Four Late-type Galaxies with Double Radio Lobes and Properties of Such Galaxies

The triggering mechanism for radio lobes from late-type galaxies is not fully understood.More samples are desired for a thorough investigation and statistics.By utilizing the optical data from the newly released Dark Energy Spectroscopic Instrument imaging surveys and the radio sources from the NRAO VLA Sky Survey and the Faint Images of the Radio Sky at Twenty-centimeter,we identify four Late-type Galaxies with double Radio Lobes(La GRLs):J0217-3645,J0947+6220,J1412+3723 and J1736+5108.Including previously known La GRLs,we confirm the correlation between radio power P_(1.4GHz)and stellar mass M_(*)of host galaxies.Most(25/35)La GRLs belong to the blue cloud galaxies,while the newly identified cases in this work are located within the region of the red sequence.We find a clear correlation between the differential radio power,i.e.,the offset from the P_(1.4GHz)-M_(*)relation,and the galaxy color,indicating that bluer galaxies at a fixed M_(*)tend to host more powerful radio lobes.Furthermore,the majority(31/36)of La GRLs are either located in a galaxy group or displaying a disturbed morphology.We suggest that all of the galaxy mass,color and surrounding environment could play important roles in triggering radio lobes in late-type galaxies.

An X-Ray Study of Lobe-Dominated Radio-Loud Quasars with XMM-Newton

We report on our results of X-ray spectral analysis for a sample of radio-loud quasars covering a wide range of the radio core-dominance parameter, R, from core- dominated to lobe-dominated objects, using data obtained mostly with the XMM-Newton Observatory. We find that the spectral shape of the underlying power-law continuum is flat even for the lobe-dominated objects （average photon index ~ 1.5）, indistinguishable from that of core-dominated quasars. For lobe-dominated objects, contribution of X-rays from the jets is expected to be very small based on previous unification schemes, more than one order of magnitude lower than the observed X-ray luminosities. Assuming that radio-loud quasars follow the same X-ray-UV/optical luminosity relation for the disk-corona emission as found for radio-quiet quasars, we estimate the X-ray flux contributed by the disk-corona component from the optical/UV continuum. We find that neither the luminosity, nor the spectral shape, of the disk-corona X-ray emission can account for the bulk of the observed X-ray properties. Thus in lobe-dominated quasars, either the disk-corona X-ray emission is much enhanced in strength and flatter in spectral shape （photon index - 1.5） compared to normal radio-quiet quasars, or their jet X-ray emission is much enhanced compared to their weak radio core-jet emission. If the latter is the case, our result may imply that the jet emission in X-rays is less Doppler beamed than that in the radio. As a demonstrating example, we test this hypothesis by using a specific model in which the X-ray jet has a larger opening angle than the radio jet.

The pc-scale radio structure of MIR-observed radio galaxies

We investigated the relationship between the accretion process and jet properties by utilizing very long baseline array （VLBA） and mid-infrared （MIR） data for a sample of 45 3CRR radio galaxies selected with a flux density at 178MHz 〉 16.4Jy, 5 GHz very large array （VLA） core flux density ≥7 mJy and MIR observations. The pc-scale radio structure at 5 GHz is presented by using our VLBA observations for 21 sources acquired in February, 2016, the analysis of archival data for 16 objects and directly obtaining measurements for eight radio galaxies available from literatures. The accretion mode is constrained from the Eddington ratio with a dividing value of 0.01, which is estimated from the MIR-based bolometric luminosity and the black hole masses. While most Fanaroff-Riley type II radio galaxies （FRIIs） have higher Eddington ratio than Fanaroff-Riley type I radio galaxies （FRIs）, we found that there is indeed no single correspondence between the FR morphology and accretion mode with eight FRIIs at low accretion rate and two FRIs at high accretion rate. There is a significant correlation between the VLBA core luminosity at 5 GHz and the Eddington ratio. Various morphologies are identi- fied in our sample, including core only, single-sided core-jet and two-sided core-jet structures. We found that the higher accretion rate may be more likely related with the core-jet structure, thus generating a more extended jet. These results imply that the higher accretion rates are likely able to produce more powerful jets. There is a strong correlation between the MIR luminosity at 15 ktm and VLBA 5 GHz core luminosity, in favor of the tight relation between the accretion disk and jets. In our sample, the core brightness temperature ranges from 109 to 101338 K with a median value of 10^11.09K, indicating that systematically the beaming effect may not be significant. The exceptional cases, FRIs at high accretion rates and FRIIs at low accretion rates, are exclusively at the high and low ends, respectively, of the distribution of the flux ratio for VLBA core to 178 MHz flux density. It is not impossible that the locations of these sources are due to the recent shining or weakening of their central engines （i.e., both accretion and jet）.

