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).