Browsing by Author "Lähteenmäki, Anne"
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- A 22 GHz prototype receiver for continuous comparison polarimetry
Sähkötekniikan korkeakoulu | Master's thesis(2016-05-09) Haarto, SamRadio astronomy is a subfield of astronomy that studies celestial objects that emit radio waves. As radio waves can penetrate dust, radio astronomy can study things that can't be seen in visible light. Radio astronomy studies the Sun, planets, gas and dust clouds of the Milky Way, pulsars, radio galaxies, quasars and cosmic background radiation. Polarimetry has been a quite recent addition to radio astronomy. Polarimetry studies the polarization of light and other transverse waves. The applications are present in a variety fields of astrophysics ranging from solar physics to cosmology. Polarimetry can be used to study for example the strength and orientation of magnetic fields in the space between planets in the Solar system and other planetary systems. It has given us insight into physical processes occurring in systems that range from our own solar system to high-redshift galaxies. The goal of this thesis was to build a prototype receiver for continuous comparison polarimetry. This prototype would be used as a testing device for the back-end planned for the Metsähovi's continuous comparison receiver. With this prototype receiver, one hopes to find and solve the possible problems that the final receiver might have, and also to ease with the adaptation of the new back-end. In addition to building a prototype receiver, the importance of polarization in radio astronomy was presented. Although a working prototype could not be achieved during this thesis an insight into the designing process was given. Designing, manufacturing and debugging of different components of the receiver was shown and future plans for the prototype was presented. Quite lossy 180-degree hybrids were produced. To proceed with the back-end testing new amplifier cards and a working back-end module should be acquired. Furthermore, the orthomode transducers of the prototype also need further testing to ensure their validity. - Absorbed relativistic jets in radio-quiet narrow-line Seyfert 1 galaxies
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-04-17) Berton, Marco; Järvelä, Emilia; Crepaldi, L.; Lähteenmäki, Anne; Tornikoski, Merja; Congiu, E.; Kharb, P.; Terreran, G.; Vietri, A.Narrow-line Seyfert 1 (NLS1) galaxies are peculiar active galactic nuclei. Most of them do not show strong radio emission, but seven radio-quiet (or radio-silent) NLS1s have recently been detected flaring multiple times at 37 GHz by the Metsahovi Radio Telescope, indicating relativistic jets in these peculiar sources. We observed them with the Karl G. Jansky Very Large Array (JVLA) in A configuration at 1.6, 5.2, and 9.0 GHz. Our results show that these sources are either extremely faint or not detected in the JVLA bands. At these frequencies, the radio emission from their relativistic jet must be absorbed, either through synchrotron self-absorption as it occurs in gigahertz-peaked sources, or more likely, through free-free absorption by a screen of ionized gas associated with starburst activity or shocks. Our findings cast new shadows on the radio-loudness criterion, which seems to be increasingly frequently a misleading parameter. New high-frequency and high-resolution radio observations are essential to test our hypotheses. - Aktiivisten galaksien hyväksyminen suurienergisten neutriinojen säteilijöiksi: havaitseminen IceCube-ilmaisimella sekä hyväksymisen vaikeudet
Sähkötekniikan korkeakoulu | Bachelor's thesis(2024-05-25) Hendolin, MatiasIceCube-neutriinoilmaisin on hieman yli kymmenen vuoden toimintansa aikana havainnut suurienergisiä TeV–PeV:n kosmisia neutriinoja. Vielä on epäselvää, missä ja mistä prosesseista havaitut neutriinot ovat syntyneet. IceCube on havainnut mittaushistoriansa aikana neutriinoja tiettyjen aktiivisten galaksien suunnilta. IceCube Collaboration on nimennyt neljä merkittävintä neutriinokandidaattia, eli mahdollista suurienergisten neutriinojen säteilijää. Myös muutamien aktiivisten galaksien suunnista on havaittu neutriinoja niiden sähkömagneettisten purkausten aikana. Purkausten aikaisista havainnoista on päätelty, että purkauksilla ja neutriinojen synnyllä on yhteys. Tutkimuksissa ja kandidaattien lopullisessa validoinnissa on kuitenkin useita ongelmia: IceCuben erottelukyky on heikko, taustakohina on suurta, havaittujen kosmisten neutriinojen lukumäärä on liian pieni johtopäätöksien luomiseen ja neutriinojen syntyprosesseja aktiivissa galakseissa ei täysin tiedetä. Työn tavoitteena on selvittää, kuinka IceCube havaitsee kosmisia neutriinoja, miten aktiiviset galaksit hyväksytään neutriinokandidaateiksi, mikä on purkausten yhteys neutriinoihin ja mitkä seikat vaikeuttavat kandidaattien lopullista validointia. Työssä tutkitaan IceCube Collaborationin ja muiden tutkimusten tekemiä analyyseja aktiivisista galakseista neutriinosäteilijöinä. Työssä osoitetaan, että vaikka kosmisia neutriinoja on havaittu aktiivisten galaksien suunnilta, jää niiden lopullinen validointi tulevien tutkimusten ja tarkempien havaintojen varaan. Purkausten aikaisia neutriinoja ei ole havaittu vielä tarpeeksi monta, että selvää yhteyttä neutriinoihin voisi muodostaa, mutta yhteyttä ei poissuljeta. Lisäksi, jos aktiiviset galaksit ovat neutriinosäteilijöitä, niitä on todennäköisesti kahta populaatiota: Seyfert-galaksit ja blasaarit, joilla on eri säteilytehot, havainnointikulmat ja neutriinojen syntytavat. - Analyzing the characteristic radio variability of AGNs on up to 40 years of 37 GHz data from the Metsähovi Radio Observatory
Sähkötekniikan korkeakoulu | Master's thesis(2021-03-15) Suutarinen, SofiaActive galactic nuclei (AGNs) are exceptionally bright compact sources located at the centers of some galaxies. The supermassive black hole at the center of the AGN drives the variability of the source causing visible changes in the observed light curve over different frequencies. This variability is a common subject of studies. The amount of data in AGN radio analyses is often limited to relatively short monitoring periods of e.g., 5 years. However, it has been shown that longer monitoring periods are usually needed in order to identify variability timescales from the data. Identifying such characteristic timescales could help in understanding the underlying processes governing AGN variability and they could potentially be linked to physical conditions in the analyzed sources. The aim of this thesis was to characterize AGN variability timescales from uniquely long radio AGN data from the Metsähovi Radio Observatory 37 GHz monitoring sample and specifically to identify how the results are dependent on the monitoring period length. Especially of interest was to see, if a simple power law is sufficient in characterizing the underlying noise process of AGNs in radio frequencies. The used methods included the periodogram, Lomb-Scargle periodogram, structure function, and discrete correlation function. The results showed that the monitoring period length has a significant role on the estimated power spectrum of the sources. In many cases, the simple power law seemed inadequate in describing the noise process of the sources for long-term data. In contrast, shorter monitoring segments of 5 years were more often in apparent agreement with the null hypothesis. For many sources, the poor fits in long-term data appeared to be caused by the power spectrum experiencing a flattening of the slope after a characteristic timescale. The results also indicated that for some sources even 30-40 years of monitoring may not be enough to reveal a characteristic timescale. - Can CMB surveys help the AGN community?
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-08-30) Partridge, Bruce; Bonavera, Laura; López-Caniego, Marcos; Datta, Rahul; Gonzalez-Nuevo, Joaquin; Gralla, Megan; Herranz, Diego; Lähteenmäki, Anne; Mocanu, Laura; Prince, Heather; Vieira, Joaquin; Whitehorn, Nathan; Zhang, LizhongContemporary projects to measure anisotropies in the cosmic microwave background (CMB) are now detecting hundreds to thousands of extragalactic radio sources, most of them blazars. As a member of a group of CMB scientists involved in the construction of catalogues of such sources and their analysis, I wish to point out the potential value of CMB surveys to studies of AGN jets and their polarization. Current CMB projects, for instance, reach mJy sensitivity, offer wide sky coverage, are "blind" and generally of uniform sensitivity across the sky (hence useful statistically), make essentially simultaneous multi-frequency observations at frequencies from 30 to 857 GHz, routinely offer repeated observations of sources with interesting cadences and now generally provide polarization measurements. The aim here is not to analyze in any depth the AGN science already derived from such projects, but rather to heighten awareness of their promise for the AGN community. - CMB-S4: Forecasting Constraints on Primordial Gravitational Waves
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-02-01) Abazajian, Kevork; Addison, Graeme E.; Adshead, Peter; Ahmed, Zeeshan; Akerib, Daniel; Ali, Aamir; Allen, Steven W.; Alonso, David; Alvarez, Marcelo; Amin, Mustafa A.; Anderson, Adam; Arnold, Kam S.; Ashton, Peter; Baccigalupi, Carlo; Bard, Debbie; Barkats, Denis; Barron, Darcy; Barry, Peter S.; Bartlett, James G.; Basu Thakur, Ritoban; Battaglia, Nicholas; Bean, Rachel; Bebek, Chris; Bender, Amy N.; Benson, Bradford A.; Bianchini, Federico; Bischoff, Colin A.; Bleem, Lindsey; Bock, James J.; Bocquet, Sebastian; Boddy, Kimberly K.; Richard Bond, J.; Borrill, Julian; Bouchet, François R.; Brinckmann, Thejs; Brown, Michael L.; Bryan, Sean; Buza, Victor; Byrum, Karen; Hervias Caimapo, Carlos; Calabrese, Erminia; Calafut, Victoria; Caldwell, Robert; Carlstrom, John E.; Carron, Julien; Cecil, Thomas; Challinor, Anthony; Chang, Clarence L.; Chinone, Yuji; Sherry Cho, Hsiao Mei; Cooray, Asantha; Coulton, Will; Crawford, Thomas M.; Crites, Abigail; Cukierman, Ari; Cyr-Racine, Francis Yan; De Haan, Tijmen; Delabrouille, Jacques; Devlin, Mark; Di Valentino, Eleonora; Dierickx, Marion; Dobbs, Matt; Duff, Shannon; Dvorkin, Cora; Eimer, Joseph; Elleflot, Tucker; Errard, Josquin; Essinger-Hileman, Thomas; Fabbian, Giulio; Feng, Chang; Ferraro, Simone; Filippini, Jeffrey P.; Flauger, Raphael; Flaugher, Brenna; Fraisse, Aurelien A.; Frolov, Andrei; Galitzki, Nicholas; Gallardo, Patricio A.; Galli, Silvia; Ganga, Ken; Gerbino, Martina; Gluscevic, Vera; Goeckner-Wald, Neil; Green, Daniel; Grin, Daniel; Grohs, Evan; Gualtieri, Riccardo; Gudmundsson, Jon E.; Gullett, Ian; Gupta, Nikhel; Habib, Salman; Halpern, Mark; Halverson, Nils W.; Hanany, Shaul; Harrington, Kathleen; Hasegawa, Masaya; Hasselfield, Matthew; Hazumi, Masashi; Heitmann, Katrin; Henderson, Shawn; Hensley, Brandon; Hill, Charles; Colin Hill, J.; Hlozek, Renée; Patty Ho, Shuay Pwu; Hoang, Thuong; Holder, Gil; Holzapfel, William; Hood, John; Hubmayr, Johannes; Huffenberger, Kevin M.; Hui, Howard; Irwin, Kent; Jeong, Oliver; Johnson, Bradley R.; Jones, William C.; Hwan Kang, Jae; Karkare, Kirit S.; Katayama, Nobuhiko; Keskitalo, Reijo; Kisner, Theodore; Knox, Lloyd; Koopman, Brian J.; Kosowsky, Arthur; Kovac, John; Kovetz, Ely D.; Kuhlmann, Steve; Kuo, Chao Lin; Kusaka, Akito; Lähteenmäki, Anne; Lawrence, Charles R.; Lee, Adrian T.; Lewis, Antony; Li, Dale; Linder, Eric; Loverde, Marilena; Lowitz, Amy; Lubin, Phil; Madhavacheril, Mathew S.; Mantz, Adam; Marques, Gabriela; Matsuda, Frederick; Mauskopf, Philip; McCarrick, Heather; McMahon, Jeffrey; Daniel Meerburg, P.; Melin, Jean Baptiste; Menanteau, Felipe; Meyers, Joel; Millea, Marius; Mohr, Joseph; Moncelsi, Lorenzo; Monzani, Maria; Mroczkowski, Tony; Mukherjee, Suvodip; Nagy, Johanna; Namikawa, Toshiya; Nati, Federico; Natoli, Tyler; Newburgh, Laura; Niemack, Michael D.; Nishino, Haruki; Nord, Brian; Novosad, Valentine; O'Brient, Roger; Padin, Stephen; Palladino, Steven; Partridge, Bruce; Petravick, Don; Pierpaoli, Elena; Pogosian, Levon; Prabhu, Karthik; Pryke, Clement; Puglisi, Giuseppe; Racine, Benjamin; Rahlin, Alexandra; Sathyanarayana