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(A) Side view of a BH magnetosphere. Photons are emitted from infrared to soft gamma-ray energies by the hot gas falling toward the BH in the equatorial, accretion (cyan) region. The soft gamma-rays collide each other to create electron-positron pairs in the polar funnel (white region). The created pairs are separated and accelerated into the opposite directions by the electric field $E_|| that is exerted along the magnetic field lines (in yellow-purple colored region). The outwardly accelerated electrons have ultra-relativistic energies to emit copious hard gamma-rays. (B) Spectra of the hard gamma-rays. The four thin curves (on the left-hand side) corresponds to the spectra from the equatorial inflow at four discrete mass accretion rates onto the BH: the red dotted, blue dashed, black solid, and green dash-dotted curves correspond to the accretion rate of 3.2e-3, 1.8e-3, 1e-3 and 5.6e-4, in the unit of the so-called "Eddington accretion rate." The distance is assumed to be 3260 light years. The thick four lines (on the right-hand side) denote the spectra of the hard gamma-rays emitted from the lepton accelerator (yellow-purple region in panel A) at each corresponding accretion rate. In the upper right corner, the gamma-ray detection limits with the current and near-future gamma-ray telescopes are denoted by the thin solid, dashed, and dotted curves with the labels LAT, CTA (South), and CTA (North).
Lightning black holes in dense molecular clouds
Luminosity evolution of pulsar outer magnetospheric accelerators as a function of neutron star spin down luminosity. Two extreme chemical compositions of the neutron star envelopes are considered. The red curves correspond to a heavy element envelope, while the blue and black curves correspond to a light element envelope. The solid, dash-dotted, and dash-dot-dot-dot curves represent numerical solutions, while dashed and dotted ones represent analytical solutions. The circles, squares, and triangles designate the pulsars detected by the Fermi satellite: the green filled circles show the radio loud gamma-ray pulsars, while the blue filled squares show the radio quiet ones. From Hirotani 2013, ApJ, 766, 98.
Luminosity evolution of pulsar outer magnetospheric accelerators as a function of neutron star spin down luminosity.
Schematic picture (side view) of a pulsar magnetosphere. The filled circle on the left denotes the neutron star, which rotates along the vertical axis (dash-dotted line) with angular frequency "Omega". The magnetic dipole axis (short dashed line) is inclined to the rotation axis with angle "alpha". The neutron star has the magnetic dipole moment with strength. As the neutron star spins down, its rotational energy is dissipated in the form of the Poynting flux (i.e., outward flow of electro-magnetic energy), rest-mass and kinetic energies of the electrons and positrons, and the gamma-ray energies. The solid curves designate the magnetic field lines. In the convex side of the lower bounding magnetic field line, a high vacuum is maintained, because charged particles efficiently escape across the light cylinder (vertical long dashed line on the right). As a result, an electric field arises along the local magnetic field lines in the red, shaded region. In this ‘outer-magnetospheric particle accelerator’, electrons (e-) and positrons (e+) are created by photon-photon collisions and accelerated by the magnetic-field-aligned electric field in the opposite directions along the magnetic field lines. Gamma-rays are emitted mostly outwards by the out-going particles (e+). The gamma-ray luminosity is essentially determined by the trans-magnetic-field thickness of the accelerator, which is, in turn, controlled by the efficiency of the photon-photon collisions that take place within the accelerator.
Schematic picture (side view) of a pulsar magnetosphere.
Spectral energy distribution of pulsed emission from a middle-aged pulsar B1951+32. The abscissa denotes photon energies in Million electron volts (MeV), while the ordinate denotes photon energy fluxes. The green solid line designates the theoretical pred
Spectral energy distribution of pulsed emission from a middle-aged pulsar B1951+32
Outer-gap death line on the period vs. derivative period plane. Left: entire parameter space. Right: close-up of the millisecond parameter range.
Death Line of Gamma-ray Pulsars with Outer Gaps
Phase-averaged spectrum of the pulsed emission from the Crab pulsar predicted by the self-consistent outer gap model.
Pulsed Gamma-Ray Emission from the Crab Pulsar
Evolution of the photon index Γ (top panel) and the cutoff energy Ec (bottom panel) with the rotational phase is depicted by the (red) thick solid curve.
Spectral Hardening in the Trailing Peak of Gamma-ray Pulsar Light Curve
Figure 5 of "Pulsar Outer-gap Electrodynamics: Hardening of Spectral Shape in the Trailing Peak in Gamma-ray Light Curve", Kouichi Hirotani, Astrophys. J. 733, Letters 49-53 (2011).
Spectral Hardening in the Trailing Peak of Gamma-ray Pulsar Light Curve
Figure 15 of "Observations of the Crab pulsar above 25 GeV with the MAGIC I telescope", Aleksic et al. ApJ 742, 43 (2011)
Pulsed Gamma-Ray Emission from the Crab Pulsar
Figure 2 of "Death Line of Gamma-ray Pulsars with Outer Gaps", Ren-Bo Wang and Kouichi Hirotani, ApJ 736, 127 (2011).
