DOI QR코드

DOI QR Code

Probing Gamma-ray Emission of Geminga and Vela with Non-stationary Models

Chai, Yating;Cheng, Kwong-Sang;Takata, Jumpei

  • 투고 : 2016.05.10
  • 심사 : 2016.06.02
  • 발행 : 2016.06.15

초록

It is generally believed that the high energy emissions from isolated pulsars are emitted from relativistic electrons/positrons accelerated in outer magnetospheric accelerators (outergaps) via a curvature radiation mechanism, which has a simple exponential cut-off spectrum. However, many gamma-ray pulsars detected by the Fermi LAT (Large Area Telescope) cannot be fitted by simple exponential cut-off spectrum, and instead a sub-exponential is more appropriate. It is proposed that the realistic outergaps are non-stationary, and that the observed spectrum is a superposition of different stationary states that are controlled by the currents injected from the inner and outer boundaries. The Vela and Geminga pulsars have the largest fluxes among all targets observed, which allows us to carry out very detailed phase-resolved spectral analysis. We have divided the Vela and Geminga pulsars into 19 (the off pulse of Vela was not included) and 33 phase bins, respectively. We find that most phase resolved spectra still cannot be fitted by a simple exponential spectrum: in fact, a sub-exponential spectrum is necessary. We conclude that non-stationary states exist even down to the very fine phase bins.

키워드

Vela;Geminga;superposition model

참고문헌

  1. Abdo AA, Ackermann M, Ajello M, Allafort A, Atwood WB, et al., The Vela pulsar: results from the first year of Fermi LAT observations, Astrophys. J. 713, 154-165 (2010a). http://dx.doi.org/10.1088/0004-637X/713/1/154 https://doi.org/10.1088/0004-637X/713/1/154
  2. Abdo AA, Ackermann M, Ajello M, Baldini L, Ballet J, et al., Fermi-LAT observations of the Geminga pulsar, Astrophys. J. 720, 272-283 (2010b). http://dx.doi.org/10.1088/0004-637X/720/1/272 https://doi.org/10.1088/0004-637X/720/1/272
  3. Cheng KS, Zhang JL, General radiation formulae for a relativistic charged particle moving in curved magnetic field lines: the synchrocurvature radiation mechanism, Astrophys. J. 463, 271-283 (1996). https://doi.org/10.1086/177239
  4. Cheng KS, Ho C, Ruderman M, Energetic radiation from rapidly spinning pulsars. I. Outer magnetosphere gaps. II. VELA and Crab, Astrophys. J. 300, 500–539 (1986). https://doi.org/10.1086/163829
  5. Cheng KS, Ruderman M, Zhang LA, Three-dimensional outer magnetospheric gap model for Gamma-ray pulsars: geometry, pair production, emission morphologies, and phase-resolved spectra, Astrophys. J. 537, 964–976 (2000). http://dx.doi.org/10.1086/309051 https://doi.org/10.1086/309051
  6. Daugherty JK, Harding AK, Polar CAP models of gamma-ray pulsars: emission from single poles of nearly aligned rotators, Astrophys. J. 429, 325–330 (1994). https://doi.org/10.1086/174321
  7. Daughter JK, Harding AK, Gamma ray pulsars: extended polar CAP cascades from nearly aligned rotators, Astron. Astrophys. Suppl. Ser. 120, 107-110 (1996). https://doi.org/10.1051/aas:1996270
  8. De Oña Wilhelmi E, Cherenkov telescopes results on pulsar wind nebulae and pulsars, High-energy emission from pulsars and their systems: Proceedings of the first session of the Sant Cugat Forum on Astrophysics, eds. Rea N, Torres DF (Springer, Heidelberg, 2011), 435-452.
  9. Hirotani K, High energy emission from rotation-powered pulsars: outer-gap vs. slot-gap models, eprint arXiv: 0809.1283 (2008). http://adsabs.harvard.edu/abs/2008arXiv0809.1283H
  10. Hirotani K, Three-dimensional non-vacuum pulsar outer-gap model: localized acceleration electric field in the higher altitudes, Astrophys. J. Lett. 798, L40 (2015). http://dx.doi.org/10.1088/2041-8205/798/2/L40 https://doi.org/10.1088/2041-8205/798/2/L40
  11. Takata J, Shibata S, Hirotani K, A pulsar outer gap model with trans-field structure, Mon. Not. Roy. Astron. Soc. 354, 1120-1132 (2004). http://dx.doi.org/10.1111/j.1365-2966.2004.08270.x https://doi.org/10.1111/j.1365-2966.2004.08270.x
  12. Hirotani K, Shibata S, One-dimensional electric field structure of an outer gap accelerator - I. γ-ray production resulting from curvature radiation, Mon. Not. Roy. Astron. Soc. 308, 54-66 (1999). http://dx.doi.org/10.1046/j.1365-8711.1999.02696.x https://doi.org/10.1046/j.1365-8711.1999.02696.x
  13. Kramer M, Johnston S, Van Straten W, High-resolution single-pulse studies of the Vela pulsar, Mon. Not. Roy. Astron. Soc. 334, 523-532 (2002). http://dx.doi.org/10.1046/j.1365-8711.2002.05478.x https://doi.org/10.1046/j.1365-8711.2002.05478.x
  14. Takata J, Chang HK, Non-thermal emissions from outer magnetospheric accelerators of middle-aged pulsars, Mon. Not. Roy. Astron. Soc. 392, 400-412 (2009). http://dx.doi.org/10.1111/j.1365-2966.2008.14067.x https://doi.org/10.1111/j.1365-2966.2008.14067.x
  15. Takata J, Ng CW, Cheng KS, Probing gamma-ray emissions of Fermi -LAT pulsars with a non-stationary outer gap model, Mon. Not. Roy. Astron. Soc. 455, 4249-4266 (2016). http://dx.doi.org/10.1093/mnras/stv2612 https://doi.org/10.1093/mnras/stv2612
  16. Tang APS, Takata T, Jia JJ, Cheng KS, A re-visit of the Phase-resolved X-ray and Gamma-ray Spectra of the Crab Pulsar, Astrophys. J. 676, 562-572 (2008). http://dx.doi.org/10.1086/527029 https://doi.org/10.1086/527029
  17. Viganò D, Torres DF, Modelling of the γ-ray pulsed spectra of Geminga, Crab, and Vela with synchro-curvature radiation Mon. Not. Roy. Astron. Soc. 449, 3755-3765 (2015). http://dx.doi.org/10.1093/mnras/stv579 https://doi.org/10.1093/mnras/stv579
  18. Wang Y, Takata J, Cheng KS, Three-dimensional two-layer outer gap model: Fermi energy-dependent light curves of the Vela pulsar, Mon. Not. Roy. Astron. Soc. 414, 2664-2673 (2011). http://dx.doi.org/10.1111/j.1365-2966.2011.18577.x https://doi.org/10.1111/j.1365-2966.2011.18577.x