arXiv subjects

S. Komossa

Publications and source records attributed to S. Komossa.

At least 37 records · Page 2Linked to original sources

arXiv2024

On the nature of the radio calibrator and gamma-ray emitting NLS1 galaxy 3C 286 and its multiwavelength variability

The quasar 3C 286, a well-known calibrator source in radio astronomy, was found to exhibit exceptional multiwavelength properties. Its rich and complex optical emission-line spectrum revealed its narrow-line Seyfert 1 (NLS1) nature. Given its strong radio emission, this makes 3C 286 one of the radio-loudest NLS1 galaxies known to date. 3C 286 is also one of very few known compact steep-spectrum (CSS) sources detected in the gamma-ray regime. Observations in the X-ray regime, rarely carried out so far, revealed evidence for variability, raising the question if driven by the accretion disk or jet. 3C 286 is also well known for its damped Lyman alpha system from an intervening absorber at z = 0.692, triggering a search for the corresponding X-ray absorption along the line-of-sight. Here, we present new observations in the radio, X-ray, optical and UV band. The nature of the X-ray variability is addressed. Spectral evidence suggests that it is primarily driven by the accretion disk (not the jet), and the X-ray spectrum is well fit by a powerlaw plus soft excess model. The radio flux density and polarization remain constant at the Effelsberg telescope resolution, reconfirming the use of 3C 286 as radio calibrator. The amount of reddening/absorption along the line-of-sight {\em{intrinsic}} to 3C 286 is rigorously assessed. None is found, validating the derivation of a high Eddington ratio (L/L-Edd ~ 1) and of the very high radio-loudness index of 3C 286. Based on the first deep Chandra image of 3C 286, tentative evidence for hard X-ray emission from the SW radio lobe is reported. A large variety of models for the gamma-ray emission of 3C 286 is briefly discussed.

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arXiv2024

A Hot Mess: The Rich and Complex Soft Emitting Regions Surrounding the Reflection Dominated Flaring Central Engine of Mrk 1239

Previous X-ray works on Mrk 1239 have revealed a complex Narrow Line Seyfert 1 (NLS1) that exhibits substantial absorption and strong emission from both collisional (CIE) and photoionized (PIE) plasmas. Here, we report on deep-pointed observations with $XMM{\rm -}Newton$ and $NuSTAR$, along with $Swift$ monitoring, to understand the $0.3-30$ keV continuum emission and the central engine geometry. A strong X-ray flare, where the AGN brightens by a factor of five in $\sim30$ ks, is captured between $4-30$ keV and can be attributed to a brightening of the primary continuum. However, the lack of any variability below $\sim3$ keV on long- or short-time scales requires complete absorption of the AGN continuum with a neutral medium of column density $\sim 10^{23.5}{\rm cm}^{-2}$. The timing and spectral properties are consistent with a blurred reflection interpretation for the primary emission. The variability and presence of a Compton hump disfavours ionized partial covering. The neutral absorber, if outflowing, could be crashing into the surrounding medium and ISM to produce the low-energy continuum and CIE. Scattered emission off the inner torus could produce the PIE. The intricate scenario is demanded by the data and highlights the complexity of the environment that is normally invisible when overwhelmed by the AGN continuum. Objects like Mrk 1239 serve as important sources for unveiling the interface between the AGN and host galaxy environments.

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arXiv2024

Investigating the {Origin} of the Absorption-Line Variability in Narrow-Line Seyfert 1 Galaxy WPVS 007

Broad Absorption Line Quasars (BALQs) are actively accreting supermassive black holes that have strong outflows characterized by broad absorption lines in their rest-UV spectra. Variability in these absorption lines occurs over months to years depending on the source. WPVS 007, a low-redshift, low-luminosity Narrow-line Seyfert 1 (NLS1) shows strong variability over shorter timescales, providing a unique opportunity to study the driving mechanism behind this variability that may mimic longer scale variability in much more massive quasars. We present the first variability study using {the} spectral synthesis code SimBAL, which provides velocity-resolved changes in physical conditions of the gas using constraints from multiple absorption lines. Overall, we find WPVS 007 to have a highly ionized outflow with a large mass-loss rate and kinetic luminosity. We determine the primary cause of the absorption-line variability in WPVS 007 to be a change in covering fraction of the continuum by the outflow. This study is the first SimBAL analysis where multiple epochs of observation were fit simultaneously, demonstrating the ability of SimBAL to use the time-domain as an additional constraint in spectral models.

