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AT 2019avd is a nuclear transient detected from infrared to soft X-rays, though its nature is yet unclear. The source has shown two consecutive flaring episodes in the optical and the infrared bands and its second flare was covered by X-ray monitoring programs. During this flare, the UVOT/Swift photometries revealed two plateaus: one observed after the peak and the other one appeared ~240 days later. Meanwhile, our NICER and XRT/Swift campaigns show two declines in the X-ray emission, one during the first optical plateau and one 70-90 days after the optical/UV decline. The evidence suggests that the optical/UV could not have been primarily originated from X-ray reprocessing. Furthermore, we detected a timelag of ~16-34 days between the optical and UV emission, which indicates the optical likely comes from UV reprocessing by a gas at a distance of 0.01-0.03 pc. We also report the first VLA and VLBA detection of this source at different frequencies and different stages of the second flare. The information obtained in the radio band - namely a steep and a late-time inverted radio spectrum, a high brightness temperature and a radio-loud state at late times - together with the multiwavelength properties of AT 2019avd suggests the launching and evolution of outflows such as disc winds or jets. In conclusion, we propose that after the ignition of black hole activity in the first flare, a super-Eddington flaring accretion disc formed and settled to a sub-Eddington state by the end of the second flare, associated with a compact radio outflow., 20 pages, 10 figures, 1 table. Accepted for publication in MNRAS

Binary black hole systems in close orbits are thought to be the precursors of gravitational wave events and their identification has fundamental implications for our understanding of black hole growth and evolution. However, a gravitationally bound companion orbiting closer than about a milli-parsec to an accreting supermassive black hole (SMBH, mass ≥106 solar masses) in an external galaxy cannot be spatially resolved with present-day instruments. Instead, its detection requires a combination of indirect observational methods and advanced modelling. Here we report the detection of quasi-periodic variability in X-ray spectral features after an outburst from a previously low-luminosity Active Galactic Nucleus (AGN) in a galaxy at redshift z=0.056. We interpret this variability as due to Quasi-Periodic Outflows (QPOuts) from the SMBH. The puzzling phenomenon repeats roughly once every 8.5 days and photo-ionization modeling of the energy spectra implies that the outflowing material moves with a high velocity of about a third of the speed of light. The mass of the central black hole, roughly 30 million solar masses, as derived from the optical broad line--SMBH mass scaling relation, implies that the outflows are launched from a few tens of gravitational radii from the SMBH event horizon. By performing 2D and 3D general relativistic magnetohydrodynamic (GRMHD) simulations and by comparing their results over a broad range of the system parameters we show that these QPOuts can be explained with an orbiting intermediate-mass black hole (IMBH) secondary (mass range of 100--10,000 solar masses) at a distance of about 100 gravitational radii (less than a milli-parsec) from the primary SMBH. Outflows are naturally enhanced when the secondary object punches through the SMBH's inner accretion disc during each orbital period and this is revealed as regular increases in X-ray absorption along our line of sight. The overall optical, UV and X-ray outburst properties indicate that a major accretion episode -- perhaps from a stellar tidal disruption by the SMBH -- could have provided the gas to illuminate the presence of the pre-existing IMBH secondary. Our work highlights the new astrophysical phenomenon of QPOuts and the importance of high cadence X-ray monitoring observations to potentially uncover electromagnetic signatures of such tight binary black hole systems.

The tidal forces of a black hole can rip apart a star that passes too close to it, resulting in a stellar Tidal Disruption Event (TDE, (1)). In some such encounters, the black hole can launch a powerful relativistic jet (2-6). If this jet fortuitously aligns with our line of sight, the overall brightness is Doppler boosted by several orders of magnitude. Consequently, such on-axis relativistic TDEs have the potential to unveil cosmological (redshift z>1) quiescent black holes and are ideal test beds to understand the radiative mechanisms operating in super-Eddington jets. Here, we present multi-wavelength (X-ray, UV, optical, and radio) observations of the optically discovered transient AT 2022cmc at z=1.193 (7). Its unusual X-ray properties, including a peak observed luminosity of >1048 erg s-1, systematic variability on timescales as short as 1000 seconds, and overall duration lasting more than 30 days in the rest-frame are traits associated with relativistic TDEs. This makes AT 2022cmc only the fourth member of this rare class and the first one identified in the optical and with well-sampled optical data. The X-ray to radio spectral energy distributions spanning 5-50 days after discovery can be explained as synchrotron emission from a relativistic jet (radio), synchrotron self-Compton (X-rays), and thermal emission similar to that seen in low-redshift TDEs (UV/optical). Our modeling implies a beamed, highly relativistic jet akin to blazars (e.g., (8,9)) but requires extreme matter-domination, i.e, high ratio of electron-to-magnetic field energy densities in the jet, and challenges our theoretical understanding of jets. This work provides one of the best multi-wavelength datasets of a newborn relativistic jet to date and will be invaluable for testing more sophisticated jet models, and for identifying more such events in transient surveys.

