KVN observations reveal multiple γ-ray emission regions in 3C 84?

The Astrophysical Journal, 2018

We analyzed Suzaku/XIS data (2006-2015) and Fermi/LAT data (2008-2015) of the gamma-ray emitting radio galaxy NGC 1275. Correlated brightening of the nucleus in both the X-ray and GeV gamma-ray energy bands was found for the period 2013-2015. This is the first evidence of correlated variability between these two energy bands for NGC 1275. We also analyzed Swift/XRT data and found that the X-ray flux increased over several days in 2010, coincidentally with the GeV gamma-ray flare. During the flare, the X-ray spectra were softer, with a photon index of ∼2 compared with 1.5-2.1 of the other periods, suggesting the brightening of a synchrotron component. The GeV gamma-ray band also showed a higher flux with a harder spectrum during the 2010 flare. Simultaneous X-ray and GeV gamma-ray flux increase in the flare could be explained by the shock-in-jet scenario. On the other hand, a long-term gradual brightening of radio, X-ray, and GeV gamma-ray flux with a larger gamma-ray amplitude could have an origin other than internal shocks, and some of these possibilities are discussed.

Galaxies

Gamma-ray emission from the bright radio source 3C 84, associated with the Perseus cluster, is ascribed to the radio galaxy NGC 1275 residing at the centre of the cluster. Study of the correlated X-ray/gamma-ray emission from this active galaxy, and investigation of the possible disk-jet connection, are hampered because the X-ray emission, particularly in the soft X-ray band (2–10 keV), is overwhelmed by the cluster emission. Here we present a method to spectrally decouple the cluster and active galactic nucleus (AGN) emission in imaging X-ray detectors. We use three sets of simultaneous Niel Gehrels Swift XRT and NuStar data. These observations were made during the period 2015 November to 2017 February, when a huge increase in the gamma-ray emission was observed. We find that the gamma-ray emission shows a very high degree of variability (40%–50%) on time scales of 1–10 days, whereas the hard X-ray emission, associated with the AGN, shows a low variability (∼15%–30%), on various ti...

Monthly Notices of The Royal Astronomical Society, 2011

We present the results of a ~ 3 year campaign to monitor the low luminosity active galactic nucleus (LLAGN) NGC 7213 in the radio (4.8 and 8.4 GHz) and X-ray bands (2-10 keV). With a reported X-ray Eddington ratio of 7 x 10^-4 L_Edd, NGC 7213 can be considered to be comparable to a hard state black hole X-ray binary. We show that a weak correlation exists between the X-ray and radio light curves. We use the cross-correlation function to calculate a global time lag between events in the X-ray and radio bands to be 24 +/- 12 days lag (8.4 GHz radio lagging X-ray), and 40 +/- 13 days lag (4.8 GHz radio lagging X-ray). The radio-radio light curves are extremely well correlated with a lag of 20.5 +/- 12.9 days (4.8 GHz lagging 8.4 GHz). We explore the previously established scaling relationship between core radio and X-ray luminosities and black hole mass L_{R} \propto M^{0.6-0.8} L_{X}^{0.6}, known as the `fundamental plane of black hole activity', and show that NGC 7213 lies very close to the best-fit `global' correlation for the plane as one of the most luminous LLAGN. With a large number of quasi-simultaneous radio and X-ray observations, we explore for the first time the variations of a single AGN with respect to the fundamental plane. Although the average radio and X-ray luminosities for NGC 7213 are in good agreement with the plane, we show that there is intrinsic scatter with respect to the plane for the individual data points.

Science, 2009

The Astrophysical Journal, 2012

Following the discovery of a new radio component right before the GeV γ -ray detection since 2008 August by the Fermi Gamma-ray Space Telescope, we present a detailed study of the kinematics and light curve on the central sub-parsec scale of 3C 84 using the archival Very Long Baseline Array 43 GHz data covering the period between 2002 January and 2008 November. We find that the new component "C3," previously reported by the observations with the Very Long Baseline Interferometer Exploration of Radio Astrometry, was already formed in 2003. The flux density of C3 increases moderately until 2008, and then it becomes brighter rapidly after 2008. The radio core, C1, also shows a similar trend. The apparent speed of C3 with reference to the core C1 shows moderate acceleration from 0.10c to 0.47c between 2003 November and 2008 November, but is still sub-relativistic. We further try to fit the observed broadband spectrum by the one-zone synchrotron self-Compton model using the measured apparent speed of C3. The fit can reproduce the observed γ -ray emission, but does not agree with the observed radio spectral index between 22 and 43 GHz.

The Astrophysical Journal, 2019

This paper reports a systematic search of X-ray cavities, density jumps and shocks in the inter-galactic environment of the galaxy group IC 1262 using Chandra, GMRT and VLA archival observations. The X-ray imaging analysis reveals a pair of X-ray cavities on the north and south of the X-ray peak, at projected distances of 6.48 kpc and 6.30 kpc respectively. Total mechanical power contained in both these cavities is found to be ∼12.37×10 42 erg s −1 , and compares well with the X-ray luminosity, within the cooling radius, measured to be ∼ 3.29 × 10 42 erg s −1 , suggesting that the mechanical power injected by the central AGN efficiently balances the radiative loss. We detect a previously unknown X-ray cavity at the position of southern radio lobe in the intra-group medium and find a loop of excess X-ray emission extending ∼100 kpc southwest from the central galaxy. The X-ray cavity at the position of southern radio lobe probably represents a first generation X-ray cavity. Two surface brightness edges are evident to the west and east−north of the center of this group. The radio galaxy at the core of the IC 1262 group is a rare low-redshift ultra-steep radio galaxy, its spectral index being α ∼ −1.73 (including the central AGN) and α ∼ −2.08 (excluding the central AGN). We detect a radio phoenix embedded within the southern radio lobe, for the first time in a poor group, with a spectral index (α ≤ −1.92). The spectral index distribution across the phoenix steepens with increasing distance from its intensity peak.