Rao, Mayuri; Raveri, Marco; Reichardt, Christian L.; Remazeilles, Mathieu; Rocha, Graca; Roe, Natalie A.; Roy, Anirban; Ruhl, John E.; Salatino, Maria; Saliwanchik, Benjamin; Schaan, Emmanuel; Schillaci, Alessandro; Schmitt, Benjamin; Schmittfull, Marcel M.; Scott, Douglas; Sehgal, Neelima; Shandera, Sarah; Sherwin, Blake D.; Shirokoff, Erik; Simon, Sara M.; Slosar, Anze; Spergel, David; St. Germaine, Tyler; Staggs, Suzanne T.; Stark, Antony; Starkman, Glenn D.; Stompor, Radek; Stoughton, Chris; Suzuki, Aritoki; Tajima, Osamu; Teply, Grant P.; Thompson, Keith; Thorne, Ben; Timbie, Peter; Tomasi, Maurizio; Tristram, Matthieu; Tucker, Gregory; Umiltà, Caterina; Van Engelen, Alexander; Vavagiakis, Eve M.; Vieira, Joaquin D.; Vieregg, Abigail G.; Wagoner, Kasey; Wallisch, Benjamin; Wang, Gensheng; Watson, Scott; Westbrook, Ben; Whitehorn, Nathan; Wollack, Edward J.; Kimmy Wu, W. L.; Xu, Zhilei; Eric Yang, H. Y.; Yasini, Siavash; Yefremenko, Volodymyr G.; Won Yoon, Ki; Young, Edward; Yu, Cyndia; Zonca, AndreaCMB-S4-the next-generation ground-based cosmic microwave background (CMB) experiment-is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2-3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5 sigma, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL. - The connection between the parsec-scale radio jet and gamma-ray flares in the blazar 1156+295
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2014) Ramakrishnan, Venkatessh; León-Tavares, Jonathan; Rastorgueva-Foi, Elizaveta A.; Wiik, Kaj; Jorstad, Svetlana G.; Marscher, Alan P.; Tornikoski, Merja; Agudo, Iván; Lähteenmäki, Anne; Valtaoja, Esko; Aller, Margo F.; Blinov, Dmitry A.; Casadio, Carolina; Efimova, Natalia V.; Gurwell, Mark A.; Gómez, José L.; Hagen-Thorn, Vladimir A.; Joshi, Manasvita; Järvelä, Emilia; Konstantinova, Tatiana S.; Kopatskaya, Evgenia N.; Larionov, Valeri M.; Larionova, Elena G.; Larionova, Liudmilla V.; Lavonen, Niko; MacDonald, Nicholas R.; McHardy, Ian M.; Molina, Sol N.; Morozova, Daria A.; Nieppola, Elina; Tammi, Joni; Taylor, Brian W.; Troitsky, Ivan S. - The Connection between the Radio Jet and the γ-ray Emission in the Radio Galaxy 3C 120 and the Blazar CTA 102
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-09-27) Casadio, Carolina; Gómez, José; Jorstad, Svetlana G.; Marscher, Alan P.; Grandi, Paola; Larionov, Valeri M.; Lister, Matthew; Smith, Paul S.; Gurwell, Mark A.; Lähteenmäki, Anne; Agudo, Iván; Molina, Sol N.; Bala, Vishal; Joshi, Manasvita; Taylor, Brian; Williamson, Karen E.; Kovalev, Yuri; Savolainen, Tuomas; Pushkarev, Alexander B.; Arkharov, Arkady A.; Blinov, Dmitry A.; Borman, George A.; Di Paola, Andrea; Grishina, Tatiana S.; Hagen-Thorn, Vladimir A.; Itoh, Ryosuke; Kopatskaya, Evgenia N.; Larionova, Elena G.; Larionova, Liudmila V.; Morozova, Daria; Rastorgueva-Foi, Elizaveta; Sergeev, Sergey G.; Tornikoski, Merja; Troitsky, Ivan; Thum, Clemens; Wiesemeyer, HelmutWe present multi-wavelength studies of the radio galaxy 3C 120 and the blazar CTA 102 during unprecedented γ-ray flares for both sources. In both studies the analysis of γ-ray data has been compared with a series of 43 GHz VLBA images from the VLBA-BU-BLAZAR program, providing the necessary spatial resolution to probe the parsec scale jet evolution during the high energy events. To extend the radio dataset for 3C 120 we also used 15 GHz VLBA data from the MOJAVE sample. These two objects which represent very different classes of AGN, have similar properties during the γ-ray events. The γ-ray flares are associated with the passage of a new superluminal component through the mm VLBI core, but not all ejections of new components lead to γ-ray events. In both sources γ-ray events occurred only when the new components are moving in a direction closer to our line of sight. We locate the γ-ray dissipation zone a short distance from the radio core but outside of the broad line region, suggesting synchrotron self-Compton scattering as the probable mechanism for the γ-ray production. - Core shift effect in blazars