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arXiv2024

The calm before the (next) storm: no third outburst in 2019--2020, and ongoing monitoring of the transient AGN IC 3599

We report on follow-up observations of the Seyfert 1.9 galaxy IC 3599 with the NASA Neil Gehrels Swift mission. The detection of a second X-ray outburst in 2010 by Swift after the first discovery of a bright X-ray outburst in 1990 by ROSAT led to the suggestion of two very different explanations: The first one assumed that IC 3599 exhibits outbursts due to repeated partial tidal stripping of a star, predicting another outburst of IC 3599 in 2019/2020. The second, alternative scenario assumed that the event observed in X-rays is due to an accretion disk instability which would suggest a much longer period between the large outbursts. Our continued monitoring campaign by Swift allowed us to test the first scenario which predicted a repetition of high amplitude flaring activity in 2019/2020. We do not find any evidence of dramatic flaring activity with factors of 100 since the last X-ray outburst seen in 2010. These observations support the accretion disk scenario. Further, while IC 3599 remains in low emission states, the long-term X-ray light curve of IC 3599 reveals ongoing strong variability of a factor of a few. The most remarkable event is a mini flare of a factor of 10 in X-rays in December 2022. After that flare, the otherwise supersoft X-ray spectrum shows an exceptional hardening, reminiscent of a temporary corona formation.

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arXiv2024

Changing-look NLS1 galaxies, their detection with SVOM, and the case of NGC 1566

We discuss applications of the study of the new and barely explored class of changing-look (CL) narrow-line Seyfert 1 (NLS1) galaxies and comment on their detection with the space mission SVOM (Space Variable Objects Monitor). We highlight the case of NGC 1566, which is outstanding in many respects, for instance as one of the nearest known CL AGN undergoing exceptional outbursts. Its NLS1 nature is discussed, and we take it as a nearby prototype for systems that could be discovered and studied in the near future, including with SVOM. Finally, we briefly examine the broader implications and applications of CL events in NLS1 galaxies and show that such systems, once discovered in larger numbers, will greatly advance our understanding of the physics of the environment of rapidly growing supermassive black holes. This White Paper is part of a sequence of publications which explore aspects of our understanding of (CL) NLS1 galaxy physics with future missions.

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arXiv2023

Multiwavelength variability of gamma-ray emitting narrow-line Seyfert 1 galaxies

As one of the drivers of feedback in active galactic nuclei (AGNs), the jets launched from supermassive black holes (SMBHs) are important for understanding the co-evolution of SMBHs and their host galaxies. However, the formation of AGN jets is far from clear. The discovery of gamma-ray narrow-line Seyfert 1 (NLS1) galaxies during the past two decades has provided us with a new means of studying the link between jets and accretion processes and the formation of jets. Here, we explore the coupling of jet and accretion discs in seven bright gamma-ray NLS1 galaxies by studying simultaneous optical/ultraviolet and X-ray observations of these systems taken by Swift. The results show that, except for 1H 0323+342 in which the X-rays are significantly contributed from the accretion disc, the observed X-ray emission of the other sources is dominated by the jet, and accretion process makes little contribution if not absent. Although the origin of the X-ray emission is different, the broad-band spectral shape characterized by alpha_ox and the X-ray flux is found to follow the same evolutionary trend in 1H 0323+342, PMN J0948+0022, and PKS 1502+036. For the remaining sources, the trend is not observed or the sampling is not dense enough.

