Radiografía X del cielo γ : La conexión rayos–X a rayos–γ en blazares

Esta Tesis se basa mayormente en observaciones en rayos-X y óptico, llevadas a cabo con el X-ray Telescope (XRT) a bordo del satélite Neil Gehreils Swift, y con un número de telescopios ópticos en tierra; todas asociadas a objetos observados por el telescopio de rayos-γ Large Area Telescope (LAT) a bordo del satélite Fermi. Todos los resultados mostrados en esta Tesis fueron o están en proceso de ser publicados en revistas internacionales con referato. En el Capítulo 1 se resume un breve contexto histórico de los Núcleos Activos de Galaxias (AGN), los conceptos básicos del modelo AGN y sus principales propiedades observacionales. En el Capítulo 2 describimos los principales escenarios teóricos utilizados en los Capítulos subsiguientes, principalmente los procesos de radiación Sincrotrón y Compton Inverso en el contexto de blazares, el efecto que la magnificación Doppler tiene en las observaciones, la conexión entre estos procesos descripta por el modelo de Sincrotrón-auto Compton, y otros modelos alternativos que pueden explicar la emisión observada en blazares. El Capítulo 3 es una descripción del proceso de selección de la muestra. Comentamos las razones detrás de los criterios de selección, y discutimos sobre las muestras inicial y final de BL Lacs Fermi y de objetos de rayos gamma sin identificar (UGS, del inglés Unidentified Gamma-ray Source) que fueron analizadas en este trabajo con el uso de datos en rayos X. Además, describimos cómo elegimos una fracción de estos objetos para ser observados en longitudes de onda del rango óptico, para obtener sus espectros. El Capítulo 4 está dedicado a los instrumentos y los datos utilizados en este trabajo. Comentamos brevemente las capacidades de cada uno de los observatorios usados, y describimos en más detalle el proceso de reducción de datos tanto del Swift/XRT como de la espectroscopía óptica. En el Capítulo 5 reportamos los resultados obtenidos con nuestra muestra de BL Lacs Fermi observados por Swift/XRT. Buscamos por propiedades generales en rayos-X que puedan diferenciarlos de otros objetos emisores de rayos-X. Analizamos sus posiciones con respecto a sus contrapartes en rayos-γ, la tasa de detección en rayos X, sus flujos y valores de Cociente de Dureza (del inglés Hardness Ratio, HR). También comparamos esto con datos multifrecuencia recolectados de catálogos online, principalmente colores del infrarrojo medio. Establecemos criterios, basados en esta información, para seleccionar objetos de tipo BL Lac. En el Capítulo 6 procedemos a comparar nuestros resultados en rayos-X obtenidos para BL Lacs emisores de rayos-γ, con una muestra de UGSs de rayos-γ observados en rayos-X. Aseguramos que las muestras son comparables, basándonos en nuestros criterios de selección estrictos. Buscamos características de BL Lac en las contrapartes de rayos-X de los UGSs, y analizamos la solidez de nuestras predicciones analizando nuestros candidatos a contrapartes en otras longitudes de onda. En el Capítulo 7 reportamos los espectros ópticos obtenidos para una muestra de 50 contrapartes ópticas de UGSs, del tipo BL Lac. De estos, 17 son también parte de la muestra analizada en el Capítulo 6. Comparamos nuestras predicciones basadas en datos de rayos-X con esta muestra de BL Lacs confirmados espectroscópicamente, considerando también 23 espectros más obtenidos de la literatura. Reportamos asimismo nuestras asociaciones de 53 candidatos a blazar de tipo incierto (BCUs) Fermi con BL Lacs confirmados con espectroscopía óptica. Finalmente, en el Capítulo 8, resumimos nuestros resultados y nuestras conclusiones.Esta Tesis de Doctorado fue realizada bajo un convenio de co-tutela entre la Universidad Nacional de La Plata y la Università degli Studi di Torino, Turín, Italia.Facultad de Ciencias Astronómicas y GeofísicasUniversità degli Studi di Torin

