Now showing items 1-20 of 2560

    • FERMI LARGE AREA TELESCOPE DETECTION OF GRAVITATIONAL LENS DELAYED γ-RAY FLARES FROM BLAZAR B0218+357 

      Cheung, C. C.; Larsson, S.; Scargle, J. D.; Amin, M. A.; Blandford, R. D.; Bulmash, D.; Chiang, J.; Ciprini, S.; Corbet, R. H. D.; Falco, E. E.; Marshall, P. J.; Wood, D. L.; Ajello, M.; Bastieri, D.; Chekhtman, A.; D'Ammando, F.; Giroletti, M.; Grove, J. E.; Lott, B.; Ojha, R.; Orienti, M.; Perkins, J. S.; Razzano, M.; Smith, A. W.; Thompson, D. J.; Wood, K. S. (IOP, 2014-01-30)
      Using data from the Fermi Large Area Telescope (LAT), we report the first clear γ-ray measurement of a delay between flares from the gravitationally lensed images of a blazar. The delay was detected in B0218+357, a known ...
    • Extended X-ray emission in PKS 1718−649 

      Beuchert, T.; Rodríguez-Ardila, A.; Moss, V. A.; Schulz, R.; Kadler, M.; Wilms, J.; Angioni, R.; Callingham, J. R.; Gräfe, C.; Krauß, F.; Kreikenbohm, A.; Langejahn, M.; Leiter, K.; Maccagni, F. M.; Müller, C.; Ojha, R.; Ros, E.; Tingay, S. J. (EDP sciences, 2018-04-30)
      PKS 1718−649 is one of the closest and most comprehensively studied candidates of a young active galactic nucleus (AGN) that is still embedded in its optical host galaxy. The compact radio structure, with a maximal extent ...
    • Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC 612 (PKS 0131−36) 

      Emonts, B. H. C.; Morganti, R.; Oosterloo, T. A.; Holt, J.; Tadhunter, C. N.; Van Der Hulst, J. M.; Ojha, R.; Sadler, E. M. (Oxford University Press, 2008-05-09)
      We present the detection of an enormous disc of cool neutral hydrogen (H I) gas surrounding the S0 galaxy NGC 612, which hosts one of the nearest powerful radio sources (PKS 0131−36). Using the Australia Telescope Compact ...
    • Exceptional NIR flare in gamma-ray loud FSRQ PKS B1424-418 

      Nesci, R.; Ojha, R.; Kadler, M. (2015-01-26)
      The gamma-ray loud flat spectrum radio quasar PKS 1424-418 has been steadily increasing its luminosity since August 2017 and is now (2018-01-21) at its historic recorded maximum of J=13.73 +/- 0.05. These observations were ...
    • Energetic Particles of Cosmic Accelerators II: Active Galactic Nuclei and Gamma-ray Bursts 

      Venters, Tonia M.; Guiriec, Sylvain; Lien, Amy Y.; Ojha, Roopesh
      The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Our pursuit of more than a century to uncover the ...
    • Energetic Particles of Cosmic Accelerators I: Galactic Accelerators 

      Venters, Tonia M.; Hamaguchi, Kenji; Ojha, Roopesh
      The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Our pursuit of more than a century to uncover the ...
    • Dual-frequency VLBI study of Centaurus A on sub-parsec scales. The highest-resolution view of an extragalactic jet 

      Müller, C.; Kadler, M.; Ojha, R.; Wilms, J.; Böck, M.; Edwards, P. G.; Fromm, C. M.; Hase, H.; Horiuchi, S.; Katz, U.; Lovell, J. E. J.; Plötz, C.; Pursimo, T.; Richers, S.; Ros, E.; Rothschild, R. E.; Taylor, G. B.; Tingay, S. J.; Zensus, J. A. (EDP sciences, 2011-05-20)
      Context. Centaurus A is the closest active galactic nucleus. High resolution imaging using Very Long Baseline Interferometry (VLBI) enables us to study the spectral and kinematic behavior of the radio jet–counterjet system ...
    • DUAL-FREQUENCY OBSERVATIONS OF 140 COMPACT, FLAT-SPECTRUM ACTIVE GALACTIC NUCLEI FOR SCINTILLATION-INDUCED VARIABILITY 

      Koay, J. Y.; Macquart, J.-P.; Rickett, B. J.; Bignall, H. E.; Lovell, J. E. J.; Reynolds, C.; Jauncey, D. L.; Pursimo, T.; Kedziora-Chudczer, L.; Ojha, R. (IOP, 2011-08-30)
      The 4.9 GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey detected a drop in interstellar scintillation (ISS) for sources at redshifts z gsim 2, indicating an apparent increase in angular diameter or a ...
    • Detection of the blazar S4 0954+65 at very-high-energy with the MAGIC telescopes during an exceptionally high optical state 

      González, J. Becerra; Ojha, R. (EDP sciences, 2018-09-13)
      Aims. The very high energy (VHE ≳100 GeV) γ-ray MAGIC observations of the blazar S4 0954+65, were triggered by an exceptionally high flux state of emission in the optical. This blazar has a disputed redshift of z = 0.368 ...
    • Detection of a Gamma-Ray Flare from the High-redshift Blazar DA 193 