Radio Identifications of Markarian Galaxies and the Correlation between Radio and Far-Infrared Properties

By checking DSS optical images and NVSS radio images, 782 Markarian galaxies were identified to be NVSS radio sources. A comparison of the radio luminosity at 1.4GHz and the far-infrared （FIR） luminosity for 468 “normal” galaxies shows a tight correlation. Most of the Seyfert galaxies and quasars follow the radio-FIR relation deduced from the “normal” galaxy sample, but with a somewhat larger scatter. A total 167 Markarian galaxies, comprising 100 “normal” galaxies, 66 Seyfert galaxies and one quasar, have either excess radio emission or much lower FIR spectral index α（25 μm, 60 μm）. These galaxies may be classified as “AGN-powered”. For “normal” galaxies, the average q value （defined as the log ratio between FIR and radio luminosities） is 2.3. There seems a trend for q to slightly decrease with increasing radio luminosity. This may imply that the ongoing active star formation in galaxies with higher radio luminosities is more efficient in heating the cosmic-ray electrons.

Properties of the Narrow Line Seyfert 1 Galaxies Revisited

There is growing evidence to suggest that the black hole mass has been previously underestimated with the Hb line width for certain Active Galactic Nuclei (AGN). With the assumption of the flatter rather than isotropic velocity distribution of gases in the broad-line region of AGN, we investigated the properties of Narrow Line Seyfert 1 (NLS1) galaxies, like the black hole mass and the Eddington ratio, and compared with Broad Line Seyfert 1 (BLS1) galaxies. Since gamma-rays detected in a few NLS1s which favored a smaller viewing angle in NLS1s than BLS1s, with the projection effect, we estimated the relative black hole mass and Eddington ratio for NLS1s and BLS1s. The result implies that the NLS1s and BLS1s have similar black hole masses and Eddington ratios, peaked at a larger black hole mass and lower Eddington ratio for the NLS1s than thought before. Furthermore, with applying the correction factor 6 of average black hole mass as derived from the modeling of both optical and UV data in radio-loud NLS1s by Calderone et al., to the Xu et al. sample, we find that the NLS1s and BLS1s also show similar black hole masses and Eddington ratios, peaked at 2.0 × 107 solar masses and 0.12 (Eddington ratio) for the NLS1s. The relation due to the enhanced black hole masses of NLS1s is discussed. In addition, there seems to show a linear correlation between jet power and disk luminosity for the flat spectrum radio-loud NLS1 sample, which implies an accretion dominated rather than black hole spin dominated jet.

Non-ballistic motion and precessing helical trajectory in quasar NRAO 150

NRAO 150 is a very special radio quasar in which prominent non-ballistic superluminal motion has been observed in its inner-jet region. We apply model-fittings to the kinematics of the superluminal knots（trajectory, distance from the core and apparent velocity） in terms of a helical precessing jet-nozzle model.Five cases are considered in which the angle between the jet axis and the line of sight is assumed to be 6？,3？, 1？, 0.6？ and 0.12？, respectively. It is shown that the superluminal components have intrinsic acceleration in the innermost regions（≤0.2 mas from the core）. The phenomenon of precessing nozzle/trajectory can be understood on the basis of relativistic magnetohydrodynamic theories for relativistic jets.

