arXiv subjects

P. Arévalo

Publications and source records attributed to P. Arévalo.

At least 19 recordsLinked to original sources

arXiv2026

Continuum Variability in AGN: Evidence for Systematically Suppressed Fluctuations in the BAL Population

We aim to compare the flux variability of Broad Absorption Line quasars (BAL) to non-BAL quasars, controlling for black hole parameters to inform models concerning the generation of the BAL phenomenon. Using SDSS DR16 and ZTF $g$- and $r$-band light curves, we select quasars with $1.57 \leq z \leq 2.00$ and $18.5 \leq rmag \leq 19.8$. This redshift range ensures that the $g$-band covers the C IV emission line (and trough in BALs) while the $r$-band probes continuum variability, and allows black hole mass (MBH) estimates via Mg II. We quantify variability using excess variance and damped random walk (DRW) parameters ($σ_{\mathrm{DRW}}$, $τ_{\mathrm{DRW}}$). We also compared the DRW metrics in bins of MBH and Eddington ratio (REdd) to isolate the influence of the BAL phenomenon in objects with the same physical properties. Excess variance and $σ_{\mathrm{DRW}}$ are consistently smaller for BALs, confirming lower long-term variability, while the $g$-band exhibits higher variability than the $r$-band across both populations. These differences persist in fixed bins of MBH and REdd, indicating that the suppressed variability in BALs is not simply driven by differences in these properties between BAL and non-BAL samples. These results show that BAL quasars are systematically less variable than non-BAL quasars in both bands, confirming that this suppression is an intrinsic feature of the continuum rather than an effect of emission or absorption line contamination. The samples could be made to agree if BAL MBH values were systematically overestimated by a factor $\gtrsim 4$, implying a significantly higher REdd. Alternatively, the lower variability in BALs can be related to their lower X-ray luminosities, or to significant nuclear obscuration, if the inner part of the accretion disc were more obscured in BALs and more variable than the rest of the disc.

astro-ph.GA↗

arXiv2026

The X-ray-Weak Tail of the Quasar Population: Physical Properties and Redshift Evolution of Variability-Selected AGN in eFEDS

(abridged) Aims: To characterize variability-selected AGN candidates within the eROSITA Final Equatorial-Depth Survey (eFEDS), leveraging the synergy between optical variability and deep X-ray observations by SRG (Spectrum Roentgen Gamma)/eROSITA, to compare the physical properties of AGN populations selected through complementary methods. Methods: We used a sample of AGN candidates selected via optical variability by Arévalo et al. and cross-match it to the X-ray selected eFEDS AGN sample. Spectroscopic characterizations are obtained for the matched samples from the Dark Energy Spectroscopic Instrument public data products. Results: We find a high classification purity with 98% candidates confirmed as broad-line AGN/QSOs. We identify a significant population (25%) that lack X-ray counterparts (X-U) in the eFEDS survey. We find that the X-D and X-U samples exhibit distinct physical properties and redshift distributions. The X-U sample peaks at $z = 2$ while the X-D sample at $z =1$, with nearly half of the variability-selected AGN at $z > 2.5$ remaining undetected in X-rays. This missing fraction can be attributed to K-correction effects and SED evolution with luminosity, mainly resulting in high accretion rate objects falling out of the X-D sample at higher redshifts. X-ray variability accounts for a part of the missing fraction but its dependence with redshift is less clear. Ensemble spectral analysis reveals that X-D sources have steeper optical continua and stronger broad emission lines than their X-U counterparts, while the forbidden and semi-forbidden lines have equal EWs in both samples. Finally, broad absorption line (BAL) features are found almost exclusively in the X-U population. This "missing" X-ray population must be accounted for when extrapolating X-ray-selected AGN to the broader Type I population and could impact cosmic estimates of massive black hole growth.

astro-ph.GA↗

arXiv2026

Simultaneous radio, optical and X-ray monitoring of hard X-ray selected AGN: a variability study

AGN emission is intrinsically variable across the electromagnetic spectrum. Mapping the coupling between the accretion disk, the X-ray corona, and ejection flows is key to understanding the energy flow within the central engine. We characterize the multi-wavelength variability of 14 hard X-ray selected AGN from the INTEGRAL/IBIS catalog in the radio, optical, and X-ray bands, to determine the coupling between these frequencies and how variability relates to the physical properties of the central engine, with emphasis on the radio band. We analyzed multi-epoch observations from AMI-LA at 15 GHz, ZTF in the g and r bands, and Swift/XRT over 2018--2020. Variability was quantified using the normalized excess variance, the fractional variability amplitude, and the Mexican Hat filter at 70- and 200-day timescales. We also characterized the radio-loudness of the sample and evaluated the impact of variability on the Fundamental Plane of black hole activity by comparing time-averaged with strictly simultaneous data. Significant variability is detected in 86% of the sample, with a clear amplitude stratification: the fractional rms amplitude is highest in X-rays, with a median of 30% (11-67%), followed by the optical g and r bands at 19% (2-33%) and 8.5% (0.2-24%), and the radio band at 10% (4-23%). The Mexican Hat analysis reveals a red-noise power spectrum dominated by long-term fluctuations. The sample follows the expected Fundamental Plane scaling; although individual sources shift within the relation due to stochastic fluctuations, this dispersion accounts for only ~3% of the total scatter. Our findings support a core-dominated origin for the 15 GHz emission, likely a compact jet base or a magnetized corona, while differences in variability patterns, radio-loudness, and Fundamental Plane location point toward distinct accretion/ejection processes and degrees of corona-jet coupling.

astro-ph.HE↗

arXiv2026

VAR-PZnn: A machine-learning framework for AGN photometric redshifts using color and variability-based features

Photometric redshift estimation for active galactic nuclei (AGNs) remains a fundamental challenge for current and upcoming large-scale photometric surveys. Traditional spectral energy distribution (SED) fitting suffers from color-redshift degeneracies, particularly for AGNs whose power-law continua hide the strong spectral features required to anchor redshift estimates. While AGN variability provides additional constraining power, existing frameworks require multi-band light curves that are not always available. This work presents VAR-PZnn, a fully connected mixture density network that integrates 26 variability features extracted from ZTF g-band light curves with optical photometry from Pan-STARRS1, mid-infrared (MIR) photometry from CatWISE, and, for a subsample, NIR photometry from UKIDSS. The model is trained and tested on 72,728 spectroscopically confirmed AGNs/QSOs spanning 0.01 < z < 4.5 and g-band magnitudes from 17 to 21.5. For the main sample, we achieve σ_{NMAD} = 0.058 and an outlier fraction of η= 8.2%, which reduces to 5.4% when the 10% of sources with the highest predicted uncertainty are excluded. An ablation study demonstrates that MIR photometry provides the dominant constraint for photo-z accuracy, while variability features serve as a secondary refiner. Using UKIDSS NIR data as a proxy for future synergies between LSST and space-based missions like Euclid and Roman, we obtain η= 13.3% without MIR data and η= 4.6% when MIR is available. We benchmark against Low-Resolution Templates (LRT) SED fitting (η= 28.7%) and the VAR-PZ framework; applying single-band VAR-PZ priors worsens LRT performance to η= 39.4% due to single-band light-curve degeneracies, confirmed via simulations (η= 27.6% to 28.1%). This framework provides a scalable approach for the Legacy Survey of Space and Time (LSST).

astro-ph.GA↗

arXiv2026

Spatially resolved optical and mid-infrared spectroscopy of SDSS1335+0728: implications for the origin of the Ansky event

