Browsing by Department "California Institute of Technology"

Now showing 1 - 9 of 9
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    Erratic flaring of BL LAC in 2012-2013
    (2016-01-10) Wehrle, Ann E.; Grupe, Dirk; Jorstad, Svetlana G.; Marscher, Alan P.; Gurwell, Mark; Baloković, Mislav; Hovatta, Talvikki; Madejski, Grzegorz M.; Harrison, Fiona H.; Stern, Daniel; Space Science Institute; Morehead State University; St. Petersburg State University; Boston University; Harvard-Smithsonian Center for Astrophysics; Cahill Center for Astronomy and Astrophysics; SLAC National Accelerator Laboratory; California Institute of Technology
    BL Lac, the eponymous blazar, flared to historically high levels at millimeter, infrared, X-ray, and gamma-ray wavelengths in 2012. We present observations made with Herschel, Swift, NuSTAR, Fermi, the Submillimeter Array, CARMA, and the VLBA in 2012-2013, including three months with nearly daily sampling at several wavebands. We have also conducted an intensive campaign of 30 hr with every-orbit observations by Swift and NuSTAR, accompanied by Herschel, and Fermi observations. The source was highly variable at all bands. Time lags, correlations between bands, and the changing shapes of the spectral energy distributions can be explained by synchrotron radiation and inverse Compton emission from nonthermal seed photons originating from within the jet. The passage of four new superluminal very long baseline interferometry knots through the core and two stationary knots about 4 pc downstream accompanied the high flaring in 2012-2013. The seed photons for inverse Compton scattering may arise from the stationary knots and from a Mach disk near the core where relatively slow-moving plasma generates intense nonthermal radiation. The 95 spectral energy distributions obtained on consecutive days form the most densely sampled, broad wavelength coverage for any blazar. The observed spectral energy distributions and multi-waveband light curves are similar to simulated spectral energy distributions and light curves generated with a model in which turbulent plasma crosses a conical shock with a Mach disk.
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    Fast thermometry with a proximity Josephson junction
    (2018-01-01) Wang, L. B.; Saira, O. P.; Pekola, J. P.; Centre of Excellence in Quantum Technology, QTF; California Institute of Technology; Department of Applied Physics
    We couple a proximity Josephson junction to a Joule-heated normal metal film and measure its electron temperature under steady state and nonequilibrium conditions. With a timed sequence of heating and temperature probing pulses, we are able to monitor its electron temperature in nonequilibrium with effectively zero back-action from the temperature measurement in the form of additional dissipation or thermal conductance. The experiments demonstrate the possibility of using a fast proximity Josephson junction thermometer for studying thermal transport in mesoscopic systems and for calorimetry.
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    High-energy gamma-ray observations of the accreting black hole V404 Cygni during its 2015 June outburst
    (2016-10-11) Loh, A.; Corbel, S.; Dubus, G.; Rodriguez, J.; Grenier, I.; Hovatta, T.; Pearson, T.; Readhead, A.; Fender, R.; Mooley, K.; Centre National de la Recherche Scientifique (CNRS); Université Grenoble Alpes; Metsähovi Radio Observatory; California Institute of Technology; University of Oxford; Department of Radio Science and Engineering
    We report on Fermi/Large Area Telescope observations of the accreting black hole low-mass X-ray binary V404 Cygni during its outburst in 2015 June-July. Detailed analyses reveal a possible excess of γ -ray emission on 2015 26 June, with a very soft spectrum above 100 MeV, at a position consistent with the direction of V404 Cyg (within the 95 per cent confidence region and a chance probability of 4 × 10-4). This emission cannot be associated with any previously known Fermi source. Its temporal coincidence with the brightest radio and hard X-ray flare in the light curve of V404 Cyg, at the end of the main active phase of its outburst, strengthens the association with V404 Cyg. If the γ -ray emission is associated with V404 Cyg, the simultaneous detection of 511 keV annihilation emission by INTEGRAL reqires that the high-energy γ -rays originate away from the corona, possibly in a Blandford-Znajek jet. The data give support to models involving a magnetically arrested disc where a bright γ -ray jet can re-form after the occurrence of a major transient ejection seen in the radio.