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arXiv2023

Absence of the predicted 2022 October outburst of OJ 287 and implications for binary SMBH scenarios

The project MOMO (Multiwavelength Observations and Modelling of OJ 287) was set up to test predictions of binary supermassive black hole (SMBH) scenarios and to understand disk-jet physics of the blazar OJ 287. After a correction, the precessing binary (PB) SMBH model predicted the next main outburst of OJ 287 in 2022 October, no longer in July, making the outburst well observable and the model testable. We have densely covered this period in our ongoing multi-frequency radio, optical, UV, and X-ray monitoring. The predicted outburst was not detected. Instead, OJ 287 was at low optical-UV emission levels, declining further into November. The predicted thermal bremsstrahlung spectrum was not observed either, at any epoch. Further, applying scaling relations, we estimate a SMBH mass of OJ 287 of 10^8 M_sun. The latest in a sequence of deep low-states that recur every 1-2 yrs is used to determine an upper limit on the Eddington ratio and on the accretion-disk luminosity. This limit is at least a factor of 10 lower than required by the PB model with its massive primary SMBH of >10^{10} M_sun. All these results favor alternative binary SMBH models of OJ 287 that neither require strong orbital precession nor a very large mass of the primary SMBH.

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arXiv2023

MOMO VI: Multifrequency radio variability of the blazar OJ 287 from 2015-2022, absence of predicted 2021 precursor-flare activity, and a new binary interpretation of the 2016/2017 outburst

Based on our dedicated Swift monitoring program, MOMO, OJ 287 is one of the best-monitored blazars in the X-ray--UV--optical regime. Here, we report results from our accompanying, dense, multi-frequency (1.4--44 GHz) radio monitoring of OJ 287 between 2015 and 2022 covering a broad range of activity states. Fermi gamma-ray observations are added. We characterize the radio flux and spectral variability in detail, including DCF and other variability analyses, and discuss its connection with the multiwavelength emission. Deep fades of radio and optical--UV fluxes are found to occur every 1--2 years. Further, it is shown that a precursor flare of thermal bremsstrahlung predicted by one of the binary supermassive black hole (SMBH) models of OJ 287 was absent. We then focus on the nature of the extraordinary, nonthermal 2016/2017 outburst that we initially discovered with Swift. We interpret it as the latest of the famous optical double-peaked outbursts of OJ 287, favoring binary scenarios that do not require a highly precessing secondary SMBH.

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arXiv2023

UV/Optical disk reverberation lags despite a faint X-ray corona in the AGN Mrk 335

We present the first results from a 100-day Swift, NICER and ground-based X-ray/UV/optical reverberation mapping campaign of the Narrow-Line Seyfert 1 Mrk 335, when it was in an unprecedented low X-ray flux state. Despite dramatic suppression of the X-ray variability, we still observe UV/optical lags as expected from disk reverberation. Moreover, the UV/optical lags are consistent with archival observations when the X-ray luminosity was >10 times higher. Interestingly, both low- and high-flux states reveal UV/optical lags that are 6-11 times longer than expected from a thin disk. These long lags are often interpreted as due to contamination from the broad line region, however the u band excess lag (containing the Balmer jump from the diffuse continuum) is less prevalent than in other AGN. The Swift campaign showed a low X-ray-to-optical correlation (similar to previous campaigns), but NICER and ground-based monitoring continued for another two weeks, during which the optical rose to the highest level of the campaign, followed ~10 days later by a sharp rise in X-rays. While the low X-ray countrate and relatively large systematic uncertainties in the NICER background make this measurement challenging, if the optical does lead X-rays in this flare, this indicates a departure from the zeroth-order reprocessing picture. If the optical flare is due to an increase in mass accretion rate, this occurs on much shorter than the viscous timescale. Alternatively, the optical could be responding to an intrinsic rise in X-rays that is initially hidden from our line-of-sight.