The galaxy SDSS1335+0728 brightened abruptly in December 2019 (the Ansky event) and has since been confirmed as the host of extreme X-ray quasi-periodic eruptions (QPEs) of debated origin. We constrain the origin of its transient activity by characterising the galaxy properties and nuclear accretion history with spatially resolved VLT/MUSE and JWST MIRI/MRS spectroscopy. We extract stellar and gas kinematics and emission-line fluxes, construct emission-line ionisation diagnostic maps, reconstruct the nuclear ionisation history via a Balmer-line light-echo analysis, and measure the mid-infrared silicate feature strength. The stellar kinematics reveal two counter-rotating stellar regions and kinematically cold gas ($σ_{\rm gas} \lesssim 60$ km s$^{-1}$), consistent with a past minor merger. Stellar populations show an old host with ongoing star formation confined to a ring at intermediate radii. Ionisation diagnostics reveal a three-zone structure: a central region powered by SMBH accretion, where high-ionisation coronal lines ([NeVI]$\lambda7.65μ$m, [NeV]$\lambda14.32μ$m, [OIV]$\lambda25.89μ$m) are confined, a star-forming ring, and a LINER-like outer region. A Balmer-line light-echo analysis yields a minimum ionising luminosity $\log L_{\rm ion,min} \approx 40.5$ erg s$^{-1}$ sustained over at least $\sim 1\,500$ yr. Broad silicate emission at 9.7 and 18$μ$m indicates optically thin dust, inconsistent with a classical active galactic nucleus (AGN) dusty torus. The data are consistent with two scenarios for the pre-2019 accretion: a persisting or gradually fading low-luminosity AGN, or a long-lived tidal disruption event (TDE) remnant disc. In both, Ansky corresponds to a slow, faint transient in a $\sim\!10^6\,M_{\odot}$ SMBH with already ongoing accretion, challenging the "faded AGN" interpretation proposed for some QPE hosts.

astro-ph.GA↗

arXiv2026

Seeing through the dust: Unraveling near-infrared variability in type 2 active galactic nuclei

Near-infrared (NIR) variability studies of active galactic nuclei (AGNs) are still limited, as long-term multiepoch monitoring in the NIR is observationally challenging. The depth, wavelength coverage, and 14-year temporal baseline of UltraVISTA make it one of the few surveys capable of providing a detailed characterization of AGN variability in this regime. We aim to quantify the NIR variability of known AGNs in the COSMOS field and to investigate the physical origin of variability in type 2 AGNs. In particular, we examine how NIR variability can help clarify the discrepancies between optical and X-ray classifications. Using the 14-year multiepoch UltraVISTA DR6 dataset in the YJHKs bands, we constructed calibrated NIR light curves and quantified their variability through a set of metrics. AGN-like stochastic variability was identified by modeling the light curves with a damped random walk (DRW) process. We find that about 7-17% of the 533 type 2 AGNs are variable in the NIR, with variability fractions increasing toward Ks, where the dusty torus dominates the emission. Based on the wavelength dependence of the DRW variability amplitude, we classify variable type 2 AGNs into disk-dominated, torus-dominated, and highly obscured groups. About one third of the X-ray unobscured (XR I) type 2 AGNs are variable in the NIR, consistent with misclassified weak type 1 or true type 2 AGNs. On the other hand, 21.4% (30/140) of the X-ray obscured (XR II) type 2 AGNs show detectable variability in the NIR, most of them only in H or Ks, consistent with obscuration of the bluer (accretion disk) bands. Type 2 AGNs without X-ray counterparts (165) show the smallest fraction (3.6%) of variable objects. NIR variability provides an effective and independent diagnostic for confirming optical classifications and for identifying weak or misclassified type 1 AGNs in deep extragalactic surveys.

astro-ph.GA↗

arXiv2025

Unlocking AGN Variability with Custom ZTF Photometry for High-Fidelity Light Curves and Robust Selection

(Abridged)We explore the potential of optical variability selection methods to identify AGN, including those challenging to detect with conventional techniques. Using the unprecedented combination of depth, sky coverage, and cadence of the ZTF survey, we target even starlight-dominated AGN, known for their redder colours, weaker variability signals, and difficult nuclear photometry due to their resolved hosts. We perform aperture photometry on ZTF reference-subtracted images for 40 million sources across 8,000 deg^2, assemble light curves and classify objects employing an RF algorithm into 14 classes, including 341,938 candidate AGN. We compare variability metrics derived from our photometry to those obtained from ZTF Data Release light curves (DR11-psf), to assess the impact of our analysis. We find that the fraction of low-z quiescent galaxies exhibiting significant variability drops dramatically (from 98\% of the sample to 7\%) when replacing the DR11-psf light curves with our difference image, aperture photometry (DI-Ap) version. The overall number of variable low-z AGN remains high (99\% when using DR11-psf lightcurves, 83\% when using DI-Ap), however, implying that our photometry can detect the fainter variability in host dominated AGN. The classifier effectively distinguishes between AGN and other sources, demonstrating high recovery rates even for AGN in resolved nearby galaxies. AGN candidates in eROSITA's eFEDS field, detected in X-rays and bright enough for ZTF optical observations, were classified as AGN (79\%) and non-variable galaxies (20\%). These groups show a 2 dex difference in X-ray luminosity but not in X-ray flux. A significant fraction of X-ray AGN are optically too faint for ZTF, and conversely, a quarter of ZTF AGN in the eFEDS area lack X-ray detections, highlighting a wide range of X-ray-to-optical flux ratios in AGN.

astro-ph.GA↗

arXiv2025

NICER observations reveal doubled timescales in Ansky's quasi-periodic eruptions (QPEs)

Quasi-periodic eruptions (QPEs) are recurring X-ray bursts originating from the vicinity of supermassive black holes, but their driving mechanisms remain under debate. This study analyzes new NICER observations of QPEs in Ansky (a transient event in the nucleus of the galaxy SDSS J1335+0728), taken between January and June 2025. By examining flare durations, peak-to-peak recurrence times, and profiles, we compare the 2025 data with those from 2024 to investigate changes in energy, timescales, and flare shapes. The 2025 QPEs are found to be four times more energetic, with recurrence times of approximately 10 days and flare durations ranging from 2.5 to 4 days, making them both about twice as long as in 2024. Additionally, the flare profiles have become more asymmetric, showing longer decays. We explore different theoretical scenarios to explain the observed properties of the QPEs in Ansky, including evolving stream-disk interactions in an extreme mass-ratio inspiral (EMRI) system as a potential mechanism behind the observed changes in recurrence time and energetics, while also considering alternative models based on mass transfer and accretion disk instabilities. Continued observational efforts will be crucial for unveiling the nature of Ansky.

astro-ph.HE↗

arXiv2025

Probing the rest-frame wavelength dependence of quasar variability : Insights from the Zwicky Transient Facility Survey

Context: Quasar variability can potentially unlock crucial insights into the accretion process. Understanding how this variability is influenced by wavelength is crucial for validating and refining quasar variability models. Aims: This paper aims to enhance the understanding of the dependence of variability on the rest-frame wavelength ($λ_{RF}$) by isolating the variance in different timescales in well-defined wavelength bins and examining the corona-heated accretion-disk (CHAR) model. Methods: We investigated the relation between variance and rest-frame wavelength ($λ_{RF}$) using optical g- and r-band light curves from the Zwicky Transient Facility (ZTF) Data Release 15 for $\sim 5000$ quasars within narrow ranges of black hole mass ($M_{BH}$) and Eddington ratio ($R_{Edd}$). A spectral model taking into account disk continuum emission, Balmer transitions, Fe II pseudo-continuum emission, and other emission lines is necessary to best interpret the variance spectrum. Results: Our analysis indicates a strong anticorrelation between median variance and $λ_{RF}$ for quasars with $M_{BH} = 10^{8}$ and $R_{Edd} = 10^{-1}$ at different timescales. This anti-correlation is more pronounced at shorter timescales. The results align well with a bending power-law power spectrum density (PSD) model with both the damping timescale and the high-frequency slope of the PSD depending on the wavelength. The predictions provided by the CHAR model on the variance spectrum across most timescales studied showcase its potential in constraining temperature variations within the accretion disk. Key words. accretion, accretion discs; galaxies:active; quasars: supermassive black holes

astro-ph.GA↗

arXiv2024

The Success of Optical Variability in Uncovering AGNs in Low-stellar Mass Galaxies

We used random forest algorithms to classify all objects in a large portion of the sky, using optical light curves obtained, or built from images provided, by the Zwicky Transient Facility (ZTF). We compare different selection sets based on alerts or complete light curves derived from different photometric selection algorithms. The AGN candidates thus selected are cross-matched with objects in the NASA-Sloan Atlas (NSA) of local galaxies, with $M_*<2\times10^{10}M_\odot$. The AGN nature of these candidates is verified and characterized using archival optical spectra from SDSS. We further establish the fraction of candidates with counterparts in the eROSITA data release 1 catalog of X-ray sources. From an initial sample of 506 candidates, 415 have good-quality spectra. Among these 415 objects, we found significant broad Balmer lines in the spectra for $86\%$ (357) of the candidates. When considering BPT classifications, an additional 5 candidates were confirmed, resulting in $87\%$ (362) confirmed candidates. Specifically, broad Balmer lines were detected in $94\%$-$98\%$ of the AGN candidates selected from complete light curves and in $80\%$ of those selected from the less frequent ZTF alerts. The black hole masses estimated from the spectra range from $2.2\times10^6M_\odot$ to $4.2\times10^7M_\odot$, reaching lower values for the candidates selected using the more sensitive light curves. The black hole masses obtained cluster around $0.1\%$ of the stellar mass of the host from the NSA catalog. Two-thirds of the AGN candidates are classified as Seyfert or Composite by their narrow emission line ratios (BPT diagnostics) while the rest are star-forming. Almost all the candidates classified as Seyfert and over $50\%$ of those classified as star-forming have significant BELs. We found X-ray counterparts for $67\%$ of the candidates that fall in the footprint of the eROSITA-DE DR1.

astro-ph.GA↗

arXiv2024

AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system

With a growing number of facilities able to monitor the entire sky and produce light curves with a cadence of days, in recent years there has been an increased rate of detection of sources whose variability deviates from standard behavior, revealing a variety of exotic nuclear transients. The aim of the present study is to disentangle the nature of the transient AT 2021hdr, whose optical light curve used to be consistent with a classic Seyfert 1 nucleus, which was also confirmed by its optical spectrum and high-energy properties. From late 2021, AT 2021hdr started to present sudden brightening episodes in the form of oscillating peaks in the Zwicky Transient Facility (ZTF) alert stream, and the same shape is observed in X-rays and UV from Swift data. The oscillations occur every about 60-90 days with amplitudes of around 0.2 mag in the g and r bands. Very Long Baseline Array (VLBA) observations show no radio emission at milliarcseconds scale. It is argued that these findings are inconsistent with a standard tidal disruption event (TDE), a binary supermassive black hole (BSMBH), or a changing-look active galactic nucleus (AGN); neither does this object resemble previous observed AGN flares, and disk or jet instabilities are an unlikely scenario. Here, we propose that the behavior of AT 2021hdr might be due to the tidal disruption of a gas cloud by a BSMBH. In this scenario, we estimate that the putative binary has a separation of about 0.83 mpc and would merge in about 70000 years. This galaxy is located at 9 kpc from a companion galaxy, and in this work we report this merger for the first time. The oscillations are not related to the companion galaxy.

astro-ph.GA↗

arXiv2024

SDSS1335+0728: The awakening of a $\sim 10^6 M_{\odot}$ black hole

The galaxy SDSS1335+0728, which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). Its behaviour suggests that SDSS1335+0728 hosts a $\sim 10^6 M_{\odot}$ black hole (BH) that is currently in the process of `turning on'. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. We used archival photometry and spectroscopic data to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We find that: (a) since 2021, the UV flux is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1-W2 WISE colour has become redder; (c) since February 2024, the source has begun showing X-ray emission; (d) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (e) broad emission lines are not detected; and (f) the [OIII] line increased its flux $\sim 3.6$ years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. We conclude that the variations observed in SDSS1335+0728 could be either explained by an AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGN observed in the process of activating. If the latter, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour.

