ABSTRACT The detection of periodicity in the broadband non-thermal emission of blazars has so far been proven to be elusive. However, there are a number of scenarios that could lead to quasi-periodic ...variations in blazar light curves. For example, an orbital or thermal/viscous period of accreting matter around central supermassive black holes could, in principle, be imprinted in the multi-wavelength emission of small-scale blazar jets, carrying such crucial information about plasma conditions within the jet launching regions. In this paper, we present the results of our time series analysis of the ∼9.2 yr long, and exceptionally well-sampled, optical light curve of the BL Lac object OJ 287. The study primarily used the data from our own observations performed at the Mt. Suhora and Kraków Observatories in Poland, and at the Athens Observatory in Greece. Additionally, SMARTS observations were used to fill some of the gaps in the data. The Lomb-Scargle periodogram and the weighted wavelet Z-transform methods were employed to search for possible quasi-periodic oscillations in the resulting optical light curve of the source. Both methods consistently yielded a possible quasi-periodic signal around the periods of ∼400 and ∼800 days, the former with a significance (over the underlying colored noise) of . A number of likely explanations for this are discussed, with preference given to a modulation of the jet production efficiency by highly magnetized accretion disks. This supports previous findings and the interpretation reported recently in the literature for OJ 287 and other blazar sources.
Starting from the Cambridge Catalogues of radio sources, we have created a sample of 401 Fanaroff-Riley type II (FR II) radio sources that have counterparts in the main galaxy sample of the seventh ...Data release of the Sloan Digital Sky Survey (SDSS) and analyse their radio and optical properties.
We find that the luminosity in the Hα line - which we argue gives a better measure of the total emission-line flux than the widely used luminosity in O iii- is strongly correlated with the radio luminosity P
1.4 GHz. We show that the absence of emission lines in about one third of our sample is likely due to a detection threshold and not to a lack of optical activity. We also find a very strong correlation between the values of L
Hα and P
1.4 GHz when scaled by 'M
BH', an estimate of the black hole mass.
We find that the properties of FR II galaxies are mainly driven by the Eddington parameter L
Hα/'M
BH' or, equivalently, P
1.4 GHz/'M
BH'. Radio galaxies with hotspots are found among the ones with the highest values of P
1.4 GHz/'M
BH'.
Compared to classical active galactic nuclei (AGN) hosts in the main galaxy sample of the SDSS, our FR II galaxies show a larger proportion of objects with very hard ionizing radiation field and large ionization parameter. A few objects are, on the contrary, ionized by a softer radiation field. Two of them have double-peaked emission lines and deserve more attention.
We find that the black hole masses and stellar masses in FR II galaxies are very closely related: 'M
BH'∝M
1.13
* with very little scatter. A comparison sample of line-less galaxies in the SDSS follows exactly the same relation, although the masses are, on average, smaller. This suggests that the FR II radio phenomenon occurs in normal elliptical galaxies, preferentially in the most massive ones. Although most FR II galaxies are old, some contain traces of young stellar populations. Such young populations are not seen in normal line-less galaxies, suggesting that the radio (and optical) activity in some FR II galaxies may be triggered by recent star formation. The 'M
BH'-M
* relation in a comparison sample of radio-quiet AGN hosts from the SDSS is very different, suggesting that galaxies which are still forming stars are also still building their central black holes.
Globally, our study indicates that, while radio and optical activity are strongly related in FR II galaxies, the features of the optical activity in FR IIs are distinct from those of the bulk of radio-quiet active galaxies.
An appendix (available as Supporting Information with the online version of the article) gives the radio maps of our FR II galaxies, superimposed on the SDSS images, and the parameters derived for our analysis that were not publicly available.
We present a systematic analysis of the mid-infrared (MIR) properties of the youngest radio galaxies, based on low-resolution data provided by the Wide-field Infrared Survey Explorer and IRAS ...satellites. We restrict our analysis to sources with available X-ray data that constitute the earliest phase of radio galaxy evolution, i.e., those classified as gigahertz-peaked spectrum and/or compact symmetric objects. In our sample of 29 objects, we find that the host galaxies are predominantly red/yellow ellipticals, with some of them displaying distorted morphology. We find a variety of MIR colors and observe that the sources in which the MIR emission is dominated by the ISM component uniformly populate the region occupied by galaxies with a wide range of pronounced (≥0.5M yr−1) star formation activity. We compare the MIR color distribution in our sample to that in the general population of local active galactic nuclei (AGNs), in the population of evolved FR II radio galaxies, and also in the population of radio galaxies with recurrent jet activity. We conclude that the triggering of radio jets in AGNs does not differentiate between elliptical hosts with substantially different fractions of young stars; instead, there is a relationship between the jet duty cycle and the ongoing star formation. The distribution of the subsample of our sources with z < 0.4 on the low-resolution MIR versus absorption-corrected X-ray luminosity plane is consistent with the distribution of a sample of local AGNs. Finally, we comment on the star formation rates of the two γ-ray-detected sources in our sample, 1146+596 and 1718-649.