Radio weak BL Lac objects in the Fermi era

The existence of “radio weak BL Lac objects” (RWBLs) has been an open question, still unsolved, since the discovery that quasars could be radio-quiet or radio-loud. Recently several groups identified RWBL candidates, mostly found while searching for low energy counterparts of the unidentified/ unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs or weak emission line quasars when there are not sufficient data to precisely draw their broad band spectral energy distribution and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs and BL Lacs using the [3.4]-[4.6]-[12]μm color-color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with those of the BL Lac population.Facultad de Ciencias Astronómicas y Geofísica

Radio Luminosity Function of Flat-spectrum Radio Quasars

We present the radio luminosity function (LF) of flat-spectrum radio quasars (FSRQ), using the the largest and most complete sample to date. Cross-matching between the FIRST 20 cm and GB6 6 cm radio surveys, we find 638 flat-spectrum radio sources above 220 mJy at 1.4 GHz; of these, 327 are are classified and verified using optical spectroscopy data, mainly from Sloan Digital Sky Survey Data Release 12. We also considered flat-spectrum radio sources that lack both literature references and optical spectroscopy, and we identified 12 out of the 43 such sources to potentially be FSRQs, using their WISE colors. From the fully identified sample of 242 FSRQs, we derived the radio LF and cosmic evolution of blazars at 1.4 GHz, finding good agreement with previous work at 5 GHz. The number density of FSRQs increases dramatically to a redshift of z ∼ 2 and then declines for higher redshifts. Furthermore, the redshift at which the quasar density peaks is clearly dependent on luminosity, with more luminous sources peaking at higher redshifts. The approximate best-fit LF for a luminosity-dependent evolutionary model is a broken power-law with slopes ∼0.7 and ∼1.7 below and above the break luminosity, log L1.4 ∼ 43.8 erg s-1, respectively.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Radio weak BL Lac objects in the Fermi era

The existence of “radio weak BL Lac objects” (RWBLs) has been an open question, still unsolved, since the discovery that quasars could be radio-quiet or radio-loud. Recently several groups identified RWBL candidates, mostly found while searching for low energy counterparts of the unidentified/ unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs or weak emission line quasars when there are not sufficient data to precisely draw their broad band spectral energy distribution and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs and BL Lacs using the [3.4]-[4.6]-[12]μm color-color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with those of the BL Lac population.Facultad de Ciencias Astronómicas y Geofísica

Looking for blazars in a sample of unidentified high-energy emitting Fermi sources

Context. Based on their overwhelming dominance among associated Fermi γ-ray catalogue sources, it is expected that a large fraction of the unidentified Fermi objects are blazars. Through crossmatching between the positions of unidentified γ-ray sources from the First Fermi Catalog of γ-ray sources emitting above 10 GeV (1FHL) and the ROSAT and Swift/XRT catalogues of X-ray objects and between pointed XRT observations, a sample of 36 potential associations was found in previous works with less than 15 arcsec of positional offset. One-third of them have recently been classified; the remainder, though believed to belong to the blazar class, still lack spectroscopic classifications. Aims. We study the optical spectrum of the putative counterparts of these unidentified gamma-ray sources in order to find their redshifts and to determine their nature and main spectral characteristics. Methods. An observational campaign was carried out on the putative counterparts of 13 1FHL sources using medium-resolution optical spectroscopy from the Osservatorio Astronomico di Bologna in Loiano, Italy; the Telescopio Nazionale Galileo and the Nordic Optical Telescope, both in the Canary Islands, Spain; and the Observatorio Astronómico Nacional San Pedro Mártir in Baja California, Mexico. Results. We were able to classify 14 new objects based on their continuum shapes and spectral features. Conclusions. Twelve new blazars were found, along with one new quasar and one new narrow line Seyfert 1 (NLS1) to be potentially associated with the 1FHL sources of our sample. Redshifts or lower limits were obtained when possible alongside central black hole mass and luminosity estimates for the NLS1 and the quasar.Fil: Marchesini, Ezequiel Joaquín. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Masetti, Nicola. Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna; ItaliaFil: Chavushyan, V.. Instituto Nacional de Astrofísica, Óptica y Electrónica; MéxicoFil: Cellone, Sergio Aldo. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Andruchow, Ileana. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Bassani, L.. Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna; ItaliaFil: Bazzano, A.. Istituto di Astrofisica e Planetologia Spaziali; ItaliaFil: Jiménez-Bailón, E.. Universidad Nacional Autónoma de México; MéxicoFil: Landi, R.. Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna; ItaliaFil: Malizia, A.. Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna; ItaliaFil: Palazzi, E.. Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna; ItaliaFil: Patiño Álvarez, V.. Instituto Nacional de Astrofísica, Óptica y Electrónica; MéxicoFil: Rodríguez Castillo, G. A.. Osservatorio Astronomico di Roma; ItaliaFil: Stephen, J. B.. Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna; ItaliaFil: Ubertini, P.. Istituto di Astrofisica e Planetologia Spaziali; Itali