astro-ph.GA↗

arXiv2024

A Newborn AGN in a Starforming Galaxy

We report on the finding of a newborn AGN, i.e. current AGN activity in a galaxy previously classified as non-active, and characterize its evolution. Black hole ignition event candidates were selected from a parent sample of spectrally classified non-active galaxies (2.394.312 objects), that currently show optical flux variability indicative of a type I AGN, according to the ALeRCE light curve classifier. A second epoch spectrum for a sample of candidate newborn AGN were obtained with the SOAR telescope to search for new AGN features. We present spectral results for the most convincing case of new AGN activity, for a galaxy with a previous star-forming optical classification, where the second epoch spectrum shows the appearance of prominent, broad Balmer lines without significant changes in the narrow line flux ratios. Long term optical lightcurves show a steady increase in luminosity starting 1.5 years after the SDSS spectrum was taken and continuing for at least 7 years. MIR colors from the WISE catalog have also evolved from typical non active galaxy colors to AGN-like colors and recent X-ray flux detections confirm its AGN nature.

astro-ph.GA↗

arXiv2023

Improving the selection of changing-look AGNs through multi-wavelength photometric variability

We present second epoch optical spectra for 30 changing-look (CL) candidates found by searching for Type-1 optical variability in a sample of active galactic nuclei (AGNs) spectroscopically classified as Type 2. We use a random-forest-based light curve classifier and spectroscopic follow-up, confirming 50 per cent of candidates as turning-on CLs. In order to improve this selection method and to better understand the nature of the not-confirmed CL candidates, we perform a multi-wavelength variability analysis including optical, mid-infrared (MIR) and X-ray data, and compare the results from the confirmed and not-confirmed CLs identified in this work. We find that most of the not-confirmed CLs are consistent with weak Type 1s dominated by host-galaxy contributions, showing weaker optical and MIR variability. On the contrary, the confirmed CLs present stronger optical fluctuations and experience a long (from five to ten years) increase in their MIR fluxes and the colour W1-W2 over time. In the 0.2-2.3 keV band, at least four out of 11 CLs with available SRG/eROSITA detections have increased their flux in comparison with archival upper limits. These common features allow us to select the most promising CLs from our list of candidates, leading to nine sources with similar multi-wavelength photometric properties to our CL sample. The use of machine learning algorithms with optical and MIR light curves will be very useful to identify CLs in future large-scale surveys.

astro-ph.GA↗

arXiv2023

Persistent and occasional: searching for the variable population of the ZTF/4MOST sky using ZTF data release 11

We present a variability, color and morphology based classifier, designed to identify transients, persistently variable, and non-variable sources, from the Zwicky Transient Facility (ZTF) Data Release 11 (DR11) light curves of extended and point sources. The main motivation to develop this model was to identify active galactic nuclei (AGN) at different redshift ranges to be observed by the 4MOST ChANGES project. Still, it serves as a more general time-domain astronomy study. The model uses nine colors computed from CatWISE and PS1, a morphology score from PS1, and 61 single-band variability features computed from the ZTF DR11 g and r light curves. We trained two versions of the model, one for each ZTF band. We used a hierarchical local classifier per parent node approach, where each node was composed of a balanced random forest model. We adopted a 17-class taxonomy, including non-variable stars and galaxies, three transient classes, five classes of stochastic variables, and seven classes of periodic variables. The macro averaged precision, recall and F1-score are 0.61, 0.75, and 0.62 for the g-band model, and 0.60, 0.74, and 0.61, for the r-band model. When grouping the four AGN classes into one single class, its precision, recall, and F1-score are 1.00, 0.95, and 0.97, respectively, for both the g and r bands. We applied the model to all the sources in the ZTF/4MOST overlapping sky, avoiding ZTF fields covering the Galactic bulge, including 86,576,577 light curves in the g-band and 140,409,824 in the r-band. Only 0.73\% of the g-band light curves and 2.62\% of the r-band light curves were classified as stochastic, periodic, or transient with high probability ($P_{init}\geq0.9$). We found that, in general, more reliable results are obtained when using the g-band model. Using the latter, we identified 384,242 AGN candidates, 287,156 of which have $P_{init}\geq0.9$.

astro-ph.IM↗

arXiv2023

Multiwavelength monitoring of the nucleus in PBC J2333.9-2343: the giant radio galaxy with a blazar-like core

