Estudio de la variabilidad del núcleo galáctico activo ESO 362-G18 en las bandas óptica y de rayos X : escalas de tiempo desde días a años

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de la Tierra, Astronomía y Astrofísica II, leída el 25-01-2017El modelo unificado (UM) de los núcleos galácticos activos (AGN), establecido hace 30 años, se fundamenta en la existencia de una estructura toroidal, compuesta por gas y polvo, capaz de absorber la emisión central del AGN y que rodea el agujero negro supermasivo (SMBH) y el disco de acreción. Así, la complicada taxonomía de estos objetos simplemente refleja diferentes ángulos de visión de una geometría con simetría axial. En los AGNs tipo 1 se tienen una visión directa del material próximo al SMBH, por lo tanto vemos líneas anchas de emisión en los espectros ópticos/UV. En los AGNs tipo 2 el toro bloquea la visión del núcleo y la líneas anchas desaparecen. Este esquema se consolidó con el descubrimiento de líneas anchas polarizadas (PBLs) en AGNs tipo 2, lo que confirma una naturaleza común entre ambos tipos de objetos. Actualmente las observaciones no concuerdan con las predicciones. El UM establece un toro homogéneo e uniforme, sin embargo, a partir de diversos estudios (sobre todo en el infrarrojo) se obtienen pruebas de que esta estructura no es uniforme sino grumosa. El principal objetivo de esta tesis es avalar la necesidad de un toroide más complejo desde las bandas óptica y de rayos X, estudiando la variabilidad de absorción de la galaxia Seyfert: ESO~362-G18. Esta fuente merece toda nuestra atención debido a su intrigante comportamiento: usualmente se clasifica como Seyfert tipo 1, sin embargo, se ha recuperado un espectro tipo 2 del catálogo 6dFGS. Los AGNs clasificables en ambos tipos representan una violación del UM y constituyen una prueba más de que un modelo dependiente en exclusiva de la inclinación es insuficiente. Con el fin de profundizar en la naturaleza de estos objetos clave y poco frecuentes, decidimos emprender un estudio multi-longitud de onda de ESO 362-G18 que nos permitiese obtener diferentes visiones complementarias. Comenzamos con un seguimiento multi-época en rayos X con distintos observatorios para determinar sus cambios espectrales y de flujo en distintas escalas temporales (9 observaciones a lo largo de 4 años y 2 meses). Detectamos reflexión relativista con un espín del SMBH de 0.92 al 99\% de nivel de confianza (rotación máxima) así como un tamaño de la región emisora de rayos de X menor de 50 radios gravitaciones. Además obtuvimos una inclinación relativamente alta, 53º, por lo que lo más probable es que nuestra LOS esté interceptando la parte superior del toro, de modo que su supuesta grumosidad podría explicar los cambios de estado de ESO 362-G18. De hecho, obtenemos que una de las observaciones es absorbida por una una nube perteneciente al toro que cubre por completo la fuente. Otro seguimiento de la fuente con el satélite Swift mucho más detallado, 36 observaciones en 2 meses, nos brindó la oportunidad de monitorizar un eclipse casi en su totalidad y establecer con mayor precisión las propiedades de la nube absorbente, al mismo tiempo que pudimos corroborar nuestra interpretación relativista de este AGN...The standard UnifiedModel (UM) of Active Galactic Nuclei, established 30 years ago, has been key to shed light in the taxonomy of such a heterogenous class of objects. Its basic premise is the ubiquitous presence of an obscuring torus around the central engine, so that the observed diversity simply reflects different viewing angles of an axisymmetric geometry. Consequently, type 1 AGNs are observed with a direct view of fast moving material close to the super massive black hole (SMBH), resulting in broad emission lines in their optical/UV spectra, while type-2 AGNs are observed from a more edge-on view, intercepting the obscuring torus that blocks the broad emission line region (BLR) component from our line of sight (LOS). This scheme was consolidated with the discovery of polarized broad emission lines (PBLs), also known as hidden broad-line regions (HBLRs), in the type 2 AGN, hence presenting the same properties as type 1 nuclei in polarized light. Nowadays, additional ingredients are likely needed to account for some observational facts that are apparently in conflict with the predictions. For instance, the UM predicts the absorbing torus as an homogeneous and uniform structure. There is broad evidence, especially at infrared wavelengths, that the dusty torus is indeed clumpy instead uniform. The general goal of this thesis is to endorse the current evidence for the clumplyness of the key element of the standard UM from other wavelengths: X-rays, UV and optical. To this end, we will focus on the study of the absorption variability performed by an interesting Seyfert galaxy: ESO 362-G18. This source gets our whole attention because it is usually classified as a type 1 AGN, however a spectrum retrieved from the 6 degree Galaxy Survey (6dFGS) shows the optical spectrum of ESO 362-G18 to lack its broad emission lines. This type 2 spectrum suggests ESO 362-G18 to be a changing look Seyfert galaxy. This rare type of sources represents a violation of the UMand probes that its corresponding classification is not only angle-dependent. Thus, we decided to start a deep multi-wavelength analysis of ESO 362-G18 to get as many complementary views as possible and approach the intriguing nature of this source...Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEunpu

A changing-look AGN to be probed by X-ray polarimetry

Active galactic nuclei (AGN) produce the highest intrinsic luminosities in the Universe from within a compact region. The central engine is thought to be powered by accretion onto a supermassive black hole. A fraction of this huge release of energy influences the evolution of the host galaxy, and in particular, star formation. Thus, AGN are key astronomical sources not only because they play an important role in the evolution of the Universe, but also because they constitute a laboratory for extreme physics. However, these objects are under the resolution limit of current telescopes. Polarimetry is a unique technique capable of providing us with information on physical AGN structures. The incoming new era of X-ray polarimetry will give us the opportunity to explore the geometry and physical processes taking place in the innermost regions of the accretion disc. Here we exploit this future powerful tool in the particular case of changing-look AGN, which are key for understanding the complexity of AGN physics.Comment: 9 pages, 1 figures, published by Galaxies under the special issue "The Bright Future of Astronomical X-ray Polarimetry

The ionised X-ray outflowing torus in ESO 323-G77: low-ionisation clumps confined by homogeneous warm absorbers

We report on the long- and short-term X-ray spectral analysis of the polar-scattered Seyfert 1.2 galaxy ESO 323-G77, observed in three epochs between 2006 and 2013 with Chandra and XMM-Newton. Four high-resolution Chandra observations give us a unique opportunity to study the properties of the absorbers in detail, as well as their short time-scale (days) variability. From the rich set of absorption features seen in the Chandra data, we identify two warm absorbers with column densities and ionisations that are consistent with being constant on both short and long time-scales, suggesting that those are the signature of a rather homogeneous and extended outflow. A third absorber, ionised to a lesser degree, is also present and it replaces the strictly neutral absorber that is ubiquitously inferred from the X-ray analysis of obscured Compton-thin sources. This colder absorber appears to vary in column density on long time-scales, suggesting a non-homogeneous absorber. Moreover, its ionisation responds to the nuclear luminosity variations on time-scales as short as a few days, indicating that the absorber is in photoionisation equilibrium with the nuclear source on these time-scales. All components are consistent with being co-spatial and located between the inner and outer edges of the so-called dusty, clumpy torus. Assuming co-spatiality, the three phases also share the same pressure, suggesting that the warm / hot phases confine the colder, most likely clumpy, medium. We discuss further the properties of the outflow in comparison with the lower resolution XMM-Newton data.Comment: 16 pages, 7 figures, 6 tables. Accepted for publication in MNRA

The size of the X-ray emitting region in SWIFT J2127.4+5654 via a broad line region cloud X-ray eclipse

We present results obtained from the time-resolved X-ray spectral analysis of the Narrow-Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a ~130 ks XMM-Newton observation. We reveal large spectral variations, especially during the first ~90 ks of the XMM-Newton exposure. The spectral variability can be attributed to a partial eclipse of the X-ray source by an intervening low-ionization/cold absorbing structure (cloud) with column density N_H = 2.0^{+0.2}_{-0.3}e22 cm^-2 which gradually covers and then uncovers the X-ray emitting region with covering fraction ranging from zero to ~43 per cent. Our analysis enables us to constrain the size, number density, and location of the absorbing cloud with good accuracy. We infer a cloud size (diameter) of $D_c < 1.5e13 cm, corresponding to a density of n_c > 1.5e9 cm^-3 at a distance of R_c > 4.3e16 cm from the central black hole. All of the inferred quantities concur to identify the absorbing structure with one single cloud associated with the broad line region of SWIFT J2127.4+5654. We are also able to constrain the X-ray emitting region size (diameter) to be D_s < 2.3e13 cm which, assuming the black hole mass estimated from single-epoch optical spectroscopy (1.5e7 M_sun), translates into D_s < 10.5 gravitational radii (r_g) with larger sizes (in r_g) being associated with smaller black hole masses, and viceversa. We also confirm the presence of a relativistically distorted reflection component off the inner accretion disc giving rise to a broad relativistic Fe K emission line and small soft excess (small because of the high Galactic column density), supporting the measurement of an intermediate black hole spin in SWIFT J2127.4+5654 that was obtained from a previous Suzaku observation.Comment: 8 pages, 7 figures, accepted for publication in MNRA

Polarized blazar X-rays imply particle acceleration in shocks

Most of the light from blazars, active galactic nuclei with jets of magnetized plasma that point nearly along the line of sight, is produced by high-energy particles, up to around 1 TeV. Although the jets are known to be ultimately powered by a supermassive black hole, how the particles are accelerated to such high energies has been an unanswered question. The process must be related to the magnetic field, which can be probed by observations of the polarization of light from the jets. Measurements of the radio to optical polarization—the only range available until now—probe extended regions of the jet containing particles that left the acceleration site days to years earlier1,2,3, and hence do not directly explore the acceleration mechanism, as could X-ray measurements. Here we report the detection of X-ray polarization from the blazar Markarian 501 (Mrk 501). We measure an X-ray linear polarization degree ΠX of around 10%, which is a factor of around 2 higher than the value at optical wavelengths, with a polarization angle parallel to the radio jet. This points to a shock front as the source of particle acceleration and also implies that the plasma becomes increasingly turbulent with distance from the shock

X-ray Polarization Observations of BL Lacertae

Blazars are a class of jet-dominated active galactic nuclei with a typical double-humped spectral energy distribution. It is of common consensus the Synchrotron emission to be responsible for the low frequency peak, while the origin of the high frequency hump is still debated. The analysis of X-rays and their polarization can provide a valuable tool to understand the physical mechanisms responsible for the origin of high-energy emission of blazars. We report the first observations of BL Lacertae performed with the Imaging X-ray Polarimetry Explorer ({IXPE}), from which an upper limit to the polarization degree $\Pi_X<$12.6\% was found in the 2-8 keV band. We contemporaneously measured the polarization in radio, infrared, and optical wavelengths. Our multiwavelength polarization analysis disfavors a significant contribution of proton synchrotron radiation to the X-ray emission at these epochs. Instead, it supports a leptonic origin for the X-ray emission in BL Lac.Comment: 17 pages, 5 figures, accepted for publication in ApJ

A search for ionised gas outflows in an Halpha imaging atlas of nearby LINERs

Outflows play a major role in the evolution of galaxies. However, we do not have yet a complete picture of their properties (extension, geometry, orientation and clumpiness). For low-luminosity Active Galactic Nuclei (AGNs), in particular, low-ionisation nuclear emission line regions (LINERs), the rate of outflows and their properties are largely unknown. The main goal of this work is to create the largest, up-to-date atlas of ionised gas outflow candidates in a sample of 70 nearby LINERs. We use narrow-band, imaging data to analyse the morphological properties of the ionised gas nuclear emission of these galaxies and to identify signatures of extended emission with distinctive outflow-like morphologies. We obtained new imaging data from ALFOSC/NOT for 32 LINERs. We complemented it with HST archival data for 6 objects and with results from the literature for other 32 targets. We additionally obtained soft X-ray data from Chandra archive to compare with the ionised gas. The distribution of the ionised gas in these LINER shows that $\sim$32% have bubble-like emission, $\sim$28% show a 'Core-halo', unresolved emission, and $\sim$21% have a disky-like distribution. Dust lanes prevent a detailed classification for $\sim$11% of the sample ('Dusty'). If we account for the kinematical information, available for 60 galaxies, we end up with 48% of the LINERs with detected outflows/inflows (50% considering only kinematical information based on Integral Field Spectroscopy). Our results suggest that the incidence of outflows in LINERs may vary from 41% up to 56%, based on both the Halpha morphology and the kinematical information from the literature. The ionised gas is co-spatial with the soft X-ray emission for the majority of cases ($\sim$60%), so that they may have a common origin. We discuss the use of Halpha imaging for the pre-selection of candidates likely hosting ionised gas outflows.Comment: 30 pages, 7 figures. Accepted for publication in A&

X-Ray Polarization of the BL Lacertae Type Blazar 1ES 0229+200

International audienceWe present polarization measurements in the 2-8 keV band from blazar 1ES 0229+200, the first extreme high synchrotron peaked source to be observed by the Imaging X-ray Polarimetry Explorer (IXPE). Combining two exposures separated by about two weeks, we find the degree of polarization to be ΠX = 17.9% ± 2.8% at an electric-vector position angle ψ X = 25.°0 ± 4.°6 using a spectro-polarimetric fit from joint IXPE and XMM-Newton observations. There is no evidence for the polarization degree or angle varying significantly with energy or time on both short timescales (hours) or longer timescales (days). The contemporaneous polarization degree at optical wavelengths was >7× lower, making 1ES 0229+200 the most strongly chromatic blazar yet observed. This high X-ray polarization compared to the optical provides further support that X-ray emission in high-peaked blazars originates in shock-accelerated, energy-stratified electron populations, but is in tension with many recent modeling efforts attempting to reproduce the spectral energy distribution of 1ES 0229+200, which attribute the extremely high energy synchrotron and Compton peaks to Fermi acceleration in the vicinity of strongly turbulent magnetic fields