Gamma-ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders
Creators: name: Abbasi, R. U.
name: Abu-Zayyad, T.
name: Allen, M.
name: Barcikowski, E.
name: Belz, J. W.
name: Bergman, D. R.
name: Blake, S. A.
name: Byrne, M.
name: Cady, R.
name: Cheon, B. G.
name: Chiba, J.
name: Chikawa, M.
name: Fujii, T.
name: Fukushima, M.
name: Furlich, G.
name: Goto, T.
name: Hanlon, W.
name: Hayashi, Y.
name: Hayashida, N.
name: Hibino, K.
name: Honda, K.
name: Ikeda, D.
name: Inoue, N.
name: Ishii, T.
name: Ito, H.
name: Ivanov, D.
name: Jeong, S.
name: Jui, C. C. H.
name: Kadota, K.
name: Kakimoto, F.
name: Kalashev, O.
name: Kasahara, K.
name: Kawai, H.
name: Kawakami, S.
name: Kawata, K.
name: Kido, E.
name: Kim, H. B.
name: Kim, J. H.
name: Kim, J. H.
name: Kishigami, S. S.
name: Krehbiel, P. R.
name: Kuzmin, V.
name: Kwon, Y. J.
name: Lan, J.
name: LeVon, R.
name: Lundquist, J. P.
name: Machida, K.
name: Martens, K.
name: Matuyama, T.
name: Matthews, J. N.
name: Minamino, M.
name: Mukai, K.
name: Myers, I.
name: Nagataki, S.
name: Nakamura, R.
name: Nakamura, T.
name: Nonaka, T.
name: Ogio, S.
name: Ohnishi, M.
name: Ohoka, H.
name: Oki, K.
name: Okuda, T.
name: Ono, M.
name: Onogi, R.
name: Oshima, A.
name: Ozawa, S.
name: Park, I. H.
name: Pshirkov, M. S.
name: Remington, J.
name: Rison, W.
name: Rodeheffer, D.
name: Rodriguez, D. C.
name: Rubtsov, G.
name: Ryu, D.
name: Sagawa, H.
name: Saito, K.
name: Sakaki, N.
name: Sakurai, N.
name: Seki, T.
name: Sekino, K.
name: Shah, P. D.
name: Shibata, F.
name: Shibata, T.
name: Shimodaira, H.
name: Shin, B. K.
name: Shin, H. S.
name: Smith, J. D.
name: Sokolsky, P.
name: Springer, R. W.
name: Stokes, B. T.
name: Stroman, T. A.
name: Takai, H.
name: Takeda, M.
name: Takeishi, R.
name: Taketa, A.
name: Takita, M.
name: Tameda, Y.
name: Tanaka, H.
name: Tanaka, K.
name: Tanaka, M.
name: Thomas, R. J.
name: Thomas, S. B.
name: Thomson, G. B.
name: Tinyakov, P.
name: Tkachev, I.
name: Tokuno, H.
name: Tomida, T.
name: Troitsky, S.
name: Tsunesada, Y.
name: Uchihori, Y.
name: Udo, S.
name: Urban, F.
name: Vasiloff, G.
name: Wong, T.
name: Yamamoto, M.
name: Yamane, R.
name: Yamaoka, H.
name: Yamazaki, K.
name: Yang, J.
name: Yashiro, K.
name: Yoneda, Y.
name: Yoshida, S.
name: Yoshii, H.
name: Zundel, Z.
Publisher: name: arXiv
Year: 2017
Subjects: subject: Atmospheric and Oceanic Physics (physics.ao-ph)
subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Bursts of gamma ray showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700~square kilometer cosmic ray observatory located in southwestern Utah, U.S.A. In data collected between 2014 and 2016, correlated observations showing the structure and temporal development of three shower-producing flashes were obtained with a 3D lightning mapping array, and electric field change measurements were obtained for an additional seven flashes, in both cases co-located with the TASD. National Lightning Detection Network (NLDN) information was also used throughout. The showers arrived in a sequence of 2--5 short-duration ($\le$10~$μ$s) bursts over time intervals of several hundred microseconds, and originated at an altitude of $\simeq$3--5 kilometers above ground level during the first 1--2 ms of downward negative leader breakdown at the beginning of cloud-to-ground lightning flashes. The shower footprints, associated waveforms and the effect of atmospheric propagation indicate that the showers consist primarily of downward-beamed gamma radiation. This has been supported by GEANT simulation studies, which indicate primary source fluxes of $\simeq$$10^{12}$--$10^{14}$ photons for $16^{\circ}$ half-angle beams. We conclude that the showers are terrestrial gamma-ray flashes (TGFs), similar to those observed by satellites, but that the ground-based observations are more representative of the temporal source activity and are also more sensitive than satellite observations, which detect only the most powerful TGFs.