The short particle bursts during thunderstorms: EAS or lightning seeds? G. Hovsepyan, A. Chilingarian, A. Alikhanian National Laboratory, Armenia

16 detectors of Maket-ANI installation with new electronic of the readout based on FPGA are used. The photomultiplier tubes (PM-49) of the detectors are placed in the light-tight iron boxes. Logarithmic Analog to Digital Converters (ADC) are assembled just above the photomultiplier tube. Every minute spectra of ADC codes of each detectors are stored in special files. With trigger the codes of all detectors are stored in other file. Trigger condition is: coincidence of 8 plus arbitrary one of the other detectors within 1 us timing gate. The trigger detectors on figure with red cycles are indicate. The rectangle is show the building position. By CORSIKA simulation trigger condition is select the showers, initiated by Primary Cosmic Rays (PCR) with average energy ~190 TeV.

In figure daily spectra is presented. On the spectra threshold region and two power low regions are seen. “Knee” position is near 80 part./m 2. Differences between two slopes is 0.4. Outline here – the installation is OK. As first step it is important to check the trigger condition for air showers selection. For it measured showers particles density spectra is build. Here shower particles density - it is average density by all detectors data.

September at thunderstorm time from 22:44 up to 22:51 all detectors of the installation a burst of count rate is registered. First 4 minutes a count rate is increase from 420 Hz up to 800Hz and next 4 minutes reduced to normal rate. On a figure the burst of rate (by minutes) is presented. The peak time is 22:47 (or 1368 daily minute) Total event duration was 8 minutes.

The distribution of the ADC`s code for event peak time (22:47) and quite time (22:40) and event extraction in figure are presente d. – Extracted distribution have an exponential form and limited by {K 0 + (5-6)} codes, where K 0 is mode of distribution in calm time. – Upper bound of extracted energy deposit distribution in detector is ~20 Mev. – First significance bit of ADC (threshold) correspond ~5 MeV energy deposit in plastic

Wile count rate of each detectors change on ~200% in peak time, trigger rate change on ~500% - from 25.1 showers/min to 124 showers/min. If to demand so as all detectors fired - in this case trigger rate change on ~800% (from 7.73 showers/min to 64 showers/min). Trigger rate change can be by two cause: - lightning seed particles bursts, which have 1us durations - air showers enrichment  EAS are often invoked as mechanism, to explain a wide range of atmospheric phenomena, including lightning initiation, Terrestrial Gamma-ray flashes(TGF). The reason is that EAS can impulsively inject N e particles into the high field region where runaway electron avalanches are occurring. The resulting avalanche multiplication can in turn produce even larger number of runaway electrons.

The upper limit of avalanche multiplication factor estimated <10 5 and triggered showers particle densities enrichment are expected. I f trigger rate increase by cause of low energy showers enrichment, then for all shower size densities of showers particles are increase on multiplication factor time. Cutting by energy deposit in detectors (or ADC code) finally we are select high energy initiated showers which count rate are same as in calm time. For this events a density enrichment must be seen. In a figure for high threshold count rate is same but a density enrichment isn't seen. The trigger rate changes isn't based on air showers enrichment processes. Exposition time 8 min.

From previous slide You see all trigger rate increase to 500% but for fired 16 detectors it is 800%. The events power depend on wide and narrow showers selection. For narrow showers (fired =13 detectors) all additional triggers are seen. The same behavior indicate non shower dependence for trigger rate increasing.

For 8 minutes exposition time measured densities spectra for quite time and event time are build. Difference between two spectrum the lightning seed particles density spectra is shown. The lightning seed particles spectra by exponential form was approximated. The value of the parameters in figure are depicted. The exponential form is indicate on non CR nature of the lightning seed particles.

Resume  September a burst of count rate of the New- MAKET detectors is registered The count rate during 4 min. increase to 200% and then reduce to quite time value. Total time is 8 minutes.  The trigger rate is change on ~500% If to demand so as all detectors fired - in this case trigger rate change on ~800%. The fact indicate on a process wide.  Hypotheses about low energy showers enrichment and then trigger rate increase conflicted with wide and narrow showers selection.  Events time additional triggers initiated by lightning seed particles.  The lightning seed particles density in detectors have exponential form, wile cosmic ray spectrum described with power low distribution.