2022

The nearby type-II AGN 1ES1927+654 went through a violent changing-look (CL) event beginning December 2017 during which the optical and UV fluxes increased by four magnitudes over a few months, and broad emission lines newly appeared in the optical/UV. By July 2018 the X-ray coronal emission had completely vanished, only to reappear a few months later. In this work we report the evolution of the radio, optical, UV and X-rays from the pre-flare state through mid-2021 with new and archival data from the Very Long Baseline Array (VLBA), the European VLBI Network, the Very Large Array (VLA), the Telescopio Nazionale Galileo (TNG), Gran Telescopio Canarias (GTC), The Neil Gehrels Swift observatory and XMM-Newton. The main results from our work are: (1) The source has returned to its pre-CL state in optical, UV, and X-ray; the disk-corona relation has been re-established as has been in the pre-CL state, with an $\alpha_{\rm OX}\sim 1.02$. The optical spectra are dominated by narrow emission lines. (2) The UV light curve follows a shallower slope of $\propto t^{-0.91\pm 0.04}$ compared to that predicted by a tidal disruption event. We conjecture that a magnetic flux inversion event is the possible cause for this enigmatic event. (3) The compact radio emission which we tracked in the pre-CL (2014), during CL (2018) and post-CL(2021) at spatial scales $<1$ pc was at its lowest level during the changing look event in 2018, nearly contemporaneous with a low $2-10$ keV emission. The radio to X-ray ratio of the compact source $L_{\rm Radio}/L_{\rm X-ray}\sim 10^{-5.5}$, follows the Gudel-Benz relation, typically found in coronally active stars, and several AGN. (4) We do not detect any presence of nascent jets at the spatial scales of $\sim 5-10$ pc.

Publications of the Astronomical Society of Japan, 2010

Multi-epoch Very Long Baseline Interferometry (VLBI) study of a sub-pc scale jet of 3C 84 is presented. We carried out 14-epoch VLBI observations during 2006-2009 with the Japanese VLBI Network and the VLBI Exploration of Radio Astrometry, immediately following a radio outburst that began in 2005. We confirmed that the outburst was associated with the central 1 pc core, accompanying the emergence of a new component. This is striking evidence of the recurrence of jet activity. The new component became brighter during 2008, in contrast to constant -ray emission that was observed with the Fermi Gamma-ray Space Telescope during the same time. We found that the projected speed of the new component was 0.23 c from 2007/297 (2007 October 24) to 2009 /114 (2009 April 24) April 24). The direction of movement of this component differs from that of the pre-existing component by 40 ı . This was the first measurement of the kinematics of a sub-pc jet in a -ray active phase. A possible detection of jet deceleration and the jet kinematics in connection with the -ray emission is discussed.

Astronomy & Astrophysics, 2014

Context. The galaxy IC 310 has recently been identified as a γ-ray emitter by the Fermi-LAT and at very high energies (VHE, E>100 GeV) by the MAGIC telescopes. Originally classified as a head-tail radio galaxy, the nature of this object is subject of controversy because its nucleus shows blazar-like behavior. Aims. In order to understand the nature of IC 310 and the origin of the VHE emission we studied the spectral and flux variability of IC 310 from the X-ray band to the VHE γ-ray regime. Methods. The daily light curve of IC 310 above 300 GeV has been measured with the MAGIC telescopes from 2009 October to 2010 February. Contemporaneous Fermi-LAT data (2008)(2009)(2010)(2011) in the 10-500 GeV energy range were also analyzed. In the X-ray regime, archival observations from 2003 to 2007 with XMM-Newton, Chandra, and Swift-XRT in the 0.5-10 keV band were studied. Results. Several flares with similar amplitude can be seen in the MAGIC light curve. Day to day flux variability is clearly present (> 5 σ). The photon index between 120 GeV and 8 TeV is measured to be Γ ∼ 2.0 during both low and high flux states. It does not show variability, whereas the flux at 1 TeV changes by a factor of ∼ 7. Fermi-LAT detected only eight γ rays in the energy range 10 GeV-500 GeV in three years of observation. The measured photon index of Γ = 1.3 ± 0.5 in the Fermi-LAT range is very hard. The X-ray measurements show strong variability in both flux and photon index. The latter varied from 1.76 ± 0.07 to 2.55 ± 0.07. Conclusions. The rapid variability measured in γ rays and X-rays confirms the blazar-like behavior of the source. The spectral behavior measured in both energy bands suggest IC 310 could be linked to extreme high frequency peaked BL Lac objects (HBL). The apparent luminosity of IC 310 is a few orders of magnitude lower than other extreme HBLs however and, atypical for an HBL, it harbors a kiloparsec-scale radio structure. Thus, IC 310 could be a peculiar type of a HBL, i.e., an intermediate state between BL Lac and FR I radio galaxy.

Monthly Notices of the Royal Astronomical Society, 1999

We present a multiwavelength analysis of the prominent active galaxy NGC 1365, in particular looking at the radio and X-ray properties of the central regions of the galaxy.