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Register a new userX-ray, UV, and Radio Timing Observations of the Radio Galaxy 3C 120
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We report the results of monitoring of the radio galaxy 3C 120 with the Neil Gehrels Swift Observatory, Very Long Baseline Array, and Metsahovi Radio Observatory. The UV-optical continuum spectrum and R-band polarization can be explained by a superposition of an inverted-spectrum source with a synchrotron component containing a disordered magnetic field. The UV-optical and X-ray light curves include dips and flares, while several superluminal knots appear in the parsec-scale jet. The recovery time of the second dip was longer at UV-optical wavelengths, in conflict with a model in which the inner accretion disk (AD) is disrupted during a dip and then refilled from outer to inner radii. We favor an alternative scenario in which occasional polar alignments of the magnetic field in the disk and corona cause the flux dips and formation of shocks in the jet. Similar to observations of Seyfert galaxies, intra-band time lags of flux variations are longer than predicted by the standard AD model. This suggests that scattering or some other reprocessing occurs. The 37 GHz light curve is well correlated with the optical-UV variations, with a ~20-day delay. A radio flare in the jet occurred in a superluminal knot 0.14 milliarcseconds downstream of the 43 GHz core, which places the site of the preceding X-ray/UV/optical flare within the core 0.5-1.3 pc from the black hole. The inverted UV-optical flare spectrum can be explained by a nearly mono-energetic electron distribution with energy similar to the minimum energy inferred in the TeV gamma-ray emitting regions of some BL Lacertae objects.
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We present the analysis of the radio jet evolution of the radio galaxy 3C 120 during a period of prolonged gamma-ray activity detected by the Fermi satellite between December 2012 and October 2014. We find a clear connection between the gamma-ray and radio emission, such that every period of gamma-ray activity is accompanied by the flaring of the mm-VLBI core and subsequent ejection of a new superluminal component. However, not all ejections of components are associated with gamma-ray events detectable by Fermi. Clear gamma-ray detections are obtained only when components are moving in a direction closer to our line of sight.This suggests that the observed gamma-ray emission depends not only on the interaction of moving components with the mm-VLBI core, but also on their orientation with respect to the observer. Timing of the gamma-ray detections and ejection of superluminal components locate the gamma-ray production to within almost 0.13 pc from the mm-VLBI core, which was previously estimated to lie about 0.24 pc from the central black hole. This corresponds to about twice the estimated extension of the broad line region, limiting the external photon field and therefore suggesting synchrotron self Compton as the most probable mechanism for the production of the gamma-ray emission. Alternatively, the interaction of components with the jet sheath can provide the necessary photon field to produced the observed gamma-rays by Compton scattering.
We present the spectral analysis of a 200~ks observation of the broad-line radio galaxy 3C~120 performed with the high energy transmission grating (HETG) spectrometer on board the emph{Chandra} X-ray Observatory. We find (i) a neutral absorption component intrinsic to the source with column density of $text{log}N_H = 20.67pm0.05$~cm$^{-2}$, (ii) no evidence for a warm absorber with an upper limit on the column density of just $text{log}N_H < 19.7$~cm$^{-2}$ assuming the typical ionization parameter log$xi$$simeq$2.5~erg~s$^{-1}$~cm, the warm absorber may instead be replaced by (iii) a hot emitting gas with temperature $kT simeq 0.7$~keV observed as soft X-ray emission from ionized Fe L-shell lines which may originate from a kpc scale shocked bubble inflated by the AGN wind or jet with a shock velocity of about 1,000~km~s$^{-1}$ determined by the emission line width, (iv) a neutral Fe K$alpha$ line and accompanying emission lines indicative of a Compton-thick cold reflector with low reflection fraction $Rsimeq0.2$, suggesting a large opening angle of the torus, (v) a highly ionized Fe~XXV emission feature indicative of photoionized gas with ionization parameter log$xi$$=$$3.75^{+0.27}_{-0.38}$~erg~s$^{-1}$~cm and a column density of $text{log}N_H > 22$~cm$^{-2}$ localized within $sim$2~pc from the X-ray source, and (vi) possible signatures for a highly ionized disk wind. Together with previous evidence for intense molecular line emission, these results indicate that 3C~120 is likely a late state merger undergoing strong AGN feedback.