We present Gemini Multi-Object Spectrograph Integral Field Unit (GMOS-IFU) observations of the inner 1.1 kpc of the interacting Seyfert galaxy NGC 2992. From full spectral synthesis we found that the stellar population is mainly (up to 80 per cent of the total light) composed by an old (t ≥ 1.4 Gyr) metal-rich (Z ≥ 2.0) populations with a smaller but considerable contribution (up to 30 per cent) from young (t ≤ 100 Myr) metal-poor (Z ≥ 1.0) populations. The gas kinematics presents two main components: one from gas in orbit in the galaxy disk and an outflow with mass outflow rate of ˜2 Mʘ yr–1 and a kinematic power of ˜ 2 × 1040 erg s–1.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2021. Núcleos Galácticos Ativos (AGN) são regiões compactas no centro de galáxias capazes de gerar grandes quantidades de energia, de tal forma que não podem ser explicadas por fusão termonuclear pelas estrelas da galáxia, mas sim por acreção de matéria por um buraco negro supermassivo. Além de serem laboratórios para o estudo de física em condições extremas, acredita-se que AGNs são fundamentais para o entendimento da evolução das galáxias. Nesta dissertação apresentamos uma análise espacial e temporal do AGN presente na galáxia Seyfert em interação NGC 2992 usando observações em diferentes comprimentos de onda. Primeiramente, utilizando dados de Espectroscopia de Campo Integral do Telescópio Gemini, fomos capazes de resolver espacialmente as populações estelares, os mecanismos de ionização e a cinemática do gás ionizado. Utilizando síntese de populações estelares, nós mostramos que a população estelar é principalmente composta por estrelas velhas e ricas em metais, mas também por uma fração considerável, de até 30% da luz, por estrelas jovens e pobres em metais. A cinemática da Região de Linhas Estreitas (NLR) apresenta duas principais componentes: uma do gás orbitando o disco da galáxia e outra por uma ejeção (outflow) de gás, relacionada à emissão em rádio. Mostramos que apesar de a ionização pelo AGN ser o principal dos mecanismos, ionização por estrelas jovens e por choques também contribuem para as razões de linhas encontradas. Depois, apresentamos uma análise do histórico do espectro de emissão da galáxia em raios-X e no óptico. Mostramos que ela apresenta várias transições em sua classificação Seyfert, do tipo 2 para tipos intermediários, perdendo e readquirindo sua Linha de Emissão Larga (BEL) em Ha diversas vezes, portanto classificando-o como um ?Changing Look? AGN. Em raios-X, a fonte apresenta grande variabilidade com sua luminosidade corrigida por absorção variando por um fator de ~ 35. Mostramos que a presença (e o fluxo) da BEL em Ha está diretamente correlacionada com a taxa de acreção: com um valor mínimo 2.0% na razão de Eddington sendo necessário para a detecção da componente larga. Dois cenários são possíveis para explicar as transições de clasificação: o aumento (diminuição) da luminosidade do contínuo do AGN, que aumenta (diminui) a quantidade de fótons disponíveis para excitar o gás na Região de Linhas Largas (BLR), ou o desaparecimento da estrutura da BEL em si ocorre quando a baixa taxa de acreção não é capaz de suportar a taxa de fluxo de nuvens necessária. Este trabalho evidencia o papel das galáxias próximas no estudo dos fenômenos AGNs, nos quais as estruturas da escala parsec podem ser resolvidas e observações públicas em múltiplos comprimentos de onda e épocas estão disponíveis. Abstract: Active Galactic Nuclei (AGN) are compact regions at the center of galaxies that can generate large amounts of energy, such that it can not be explained by thermonuclear fusion in stars, but instead by accretion of matter onto a supermassive black hole (SMBH). Besides being a laboratory to study Physics in extreme conditions, AGNs are also believed to be fundamental for understanding galaxies? evolution. This dissertation presents a multi-wavelength spatial and temporal analysis of the AGN in the interacting Seyfert galaxy NGC 2992. First, using data taken with Gemini Multi-Object Spectrographs (GMOS), with the Integral Field Unit mode, from the inner 1.1 kiloparsecs of the galaxy, we were able to spatially resolve the stellar populations, the ionization mechanism, and kinematics of ionized gas. From full spectral synthesis, we found that the stellar population is primarily composed of old metal-rich stars with a smaller, but considerable, contributing of up to 30% of the light, from young and metal-poor populations. The Narrow Line Region kinematics presents two main components: one from gas orbiting the galaxy disk and another from a blueshifted outflow, correlated with the radio emission. We show that even though the primary ionization mechanism is the AGN radiation, ionization by young stars and shocks may also contribute to the emission line ratios found. Later, we present an analysis of the historical X-rays and optical spectra of the galaxy. We show that the nucleus of the galaxy presents multiple Seyfert type transitions from type 2 to intermediate-type, losing and regaining its Ha Broad Emission Line (BEL) recurrently, hence being a ?Changing Look? AGN. In X-rays, the source shows large intrinsic variability with the absorption corrected 2-10 keV luminosity varying by a factor of ~ 35. We show that the presence (and flux) of the Ha BEL is directly correlated with the accretion rate: a minimum Eddington ratio value of 2.0+2.0 ?1.3% is necessary for the broad line detection. Two possible scenarios for type transitions are still open: either there is a dimming (brightening) of the AGN continuum luminosity, which reduces (increases) the supply of ionizing photons available to excite the gas in the Broad Line Region (BLR), or the disappearance of the BLR structure itself occurs as the low accretion efficiency is not able to sustain the required cloud flow rate. This work evidences the role of the nearby galaxies in the study of the AGN phenomena, in which the parsec scale structures can be resolved and public multi-wavelength and multi-epoch observations are available.