Optical flux behaviour of a sample of Fermi blazars

Aims. We aim at investigating the time-behaviour of a sample of gamma-ray blazars. We present the results from a 13 month-long optical photometry monitoring campaign of the blazars PKS 0048-097, PKS 0754+100, [HB89] 0827+243, PKS 0851+202, PKS 1253-055, PKS 1510-089, PKS 1749+096, PKS 2230+114 and PKS 2251+158. Methods. We analyse the variability of each object, focusing on different time-scales (long term, short term, and microvariability), in an attempt to achieve a statistical comparison of the results. Results. After applying a geometric model to explain the variability results, we found that it is possible that a slight change in the direction of the jet generates the variations detected in some objects during this campaign.Facultad de Ciencias Astronómicas y Geofísica

Optical flux behaviour of a sample of Fermi blazars

Aims. We aim at investigating the time-behaviour of a sample of gamma-ray blazars. We present the results from a 13 month-long optical photometry monitoring campaign of the blazars PKS 0048-097, PKS 0754+100, [HB89] 0827+243, PKS 0851+202, PKS 1253-055, PKS 1510-089, PKS 1749+096, PKS 2230+114 and PKS 2251+158. Methods. We analyse the variability of each object, focusing on different time-scales (long term, short term, and microvariability), in an attempt to achieve a statistical comparison of the results. Results. After applying a geometric model to explain the variability results, we found that it is possible that a slight change in the direction of the jet generates the variations detected in some objects during this campaign.Facultad de Ciencias Astronómicas y Geofísica