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arXiv2023

The Collisional and Photoionized Plasma in the Polarized NLS1 galaxy Mrk 1239

Mrk 1239 is a highly polarized NLS1 in the optical band, whose $0.3-3$ keV spectrum has remained remarkably consistent over more than two decades of observation. Previous analysis of this object suggested that the soft X-ray band was dominated by emission lines (collisionally and/or photoionized) from the distant host galaxy as the X-ray emission from the central engine was highly obscured. New XMM-Newton data of Mrk 1239 are presented here to investigate the soft X-ray band of this galaxy with high resolution. The first RGS spectra of this source reveal a plethora of ionized emission lines originating from two distinct plasmas, one collisionally ionized and the other photoionized at approximately equal brightness. The best fit model uses {\sc apec} and {\sc xstar} grids to account for the collisionally ionized and photoionized components, respectively. The fit improves significantly if the photoionized material is allowed to outflow at $\approx 500$ km s$^{-1}$, matching the outflow velocity of the forbidden O{\sc vii} emission line. From constraints on the ionization and density of the photoionized material we can estimate the location of it to be no further than a few pc from the central source, around the outer radius of the torus, which is consistent with the O{\sc vii}$(f)$ emission line. Properties of the collisionally ionized plasma are consistent with star formation rate (SFR) of $\approx 3 M_{\odot} \textrm{yr}^{-1}$, which is comparable with several previous measurements of the SFR in this galaxy.

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arXiv2022

Extreme Accretion Events: TDEs and Changing-Look AGN

We present a review of the topics of X-ray stellar tidal disruption events (TDEs) and changing-look active galactic nuclei (AGN). Stars approaching a supermassive black hole (SMBH) can be tidally disrupted and accreted. TDEs were first discovered in the X-ray regime and appear as luminous, giant-amplitude flares from inactive galaxies. The early X-ray observations with ROSAT also established the extreme X-ray spectral softness of these events with temperatures of order 50-100 eV that continues to be seen in the majority of more recently identified events. While the majority of X-ray TDEs has been identified from {\it inactive} galaxies and some showed the highest amplitudes of variability recorded from galaxy cores (amplitudes exceeding factors of 1000--6000), a small fraction of {\it active} galactic nuclei (AGN) has been found to be highly variable as well. In AGN, this so-called changing-look phenomenon often comes with a strong change in the optical broad emission lines, leading to Seyfert-type changes between class 1 and class 2. These two forms of activity represent the extremes of variability among active and quiescent galaxies, and have opened up a new window on understanding accretion physics under extreme conditions. Finally, we introduce the term ``frozen-look AGN'' to describe systems that show constant line emission despite strong/dramatic changes in the observed ionizing continuum. These systems are best explained by strong changes of absorption along our line-of-sight.

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arXiv2022

The X-ray view of optically selected dual AGN

We present a study of optically selected dual AGN with projected separations of 3--97~kpc. Using multi-wavelength (MWL) information (optical, X-rays, mid-IR), we characterized the intrinsic nuclear properties of this sample and compared them with those of isolated systems. Among the 124 X-ray detected AGN candidates, 52 appear in pairs and 72 as single X-ray sources. Through MWL analysis, we confirmed the presence of the AGN in a fraction >80\% of the detected targets in pairs (42 over 52). X-ray spectral analysis confirms the trend of increasing AGN luminosity with decreasing separation, suggesting that mergers may have contributed in triggering more luminous AGN. Through X/mid-IR ratio $vs$ X-ray colors, we estimated a fraction of Compton-thin AGN (with 10$^{22}$ cm$^{-2}$ $<$ N$_{\rm H} <$10$^{24}$ cm$^{-2}$) of about 80\%, while about 16\% are Compton thick (CT, with N$_{\rm H}>$10$^{24}$ cm$^{-2}$) sources. These fractions of obscured sources are larger than those found in samples of isolated AGN, confirming that pairs of AGN show higher obscuration. This trend is further confirmed by comparing the de-reddened [O\ III] emission with the observed X-ray luminosity. However, the derived fraction of Compton-thick sources in this sample at early stage of merging is lower than reported for late-merging dual-AGN samples. Comparing N$_{\rm H}$ from X-rays with that derived from E(B-V) from Narrow Line Regions, we find that the absorbing material is likely associated with the torus or the Broad Line Regions. We also explored the X-ray detection efficiency of dual-AGN candidates, finding that, when observed properly (at on-axis positions and with long exposures), X-ray data represent a powerful way to confirm and investigate dual-AGN systems.