Death Line of Gamma-ray Pulsars with Outer Gaps
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期刊論文(中研院就職期間發表)

  1. Hirotani K; Shang H; Krasnopolsky R; Nishikawa K, "Formation of Limb-brightened Radio Jets by Angle-dependent Energy Extraction from Rapidly Rotating Black Holes" , ApJ: 965(1), id.50 (11 pp), Apr, 2024 [SCI] ( ADS | Fulltext )
  2. Hirotani K; Shang H; Krasnopolsky R; Nishikawa K-I, "Two-dimensional Particle-in-Cell simulations of axisymmetric black hole magnetospheres: angular dependence of the Blandford-Znajek flux" , ApJ: 943(2), id.164 (19 pp.), Feb, 2023 [SCI] ( ADS | Fulltext )
  3. Meli A; Nishikawa K; Köhn C; Duţan I; Mizuno Y; Kobzar O; Macdonald N; Gómez JL; Hirotani K, "3D PIC Simulations for relativistic jets with a toroidal magnetic field" , MNRAS: 519(4), 5410-5426, March, 2023 [SCI] ( ADS | Fulltext )
  4. Hirotani K; Krasnopolsky R; Shang H; Nishikawa K-I; Watson M, "Two-dimensional Particle-in-Cell Simulations of Axisymmetric Black Hole Magnetospheres" , ApJ: 908(1), id.88 (19pp), Feb, 2021 [SCI] ( ADS | Fulltext )
  5. MAGIC Collaboration; Acciari VA; Ansoldi S; Antonelli LA; ...; Hirotani K; et al., "Detection of the Geminga pulsar with MAGIC hints at a power-law tail emission beyond 15 GeV" , A&A: 643, id.L14 (6pp), Nov, 2020 [SCI] ( ADS | Fulltext )
  6. Nishikawa K; Mizuno Y; Gómez JL;...; Hirotani K, "Rapid Particle Acceleration due to Recollimation Shocks and Turbulent Magnetic Fields in Injected Jets with Helical Magnetic Fields" , MNRAS: 493(2), 2652-2658, Apr, 2020 [SCI] ( ADS | Fulltext )
  7. Hirotani K, "Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes" , Galaxies: 6(4), 122 (37 pp.), Dec, 2018 [SCI] ( ADS | Fulltext )
  8. Hirotani K; Pu H-Y; Outmani S; ...; Matsushita S; Kong AKH, "High-energy and Very High Energy Emission from Stellar-mass Black Holes Moving in Gaseous Clouds" , ApJ: 867(2), id. 120 (13 pp.), Nov, 2018 [SCI] ( ADS | Fulltext )
  9. Hirotani K; Pu HY; Matsushita S, "Lightning black holes as unidentified TeV sources" , JApA: 39(4), id. 50 (8 pp.), Aug, 2018 [SCI] ( ADS | Fulltext )
  10. Hirotani K; Pu H-Y; Lin LC-C; Kong AKH; Matsushita S; Asada K; et al, "Lepton Acceleration in the Vicinity of the Event Horizon: Very High Energy Emissions from Supermassive Black Holes" , ApJ: 845(1), 77, Aug, 2017 [SCI] ( ADS | Fulltext )
  11. Lin L C-C; Pu H-Y; Hirotani K; Kong AKH; Matsushita S; Chang H-K; Inoue M; Tam P-HT, "Searching for High-energy, Horizon-scale Emissions from Galactic Black Hole Transients during Quiescence" , ApJ: 845(1), 40, Aug 10, 2017 [SCI] ( ADS | Fulltext )
  12. Pu H-Y; Hirotani K; Mizuno Y; Chang H-K, "Two Types of Ergospheric Jets from Accreting Black Holes: The Dichotomy of Fanaroff-Riley Galaxies" , ApJ, 2017, Submitted [SCI] ( ADS | Fulltext )
  13. Song Y; Pu HY; Hirotani K; Matsushita S; et al., "Enhanced gamma radiation towards the rotation axis from the immediate vicinity of extremely rotating black holes" , MNRAS: 471(1), L135-L139, Oct, 2017 [SCI] ( ADS | Fulltext )
  14. Ansoldi S; Antonelli LA; Antoranz P; ...; Hirotani K; et al., "Teraelectronvolt pulsed emission from the Crab Pulsar detected by MAGIC" , A&A: 585, A133, Jan, 2016 [SCI] ( ADS | Fulltext )
  15. Hirotani K; Pu H-Y, "Energetic Gamma Radiation from Rapidly Rotating Black Hole" , ApJ: 818(1), 50, Feb, 2016 [SCI] ( ADS | Fulltext )
  16. Hirotani K; Pu H-Y; Lin LC-C; Chang H-K;Inoue M; Kong AKH; Matsushita S; Tam P-HT, "Lepton acceleration in the vicinity of the event horizon: High-energy and Very-high-energy emissions from rotating black holes with various masses" , ApJ: 833(2), 142, Dec, 2016 [SCI] ( ADS | Fulltext )