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-07) Agarwal, A.; Mohan, P.; Gupta, Alok C.; Mangalam, A.; Volvach, A.E.; Aller, M. F.; Aller, H. D.; Gu, M.F.; Lähteenmäki, Anne; Tornikoski, M.; Volvach, L.N.We studied the pc-scale core shift effect using radio light curves for three blazars, S5 0716+ 714, 3C 279 and BL Lacertae, which were monitored at five frequencies (nu) between 4.8 and 36.8 GHz using the University of Michigan Radio Astronomical Observatory (UMRAO), the Crimean Astrophysical Observatory (CrAO) and Mets " ahovi Radio Observatory for over 40 yr. Flares were Gaussian fitted to derive time delays between observed frequencies for each flare (Delta t), peak amplitude (A) and their half width. Using A alpha nu(alpha), we infer a in the range of -16.67-2.41 and using Delta t alpha nu(1/kr), we infer k(r) similar to 1, employed in the context of equipartition between magnetic and kinetic energy density for parameter estimation. From the estimated core position offset (Omega(r nu)) and the core radius (r(core)), we infer that opacity model may not be valid in all cases. The mean magnetic field strengths at 1 pc (B-1) and at the core (B-core) are in agreement with previous estimates. We apply the magnetically arrested disc model to estimate black hole spins in the range of 0.15-0.9 for these blazars, indicating that the model is consistent with expected accretion mode in such sources. The power-law-shaped power spectral density has slopes -1.3 to -2.3 and is interpreted in terms of multiple shocks or magnetic instabilities. - A Decade of Multiwavelength Observations of the TeV Blazar 1ES 1215+303: Extreme Shift of the Synchrotron Peak Frequency and Long-term Optical–Gamma-Ray Flux Increase
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-03-10) Ramazani, Vandad Fallah; Hovatta, Talvikki; Savolainen, Tuomas; Lähteenmäki, Anne; Tornikoski, Merja; , Fermi Large Area Telescope Collaboration; , VERITAS CollaborationBlazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z = 0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long Baseline Array at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed. - Design and Analysis of a Wideband Feed for Metsähovi Compact Array
Sähkötekniikan korkeakoulu | Master's thesis(2017-01-23) Alam, ARadio telescope is an astronomical instrument and an essential tool of radio astronomy. It is consists of a radio receiver and antenna system. The design of antenna system of the radio telescope is a critical issue because of the demand of wide bandwidth, high gain, directional beam, and circular polarization. Metsähovi radio observatory has proposed a project named Metsähovi compact array to build four radio telescopes in order to create new research platform in different areas, such as radio astronomy, solar research, and space physics. In this master thesis work, a wide band feed for the reflector antenna of the proposed radio telescope is analyzed and designed. Initially several solutions are studied and analyzed. Based on these studies, a two arm conical log spiral antenna (CLSA) is designed and constructed in CST. At first, a theoretical model of CLSA is developed. Further, the design equations are reformulated to simulate the model in CST. The simulation results shows good agreement with the theoretical model. Moreover, the antenna is also simulated with the bifilar lines to have an practical feeding system of the antenna. In this case the results shows poor performance due to the significant radiation coming out from the bifilar lines which is overlapping with the antenna radiation. To avoid this radiation, a hollow metal is introduced which covers the bifilar lines to block the radiation coming out from the bifilar lines. The antenna performance with bifilar lines satisfies most of the requirements that has set up for this work. Besides, a mechanical construction of the antenna is presented to protect the antenna from the outside environment. - Detection of persistent VHE gamma-ray emission from PKS 1510-089 by the MAGIC telescopes during low states between 2012 and 2017
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018) Tornikoski, Merja; Lähteenmäki, Anne; Tammi, Joni; Ramakrishnan, Venkatessh; , MAGIC Collaboration; , Fermi Large Area Telescope CollaborationPKS 1510-089 is a flat spectrum radio quasar strongly variable in the optical and GeV range. We search for low-state VHE gamma-ray emission from PKS 1510-089. We aim to characterize and model the source in a broad-band context, which would provide a baseline over which high states and flares could be better understood. We use daily binned Fermi-LAT flux measurements of PKS 1510-089 to characterize the GeV emission and select the observation periods of MAGIC during low state of activity. For the selected times we compute the average radio, IR, optical, UV, X-ray and gamma-ray emission to construct a low-state spectral energy distribution of the source. The broadband emission is modelled within an External Compton scenario with a stationary emission region through which plasma and magnetic field are flowing. We perform also the emission-model-independent calculations of the maximum absorption in the broad line region (BLR) using two different models. Results. The MAGIC telescopes collected 75 hrs of data during times when the Fermi-LAT flux measured above 1 GeV was below 3x10-8cm-2s-1, which is the threshold adopted for the definition of a low gamma-ray activity state. The data show a strongly significant (9.5{\sigma}) VHE gamma-ray emission at the level of (4.27+-0.61stat)x10-12cm-2s-1 above 150GeV, a factor 80 smaller than the highest flare observed so far from this object. Despite the lower flux, the spectral shape is consistent with earlier detections in the VHE band. The broad-band emission is compatible with the EC scenario assuming a large emission region located beyond the BLR. For the first time the gamma-ray data allow us to place a limit on the location of the emission region during a low gamma-ray state of a FSRQ. For the used model of the BLR, the 95% C.L. on the location of the emission region allows us to place it at the distance >74% of the outer radius of the BLR. - Euroopan avaruusjärjestön satelliittimissioiden vaiheet
Sähkötekniikan korkeakoulu | Bachelor's thesis(2022-12-02) Honkanen, Vilhelmiina - The extreme HBL behaviour of Markarian 501 during 2012
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-12) Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Arcaro, C.; Babić, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio, J.A.; Becerra-González, J.; Bednarek, W.; Bernardini, E.; Berti, A.; Bhattacharyya, W; Blanch, O.; Bonnoli, G.; Carosi, R.; Carosi, A.; Chatterjee, A; Colak, S M; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Cumani, P; Da Vela, P.; Dazzi, F.; De Angelis, A; De Lotto, B.; Delfino, M; Delgado, J; Di Pierro, F.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Doro, M.; Eisenacher Glawion, D.; Engelkemeier, M.; Fallah Ramazani, V.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; García López, R.J.; Garczarczyk, M.; Gaug, M.; Giammaria, P.; Godinović, N.; Gora, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Hassan, T.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Ishio, K.; Konno, Y.; Kubo, H.; Kushida, J.; Kuveždić, D.; Lelas, D.; Lindfors, E; Lombardi, S.; Longo, F.; López, M.; Maggio, C.; Majumdar, P.; Makariev, M.; Maneva, G.; Manganaro, M.; Maraschi, L.; Hovatta, Talvikki; Lähteenmäki, Anne; Tornikoski, Merja; Tammi, JoniA multiwavelength campaign was organized to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼ 0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼ 3 CU, and the peak of the high-energy spectral component was found to be at ∼ 2 TeV. This study reports very hard X-ray spectra, and the hardest VHE spectra measured to date for Mrk 501. The fractional variability was found to increase with energy, with the highest variability occurring at VHE, and a significant correlation between the X-ray and VHE bands. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency- peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The one-zone synchrotron self-Compton (SSC) scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behaviour seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays. - Far-infrared photometry of OJ 287 with the Herschel Space Observatory