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arXiv2022

Refining the prediction for OJ 287 next impact flare arrival epoch

The bright blazar OJ~287 routinely parades high brightness bremsstrahlung flares which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disk of a primary SMBH in a binary system. We begin by showing that these flares occur at times predicted by a simple analytical formula, based on the Kepler equation, which explains flares since 1888. The next impact flare, namely the flare number 26, is rather peculiar as it breaks the typical pattern of two impact flares per 12 year cycle. This will be the third bremsstrahlung flare of the current cycle that follows the already observed 2015 and 2019 impact flares from OJ~287. Unfortunately, astrophysical considerations make it difficult to predict the exact arrival epoch of the flare number 26. In the second part of the paper, we describe our recent OJ~287 observations. They show that the pre-flare light curve of flare number 22, observed in 2005, exhibits similar activity as the pre-flare light curve in 2022, preceding the expected flare number 26 in our model. We argue that the pre-flare activity most likely arises in the primary jet whose activity is modulated by the transit of the secondary SMBH through the accretion disk of the primary. Observing the next impact flare of OJ~287 in October 2022 will substantiate the theory of disk impacts in binary black hole systems.

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arXiv2022

Multiwavelength astrophysics of the blazar OJ 287 and the project MOMO

We are carrying out the densest and longest multiyear, multiwavelength monitoring project of OJ 287 ever done. The project MOMO (Multiwavelength Observations and Modelling of OJ 287) covers wavelengths from the radio to the high-energy regime. A few selected observations are simultaneous with those of the Event Horizon Telescope (EHT). MOMO aims at understanding disk-jet physics and at testing predictions of the binary black hole scenario of OJ 287. Here, we present a discussion of extreme outburst and minima states in context, and then focus on the recent flux and spectral evolution between 2021 and May 2022, including an ongoing bright radio flare. Further, we show that there is no evidence for precursor flare activity in our optical-UV-X-ray light curves that would be associated with any secondary supermassive black hole (SMBH) disk impact and that was predicted to start as thermal flare on 2021 December 23.

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arXiv2022

Host galaxy magnitude of OJ 287 from its colours at minimum light

OJ 287 is a BL Lacertae type quasar in which the active galactic nucleus (AGN) outshines the host galaxy by an order of magnitude. The only exception to this may be at minimum light when the AGN activity is so low that the host galaxy may make quite a considerable contribution to the photometric intensity of the source. Such a dip or a fade in the intensity of OJ 287 occurred in November 2017, when its brightness was about 1.75 magnitudes lower than the recent mean level. We compare the observations of this fade with similar fades in OJ 287 observed earlier in 1989, 1999, and 2010. It appears that there is a relatively strong reddening of the B$-$V colours of OJ 287 when its V-band brightness drops below magnitude 17. Similar changes are also seen V$-$R, V$-$I, and R$-$I colours during these deep fades. These data support the conclusion that the total magnitude of the host galaxy is $V=18.0 \pm 0.3$, corresponding to $M_{K}=-26.5 \pm 0.3$ in the K-band. This is in agreement with the results, obtained using the integrated surface brightness method, from recent surface photometry of the host. These results should encourage us to use the colour separation method also in other host galaxies with strongly variable AGN nuclei. In the case of OJ 287, both the host galaxy and its central black hole are among the biggest known, and its position in the black hole mass-galaxy mass diagram lies close to the mean correlation.