  17. Hirotani K, "Three-dimensional Non-vacuum Pulsar Outer-gap Model: Localized Acceleration Electric Field in the Higher Altitudes" , ApJ: 798(2), L40, Jan, 2015 [SCI] ( ADS | Fulltext )
  18. Pu H-Y; Nakamura M; Hirotani K; Mizuno Y; Wu K; Asada K, "Steady General Relativistic Magnetohydrodynamic Inflow/Outflow Solution Along Large-Scale Magnetic Fields That Thread A Rotating Black Hole" , ApJ: 801(1), 56, March, 2015 [SCI] ( ADS | Fulltext )
  19. Viganò D; Torres DF; Hirotani K; Pessah ME, "Compact formulae, dynamics and radiation of charged particles under synchro-curvature losses" , MNRAS: 447(2), 1164-1172, Feb 21, 2015 [SCI] ( ADS | Fulltext )
  20. Viganò D; Torres DF; Hirotani K; Pessah ME, "An assessment of the pulsar outer gap model - I. Assumptions, uncertainties, and implications on the gap size and the accelerating field" , MNRAS: 447(3), 2631-2648, March 1, 2015 [SCI] ( ADS | Fulltext )
  21. Viganò D; Torres DF; Hirotani K; Pessah ME, "An assessment of the pulsar outer gap model - II. Implications for the predicted γ-ray spectra" , MNRAS: 447(3), 2649-2657, March 1, 2015 [SCI] ( ADS | Fulltext )
  22. Aleksić J; Ansoldi S; Antonelli LA; ...; Hirotani K; et al., "Detection of bridge emission above 50 GeV from the Crab pulsar with the MAGIC telescopes" , A&A: 565, L12, May, 2014 [SCI] ( ADS | Fulltext )
  23. Hirotani K, "Does a strong particle accelerator arise very close to the light cylinder in a pulsar magnetosphere?" , MNRAS: 442(1), L43-L45, July, 2014 [SCI] ( ADS | Fulltext )
  24. Hirotani K, "Luminosity Evolution of Gamma-Ray Pulsars" , ApJ: 766(2), 98, April 1, 2013 [SCI] ( ADS | Fulltext )
  25. Aleksić J; ...; Hirotani K; et al., "Phase-resolved energy spectra of the Crab pulsar in the range of 50-400 GeV measured with the MAGIC telescopes" , A&A: 540, A69, April, 2012 [SCI] ( ADS | Fulltext )
  26. Pu H-Y; Hirotani K; Chang H-K, "Launching and Quenching of Black Hole Relativistic Jets at Low Accretion Rate" , ApJ: 758(2), 113, Oct 20, 2012 [SCI] ( ADS | Fulltext )
  27. Aleksić J;...; Hirotani K, "Observations of the Crab Pulsar between 25 and 100 GeV with the MAGIC I Telescope" , ApJ: 742(1), 43, Nov 20, 2011 [SCI] ( ADS | Fulltext )
  28. Hirotani K, "Pulsar Outer-gap Electrodynamics: Hardening of Spectral Shape in the Trailing Peak in the Gamma-Ray Light Curve" , ApJ: 733(2), L49, June, 2011 [SCI] ( ADS | Fulltext )
  29. Wang RB; Hirotani K, "Death Line of Gamma-Ray Pulsars with Outer Gaps" , ApJ: 736(2), 127, Aug 1, 2011 [SCI] ( ADS | Fulltext )
  30. Hirotani K, "Outer-gap versus Slot-gap Models for Pulsar High Energy Emissions: The Case of the Crab Pulsar" , ApJ: 688(1), L25-L28, Nov 20, 2008 [SCI] ( ADS | Fulltext )
  31. Albert J; Aliu E; Anderhub H; ...Hirotani K; ...; et al., "Constraints on the steady and pulsed very high energy gamma-ray emission from observations of PSR B1951+32/CTB 80 with the magic telescope" , ApJ: 669(2), 1143-1149, Nov 10, 2007 [SCI] ( ADS | Fulltext )
  32. Hirotani K, "High-energy Emission from Pulsar Outer Magnetospheres" , ApJ: 662(2), 1173-1176, Jun 20, 2007 [SCI] ( ADS | Fulltext )
  33. Hirotani K, "High-energy Emission from Pulsar Magnetospheres" , MPLA: 21(17), 1319-1337, Jun 7, 2006 [SCI] ( ADS | Fulltext )
  34. Hirotani K, "Particle Accelerator in Pulsar Magnetospheres: Super Goldreich-Julian Current with Ion Emission from the Neutron Star Surface" , ApJ: 652(2), 1475-1493, Dec 1, 2006 [SCI] ( ADS | Fulltext )
  35. Takata J; Shibata S; Hirotani K; Chang H-K, "A two-dimensional electrodynamical outer gap model for γ-ray pulsars: γ-ray spectrum" , MNRAS: 366(4), 1310-1328, Mar, 2006 [SCI] ( ADS | Fulltext )
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