Figure 2. a) 2-s time series of count rates of coincidences registered by ASNT spectrometer, shown in percent of the count rates measured at fair weather before TGE; b) energy spectra of both TGE species recovered from energy release histograms; c) 1-min time series of count rates of coincidences registered by ASNT spectrometer; d) energy spectra of both TGE species recovered from energy release histograms.
In Fig. 2c we show the same ASNT spectrometer coincidences, as in Fig. 2a but for the 1-min time series of count rates (in 2009 the ASNT electronics sampling time was 1 minute.). As we can see in Fig. 2d, the intensities of electron and gamma ray spectra are almost equal at high energies, and the electron to gamma ray ratio reaches 66% at the minute 22:49-22:50. It can happen only if a strong accelerating electric field is very low above the ground (we estimate the height to be 25-50 m) and the electron avalanche covers a sizable area on the ground. Thus, the fraction of electrons in the TGEs selected for energy spectra recovering, are much larger than the fraction of Compton scattered electrons.
Characteristics of selected TGE events with large electron content
In Table 2 we show several parameters of TGEs for with we recover the electron energy spectrum and estimate the height of the termination of the accelerated electric field. A full set of TGE parameters is available from the Mendeley data set (Chilingarian et al., 2022b)
In the first column of the table, we put the date of the TGE that occurred during 3 last years (2019-2021). In the second column of the table, we show the power-law index of the electron differential energy spectra derived from the energy release histograms measured by the
ASNT spectrometer; in the third column - the same for the gamma ray spectra. In the fourth column - integral electron spectra from 7 MeV, in the fived - the same for gamma ray spectra. In the sixth and seventh columns, maximal energies of electrons and gamma rays; in the eighth column, we post the TGE significance - the percent of flux enhancement relative to fair weather value measured just before TGE, count rate of SEVAN detector upper scintillator (combination “100”) was used (energy threshold 7 MeV). In the ninth column, we show the approximate estimate of the strong accelerating electric field termination height obtained by the equation: H(m) ≈ (1.2Eγ(max)- Ee(max))/0.2, where Eγ(max) and Ee(max)) are estimates of maximum energies of gamma rays and electrons as measured on the earth’s surface and 0.2 MeV in the denominator is an approximate value of electron energy losses in the 1 m of air (Chilingarian et al., 2021d). We assume that the maximum energy of electrons on the exit of the strong electric field can be approximated by the measured on the earth’s surface maximum energy of gamma rays multiplied by a coefficient of 1.2 (this approximate equation is valid for the electric field heights up to 200 m). Due to the fast attenuation of the electron flux, electron spectra cannot be measured reliably by the ASNT spectrometer if the accelerating electric field terminates above 200 m). In the tenth column, we post the TGE duration; in the eleventh column, we show the share of electron flux related to gamma ray flux (above 7 MeV).