Multifrequency Polarization Variations in the Quasar 0917+624

We present a detailed analysis of multi-frequency observations of linear polarization in the intraday variable quasar 0917+624 (z = 1.44). The observations were made in May 1989 at five frequencies (1.4, 2.7, 5.0, 8.3 and 15GHz) with the VLA and the Effelsberg 100 m-telescope and in December 1988 at two frequencies (2.7 and 5.0 GHz) with the latter. It is shown that the relationship between the variations of the polarized and total flux density is highly wavelength dependent, and the multi-frequency polarization behavior may be essential for investigating the mechanisms causing these variations. It is shown that the variations observed at 20 cm can be interpreted in terms of refractive interstellar scintillation. However, after subtracting the variation due to scintillation, three 'features' emerged in the light-curve of the polarized flux density, indicating an additional variable component. Interestingly, these features are shown to be correlated with the variations at 2-6 cm, thus indicating that these features and the associated variations are due to some intrinsic causes. Moreover, a very rapid polarization angle swing of - 180° observed in December 1988 which cannot be explained by refractive interstellar scintillation, may also be produced by an intrinsic mechanism. Accordingly, we use a shock model to explain the polarization variations observed at the higher frequencies, although scintillation could also exist. The shock model can explain not only the variation of intensity, but also the time variation of its degree and angle of polarization, including the rapid swing of the polarization angle. It is shown that the degree and angle of polarization of the shock need only vary slightly in order to account for the observed complicated behaviour of polarization.

Optical identification of radio-loud active galactic nuclei in the ROSAT-Green-Bank sample with SDSS spectroscopy

Results of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank （RGB） catalog are presented （Brinkmann et al. 1997） which have been spectroscopically observed in the Sloan Digital Sky Survey （SDSS） DR5. The SDSS spectra of the optical counterparts are modeled in a careful and selfconsistent way by incorporating the host galaxy＇s starlight. Optical emission line parameters are presented, which are derived accurately and reliably, along with the radio 1.4- 5 GHz spectral indices estimated using （non-simultaneous） archival data. For 72 sources, the identifications are presented for the first time. It is confirmed that the majority of strong radio/X-ray emitters are radio-loud active galactic nuclei （AGNs）, particularly blazars. Taking advantage of the high spectral quality and resolution and our refined spectral modeling, we are able to disentangle narrow line radio galaxies （NLRGs）, as vaguely termed in most previous identification work, into Seyfert II galaxies and LINERs （low-ionization nuclear emission regions）, based on the standard emission line diagnostics. The NLRGs in the RGB sample, mostly belonging to ＇weak line radio galaxies＇, are found to have optical spectra consistent predominantly with LINERs, and only a small fraction with Seyfert II galaxies. A small number of LINERs have radio power as high as 10623 - 10^26 W Hz^- 1 at 5 GHz, being among the strongest radio emitting LINERs known so far. Two sources are identified with radio-loud narrow line Seyfert 1 galaxies （NLS 1 s）, a class of rare objects. The presence is also confirmed of flat-spectrum radio quasars whose radio-optical-X-ray effective spectral indices are similar to those of High-energy peaked BL Lacs （HBLs）, as suggested by Padovani et al., although it is still a debate as to whether this is the case for their actual spectral energy distributions.