Galaxy mergers are central to our understanding of galaxy formation, especially within the context of hierarchical models. Besides having a large impact on the star formation history, mergers are also able to influence gas motions at the centre of galaxies and trigger an active galactic nucleus (AGN). In this paper, we present a case study of the Seyfert galaxy NGC 2992, which together with NGC 2993 forms the early-stage merger system Arp 245. Using Gemini Multi-Object Spectrograph integral field unit data from the inner 1.1 kpc of the galaxy, we were able to spatially resolve the stellar populations, the ionization mechanism, and kinematics of ionized gas. From full spectral synthesis, we found that the stellar population is primarily composed by old metal-rich stars (t ≥ 1.4 Gyr, Z ≥ 2.0 Z⊙), with a contribution of at most 30 per cent of the light from a young and metal-poor population (t ≤ 100 Myr, Z ≤ 1.0 Z⊙). We detect H α and H β emission from the broad-line region with a full width at half-maximum of ∼2000 kms−1⁠. The narrow-line region kinematics presents two main components: one from gas orbiting the galaxy disc and a blueshifted (velocity ≈ −200 kms−1⁠) outflow, possibly correlated with the radio emission, with mass outflow rate of ∼2 M⊙ yr−1 and a kinematic power of ∼2 × 1040 erg s−1 (⁠E˙out/Lbol ≈ 0.2 per cent). We also show even though the main ionization mechanism is the AGN radiation, ionization by young stars and shocks may also contribute to the emission line ratios presented in the innermost region of the galaxy.