Optical characterization of WISE selected blazar candidates

Context. Over the last decade more than five thousand γ-ray sources have been detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Given the positional uncertainty of the telescope, nearly 30% of these sources remain without an obvious counterpart at lower energies. This has motivated the release of new catalogs of γ-ray counterpart candidates and several follow up campaigns in the last decade. Aims. Recently, two new catalogs of blazar candidates were released. These are the improved and expanded version of the WISE Blazar-Like Radio-Loud Sources (WIBRaLS2) catalog and the Kernel Density Estimation selected candidate BL Lacs (KDEBLLACS) catalog, both selecting blazar-like sources based on their infrared colors from the Wide-field Infrared Survey Explorer (WISE). In this work we characterize these two catalogs, clarifying the true nature of their sources based on their optical spectra from SDSS data release 15, thus testing their efficiency in selecting true blazars. Methods. We first selected all WIBRaLS2 and KDEBLLACS sources with available optical spectra in the footprint of Sloan Digital Sky Survey data release 15. We then analyzed these spectra to verify the nature of each selected candidate and to measure the fraction of the catalogs composed by spectroscopically confirmed blazars. Finally, we evaluated the impact of selection effects, especially those related to optical colors of WIBRaLS2/KDEBLLACS sources and their optical magnitude distributions. Results. We found that at least ∼30% of each catalog is made up of confirmed blazars, with quasars being the major contaminants in the case of WIBRaLS2 (≈58%) and normal galaxies in the case of KDEBLLACS (≈38.2%). The spectral analysis also allowed us to identify the nature of 11 blazar candidates of uncertain type (BCUs) from the Fermi-LAT fourth Point Source Catalog (4FGL) and to find 25 new BL Lac objects.Fil: de Menezes, Raniere. Universidade Do Sao Paulo. Instituto Astronomia, Geofísica E Ciencias Atmosfericas. Departamento de Astronomia; Brasil. Università degli Studi di Torino; ItaliaFil: Peña Herazo, Harold A.. Instituto Nacional de Astrofísica; México. Università di Torino; Italia. Istituto Nazionale Di Fisica Nucleare.; Italia. Osservatorio Astrofisico di Torino; ItaliaFil: Marchesini, Ezequiel Joaquín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Istituto Nazionale Di Fisica Nucleare.; Italia. Università di Torino; ItaliaFil: D´Abrusco, Raffaele. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Masetti, Nicola. Osservatorio di Astrofisica e Scienza dello Spazio; Italia. Universidad Andrés Bello; ChileFil: Nemmen, Rodrigo. Universidade Do Sao Paulo. Instituto Astronomia, Geofísica E Ciencias Atmosfericas. Departamento de Astronomia; BrasilFil: Massaro, Francesco. Università di Torino; Italia. Istituto Nazionale Di Fisica Nucleare.; Italia. Osservatorio Astrofisico di Torino; Italia. Consorzio Interuniversitario per la Fisica Spaziale ; ItaliaFil: Ricci, Federica. Pontificia Universidad Católica de Chile; ChileFil: Landoni, Marco. Osservatorio Astronomico di Brera; ItaliaFil: Paggi, Alessandro. Università di Torino; ItaliaFil: Smith, Howard A.. Harvard-Smithsonian Center for Astrophysics; Estados Unido

Looking for blazars in a sample of unidentified high-energy emitting Fermi sources

Context. Based on their overwhelming dominance among associated Fermi γ-ray catalogue sources, it is expected that a large fraction of the unidentified Fermi objects are blazars. Through crossmatching between the positions of unidentified γ-ray sources from the First Fermi Catalog of γ-ray sources emitting above 10 GeV (1FHL) and the ROSAT and Swift/XRT catalogues of X-ray objects and between pointed XRT observations, a sample of 36 potential associations was found in previous works with less than 15 arcsec of positional offset. One-third of them have recently been classified; the remainder, though believed to belong to the blazar class, still lack spectroscopic classifications. Aims. We study the optical spectrum of the putative counterparts of these unidentified gamma-ray sources in order to find their redshifts and to determine their nature and main spectral characteristics. Methods. An observational campaign was carried out on the putative counterparts of 13 1FHL sources using medium-resolution optical spectroscopy from the Osservatorio Astronomico di Bologna in Loiano, Italy; the Telescopio Nazionale Galileo and the Nordic Optical Telescope, both in the Canary Islands, Spain; and the Observatorio Astronómico Nacional San Pedro Mártir in Baja California, Mexico. Results. We were able to classify 14 new objects based on their continuum shapes and spectral features. Conclusions. Twelve new blazars were found, along with one new quasar and one new narrow line Seyfert 1 (NLS1) to be potentially associated with the 1FHL sources of our sample. Redshifts or lower limits were obtained when possible alongside central black hole mass and luminosity estimates for the NLS1 and the quasar.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Optical flux behaviour of a sample of Fermi blazars

Aims. We aim at investigating the time-behaviour of a sample of gamma-ray blazars. We present the results from a 13 month-long optical photometry monitoring campaign of the blazars PKS 0048-097, PKS 0754+100, [HB89] 0827+243, PKS 0851+202, PKS 1253-055, PKS 1510-089, PKS 1749+096, PKS 2230+114 and PKS 2251+158. Methods. We analyse the variability of each object, focusing on different time-scales (long term, short term, and microvariability), in an attempt to achieve a statistical comparison of the results. Results. After applying a geometric model to explain the variability results, we found that it is possible that a slight change in the direction of the jet generates the variations detected in some objects during this campaign.Facultad de Ciencias Astronómicas y Geofísica