The connection between radio and γ-ray emission in Fermi/LAT blazars

We collect the second Large Area Telescope AGN catalog （2LAC） and Monitor of Jets in AGN with VLBA Equipment （MOJAVE） quasi-simultaneous data to investigate the radio-γ connection of blazars. The cross sample contains 166 sources. The statistical analysis based on this sample confirms positive correlations between these two bands, but the correlations become weaker as the γ-ray energy increases. The statistical results between various parameters show negative correla- tions of γ-ray photon spectral index with γ-ray loudness for both Flat Spectrum Radio Quasars （FSRQs） and BL Lacertae objects, positive correlations of γ-ray variability index with the γ-ray loudness for FSRQs, a negative correlation of the γ-ray variabil- ity index with the γ-ray photon spectral index for FSRQs, and negative correlations of γ-ray photon spectral index with γ-ray luminosity for FSRQs. These results suggest that the γ-ray variability may be due to changes inside the γ-ray emission region like the injected power, rather than changes in the photon density of the external radiation fields, and the variability amplitude tends to be larger as the γ-rays are closer to the high energy peak of the spectral energy distribution （SED）. No correlation of variabil- ity index found for BL Lacertae objects implies that variability behavior may differ below and above the peak energy.

Radio observations of the first three-months of Fermi AGN at 4.8 GHz

Using the Urumqi 25 m radio telescope, sources from the first three months of the Fermi-large area telescope detected active galactic nuclei （AGN） catalog with a declination of 〉 0° were observed in 2009 at 4.8 GHz. The radio flux density ap- peared to correlate with the γ-ray intensity. Intra-day variability （IDV） observations were performed in March, April and May 2009 for 42 selected γ-ray bright blazars, and ~60% of them showed evidence of flux variability at 4.8 GHz during the IDV observations. The IDV detection rate was higher than that in previous flat-spectrum AGN samples. IDV appeared more often in the very long baseline interferometry-core dominant blazars, and the non-IDV blazars showed relatively ＂steeper＂ spectral in- dices than the IDV blazars. Pronounced inter-month variability was also found in two BL Lac objects： J0112＋2244 and J0238＋1636.

Correlated Radio-Optical Variations on Intraday Timescales

Correlated radio-optical variations on intraday timescales have been observed （e.g. in BLO 0716＋714） and such radio intraday variability is suggested to have an intrinsic origin. Recently, multi-wavelength observations, simultaneous at radio, mm-submm, optical and hard X-rays, of 0716＋714, show that during a period of intraday/interday variations at radio and mm wavelengths, the apparent brightness temperature of the source exceeded the Compton-limit （-10^12 K） by 2-4 orders of magnitude, but no Compton catastrophe （or no high luminosity of inverse-Compton radiation） was detected. It is also found that the intraday/interday variations at mm-submm wavelengths are consistent with the evolutionary behavior of a standard synchrotron source and for the intraday/interday variations at centimeter wavelengths opacity effects can play a significant role, which is consistent with the interpretation suggested previously by Qian et al. Thus the apparent high brightness temperatures may probably be explained in terms of Doppler boosting effects due to bulk relativistic motion of the source. We will argue a scenario to simulate the correlations between the radio and optical variations on intraday timescales observed in BLO 0716＋714 in terms of a relativistic shock propagating through a jet with a dual structure.

Spectral Indices of Core and Extended Components of Extragalactic Radio Sources

We use observed peak and total flux densities at 6cm and 20cm to determine the spectral indices separately for the core and extended components of QSOs and galaxies, as well as their core-dominance parameters. Our results indicate that 1) Nine QSOs show both greater than 1.0 core-dominance parameters (those objects should be blazars) and greater than 0.5 spectral indices. The average core spectral index is αCore = 0.85±0.21 for the nine blazars, which implies that it is not reliable to use αradio = 0.0 for blazars. For the different subclasses, the core and extended spectral indices are as follows: for the blazars, αCore = 0.22±0.06 and αExt =0.77±0.12; the galaxies,αCore = 1.01±0.13 and αExt =0.83±0.21, and for the QSOs, αCore = 0.28±0.10 and αExt =0.68±0.08. 2) The core spectral index and core dominance parameter (R) show an anti-correlation, αC = (-1.28±0.26) log R+ (0.65 ± 0.11); 3) R is approximately linearly correlated with redshift (z).