We present the results of extensive multi-frequency monitoring of the radio galaxy 3C 120 between 2002 and 2007 at X-ray, optical, and radio wave bands, as well as imaging with the Very Long Baseline Array (VLBA). Over the 5 yr of observation, significant dips in the X-ray light curve are followed by ejections of bright superluminal knots in the VLBA images. Consistent with this, the X-ray flux and 37 GHz flux are anti-correlated with X-ray leading the radio variations. This implies that, in this radio galaxy, the radiative state of accretion disk plus corona system, where the X-rays are produced, has a direct effect on the events in the jet, where the radio emission originates. The X-ray power spectral density of 3C 120 shows a break, with steeper slope at shorter timescale and the break timescale is commensurate with the mass of the central black hole based on observations of Seyfert galaxies and black hole X-ray binaries. These findings provide support for the paradigm that black hole X-ray binaries and active galactic nuclei are fundamentally similar systems, with characteristic time and size scales linearly proportional to the mass of the central black hole. The X-ray and optical variations are strongly correlated in 3C 120, which implies that the optical emission in this object arises from the same general region as the X-rays, i.e., in the accretion disk-corona system. We numerically model multi-wavelength light curves of 3C 120 from such a system with the optical-UV emission produced in the disk and the X-rays generated by scattering of thermal photons by hot electrons in the corona. From the comparison of the temporal properties of the model light curves to that of the observed variability, we constrain the physical size of the corona and the distances of the emitting regions from the central BH.
We present XMM-Newton observations of the radio galaxy 3C 120. The hard X-ray spectrum contains a marginally resolved Fe I K-alpha emission line with FWHM=9,000 km/s and an equivalent width of 57 eV. The line arises via fluorescence in a broad-line region with covering fraction of 0.4. There is no evidence of relativistically broad Fe K-alpha, contrary to some previous reports. The normal equivalent widths of the X-ray and optical emission lines exclude a strongly beamed synchrotron component to the hard X-ray and optical continua. There is an excess of 0.3-2 keV soft X-ray continuum over an extrapolation of the hard X-ray power-law, which may arise in a disk corona. Analysis of an archival Chandra image shows that extended emission from the jet and other sources contributes <3% of the total X-ray flux. A break in the X-ray spectrum below 0.6 keV indicates an excess neutral hydrogen column density of N_H=1.57 * 10^21 cm^{-2}. However, the neutral absorber must have an oxygen abundance of <1/50 of the solar value to explain the absence of an intrinsic or intervening O I edge. There is no ionized absorption in the soft X-ray spectrum, but there is a weak, narrow O VIII Ly-alpha emission line. We do not detect previously claimed O VIII absorption from the intervening intergalactic medium. Radio observations at 37 GHz show a fast, high frequency flare starting 8 days after the XMM-Newton observation. However, this has no obvious effect on the X-ray spectrum. The X-ray spectrum, including the soft excess, became harder as the X-ray flux decreased, with an estimated pivot energy of 40 keV. The UV and soft X-ray fluxes are strongly correlated over the 120 ks duration of the XMM-Newton observation. This is qualitatively consistent with Comptonization of UV photons by a hot corona. (Abridged)
We present six-year multi-wavelength monitoring result for broad-line radio galaxy 3C 120. The source was sporadically detected by Fermi-LAT and after the MeV/GeV gamma-ray detection the 43 GHz radio core brightened and a knot ejected from an unresolved core, implying that the radio-gamma phenomena are physically connected. We show that the gamma-ray emission region is located at sub-pc distance from the central black hole, and MeV/GeV gamma-ray emission mechanism is inverse-Compton scattering of synchrotron photons. We also discuss future perspective revealed by next-generation X-ray satellite Astro-H.
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