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    Locating the gamma-ray emission site in Fermi/LAT blazars
    (2016) Ramakrishnan, V.; Hovatta, T.; Tornikoski, M.; Nilsson, K.; Lindfors, E.; Balokovic, M.; Lähteenmäki, Anne; Reinthal, R.; Takalo, L.; California Institute of Technology; Metsähovi Radio Observatory; University of Turku; Department of Radio Science and Engineering
    In an attempt to constrain and understand the emission mechanism of. gamma-rays, we perform a cross-correlation analysis of 15 blazars using light curves inmillimetre, optical and gamma-rays. We use discrete correlation function and consider only correlations significant at the 99 per cent level. A strong correlation was found between 37 and 95 GHz with a near-zero time delay in most of the sources, and similar to 1 month or longer in the rest. A similar result was obtained between the optical and. gamma-ray bands. Of the 15 sources, less than 50 per cent showed a strong correlation between the millimetre and gamma-ray or millimetre and optical bands. The primary reason for the lack of statistically significant correlation is the absence of a major outburst in the millimetre bands of most of the sources during the 2.5 yr time period investigated in our study. This may indicate that only the long-term variations or large flares are correlated between these bands. The variability of the sources at every waveband was also inspected using fractional rms variability (F-var ). The F-var displays an increase with frequency reaching its maximum in the gamma-rays.
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    Modification of electron-phonon coupling by micromachining and suspension
    (American Institute of Physics, 2020-01-14) Saira, Olli Pentti; Matheny, Matthew H.; Wang, Libin; Pekola, Jukka; Roukes, Michael; California Institute of Technology; Centre of Excellence in Quantum Technology, QTF; Department of Applied Physics
    Weak electron-phonon interaction in metals at low temperatures forms the basis of operation for cryogenic hot-electron bolometers and calorimeters. Here, we develop a thermometry scheme based on proximity supercurrent to study the thermal response of a thin gold film on a SiO 2 platform at temperatures below 100 mK. We find that the exponent of the power law describing electron-phonon coupling in the film drops by approximately 1 / 2 as the platform is micromachined and released from its substrate. This contrasts the conventional theory for bulklike geometries that predicts integer-valued exponents. We attribute the fractional change to a modified phonon spectrum described by recent theoretical developments.
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    Optical EVPA rotations in blazars
    (OXFORD UNIV PRESS INC, 2017-12) Kiehlmann, S.; Blinov, D.; Pearson, T. J.; Liodakis, I.; Metsähovi Radio Observatory; St. Petersburg State University; California Institute of Technology; Stanford University; Department of Radio Science and Engineering
    We identify rotations of the polarization angle in a sample of blazars observed for three seasons with the RoboPol instrument. A simplistic stochastic variability model is tested against this sample of rotation events. The model is capable of producing samples of rotations with parameters similar to the observed ones, but fails to reproduce the polarization fraction at the same time. Even though we can neither accept nor conclusively reject the model, we point out various aspects of the observations that are fully consistent with a random walk process.
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    Planck 2015 results
    (2016-10-01) Ade, P. A R; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Battye, R.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J. P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J. F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R. R.; Chiang, H. C.; Chluba, J.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P L; Combet, C.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; De Bernardis, P.; De Rosa, A.; De Zotti, G.; Delabrouille, J.; Désert, F. X.; Di Valentino, E.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Farhang, M.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Gauthier, C.; Gerbino, M.; Ghosh, T.; Giard, M.; Giraud-Héraud, Y.; Giusarma, E.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hamann, J.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huang, Z.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J. M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Maciás-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marchini, A.; Maris, M.; Martin, P. G.; Martinelli, M.; Martínez-González, E.; Masi, S.; Matarrese, S.; Mcgehee, P.; Meinhold, P. R.; Melchiorri, A.; Melin, J. B.; Mendes, L.; Mennella, A.; Migliaccio, M.; Millea, M.; Mitra, S.; Miville-Deschênes, M. A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J. L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rouillé D'orfeuil, B.; Rowan-Robinson, M.; Rubinõ-Martín, J. A.; Rusholme, B.; Said, N.; Salvatelli, V.; Salvati, L.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Serra, P.; Shellard, E. P S; Spencer, L. D.; Spinelli, M.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A. S.; Sygnet, J. F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Trombetti, T.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Väliviita, J.; Van Tent, F.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, M.; White, S. D M; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.; Cardiff University; CNRS/IN2P3; Service d'Astrophysique CEA; Kavli Institute for Cosmology Cambridge; University of Cambridge; International School for Advanced Studies; IRAP; Universite de Toulouse; Instituto de Física de Cantabria (CSIC-Universidad de Cantabria); Jet Propulsion Laboratory, California Institute of Technology; AstroParticule et Cosmologie; Università Degli Studi di Padova; Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy; University of Granada; University of Manchester; UMR7095; CNRS; University College London; INAF/IASF Milano; Università degli Studi di Milano; Nicolaus Copernicus Astronomical Center; California Institute of Technology; University of Toronto; University of California at Berkeley; Lawrence Berkeley National Laboratory; Universite Paris Sorbonne - Paris IV; Institut d 'Astrophysique de Paris; INAF/IASF Bologna; Università di Ferrara; INFN, Sezione di Bologna; University of Oxford; UMR 5141; LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres; Laboratoire AIM, Service d’Astrophysique, DSM\IRFU, CEA\Saclay; Institut d'Astrophysique Spatiale; Princeton University; University of KwaZulu-Natal; Johns Hopkins University; Niels Bohr Institute; Stanford University; Imperial College London; University of Southern California; Universidad de Cantabria; Università La Sapienza; INAF, Osservatorio Astronomico di Padova; UMR 7095; Ludwig Maximilian University of Munich; Max-Planck-Institut für Astrophysik; Institut Universitaire de France; European Space Agcy, European Space Agency, ESAC, Planck Sci Off; University of Oslo; Shahid Beheshti University; Osservatorio Astronomico di Trieste; University of Chicago; National Taiwan University; Stockholms universitet; NORDITA; University of Warsaw; Università Degli Studi di Trieste; Istituto Nazionale di Fisica Nucleare; CERN; University of Sydney; McGill University; Centro de Estudios de la Física del Cosmos de Aragón; Technical University of Denmark; Florida State University; University of Helsinki; European Southern Observatory Santiago; ALMA Santiago Central Offices; University of California; Université de Genève; African Institute for Mathematical Sciences; Helsinki Institute of Physics; Aix Marseille Universite; Department of Radio Science and Engineering; Metsähovi Radio Observatory; INFN, Sezione di Ferrara; Centro de Gestão e Estudos Estratégicos; RWTH Aachen University; University of Sussex; INFN, Sezione di Padova; University of California, Santa Barbara; INAF, Osservatorio Astronomico di Trieste; Universite Paris-Sud; INFN, Sezione di Roma 1; University of Heidelberg; Gran Sasso Science Institute; CEA Saclay, CEA, DSM Irfu SPP; Inter-University Centre for Astronomy and Astrophysics; CNRS Centre National de la Recherche Scientifique; University of Nottingham; National University of Ireland; University of Copenhagen; ASI Science Data Center; RAS - Pn Lebedev Physics Institute; Haverford College; INAF, Osservatorio Astronomico di Roma; Institute for Space Sciences; Université Pierre and Marie Curie; Radboud University Nijmegen; Universities Space Research Association; Instituto Astrofisico de Canarias; CSIC; Universidad de La Laguna; Università di Roma Tor Vergata; Department of Applied Physics; ROTA – Topological superfluids; University of British Columbia; Special Astrophysical Observatory, Russian Academy of Sciences; Kazan Federal University; Space Research Institute, Russian Academy of Sciences; ESTEC - European Space Research and Technology Centre; Università degli Studi e-Campus; Universidad de Oviedo; Trinity College Dublin; INAF, Osservatorio Astrofisico di Catania; University of Illinois at Urbana-Champaign
    This paper presents cosmological results based on full-mission Planck observations of temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation. Our results are in very good agreement with the 2013 analysis of the Planck nominal-mission temperature data, but with increased precision. The temperature and polarization power spectra are consistent with the standard spatially-flat 6-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations (denoted "base ΛCDM" in this paper). From the Planck temperature data combined with Planck lensing, for this cosmology we find a Hubble constant, H0 = (67.8 ± 0.9) km s-1Mpc-1, a matter density parameter Ωm = 0.308 ± 0.012, and a tilted scalar spectral index with ns = 0.968 ± 0.006, consistent with the 2013 analysis. Note that in this abstract we quote 68% confidence limits on measured parameters and 95% upper limits on other parameters. We present the first results of polarization measurements with the Low FrequencyInstrument at large angular scales. Combined with the Planck temperature and lensing data, these measurements give a reionization optical depth of τ = 0.066 ± 0.016, corresponding to a reionization redshift of \hbox{$z-{\rm re}=8.8{+1.7}-{-1.4}$}. These results are consistent with those from WMAP polarization measurements cleaned for dust emission using 353-GHz polarization maps from the High Frequency Instrument. We find no evidence for any departure from base ΛCDM in the neutrino