A Peculiar Broad Line Radio Galaxy 1938-155:VLA Observation at 90 cm

We observed 1938-155, a broad line radio galaxy (BLRG), with the Very Large Array (VLA) at 90cm with an angular resolution of 6.8' × 4.0'. The source consists of two components separated by 4 arcsec (- 20kpc, for H0 = 65km s-1 Mpc-1, q0 = 0.5) along the SE-NW direction. Both components show steep-spectra with a similar spectral index α - 0.83 ± 0.07 (Sv ∝ v-α). The bright double components are surrounded by a low-brightness cocoon. The radio properties of the two bright components are consistent with the hot spots produced by twin jets. An upper limit of - 0.0008 for the core dominance parameter (R) is inferred, suggesting there is no prominent radio core in the source. Assuming a modest viewing angle 30f77, a jet velocity is estimated - 0.07 c, based on the jet to counter-jet brightness ratio (J). The lower limit in jet speed inferred is consistent with no Doppler beaming effect on the jet. The radio galaxy 1938-155 could be an exceptional BLRG with no prominent radio core or jet.

A Composite Model for GHz Peaked Spectra of Radio Sources

GHz-Peaked Spectrum （GPS） radio sources are powerful and compact sources with convex spectra. With increasing observational findings, it has been realized that either Synchrotron Self-Absorption （SSA） alone or Free-Free Absorption （FFA） alone is not enough to account for all the spectral features. We present a model consisting of an SSA region partially covered by FFA plasma, and derive a composite spectral formula. By applying the model to a sample of 19 GPS sources having strong absorption, it is found that the external FFA process makes the SSA peak frequency linearly shift to a higher （observed） peak frequency. The shift indicates that the FFA does play a role at the frequency close to the observed peak frequency.

A Possible Periodicity in the Radio Light Curves of 3C 454.3

During the period 1966.5-2006.2 the 15 GHz and 8 GHz light curves of 3C 454.3 （z = 0.859） show a quasi-periodicity of ,-12.8 yr （-6.9 yr in the rest frame of the source） with a double-bump structure. This periodic behaviour is interpreted in terms of a rotating double-jet model in which the two jets are created from the black holes of a binary system and rotating with the period of the orbital motion. The periodic variations in the radio fluxes of 3C 454.3 are suggested to be mainly due to the lighthouse effects （or the variation in Doppler boosting） of the precessing jets caused by the orbital motion. In addition, variations in the rate of mass accreting onto the black holes may be also involved.

Extragalactic dispersion measures of fast radio bursts

Fast radio bursts show large dispersion measures, much larger than the Galactic dispersion measure foreground. Therefore, they evidently have an extragalac- tic origin. We investigate possible contributions to the dispersion measure from host galaxies. We simulate the spatial distribution of fast radio bursts and calculate the dis- persion measures along the sightlines from fast radio bursts to the edge of host galaxies by using the scaled NE2001 model for thermal electron density distributions. We find that contributions to the dispersion measure of fast radio bursts from the host galaxy follow a skew Gaussian distribution. The peak and the width at half maximum of the dispersion measure distribution increase with the inclination angle of a spiral galaxy, to large values when the inclination angle is over 70~. The largest dispersion measure produced by an edge-on spiral galaxy can reach a few thousand pc cm-3, while the dispersion measures from dwarf galaxies and elliptical galaxies have a maximum of only a few tens of pc cm-3. Notice, however, that additional dispersion measures of tens to hundreds of pc cm-3 can be produced by high density clumps in host galaxies. Simulations that include dispersion measure contributions from the Large Magellanic Cloud and the Andromeda Galaxy are shown as examples to demonstrate how to ex- tract the dispersion measure from the intergalactic medium.