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arXiv2022

Unravelling the Innermost Jet Structure of OJ 287 with the First GMVA+ALMA Observations

We present the first very-long-baseline interferometric (VLBI) observations of the blazar OJ287 carried out jointly with the Global Millimeter VLBI Array (GMVA) and the phased Atacama Large Millimeter/submillimeter Array (ALMA) at 3.5 mm on April 2, 2017. Participation of phased-ALMA not only has improved the GMVA north-south resolution by a factor of ~3, but also has enabled fringe detection with signal-to-noise ratios up to 300 at baselines longer than 2 Gλ. The high sensitivity has motivated us to image the data with the newly developed regularized maximum likelihood imaging methods, revealing the innermost jet structure with unprecedentedly high angular resolution. Our images reveal a compact and twisted jet extending along the northwest direction with two bends within the inner 200 μas that resembles a precessing jet in projection. The component at the southeastern end shows a compact morphology and high brightness temperature, and is identified as the VLBI core. An extended jet feature that lies at ~200 μas northwest of the core shows a conical shape in both total and linearly polarized intensity, and a bimodal distribution of the linear polarization electric vector position angle. We discuss the nature of this feature by comparing our observations with models and simulations of oblique and recollimation shocks with various magnetic field configurations. Our high-fidelity images also enabled us to search for possible jet features from the secondary supermassive black hole (SMBH) and test the SMBH binary hypothesis proposed for this source.

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arXiv2022

MOMO V. Effelsberg, Swift and Fermi study of the blazar and supermassive binary black hole candidate OJ 287 in a period of high activity

We report results from our ongoing project MOMO (Multiwavelength Observations and Modelling of OJ 287). In this latest publication of a sequence, we combine our Swift UVOT--XRT and Effelsberg radio data (2.6-44 GHz) between 2019 and 2022.04 with public SMA data and gamma-ray data from the Fermi satellite. The observational epoch covers OJ 287 in a high state of activity from radio to X-rays. The epoch also covers two major events predicted by the binary supermassive black hole (SMBH) model of OJ 287. Spectral and timing analyses clearly establish: a new UV-optical minimum state in 2021 December at an epoch where the secondary SMBH is predicted to cross the disk surrounding the primary SMBH; an overall low level of gamma-ray activity in comparison to pre-2017 epochs; the presence of a remarkable, long-lasting UV--optical flare event of intermediate amplitude in 2020--2021; a high level of activity in the radio band with multiple flares; and particularly a bright, ongoing radio flare peaking in 2021 November that may be associated with a gamma-ray flare, the strongest in 6 years. Several explanations for the UV--optical minimum state are explored, including the possibility that a secondary SMBH launches a temporary jet, but the observations are best explained by variability associated with the main jet.

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arXiv2022

A new X-ray tidal disruption event candidate with fast variability

During a close encounter between a star and a supermassive black hole, the star can get disrupted by the black hole's tidal forces, resulting in a tidal disruption event (TDE). The accretion of the star's material onto the black hole produces strong emission in different wavelength regimes. Here we report the discovery with ROSAT of an X-ray-selected transient source in an optically non-active galaxy. At the location RA: 13h31m57.66s and Dec: -32deg3arcmin19.7arsec a sudden rise in X-ray luminosity by a factor of 8 within 8 days has been observed. Additionally, a very soft X-ray spectrum with a black-body temperature kT=0.1 keV and a peak luminosity of at least 10^43 erg/s suggest a TDE interpretation, and the observed properties are very similar to previously identified soft X-ray (ROSAT) TDEs. An optical spectrum taken of the galaxy at the position of RXJ133157.6-324319.7 six years after the X-ray outburst does not show any emission lines as would be expected from a persistent active galactic nucleus (AGN). The redshift of the galaxy is determined to be 0.051 based on absorption lines. It is therefore likely a member of the galaxy cluster Abell 3560. The rise in X-ray luminosity happens within 8 days and thus appears to be fast for such an event. No X-ray emission was detected 170 days before and 165 days after the event, and none was detected 25 years later with the Neil Gehrels Swift Observatory. The change in X-ray luminosity is at least a factor of 40.

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