PBC J2333.9-2343 is a giant radio galaxy at z = 0.047 with a bright central core associated to a blazar nucleus. If the nuclear blazar jet is a new phase of the jet activity, then the small orientation angle suggest a dramatic change of the jet direction. We present observations obtained between September 2018 and January 2019 (cadence larger than three days) with Effeslberg, SMARTS-1.3m, ZTF, ATLAS, Swift, and Fermi-LAT, and between April-July 2019 (daily cadence) with SMARTS-1.3m and ATLAS. Large (>2x) flux increases are observed on timescales shorter than a month, which are interpreted as flaring events. The cross correlation between the SMARTS-1.3m monitoring in the NIR and optical shows that these data do not show significant time lag within the measured errors. A comparison of the optical variability properties between non-blazars and blazars AGN shows that PBC J2333.9-2343 has properties more comparable to the latter. The SED of the nucleus shows two peaks, that were fitted with a one zone leptonic model. Our data and modelling shows that the high energy peak is dominated by External Compton from the dusty torus with mild contribution from Inverse Compton from the jet. The derived jet angle of 3 degrees is also typical of a blazar. Therefore, we confirm the presence of a blazar-like core in the center of this giant radio galaxy, likely a Flat Spectrum Radio Quasar with peculiar properties.

astro-ph.HE↗

arXiv2022

A closer look at NGC 7314 nuclear region: a multiwavelength analysis of the Seyfert nucleus and its surroundings

The central regions of galaxies harbouring active galactic nuclei (AGNs) can be quite complex, especially at high activity, presenting, besides variability, a variety of phenomena related, e.g. to ionization/excitation mechanisms. A detailed study is necessary in order to understand better those objects. For that reason, we performed a multiwavelength analysis of the nuclear region of the nearby Seyfert galaxy NGC 7314, using an optical data cube obtained with the Integral Field Unit from the Gemini Multi-Object Spectrograph, together with Hubble Space Telescope images, X-ray data from the XMM-Newton and the Nuclear Spectroscopic Telescope Array and radio data from Atacama Large Millimeter/Submillimeter Array. The goals were to study the nuclear and circumnuclear emission, the emission of the AGN and the gas kinematics. The optical spectrum shows the emission of a Seyfert nucleus, with broad components in the H$α$ and H$β$ emission lines, characterising a type 1 AGN, with a spectrum rich in coronal emission lines. The spatial morphology of the [OIII]$λ$5007 suggests the presence of an ionization cone, west of the nucleus, meanwhile the east cone seems to be obscured by dust. An extended [FeVII]$λ$6087 emission was also detected, which could be possibly explained by a scenario involving photoionization+shocks mechanisms. X-rays analyses showed that there are variations in the flux; however, we did not detect any variations in the column density along the line of sight. Its variability may be a consequence of changes in the AGN accretion rate.

astro-ph.GA↗

arXiv2022

The Type 1 and Type 2 AGN dichotomy according to their ZTF optical variability

The scarce optical variability studies in spectrally classified Type 2 active galactic nuclei (AGNs) have led to the discovery of anomalous objects that are incompatible with the simplest unified models (UM). This paper focuses on the exploration of different variability features that allows to separate between obscured, Type 2 AGNs, and the variable, unobscured Type 1s. We analyse systematically the Zwicky Transient Facility, 2.5 years long light curves of ~ 15000 AGNs from the Sloan Digital Sky Survey Data Release 16, which are generally considered Type 2s due to the absence of strong broad emission lines (BELs). Consistently with the expectations from the UM, the variability features are distributed differently for distinct populations, with spectrally classified weak Type 1s showing 1 order of magnitude larger variances than the Type 2s. We find that the parameters given by the damped random walk model leads to broader Hα equivalent width for objects with τ_g > 16 d and long term structure function SF{\infty},g> 0.07 mag. By limiting the variability features, we find that ~ 11 per cent of Type 2 sources show evidence for optical variations. A detailed spectral analysis of the most variable sources (~1 per cent of the Type 2 sample) leads to the discovery of misclassified Type 1s with weak BELs and changing-state candidates. This work presents one of the largest systematic investigations of Type 2 AGN optical variability to date, in preparation for future large photometric surveys.

astro-ph.GA↗