Detection of a high-confidence quasi-periodic oscillation in radio light curve of the high redshift FSRQ PKS J0805–0111

In this work,we have searched for quasi-periodic oscillations(QPOs)in the 15 GHz light curve of the FSRQ PKS J0805-0111 monitored by the Owens Valley Radio Observatory(OVRO)40 m telescope during the period from 2008 January 9 to 2019 May 9,using the weighted wavelet Z-transform(WWZ)and the Lomb-Scargle Periodogram(LSP)techniques.This is the first time to search for a periodic radio signal in the FSRQ PKS J0805-0111 by these two methods.Both methods consistently reveal a repeating signal with a periodicity of 3.38±0.8 yr(>99.7%confidence level).In order to determine the significance of the periods,the false alarm probability method was applied,and a large number of Monte Carlo simulations were performed.As possible explanations,we discuss a number of scenarios including the thermal instability of thin disks scenario,the spiral jet scenario and the binary supermassive black hole scenario.We expect that the binary black hole scenario,where the QPO is caused by the precession of binary black holes,is the most likely explanation.FSRQ PKS J0805-0111 thus could be a good binary black hole candidate.In the binary black hole scenario,the distance between the primary black hole and the secondary black hole is about 1.71×10^(16) cm.

Estimate of an environmental magnetic field of fast radio bursts

Fast radio bursts （FRBs） are a type of newly-discovered transient astronomical phenomenon. They have short durations, high dispersion measures and a high event rate. However, due to unknown dis- tances and undetected electromagnetic counterparts at other wavebands, it is difficult to further investigate FRBs. Here we propose a method to study their environmental magnetic field using an indirect method. Starting withdispersion measures and rotation measures （RMs）, we try to obtain the parallel magnetic field component ^-B ││ which is the average value along the line of sight in the host galaxy. Because both RMs and redshifls are now unavailable, we demonstrate the dependence of ^-B ││ on these two separate quantities. This result, if the RM and redshift of an FRB are measured, would be expected to provide a clue towards understanding an environmental magnetic field of an FRB.

The dying accretion and jet in a powerful radio galaxy of Hercules A

Hercules A(Her A)is one of a rare class of dying and transition-type objects,which has a pair of giant,powerful radio lobes and a weak radio core.We reduce and analyze the radio data of Her A that were observed by the Expanded Very Large Array(EVLA)during 2010-2011 at C band.The intensity distribution is very smooth along the edge of the lobe front and the intensity also sharply decreases at the edge,which supports that magnetic fields may play an important role in radio lobes.The spectrum of the weak core is very steep and the core flux becomes weaker by about ten percent when compared to what was observed twenty years ago,which suggest that the central engine is still dying quickly.Her A deviates a lot from the relation between[O III]luminosity and low-frequency 178 MHz luminosity(LO III-L178 MHz)as defined by other FR I/II sources.However,when only radio core emission is considered,it roughly follows an LO III-L178 MHzcorrelation.This result supports that the black-hole accretion and large-scale jet in Her A did not evolve simultaneously,and indicates that although the large-scale jet is still powerful,the accretion and inner jet have changed into an inactive state.Based on the estimated Bondi accretion rate,we model the spectrum of Her A with a radiatively inefficient accretion flow and jet model.

Spectral Reversal and Stratification of the Jet in 3C 273

Quasi-simultaneous VLBI observations at 15-86 GHz have shown that in the classical superluminal radio source 3C273, the spectral index a (Sv ∝ vα) has a systematic variation along the jet. For epoch 1995.15, a spectral reversal was observed at core distance - 1.5 mas, where the superluminal knot C12 located. Similarly, for epoch 1997.18, two spectral reversals were observed at core distances of -1.8 mas and -4.2 mas, where superluminal knots C11 and C14 werel respectively. These spectral reversals are associated with local maxim of the jet width. We suggest that this phenomenon may be related to a stratification of the jet structure, i.e., its physical parameters (flow velocity, Doppler factor, electron density and energy, magnetic field strength, etc.) are substantially dependent on the distance from the jet axis. These properties may be naturally formed through gasdynamic processes when the jet expands into a lower pressure ambient medium.