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- Tim Johannsen

I am a Postdoctoral Fellow at the University of Waterloo and at Perimeter Institute for Theoretical Physics. My research expertise lies in the areas of theoretical astrophysics, gravitation, and black holes. I study the nature of these compact objects, their environment, and their implications for fundamental theories such as general relativity and string theory. I design observational tests of general relativity in the strong-field regime and predict new observational signatures of black holes across the electromagnetic spectrum. My work involves a variety of both analytical and computational methods.

I am part of the science team of the Event Horizon Telescope, a planned global array of radio telescopes with the goal to take the first ever image of a black hole and to test Einstein"s theory of general relativity. I am also part of the strong gravity science team of the Large Observatory For x-ray Timing (LOFT). LOFT will perform phase-resolved spectroscopy of galactic black holes on event horizon timescales and probe the equation of state of neutron stars. I also work with the results of current X-ray observatories such as the Rossi X-ray Timing Explorer, Chandra, and XMM-Newton, and I simulate measurements of future X-ray missions such as Astro-H and ATHENA+.

- College of Science Award for Scholarship, University of Arizona
- APS Four Corners Section Meeting Best Graduate Student Presentation Award, Tucson, AZ
- Theoretical Astrophysics Program Best Graduate Student Paper Prize, University of Arizona
- Physics Publication Award, Physics Department, University of Arizona
- Professor C. Y. Fan "FanFare" Award, Physics Department, University of Arizona
- APS Topical Group in Gravitation Best Student Presentation Award, 27th Pacific Coast Gravity Meeting, California Institute of Technology, Pasadena, CA
- Galileo Circle Award, College of Science, University of Arizona

- Johannsen, T., "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum," CQG, 33 (2016) 124001, arXiv: 1602.07694
- Johannsen, T., "Sgr A* and General Relativity," CQG, 33 (2016) 113001 , arXiv: 1512.03818
- Fish, V.L., â¦, Johannsen, T., et al., "Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales," ApJ, 820 (2016) 90, arXiv: 1602.05527
- Broderick, A.E., Fish, V.L., Johnson, M.D., Rosenfeld, K., Wang, C., Doeleman, S.S., Akiyama, K., Johannsen, T., & Roy, A.L., "Modeling Seven Years of Event Horizon Telescope Observations with Radiatively Inefficient Accretion Flow Models," ApJ, 820 (2016) 137, arXiv: 1602.07701
- García, F., Ranea-Sandoval, I.F., & Johannsen, T., "Magnetised Accretion Discs in Kerr Spacetimes II: Hot Spots," A&A, 587 (2016) A141, arXiv: 1511.09383
- Johannsen, T., Broderick, A.E., Plewa, P.M., Chatzopoulos, S., Doeleman, S.S., Eisenhauer, F., Fish, V.L., Genzel, R., Gerhard, O., & Johnson, M.D., "Testing General Relativity with the Shadow Size of Sgr A*," Phys. Rev. Lett., 116 (2016) 031101, arXiv: 1512.02640
- Johannsen, T. "X-Ray Probes of Black Hole Accretion Disks for Testing the No-Hair Theorem," PRD, 90 (2014) 064002
- Broderick, A. E., Johannsen, T., Loeb, A., & Psaltis, D. "Testing the No-hair Theorem with Event Horizon Telescope Observations of Sagittarius A*" ApJ, 784 (2014) 7, arXiv: 1311.5564
- Johannsen, T. "Photon Rings around Kerr and Kerr-like Black Holes," ApJ, 777 (2013) 170
- Johannsen, T., & Psaltis, D., "Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum. IV. Relativistically Broadened Iron Lines," ApJ, 773 (2013) 57, arXiv: 1202.6069
- Johannsen, T. "Regular Black Hole Metric with Three Constants of Motion," PRD, 88 (2013) 044002
- Johannsen, T., "Inner Accretion Disk Edges in a Kerr-Like Spacetimes," PRD, 87 (2013) 124010, arXiv: 1304.8106
- Johannsen, T., "Systematic Study of Event Horizons and Pathologies in Parametrically Deformed Kerr Spacetimes," PRD, 87 (2013) 124017, arXiv: 1304.7786
- Johannsen, T., "A Metric for Testing the Nature of Black Holes," J. Phys. Conf. Ser., 410 (2013) 012136, arXiv: 1210.0483
- Johannsen, T., Psaltis, D., Gillessen, S., Marrone, D. P., Ozel, F., Doeleman, S. S., & Fish, V. L., "Masses of Supermassive Black Holes with Very-Long Baseline Interferometry," ApJ, 758 (2012) 30, arXiv: 1201.0758
- Johannsen, T., "Testing General Relativity with Observations of Black Holes in the Electromagnetic Spectrum," PASP, 124 (2012) 1133, arXiv: 1209.3024
- Bauböck, M., Psaltis, D., Ozel, F., & Johannsen, T., "A Ray-Tracing Algorithm for Spinning Compact Object Spacetimes with Arbitrary Quadrupole Moments. II. Neutron Stars," ApJ, 753 (2012) 175, arXiv: 1110.4389
- Johannsen, T., "Testing the No-Hair Theorem with Sgr A*," Adv. Astron., 2012 (2012) 1, arXiv: 1105.5645
- Psaltis, D., & Johannsen, T., "A Ray-Tracing Algorithm for Spinning Compact Object Spacetimes with Arbitrary Quadrupole Moments. I. Quasi-Kerr Black Holes," ApJ, 745 (2012) 1, arXiv: 1011.4078
- Psaltis, D., & Johannsen, T., "Sgr A*: The Optimal Testbed of Strong-Field Gravity," J. Phys. Conf. Ser. 283 (2011) 012030, arXiv: 1012.1602
- Johannsen, T., & Psaltis, D., "Metric for Rapidly Spinning Black Holes Suitable for Astrophysical Tests of the No-Hair Theorem," PRD, 83 (2011) 124015, arXiv: 1105.3191
- Johannsen, T., & Psaltis, D., "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum," Adv. Space Res., 47 (2011) 528, arXiv: 1008.3902
- Johannsen, T., & Psaltis, D., "Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum. III. Quasi-Periodic Variability," ApJ, 726 (2011) 11, arXiv: 1010.1000
- Psaltis, D., & Johannsen, T., "Testing the No-Hair Theorem with Observations of Astrophysical Black Holes in the Electromagnetic Spectrum", in The Energetic Cosmos: From Suzaku to Astro-H, ed. K. Makishima (Tokyo: JAXA Special Publication), 240 (2010), arXiv: 0912.0022
- Johannsen, T., & Psaltis, D., "Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum. II. Black Hole Images," ApJ, 718 (2010) 446, arXiv: 1005.1931
- Johannsen, T., & Psaltis, D., "Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum. I. Properties of a Quasi-Kerr Spacetime," ApJ, 716 (2010) 187, arXiv: 1003.3415
- Johannsen, T., "Constraints on the Size of Extra Dimensions from the Orbital Evolution of the Black-Hole X-Ray Binary XTE J1118+480," A&A, 507 (2009) 617, arXiv: 0812.0809
- Johannsen, T., Psaltis, D., & McClintock, J. E., "Constraints on the Size of Extra Dimensions from the Orbital Evolution of the Black-Hole X-Ray Binaries," ApJ, 691 (2009) 997, arXiv: 0803.1835
- Tim Johannsen, Carlos Wang, Avery E. Broderick, Sheperd S. Doeleman, Vincent L. Fish, Abraham Loeb, & Dimitrios Psaltis, "Testing General Relativity with Accretion-Flow Imaging of Sgr A*," Phys. Rev. Lett. in press, arXiv: 1608.03593
- V. Fish, ..., T. Johannsen, et al. "High-Angular-Resolution and High-Sensitivity Science Enabled by Beamformed ALMA," arXiv: 1309.3519
- Feroci, M., ..., Johannsen, T., et al. "The Large Observatory for x-ray timing," SPIE, 9144 (2014) 2

- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", Canadian Institute for Theoretical Astrophysics, Toronto, ON (invited)
- "Testing Strong-Field General Relativity with Observations of Black Holes in the Electromagnetic Spectrum", AAS Winter Meeting 2013, Long Beach, CA
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", Astrophysical Seminar, University of Waterloo, ON (invited)
- "Testing the No-Hair Theorem with LOFT", Second LOFT Science Meeting, Toulouse, France
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", High-Energy Seminar, Washington University, St. Louis, MO (invited)
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", Ohio State University, Columbus, OH (invited)
- "Testing the No-Hair Theorem with VLBI Imaging of Sgr A*", Bringing Black Holes into Focus: The Event Horizon Telescope, Tucson, AZ (invited)
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", APS Four Corners Section Meeting 2011, Tucson, AZ
- "Testing the No-Hair Theorem with Quasi-Periodic Variability and Fluorescent Iron Lines", AAS High-Energy Astrophysics Division Meeting 2011, Newport, RI
- "Testing the No-Hair Theorem with Quasi-Periodic Variability", Black Hole Astrophysics, Winchester, UK
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", Harvard-Smithsonian Center for Astrophysics, Cambridge, MA
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", 27th Pacific Coast Gravity Meeting, California Institute of Technology, Pasadena, CA
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", NOAO Seminar, National Optical Astronomy Observatory, Tucson, AZ
- "Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum", MPE Seminar, Max-Planck-Institut für Extraterrestische Physik, Garching (invited)
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", COSPAR 2010, Bremen, Germany
- "Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum", AAS High-Energy Astrophysics Division Meeting 2010, Waikoloa Village, HI
- "Constraints on the Size of Extra Dimension from Black Holes", Tests of Gravity and Gravitational Physics, Cleveland, OH
- PIRSA:14110191, Testing General Relativity with the EHT, 2014-11-12,
- PIRSA:12100049, Testing Strong-Field General Relativity with Black Holes, 2012-10-04, Strong Gravity

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