sector of the theory; for example, combining Planck observations with other astrophysical data we find Neff = 3.15 ± 0.23 for the effective number of relativistic degrees of freedom, consistent with the value Neff = 3.046 of the Standard Model of particle physics. The sum of neutrino masses is constrained to â'mν < 0.23 eV. The spatial curvature of our Universe is found to be very close to zero, with | ΩK | < 0.005. Adding a tensor component as a single-parameter extension to base ΛCDM we find an upper limit on the tensor-to-scalar ratio of r0.002< 0.11, consistent with the Planck 2013 results and consistent with the B-mode polarization constraints from a joint analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP B-mode data to our analysis leads to a tighter constraint of r0.002 < 0.09 and disfavours inflationarymodels with a V(φ) φ2 potential. The addition of Planck polarization data leads to strong constraints on deviations from a purely adiabatic spectrum of fluctuations. We find no evidence for any contribution from isocurvature perturbations or from cosmic defects. Combining Planck data with other astrophysical data, including Type Ia supernovae, the equation of state of dark energy is constrained to w =-1.006 ± 0.045, consistent with the expected value for a cosmological constant. The standard big bang nucleosynthesis predictions for the helium and deuterium abundances for the best-fit Planck base ΛCDM cosmology are in excellent agreement with observations. We also constraints on annihilating dark matter and onpossible deviations from the standard recombination history. In neither case do we find no evidence for new physics. The Planck results for base ΛCDM are in good agreement with baryon acoustic oscillation data and with the JLA sample of Type Ia supernovae. However, as in the 2013 analysis, the amplitude of the fluctuation spectrum is found to be higher than inferred from some analyses of rich cluster counts and weak gravitational lensing. We show that these tensions cannot easily be resolved with simple modifications of the base ΛCDM cosmology. Apart from these tensions, the base ΛCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.
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    Plasmonic nanostructures through DNA-assisted lithography
    (2018-02-01) Shen, Boxuan; Linko, Veikko; Tapio, Kosti; Pikker, Siim; Lemma, Tibebe; Gopinath, Ashwin; Gothelf, Kurt V.; Kostiainen, Mauri A.; Toppari, J. Jussi; Biohybrid Materials; Department of Bioproducts and Biosystems; University of Jyväskylä; California Institute of Technology; Aarhus University
    Programmable self-assembly of nucleic acids enables the fabrication of custom, precise objects with nanoscale dimensions. These structures can be further harnessed as templates to build novel materials such as metallic nanostructures, which are widely used and explored because of their unique optical properties and their potency to serve as components of novel metamaterials. However, approaches to transfer the spatial information of DNA constructions to metal nanostructures remain a challenge. We report a DNA-assisted lithography (DALI) method that combines the structural versatility of DNA origami with conventional lithography techniques to create discrete, well-defined, and entirely metallic nanostructures with designed plasmonic properties. DALI is a parallel, high-throughput fabrication method compatible with transparent substrates, thus providing an additional advantage for optical measurements, and yields structures with a feature size of ~10 nm. We demonstrate its feasibility by producing metal nanostructures with a chiral plasmonic response and bowtie-shaped nanoantennas for surface-enhanced Raman spectroscopy. We envisage that DALI can be generalized to large substrates, which would subsequently enable scale-up production of diverse metallic nanostructures with tailored plasmonic features.
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    The RoboPol pipeline and control system
    (2014) King, O. G.; Blinov, D.; Ramaprakash, A. N.; Myserlis, I.; Angelakis, E.; Baloković, M.; Feiler, R.; Fuhrmann, L.; Hovatta, T.; Khodade, P.; Kougentakis, A.; Kylafis, N.; Kus, A.; Modi, D.; Paleologou, E.; Panopoulou, G.; Papadakis, I.; Papamastorakis, I.; Paterakis, G.; Pavlidou, V.; Pazderska, B.; Pazderski, E.; Pearson, T. J.; Rajarshi, C.; Readhead, A. C S; Reig, P.; Steiakaki, A.; Tassis, K.; Zensus, J. A.; California Institute of Technology; St. Petersburg State University; Inter-University Centre for Astronomy and Astrophysics India; Max Planck Institute for Radio Astronomy; Nicolaus Copernicus University in Toruń; Metsähovi Radio Observatory; Foundation for Research and Technology - Hellas; University of Crete
    We describe the data reduction pipeline and control system for the RoboPol project. The RoboPol project is monitoring the optical R-band magnitude and linear polarization of a large sample of active galactic nuclei that is dominated by blazars. The pipeline calibrates and reduces each exposure frame, producing a measurement of the magnitude and linear polarization of every source in the 13 arcmin × 13 arcmin field of view. The control system combines a dynamic scheduler, real-time data reduction, and telescope automation to allow high-efficiency unassisted observations.