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-02-01) Kidger, Mark; Zola, Staszek; Valtonen, Mauri; Lähteenmäki, Anne; Järvelä, Emilia; Tornikoski, Merja; Tammi, Joni; Liakos, Alexis; Poyner, GaryContext. The blazar OJ 287 has shown a ≈ 12 year quasi-periodicity over more than a century, in addition to the common properties of violent variability in all frequency ranges. It is the strongest known candidate to have a binary singularity in its central engine. Aim. We aim to better understand the different emission components by searching for correlated variability in the flux over four decades of frequency measurements. Methods. We combined data at frequencies from the millimetric to the visible to characterise the multifrequency light curve in April and May 2010. This includes the only photometric observations of OJ 287 made with the Herschel Space Observatory: five epochs of data obtained over 33 days at 250, 350, and 500 μm with Herschel-SPIRE. Results. Although we find that the variability at 37 GHz on timescales of a few weeks correlates with the visible to near-IR spectral energy distribution, there is a small degree of reddening in the continuum at lower flux levels that is revealed by the decreasing rate of decline in the light curve at lower frequencies. However, we see no clear evidence that a rapid flare detected in the light curve during our monitoring in the visible to near-IR light curve is seen either in the Herschel data or at 37 GHz, suggesting a low-frequency cut-off in the spectrum of such flares. Conclusions. We see only marginal evidence of variability in the observations with Herschel over a month, although this may be principally due to the poor sampling. The spectral energy distribution between 37 GHz and the visible can be characterised by two components of approximately constant spectral index: a visible to far-IR component of spectral index α = -0.95, and a far-IR to millimetric spectral index of α = -0.43. There is no evidence of an excess of emission that would be consistent with the 60 μmdust bump found in many active galactic nuclei. - The Gamma-ray Activity of the high-z Quasar 0836+71
A4 Artikkeli konferenssijulkaisussa(2013) Jorstad, Svetlana; Marscher, Alan; Larionov, Valeri; Gómez, José L.; Agudo, Iván; Angelakis, Emmanouil; Casadio, Carolina; Gurwell, Mark; Hovatta, Talvikki; Joshi, Manasvita; Fuhrmann, Lars; Karamanavis, Vassilis; Lähteenmäki, Anne; Molina, Sol; Morozova, Daria; Myserlis, Ioannis; Troitsky, Ivan; Ungerechts, Hans; Zensus, J.AntonThe Fermi LAT detected an increase in γ-ray activity of the quasar 0836+710 (z=2.17) in Spring 2011 that culminated in a sharp γ-ray flare at the end of 2011 when the source reached a flux of 2.9×10−6 phot s−1cm−2 at 0.1-200 GeV. We monitor the quasar at optical wavelengths in photometric and polarimetric modes, at millimeter and centimeter wavelengths, and with the VLBA at 43 GHz. The optical brightness of the quasar increased by ~0.5 mag in R band and the degree of polarization oscillated between ~1% and ~6% during the highest γ-ray state, while the position angle of polarization rotated by ~300°. We have identified in the VLBA images a strong, highly polarized component that moves with an apparent speed of ~20 c. The component emerged from the core in the beginning of the γ-ray event and reached a flux maximum at the peak of the γ-ray outburst. We present the results of a correlative analysis of variations at different wavelengths along with the kinematic parameters of the parsec scale jet. We discuss the location of the high γ-ray emission in the relativistic jet, as well as the emission mechanisms responsible for γ-ray production. - Host galaxies of jetted narrow-line Seyfert 1 galaxies
A4 Artikkeli konferenssijulkaisussa(2018-01-01) Järvelä, Emilia; Lähteenmäki, Anne; Berton, MarcoWe performed J-band observations of the host galaxies of nine narrow-line Seyfert 1 galaxies (NLS1). Seven of these sources have been detected at 37 GHz and are likely to host relativistic jets. Host galaxy properties of the jetted NLS1 galaxies are not yet well known, and investigating them is essential to get more insight into their characteristics and the possibly heterogeneous nature of the NLS1 population. It also helps us to understand the overall evolution of NLS1 galaxies and how do they fit into the big picture of active galactic nuclei (AGN). We used the 2D photometric image decomposition algorithm GALFIT to model the morphologies of the hosts. We were able to reliably model five of the nine host galaxies, three of which have also been detected at 37 GHz. All five host galaxies are late-type, four of them host pseudobulges, and four are barred. A surprisingly large fraction, three out of five, show signs of interaction. These results support the idea that spiral galaxies with pseudobulges are able to launch and maintain powerful jets. High fraction of interacting sources may indicate that mergers and interaction could affect the level of nuclear activity in NLS1 galaxies. This could also explain the diversity seen in the NLS1 galaxy population as a consequence of galaxy evolution via mergers and interaction. - Identification of narrow-line Seyfert 1 galaxies in a spurious source sample using spectral line profiles