      Paliya, Vaidehi S.; Ajello, M.; Ojha, R.; Angioni, R.; Cheung, C. C.; Tanada, K.; Pursimo, T.; Galindo, P.; Losada, I. R.; Siltala, L.; Djupvik, A. A.; Marcotulli, L.; Hartmann, D. (IOP, 2019-02-01)
      High-redshift (z > 2) blazars are the most powerful members of the blazar family. Yet, only a handful of them have both X-ray and γ-ray detection, thereby making it difficult to characterize the energetics of the most ...
    • Consequences of a possible jet-star interaction in the inner central parsec of Centaurus A 

      Müller, C.; Kadler, M.; Mannheim, K.; Perucho, M.; Ojha, R.; Ros, E.; Schulza, R.; Wilms, J.
      The jet-counterjet system of the closest radio-loud active galaxy Centaurus A (Cen A) can be studied with Very Long Baseline Interferometry (VLBI) on unprecedented small linear scales of ∼ 0.018 pc. These high-resolution ...
    • Compton-Pair Production Space Telescope (ComPair) for MeV Gamma-ray Astronomy 

      Moiseev, A.A.; Ajello, M.; Buckley, J.H.; Caputo, R.; Ferrara, E.C.; Hartmann, D.H.; Hays, E.; McEnery, J.E.; Mitchell, J.W.; Ojha, R.; Perkins, J.S.; Racusin, J.L.; Smith, A.W.; Thompson, D.J. (2015-09-18)
      The gamma-ray energy range from a few hundred keV to a few hundred MeV has remained largely unexplored, mainly due to the challenging nature of the measurements, since the pi- oneering, but limited, observations by COMPTEL ...
    • Characterization of long baseline calibrators at 2.3 GHz 

      Hungwe, F.; Ojha, R.; Booth, R. S.; Bietenholz, M. F.; Collioud, A.; Charlot, P.; Boboltz, D.; Fey, A. L. (Oxford University Press, 2011-12-08)
      We present a detailed multi-epoch analysis of 31 potential Southern hemisphere radio calibrators that were originally observed as part of a programme to maintain the International Celestial Reference Frame. At radio ...
    • ATCA monitoring of gamma-ray loud AGN 

      Stevens, J.; Edwards, P. G.; Ojha, R.; Kadler, M.; Hungwe, F.; Dutka, M.; Tingay, S.; Macquart, J. P.; Moin, A.; Lovell, J.; Blanchard, J. (2012-11-12)
      As a critical part of the Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry (TANAMI) program, in November 2007 the Australia Telescope Compact Array (ATCA) started monitoring the radio spectra of ...
    • Astrometry of 25 Southern Hemisphere Radio Sources from a VLBI Short-Baseline Survey 

      Fey, Alan L.; Ojha, Roopesh; Reynolds, John E.; Ellingsen, Simon P.; McCulloch, Peter M.; Jauncey, David L.; Johnston, Kenneth J. (IOP, 2004-11)
      Milliarcsecond-accurate radio positions for 25 southern hemisphere extragalactic sources are reported. These positions are derived from Mark III Very Long Baseline Interferometry observations made between 2003 September ...
    • AST/RO Observations of Atomic Carbon near the Galactic Center 

      Ojha, Roopesh; Stark, Antony A.; Hsieh, Henry H.; Lane, Adair P.; Chamberlin, Richard A.; Bania, Thomas M.; Bolatto, Alberto D.; Jackson, James M.; Wright, Gregory A. (IOP, 2001-02-10)
      We present a coarsely sampled map of the region |l| ≤ 2°, |b| ≤ 0°1 in the 492 GHz (³P₁ → ³P₀) fine-structure transition of neutral carbon, observed with the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO). ...
    • A Basic Formula for Effective International Student Services 

      Di Maria, David L. (2020-08-15)
      The effective delivery of support services for international students has been the subject of professional discourse for nearly a century (Wheeler, King & Davidson, 1925). While scholars have long examined the problem of ...
    • Angular Broadening of Intraday Variable AGNs. II. Interstellar and Intergalactic Scattering 

      Lazio, T. Joseph W.; Ojha, Roopesh; Fey, Alan L.; Kedziora-Chudczer, Lucyna; Cordes, James M.; Jauncey, David L.; Lovell, James E. J. (IOP, 2008-01-01)
      We analyze a sample of 58 multiwavelength, Very Long Baseline Array observations of active galactic nuclei (AGNs) to determine their scattering properties. Approximately 75% of the sample consists of AGNs that ...
    • ANTARES constrains a blazar origin of two IceCube PeV neutrino events 

      Ojha, R. (EDP sciences, 2015-03-30)
      The source(s) of the neutrino excess reported by the IceCube Collaboration is unknown. The TANAMI Collaboration recently reported on the multiwavelength emission of six bright, variable blazars which are positionally ...
    • All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe 

      McEnery, Julie E.; Ojha, R.; Georganopoulos, Markos; Meyer, Eileen (2019-07-10)
      The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class mission concept that will provide essential contributions to multimessenger astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity ...