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High cadence, linear, and circular polarization monitoring of OJ 287
摘要： Aims. We present a multifrequency, dense radio monitoring program of the blazar OJ 287 using the 100-m Effelsberg radio telescope. The program aims to test different binary supermassive black hole (SMBH) scenarios and studying the physical conditions in the central region of this bright blazar. Here, we analyze the evolution in total flux density, linear and circular polarization as a means to study the OJ 287 jet structure and its magnetic field geometry. Methods. We used a recently developed, high-precision data analysis methodology to recover all four Stokes parameters. We measured the total flux density of OJ 287 at nine bands from 2.64 GHz to 43 GHz, the linear polarization parameters at four bands between 2.64 GHz and 10.45 GHz, and the circular polarization at two bands, 4.85 GHz and 8.35 GHz. The mean cadence of our measurements is ten days. Results. Between December 2015 and January 2017 (MJD 57370–57785), OJ 287 showed flaring activity and complex linear and circular polarization behavior. The radio electric vector position angle (EVPA) showed a large clockwise (CW) rotation by ～340? with a mean rate of ?1.04?/day. Based on concurrent very long baseline interferometric (VLBI) polarization data at 15 GHz and 43 GHz, the rotation seems to originate within the jet core at 43 GHz (projected angular size ≤0.15 mas or 0.67 pc at the redshift of the source). Moreover, optical polarization data show a similar monotonic CW rotation with a rate of about ?1.1?/day which is superposed with shorter and faster rotations that exhibit rates of about 7.8?/day, mainly in the CW sense. Conclusions. The flux density and polarization variability of the single dish, VLBI and optical data is consistent with a polarized emission component propagating on a helical trajectory within a bent jet. We constrained the helix arc length to 0.26 pc and radius to ≤0.04 pc as well as the jet bending arc length projected on the plane of the sky to ≤1.9–7.6 pc. A similar bending has been observed also in high angular resolution VLBI images of the OJ 287 jet at its innermost regions. The helical trajectory covers only a part of the jet width, possibly its spine. In addition, our results indicate the presence of a stable polarized emission component. Its EVPA (?10?) is oriented perpendicular to the large scale jet, suggesting dominance of the poloidal magnetic field component. Finally, the EVPA rotation begins simultaneously with an optical flare and hence the two might be physically connected. That optical flare has been suggested to be linked to the interaction of a secondary SMBH with the inner accretion disk or originating in the jet of the primary.
关键词： BL Lacertae objects: individual: OJ 287,galaxies: active,quasars: supermassive black holes,magnetic fields,galaxies: jets,polarization
更新于2025-09-23 15:22:29
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Medium-resolution Optical and Near-infrared Spectral Atlas of 16 2MASS-selected NIR-red Active Galactic Nuclei at <i>z</i> ～ 0.3
摘要： We present medium-resolution spectra (R～2000–4000) at 0.4–1.0 μm and 0.7–2.5 μm of 16 active galactic nuclei (AGNs) selected with red color in the near-infrared (NIR) of J?K>2.0 mag at z～0.3. We fit the Hβ, Hα, Pβ, and Pα lines from these spectra to obtain their luminosities and line widths. We derive the E(B?V) color excess values of the NIR-red AGNs using two methods, one based on the line-luminosity ratios and another based on the continuum slopes. The two E(B?V) values agree with each other at rms dispersion ～0.249. About half of the NIR-red AGNs have g′?K<5 magnitude, and we find that these NIR-red, but blue in optical-NIR AGNs, have E(B?V)～0, suggesting that a significant fraction of the NIR color-selected red AGNs are unobscured or only mildly obscured. After correcting for the dust extinction, we estimate the black hole (BH) masses and the bolometric luminosities of the NIR-red AGNs using the Paschen lines to calculate their Eddington ratios (λEdd). The median Eddington ratios of nine NIR-red AGNs (log(λEdd)=?0.654±0.176) are only mildly higher than those of unobscured type 1 AGNs (log(λEdd)=?0.961±0.008). Moreover, we find that the MBH–σ* relation for three NIR-red AGNs is consistent with that of unobscured type 1 AGNs at similar redshift. These results suggest that the NIR-red color selection alone is not effective at picking up dusty, intermediate-stage AGNs.
关键词： quasars: general,quasars: emission lines,galaxies: Seyfert,quasars: supermassive black holes,galaxies: active,galaxies: evolution
更新于2025-09-23 15:21:21
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Spectropolarimetry of Seyfert 1 galaxies with equatorial scattering: black hole masses and broad-line region characteristics
摘要： Here we present the spectropolarimetric observations of a sample of 30 Type 1 active galactic nuclei (AGNs) and an analysis of the observed polarization in these AGNs. The observations have been performed with the 6 m telescope of SAO RAS using the modified SCORPIO-2 spectropolarimeter. We measured the Stokes parameters for the continuum and the broad H α line and obtained the values of polarization degree and the angle of polarization. We found that equatorial scattering is dominant polarization mechanism in the sample that allows us to use the observed polarization in the broad lines for determination of the central black hole (BH) masses and characteristics (the inclination and emissivity) of the broad-line region (BLR). We demonstrated that the recently proposed method of Afanasiev & Popovi′c (2015) for BH mass measurement gives accurate BH masses that are in a good correlation with the stellar velocity dispersion, and consequently, the masses determined by the polarization method can be used with calibration purposes. Additionally we found that the BLR in the sample of 30 AGNs has an averaged inclination of 35?±9? (mostly between 20? and 40?) and emissivity α ～ ?0.57 that is more flat than one expected for the classical accretion disc α ～ ?0.75.
关键词： quasars,quasars: supermassive black holes,line: profiles,emission lines,polarization,galaxies: nuclei,galaxies: active
更新于2025-09-09 09:28:46
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Linearly polarized millimeter and submillimeter continuum emission of Sgr A* constrained by ALMA
摘要： Aims. Our aim is to characterize the polarized continuum emission properties including intensity, polarization position angle, and polarization percentage of Sgr A* at ～100 (3.0 mm), ～230 (1.3 mm), ～345 (0.87 mm), ～500 (0.6 mm), and ～700 GHz (0.43 mm). Methods. We report continuum emission properties of Sgr A* at the above frequency bands, based on the Atacama Large Millimeter Array (ALMA) observations. We measured ?ux densities of Sgr A* from ALMA single pointing and mosaic observations. We performed sinusoidal ?ttings to the observed (XX-YY)/I intensity ratios, to derive the polarization position angles and polarization percentages. Results. We successfully detect polarized continuum emission from all observed frequency bands. We observed lower Stokes I intensity at ～700 GHz than that at ～500 GHz, which suggests that emission at (cid:38)500 GHz is from the optically thin part of a synchrotron emission spectrum. Both the Stokes I intensity and the polarization position angle at our highest observing frequency of ～700 GHz, may vary with time. However, as yet we do not detect variation in the polarization percentage at >500 GHz. The polarization percentage at ～700 GHz is likely lower than that at ～500 GHz. By comparing the ～500 GHz and ～700 GHz observations with the observations at lower frequency bands, we suggest that the intrinsic polarization position angle of Sgr A* varies with time. This paper also reports the measurable polarization properties from the observed calibration quasars. Conclusions. Future simultaneous multi-frequency polarization observations are required to clarify the time and frequency variation of the polarization position angle and polarization percentage.
关键词： techniques: polarimetric,techniques: interferometric,relativistic processes,quasars: supermassive black holes,radiation mechanisms: non-thermal,polarization
更新于2025-09-04 15:30:14