Sähkötekniikan korkeakoulu | Master's thesis(2019-06-17) Björklund, IreneThis thesis is a compilation of both general knowledge on galaxies and active galaxies as well as detailed knowledge on NLS1 galaxies. A recent research paper claimed that they confirmed 11001 sources to be NLS1 galaxies. The main object of this thesis was to determine how many of these sources are truly NLS1 with a high certainty. The sources were deemed most likely NLS1 galaxies by studying the emission lines of the galaxy spectra and performing mathematical analysis as well as observing the spectra by eye. After the sources had been either deemed most likely NLS1 or discarded, only 3998 sources remained. The most likely NLS1 galaxy sources were divided into two categories based on their profile type: Lorentzian (Cauchy) or Gaussian. 11 parameters of the most likely NLS1 galaxy sources were further analyzed to find possible differences between the two profile types. With the results of this thesis, researchers can study NLS1 galaxies better by not having a contaminated source sample and can hopefully find instrumental properties of NLS1 galaxies. - Implementation of a Data Packetiser and phase-tracking FXF-correlator for the Metsähovi Compact Array
School of Electrical Engineering | Master's thesis(2024-12-20) Raassina, JereMetsähovi Radio Observatory (MRO) is one of the major research and teaching infrastructures of Aalto University, where various measurements are conducted, such as solar monitoring and extragalactic radio source observations. In recent years, the commissioning of an array consisting of 5.5-metre radio telescopes known as the Metsähovi Compact Array (MCA) has taken place at the site. The MCA is intended to operate as a radio telescope interferometer, consisting of three to four telescopes, separated by baselines of up to 400 metres. This requires transmitting the data from each telescope to an upcoming software correlator for processing. The goal of this thesis was to implement a system known as the data packetiser, which is responsible of transmitting the formatted, digitised signal from an individual telescope over a network to the correlator. The data were to be provided with such information that they could be distinguishable by the correlator. This thesis also investigated the interferometric capabilities of the MCA using rudimentary software-correlator solutions in GNU Radio Companion (GRC) and a phase rotator to assist in time-aligning the signals. The work was carried out using a software-defined radio (SDR) platform from Ettus Research known as the Universal Software Radio Peripheral (USRP) X410 that was controlled using GRC programs. The data packetiser was programmed in C++ as part of GRC, to allow its use in various SDR implementations. The packetiser computer receives the data from the X410s and transmits them forward as User Datagram Protocol (UDP) packets with timestamps, sequence numbers, and information of their origin. The X410s in two MCA telescopes were supplied with 10 MHz and 1 PPS reference signals to synchronise their sampling, which resulted in the first correlations and phase tracking of a source achieved with the MCA. The phase tracking capability allows the coordinates of the baselines to be refined, which led to the first interferometric images. - Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-12) Lähteenmäki, Anne; Tammi, Joni; Tornikoski, Merja; Hovatta, Talvikki; , WEBT Collaboration; , OVRO TeamWe present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (gamma-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented gamma-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 +/- 63) x 10(-8) ph cm(-2) s(-1), corresponding to a luminosity of (2.2 +/- 0.1) x10(50) erg s(-1), was reached on 2016 December 28. These four gamma-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and gamma-ray activity is found. The gamma-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This gamma-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.
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