Galaxy mergers are central to our understanding of galaxy formation, especially within the context of hierarchical models. Besides having a large impact on the star formation history, mergers are also able to influence gas motions at the centre of galaxies and trigger an Active Galactic Nucleus (AGN). In this paper, we present a case study of the Seyfert galaxy NGC 2992, which together with NGC 2993 forms the early-stage merger system Arp 245. Using Gemini Multi-Object Spectrograph (GMOS) integral field unit (IFU) data from the inner 1.1 kpc of the galaxy we were able to spatially resolve the stellar populations, the ionisation mechanism and kinematics of ionised gas. From full spectral synthesis, we found that the stellar population is primarily composed by old metal-rich stars (t $\geq$ 1.4 Gyr, $Z \geq 2.0$\zsun), with a contribution of at most 30 per cent of the light from a young and metal-poor population (t $\leq$ 100 Myr, $Z \leq 1.0$\zsun). We detect \halpha and \hbeta emission from the Broad Line Region (BLR) with a Full Width at Half Maximum (FWHM) of $\sim$ 2000\kms. The Narrow Line Region (NLR) kinematics presents two main components: one from gas orbiting the galaxy disk and a blueshifted (velocity $\approx$ -200\kms) outflow, possibly correlated with the radio emission, with mass outflow rate of $\sim$ 2 M$_{\odot}$ yr$^{-1}$ and a kinematic power of $\sim$ 2 $\times 10^{40}$ erg s$^{-1}$ (\Eout/\Lbol $\approx$ 0.2 per cent). We also show even though the main ionisation mechanism is the AGN radiation, ionisation by young stars and shocks may also contribute to the emission line ratios presented in the innermost region of the galaxy., Comment: 20 pages, 13 Figs, Accepted for publication to the MNRAS

We present an analysis of historical multi-wavelength emission of the Changing Look (CL) Active Galactic Nucleus (AGN) in NGC 2992, covering epochs ranging from 1978 to 2021, as well as new X-ray and optical spectra. The galaxy presents multiple Seyfert type transitions from type 2 to intermediate-type, losing and regaining its H$\alpha$ BEL recurrently. In X-rays, the source shows intrinsic variability with the absorption corrected luminosity varying by a factor of $\sim$ 40. We rule out tidal disruption events or variable obscuration as causes of the type transitions and show that the presence and the flux of the broad H$\alpha$ emission line are directly correlated with the 2-10 keV X-ray luminosity (L$_{2-10}$): the component disappears at L$_{2-10} \leq 2.6\times10^{42}$\ergcms, this value translates into an Eddington ratio ($\lambda_{\rm Edd}$) of $\sim$ 1\%. The $\lambda_{\rm Edd}$ in which the BEL transitions occur is the same as the critical value at which there should be a state transition between a radiatively inefficient accretion flow (RIAF) and a thin accretion disk, such similarity suggests that the AGN is operating at the threshold mass accretion rate between the two accretion modes. We find a correlation between the narrow Fe K$\alpha$ flux and $\lambda_{\rm Edd}$, and an anti-correlation between full-width at half maximum of H$\alpha$ BEL and $\lambda_{\rm Edd}$, in agreement with theoretical predictions. Two possible scenarios for type transitions are compatible with our results: either the dimming of the AGN continuum, which reduces the supply of ionising photons available to excite the gas in the Broad Line Region (BLR), or the fading of the BLR structure itself occurs as the low accretion rate is not able to sustain the required cloud flow rate in a disk-wind BLR model., Comment: Accepted for publication at MNRAS

We report the discovery of a new ``changing-look'' active galactic nucleus (CLAGN) event, in the quasar SDSS J162829.17+432948.5 at z=0.2603, identified through repeat spectroscopy from the fifth Sloan Digital Sky Survey (SDSS-V). Optical photometry taken during 2020--2021 shows a dramatic dimming of ${\Delta}$g${\approx}$1 mag, followed by a rapid recovery on a timescale of several months, with the ${\lesssim}$2 month period of rebrightening captured in new SDSS-V and Las Cumbres Observatory spectroscopy. This is one of the fastest CLAGN transitions observed to date. Archival observations suggest that the object experienced a much more gradual dimming over the period of 2011--2013. Our spectroscopy shows that the photometric changes were accompanied by dramatic variations in the quasar-like continuum and broad-line emission. The excellent agreement between the pre- and postdip photometric and spectroscopic appearances of the source, as well as the fact that the dimmest spectra can be reproduced by applying a single extinction law to the brighter spectral states, favor a variable line-of-sight obscuration as the driver of the observed transitions. Such an interpretation faces several theoretical challenges, and thus an alternative accretion-driven scenario cannot be excluded. The recent events observed in this quasar highlight the importance of spectroscopic monitoring of large active galactic nucleus samples on weeks-to-months timescales, which the SDSS-V is designed to achieve., Comment: Published in ApJL