High-altitude observations of high-energy gamma rays and electrons

from thunder activity

H. Tsuchiya,1 T. Enoto,2 T. Torii,3 K. Nakazawa,2 T. Yuasa,2 S. Torii,2 T. Fukuyama,2 T. Yamaguchi,2

H. Kato,1 M. Okano,1 and K. Makishima1,2

1. RIKEN, 2. Univ. of Tokyo, 3. JAEA

Norikura cosmic-ray observatory

IntroductionEnergetic radiation bursts from thunderstorm activity

Short-duration bursts

Long-duration bursts

duration : milli-seconds or less.

upper atmosphere, natural and rocket-triggered lightning discharges.

Relativistic Runaway Electron Avalanche model.

almost gamma rays; electrons in BATSE TGFs (dwyer+,2008)

duration : a few seconds to a few minutes.

flight altitudes, high mountains, the coastal area of Japan Sea.

not clearly associated with lightning discharges.

gamma rays or charged particles.

1. Why do two types of radiation bursts exist ?2. What is relationship between the two bursts ?

Fishman+ (1994), Smith+ (2005),Moore+ (2001) Dwyer+ (2003)

Gurevich+ (1992), Dwyer (2007)

McCarthy & Parks (1985), Eack+(1996), Chubenko+(2000),Torii+(2002),Tsuchiya+ (2007)

Observations in Japan Coastal area of Japan Sea in Winter seasons

High mountains in Summer seasons

柏崎刈羽原子力発電所

KashiwazakiKariwa

google map

Monjyu

google map

GROWTH high-energy eventsDate DT (sec) Emax (MeV)

070106 36 10071213 66 12081223 <1 7081225 110 10090112 <1 10090125 137 15090211 12 10

Please visit a poster “E205-P006”presented by T. Enoto.

柏崎刈羽原子力発電所

Mt. Fuji (3776 m)

google map

Mt. Norikura(2770 m)

ICRR

Please visit a poster “Z178-P003”, presented by T. Torii, to know theMt. Fuji experiment.

Summer thunderclouds develop at a higher altitude than winter ones.

Norikura cosmic ray observatory (2770 m a.s.l.) 2008 Sep 4 - 2008 Oct 2. 3” spherical NaI, 10 keV - 12 MeV 45 cm X 40 cm X 0.5 cm plastic scintillator, > 500 keV 5 cm X 5 cm X 15 cm cubic BGO (inside) Optical & Electric field measurement

Electric field mill

a photodiode (320 - 1000 nm)

Experimental setup

3” spherical NaI

5 mm thick plastic scintillatorPMT

1sec resolution anti-coincidence shield

One long-duration event, and three short-duration ones were observed.

Coun

t/20

sec

50005200540056005800

Coun

t/20

sec

24002500260027002800

E (k

V/m

)

−100−50

050

100 EFM

Time (UT)15:30 15:35 15:40 15:45 15:50 15:55 16:00V

for O

pt. (

mV)

020406080

100 Opt

2008 Sep 20 NaI > 10 keV

PL >500 keV

E-field(1 sec)

Optical intensity (1 sec) no lightning were observed

Tsuchiya, Enoto, Torii, et al.,submitted to PRL

90 s

ResultsLong bursts associated with thunderclouds

count increases observed in15:45:10-15:46:40 UTNaI 1208±150 (8.1σ) PL 658±104 (6.5σ)

The observed bursts are associated with thunderclouds

Tsuchiya, Enoto, Torii, et al.,submitted to PRL

ResultsLong bursts associated with thunderclouds

Photon energy (MeV)−110 1 10

Cou

nts

(/MeV

)

10

210

310

410

50 m (21.5/16)

90 m (16.8/16)

300 m (22.2/16)

1000 m (28.1/16)

Photon spectrum with model predictions

d c2/dof

Source distance (m)210 310

2 !

15

20

25

30

35

40

99% C.L.

90% C.L.68% C.L.

c2 vs assumed source distance

Bremsstrahlung gamma rays arriving from nearby sources at 60 - 130 m (@90%C.L.)

β = 1.15± 0.09α = (2.4± 0.4)× 108F (E) = αE−β(MeV−1sr−1)d = 90 m ->

thunderclouds

acceleration region

harder part

softer part softer part

g-ray cone

Discussions

detector

electron beam

Electrons are accelerated in an acceleration region in thunderclouds by quasi-static fields.

The accelerated electrons emit gamma rays via bremsstrahlung.

The emitted gamma-ray beam forms a cone-like structure due to relativistic effects.

According to bremsstrahlung cross section, a central part of the gamma-ray cone tends to be harder (higher energy) than other parts of the cone.

The cone moves with the clouds, and thus behaves like a searchlight.

A gamma-ray searchlight model

thunderclouds

acceleration region

harder part

softer part softer part

g-ray cone

Discussions

detector

electron beam

Soft band 10 keV - 500 keV

Hard band 3 MeV - 10 MeV

A sign of soft-hard-soft behavior may appear.

A gamma-ray searchlight model

thunderclouds

acceleration region

harder part

softer part softer part

g-ray cone

Discussions

detector

electron beam

Some estimations

d = 90 m

# of 20 MeV primary electrons at source NPL = 658(+-104) : > 1 MeV electronsM.C. gives Nse = 110 (at detector), and thus Npe : 658 - 110 = 548 (at detector).# of 20 MeV primary electrons at sourceNe = Npe(90 m)2/(0.18 m2X0.08)=3.1X108

Source distance, d = 90 m Range of 20 MeV electrons : 110 m.The observed bursts are assumed to be due to 20 MeV primary electrons.

Vertical length of the acceleration region H : vertical length needed for 20 MeV electrons to produce the observed gamma rays via bremsstrahlung.Using F90(E) = 2.4X108 E-1.15 (MeV-1 sr-1) as well as Ne, H is estimated as around 200 m,assuming the cone-opening angle of 30 deg.

H

Coun

t/1 s

ec

200220240260280300320

14:10 14:12 14:14 14:16 14:18 14:20 14:22

Coun

t/1 s

ec

100150200250300350

14:10 14:12 14:14 14:16 14:18 14:20 14:22

E (k

V/m

)

−100−80−60−40−20

020406080 EFM

Time (UT)14:10 14:12 14:14 14:16 14:18 14:20 14:22V

for O

pt. (

mV)

0100020003000400050006000 Opt

ResultsShort bursts from lightning discharges

2008 Sep 21 No increase->

the burst was not dominated by photons

Remarkable enhancementsdue to charged particles

14:18:15(UT), 14:20:24(UT)7σ, 9σ

> 10 keV NaI

>500 keV PL

E-field

light Only charged particles were detected.

lightning

Summary A high-altitude observation was conducted in 2008 Sep - Oct.

One long-duration burst and three short-duration ones.

A simultaneous detection of gamma rays and electrons in the long burst.

Gamma-ray emissions : bremsstrahlung photons arriving from a source located at 60 - 130 m distance @ 90% C.L..

Electron bursts : mainly dominated by primary electrons.

The present Long burst

The present short bursts Only charged particle, likely electrons, may be observed.