J1420–0545: The Radio Galaxy Larger than 3C 236 Machalski, J; Kozieł-Wierzbowska, D; Jamrozy, M ...
Astrophysical journal/The Astrophysical journal,
05/2008, Volume:
679, Issue:
1
Journal Article
Peer reviewed
Open access
We report the discovery of the largest giant radio galaxy yet, J1420- 0545: a FR type II radio source with an angular size of 17.4 super(image ), identified with an optical galaxy at image. Thus, the ...projected linear size of the radio structure is 4.69 Mpc (if we assume that image km s super(-1) Mpc super(-1), image, and image). This makes it larger than 3C 236, which is the largest double radio source known to date. New radio observations with the 100 m Effelsberg telescope and the Giant Metrewave Radio Telescope, as well as optical identification with a host galaxy and its optical spectroscopy with the William Herschel Telescope, are reported. The spectrum of J1420-0545 is typical of elliptical galaxies in which continuum emission with the characteristic 4000 Aa discontinuity and the H and K absorption lines are dominated by evolved stars. The dynamical age of the source, its jets' power, the energy density, and the equipartition magnetic field are calculated and compared with the corresponding parameters of other giant and normal-sized radio galaxies from a comparison sample. The source is characterized by the exceptionally low density of the surrounding IGM and an unexpectedly high expansion speed of the source along the jet axis. All of these may suggest a large inhomogeneity of the IGM.
We present results of the modelling of multicolour light curves of 10 contact binary systems: V376 And, V523 Cas, CC Com, BX Dra, FG Hya, UZ Leo, XY Leo, AM Leo, EX Leo and RT LMi. The solutions ...resulted in a contact configuration for all systems. We found only FG Hya and UZ Leo to be in deep contact, the latter almost filling the outer critical lobe. The absolute parameters of the components have been determined with an accuracy of about a few per cent based on combined photometric and radial velocity curves, enlarging the sample of systems to 58 for which the physical parameters have been obtained in a uniform way. All but three systems (BX Dra, AM Leo and RT LMi) show asymmetries and peculiarities in the observed light curves, interpreted as resulting from their magnetic activity.
We announce the discovery of a unique combination of features in a radio source identified with the merger galaxy CGCG 292−057. The radio galaxy both exhibits a highly complex, X-like structure and ...shows signs of recurrent activity in the form of double-double morphology. The outer lobes of CGCG 292−057 are characterized by low radio power, P
1400 MHz≃ 2 × 1024 W Hz−1, placing this source below the FR II/FR I luminosity threshold, and are highly polarized (almost 20 per cent at 1400 MHz) as is typical of X-shaped radio sources. The host is a low-ionization nuclear emission-line region-type galaxy with a relatively low black hole mass and double-peaked narrow emission lines. These features make this galaxy a primary target for studies of merger-triggered radio activity.
We compare the optical properties of the host galaxies of radio-quiet (RQ) and radio-loud (RL) Type 2 active galactic nuclei (AGNs) to infer whether the jet production efficiency depends on the host ...properties or is determined just by intrinsic properties of the accretion flows. We carefully select galaxies from SDSS, FIRST, and NVSS catalogs. We confirm previous findings that the fraction of RL AGNs depends on the black-hole (BH) masses, and on the Eddington ratio. The comparison of the nature of the hosts of RL and RQ AGNs, therefore, requires pair-matching techniques. Matching in BH mass and Eddington ratio allows us to study the differences between galaxies hosting RL and RQ AGNs that have the same basic accretion parameters. We show that these two samples differ predominantly in the host-galaxy concentration index, morphological type (in the RL sample the frequency of elliptical galaxies becoming larger with increasing radio loudness), and nebular extinction (galaxies with highest radio loudness showing only low nebular extinction). Contrary to some previous studies, we find no significant difference between our radio-loud and radio-quiet samples regarding merger/interaction features.
