early Science Programme (ESP) of the RadioAstron} mission, is used here to test the polarimetric performance of the orbiting Space Radio Telescope (SRT) employed by the mission, to establish a methodology for making full Stokes polarimetry with space VLBI at 1.6 GHz, and to study the polarized emission in the target object on sub-milliarcsecond scales. Polarization leakage of the SRT at 18 cm is found to be within 9 percents in amplitude, demonstrating the feasibility of high fidelity polarization imaging with RadioAstron at this wavelength. A polarimetric image of 0642+449 with a resolution of 0.8 mas (signifying an ~4 times improvement over ground VLBI observations at the same wavelength) is obtained. The image shows a compact core-jet structure with low (~2%) polarization and predominantly transverse magnetic field in the nuclear region. The VLBI data also uncover a complex structure of the nuclear region, with two prominent features possibly corresponding to the jet base and a strong recollimation shock. The maximum brightness temperature at the jet base can be as high as 4*10^13 K.

Determination of the Magnitude of the Spins of Supermassive Black Holes and the Magnetic Fields in Active Galactic Nuclei

Limits on the value of the spins of supermassive black holes (SMBH) in Seyfert-type active galactic nuclei (AGN) are calculated using two hybrid models for the generation of relativistic jets: the Meier model and a model of tandem Blandford-Znajek and Blandford-Payne processes. A comparison of our calculations with limits on the spin obtained by x-ray reflection spectroscopy shows that they are in good agreement for the tandem model. This shows that the magnetic field pressure is roughly equal to the radiation ressure in the accretion disk in the region of the last stable orbit. The magnitudes of the magnetic fields at the radii of the last stable orbit in the accretion disk and the event horizon of a supermassive black hole are also determined for objects in a list of 28 radio quasars. The important result is that the magnetic energy density near the radius of the event horizon turns out to be significantly higher than the energy density of the accretion gas. This may indicate the existence of a mechanism for amplification of the magnetic field near the event horizon of black holes located in the center of powerful radio quasars.

Signatures of large-scale magnetic fields in active galactic nuclei jets: transverse asymmetries

We investigate the emission properties that a large-scale helical magnetic field imprints on AGN jet synchrotron radiation. A cylindrically symmetric relativistic jet and large-scale helical magnetic field produce significant asymmetrical features in transverse profiles of fractional linear polarization, intensity, Faraday rotation, and spectral index. The asymmetrical features of these transverse profiles correlate with one another in ways specified by the handedness of the helical field, the jet viewing angle (theta_ob), and the bulk Lorentz factor of the flow (Gamma). Thus, these correlations may be used to determine the structure of the magnetic field in the jet. In the case of radio galaxies (theta_ob~1 radian) and a subclass of blazars with particularly small viewing angles (theta_ob << 1/Gamma), we find an edge-brightened intensity profile that is similar to that observed in the radio galaxy M87. We present observations of the AGNs 3C 78 and NRAO 140 that display the type of transverse asymmetries that may be produced by large-scale helical magnetic fields.

Magnetic fields in active galactic nuclei and microquasars

Observations of active galactic nuclei and microquasars by ASCA, RXTE, Chandra and XMM-Newton indicate the existence of wide X-ray emission lines of heavy ionized elements in their spectra. The emission can arise in the inner parts of accretion discs where the effects of general relativity must be counted; moreover, such effects can dominate. We describe a procedure to estimate an upper limit of the magnetic fields in the regions where X-ray photons are emitted. We simulate typical profiles of the iron K α line in the presence of a magnetic field and compare them with observational data. As an illustration, we find H < 10 1 0 -10 1 1 Gs for Seyfert galaxy MCG-6-30-15. Using the perspective facilities of measurement devices (e.g. Constellation-X mission) a better resolution of the blue peak structure of the iron K α line will allow us to find the value of the magnetic fields if the latter are high enough.

VLBA Imaging of a Large Sample of Blazars

AbstractAs part of our continuing study of parsec-scale magnetic fields in active galactic nuclei we have obtained deep polarization-sensitive images of the blazar 1055+018 with the VLBA at 5 GHz. These dramatic images reveal a magnetized layer of material on the outer surfaces of the jet, distinct from the bulk of the jet. This morphology suggests interaction of the jet with the surrounding medium, the resulting shear stretching the magnetic field lines in the direction of the flow. Further multi-frequency polarization-sensitive observations of 1055+018 offer the opportunity to study radio jet-ambient medium interactions in detail.

Escape of TeV Gamma Rays from Anisotropic Thermal Photon Fields in Active Galactic Nuclei

We calculate the optical depth of TeV γ-rays that result from the anisotropic IR-UV thermal radiation of the α-disk model proposed by Shakura & Sunyaev. Our calculations yield the dependences of the optical depth of high-energy γ-rays on the disk parameters (i.e., α, M8, and 26), photon energy, and Φ, the angle between the propagation direction and the rotation axis of the accretion disk. Our results indicate that TeV γ-rays can escape more easily from the central engine with lower values of α ( 0.01) and Φ. We conclude that the optical depth of TeV γ-rays in the anisotropic thermal radiation field places certain constraints on the possible values of the parameter α and the position of the emission region.

Dissipation of magnetic fields in active galactic nuclei

Dissipation of magnetic fields in active galactic nuclei

New Evidence for an Anisotropic Radiation Field in NGC 5252

view Abstract Citations (24) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New Evidence for an Anisotropic Radiation Field in NGC 5252 Prieto, M. Almudena ; Freudling, Wolfram Abstract Observational evidence accumulated over the last decade strongly supports the idea that the ionizing radiation field in active galactic nuclei (AGNs) is anisotropic. Here we report on new evidence for this anisotropy in the particular case of the Seyfert 2 galaxy NGC 5252. H I observations of this galaxy reveal neutral gas surrounding the nucleus but located outside the bicone of ionized gas that notably characterizes this object. The neutral gas is at a distance from the nucleus where it could be reached by the ionizing radiation if this were isotropically distributed. Publication: The Astrophysical Journal Pub Date: December 1993 DOI: 10.1086/173426 Bibcode: 1993ApJ...418..668P Keywords: GALAXIES: ACTIVE; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 5252; GALAXIES: SEYFERT; RADIO CONTINUUM: GALAXIES full text sources ADS | data products SIMBAD (6) NED (1)