Baishya, R

CERN Document Server

29th International Cosmic Ray Conference Pune (2005)  9, 111-114  Characteristics of VLF-LF radio emission (RE) from Giant Air Shower (GAS)   R. Baishyaa and P. Dattab (a) Department of Physics, Pragjyotish College, Bharalumukh, Guwahat- 781 009, Assam, India (b) Professor, Department of Electronics Science, Gauhati University, Guwahati  781 014, Assam, India  Presenter: R. Baishya (runima_b@yahoo.co.in), ind-baishya-R-abs1-he22-oral  Experimental works on radiation and particle component of Giant Air Showers (GAS) are going on in different laboratories all over the globe. In this paper, a theoretical investigation is made on different components of VLF-LF radio emission associated with GAS. Findings of this work will be reported at the conference.   1. Introduction  Studies of Giant Air Showers (GAS) is one of the major challenges in recent times. Nature, origin, acceleration mechanism and high energy (HE) interaction associated with the cosmic ray (CR) particle  producing GAS is still not clear.  Results obtained over last two decades using broad air shower detectors, such as Fly’s Eye, AGASA and the Yakutsk installation, have made it possible to collect database of UHE cosmic rays. AGASA group has reported 57 events of energy > 4x 1019 eV and 8 events with E >1020 eV [1].  At present much attention is being given on detection of neutrino with E >1019 eV, investigating the radio emission (RE) emitted by neutrino initiated showers, viz, Extensive Ice Showers (EIS) and Lunar Regolith Showers(LRS)[2,3,4,5,6], since detection of such neutrino will be useful for solving the GZK puzzle. As the neutrino astronomy based on Radio method originates from the extensive study of RE from EAS, for concretising the theoretical model of radio method of neutrino detection, support from the investigation of RE from GAS is very much essential. Moreover, at present quite a good number of Giant Shower Projects is in successful operation (Augur, G.U., Yakutsk etc). These two factors point towards the necessity of investigation of RE from GAS.  Observed higher field strengths from EAS in the LF-MF band may be due to Transition Radiation (TR) mechanism which is different from RCR. Field strength due to TR mechanism shows an increasing trend as the frequency is lowered [7].  Hence, in this paper different characteristics of RE associated with GAS is investigated in the light of TR mechanism.    2. Method  When a charged particle moving uniformly in a medium, enters suddenly into another medium, radiation is emitted in the forward as well as backward direction. This radiation is called Transition Radiation (TR).When the particles of EAS hit the ground, the phenomenon of TR must occur. For the VLF-LF band all the charged particles of the shower may be assumed, for mathematical convenience, to be concentrated at a point instead of distribution over a region and only the excess negative charge, in effect, will contribute to TR.    112                                                                             R. Baishya and P.Datta  For a particle of charge e moving with relativistic velocity v crossing the boundary plane Z = 0 at t = 0, the radiation field in the first medium is given by z)1(λcosvς22π 1η1ekλz)1λcos(znˆvς22π1η2ekz)1(λsinvς22π 1η1ekλz)1(λsinznˆvς22π 1η2ekω1/E ii +++=    (1)  For a vertical air shower, the magnitude of the vertical component of the field is vς22πθ2cos 2k1εNeηωvE =                 (2) Where  N  =  Total number of shower particles at ground level   εΝe   =  excess negative charge, k   =  ω/c = wave number λ12 = (ω/c)2χ1 – k2   :  χ1 =  ε1 µ1  and  λ22 = (ω/c)2χ2 – k2   : χ2 =  ε2 µ2 2222212222121)χ/c(ωkv/ω-1)χ/c(ωkv/ω/εε                    η −++−−= λλ   ζ = λ2 ε1 +  λ1 ε2  ε1, ε2    =  dielectric constant of the first and second medium  µ1, µ2   =  permeability  of the first and second  medium   tan θ  =  Z/R , Z  = height of the antenna from the ground, R = core distance  The Eq. 2 can be used for calculating the field strength for air shower striking the ground. The number of excess electrons in the shower is obtained by assuming ε = 20% [8]. Number of shower particles hitting the ground for different primary energy (Ep) and different primary particles is estimated from Nmax and Smax [9,10].    