Starting from the Cambridge Catalogues of radio sources, we have created a sample of 401 Fanaroff-Riley type II (FRII) radio sources that have counterparts in the main galaxy sample of the seventh ...Data release of the Sloan Digital Sky Survey (SDSS) and analyse their radio and optical properties. We find that the luminosity in the Hα line - which we argue gives a better measure of the total emission-line flux than the widely used luminosity in Oiii- is strongly correlated with the radio luminosity P1.4GHz. We show that the absence of emission lines in about one third of our sample is likely due to a detection threshold and not to a lack of optical activity. We also find a very strong correlation between the values of LHα and P1.4GHz when scaled by 'MBH', an estimate of the black hole mass. We find that the properties of FRII galaxies are mainly driven by the Eddington parameter LHα/'MBH' or, equivalently, P1.4GHz/'MBH'. Radio galaxies with hotspots are found among the ones with the highest values of P1.4GHz/'MBH'. Compared to classical active galactic nuclei (AGN) hosts in the main galaxy sample of the SDSS, our FRII galaxies show a larger proportion of objects with very hard ionizing radiation field and large ionization parameter. A few objects are, on the contrary, ionized by a softer radiation field. Two of them have double-peaked emission lines and deserve more attention. We find that the black hole masses and stellar masses in FRII galaxies are very closely related: 'MBH'M1.13* with very little scatter. A comparison sample of line-less galaxies in the SDSS follows exactly the same relation, although the masses are, on average, smaller. This suggests that the FRII radio phenomenon occurs in normal elliptical galaxies, preferentially in the most massive ones. Although most FRII galaxies are old, some contain traces of young stellar populations. Such young populations are not seen in normal line-less galaxies, suggesting that the radio (and optical) activity in some FRII galaxies may be triggered by recent star formation. The 'MBH'-M* relation in a comparison sample of radio-quiet AGN hosts from the SDSS is very different, suggesting that galaxies which are still forming stars are also still building their central black holes. Globally, our study indicates that, while radio and optical activity are strongly related in FRII galaxies, the features of the optical activity in FRIIs are distinct from those of the bulk of radio-quiet active galaxies. An appendix (available as Supporting Information with the online version of the article) gives the radio maps of our FRII galaxies, superimposed on the SDSS images, and the parameters derived for our analysis that were not publicly available. PUBLICATION ABSTRACT
We explore the disk-jet connection in the broad-line radio quasar 4C+74.26, utilizing the results of multiwavelength monitoring of the source. The target is unique in that its radiative output at ...radio wavelengths is dominated by a moderately beamed nuclear jet, at optical frequencies by the accretion disk, and in the hard X-ray range by the disk corona. Our analysis reveals a correlation (local and global significance of 96% and 98% respectively) between the optical and radio bands, with the disk lagging behind the jet by 250 42 days. We discuss the possible explanation for this, speculating that the observed disk and the jet flux changes are generated by magnetic fluctuations originating within the innermost parts of a truncated disk, and that the lag is related to a delayed radiative response of the disk when compared with the propagation timescale of magnetic perturbations along a relativistic outflow. This scenario is supported by re-analysis of NuSTAR data, modeled in terms of a relativistic reflection from the disk illuminated by the coronal emission, which returns an inner disk radius . We discuss the global energetics in the system, arguing that while the accretion proceeds at the Eddington rate, with the accretion-related bolometric luminosity Lbol ∼ 9 × 1046 erg s−1 ∼ 0.2LEdd, the jet total kinetic energy Lj ∼ 4 × 1044 erg s−1, inferred from the dynamical modeling of the giant radio lobes in the source, constitutes only a small fraction of the available accretion power.
ABSTRACT
This paper presents the results of a combined spectroscopic and photometric study of 20 contact binary systems: HV Aqr, OO Aql, FI Boo, TX Cnc, OT Cnc, EE Cet, RW Com, KR Com, V401 Cyg, ...V345 Gem, AK Her, V502 Oph, V566 Oph, V2612 Oph, V1363 Ori, V351 Peg, V357 Peg, Y Sex, V1123 Tau, and W UMa, which was conducted in the frame of the W UMa Project. Together with 51 already covered by the project and an additional 67 in the existing literature, these systems bring the total number of contact binaries with known combined spectroscopic and photometric solutions to 138. It was found that mass, radius, and luminosity of the components follow certain relations along the MS and new empirical power relations are extracted. We found that 30 per cent of the systems in the current sample show extreme values in their parameters, expressed in their mass ratio or fill-out factor. This study shows that, among the contact binary systems studied, some have an extremely low mass ratio (q < 0.1) or an ultrashort orbital period (Porb < 0.25 d), which are expected to show evidence of mass transfer progress. The evolutionary status of these components is discussed with the aid of correlation diagrams and their physical and orbital parameters compared to those in the entire sample of known contact binaries. The existence of very short orbital periods confirms the very slow nature of the merging process, which seems to explain why their components still exist as MS stars in contact configurations even after several Gyr of evolution.
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