3. Result  Frequency spectra for vertical component of field strength obtained from Eq. 2 is presented in Fig.1 for gamma initiated, proton-initiated and iron-initiated shower with Ep = 1018 eV.  0102030405060700.00E+00 5.00E+04 1.00E+05 1.50E+05 2.00E+05 2.50E+05 3.00E+05 3.50E+05Frequency in HzField strength in mV/mEp = 1018 eVγpFe Figure. 1  Frequency spectra of vertical component of Field strength  Characteristics of VLF-LF radio…                                                           113  Fig. 2 shows frequency spectra for vertical component of field strength for gamma initiated, proton-initiated and iron-initiated shower with Ep = 1019 eV. 01002003004005006007000.00E+00 5.00E+04 1.00E+05 1.50E+05 2.00E+05 2.50E+05 3.00E+05 3.50E+05Frequency in HzField strength in mV/m Ep = 1019 eVγpFe Figure. 2  Frequency spectra of vertical component of Field strength   Variation of vertical component of field strength at 100 kHz with primary energy (Ep), for proton-initiated shower is presented in Fig. 3. 01002003004005006007008009000.00E+00 1.00E+19 2.00E+19 3.00E+19 4.00E+19 5.00E+19 6.00E+19Primary Energy Ep in eVField Strength in mV/mFrequency = 100 kHz Figure 3. Variation of vertical component of Field strength with Primary Energy Ep for proton initiated shower.    114                                                                             R. Baishya and P.Datta  4. Discussion and Conclusions  Frequency spectra for gamma initiated, proton-initiated and iron-initiated shower shows that with lowering of frequency field strength increases (Fig. 1), for primary energy, Ep = 1018 eV. For a particular frequency, field strength for gamma initiated shower is maximum whereas for iron-initiated shower is minimum. For primary energy, Ep = 1019 eV field strength due to gamma and proton initiated showers increases more rapidly than iron-initiated shower towards the lower frequency region. Field strength due to gamma initiated shower is slightly higher than the proton initiated shower for this energy range (Fig. 2). Field strength due to proton initiated shower shows an increasing trend as the energy of the primary particle increases up to Ep =1019. 5 eV.  The encouraging result of this investigation may be useful for detecting Giant Air Shower by radio method. Radio detection of GAS will be a sophisticated and cost effective technique.  As Eq. 2 has three unknowns, simultaneous measurement of field strength at a minimum of three antennas at different positions, along with conventional particle detector array, will make it possible to estimate shower size, N and core distance, R.   Hence from graphs similar to Figs. 1 and 2, primary particle may be identified. However, for improved accuracy of the final results more characters of VLF-LF radio emission are to be investigated.   5. Acknowledgements  The computational works of the present paper are done at DST-FIST sponsored computer laboratory of the Department of Electronics Science, Gauhati University. The authoresses are, therefore, thankful to the Department of Science and Technology (DST), Government of India for the FIST grant to the department.   References  [1] AGASA collaboration, Astro part. Phys, 19, 447 (2003). [2] A.R. Beresnyak et al, Astronomy Reports, 49, No.2, 2005, 149. [3] I. Kravchenko et al (RICE, collaboration), Astro part. Phys, 20, 195 (2003). [4] P.W. Gorham et al. Proc. RADHEP – 2000(2001), 177. [5] K. RoySingha et al, Proc. 27th ICRC(2001), 3 , 1309 [6] K. RoySingha et al (this conference). [7] R. Baishya  et al., RAHEP, 2000 (2001), 98 [8] Saltzbery et al, RADHEP, 2000 (2001), 225. [9] C. Song.for the HiRes Collaboration, Proc 27th ICRC (2001), 2, 490. [10] O. Catalano  et al, PROC 27th ICRC( 2001), 2, 498.   

Characteristics of VLF-LF radio emission (RE) from Giant Air Shower (GAS)

Abstract

Similar works

Full text

Available Versions

CERN Document Server