Towards the all-particle energy spectrum of cosmic rays measured with LORA an air shower array for LOFAR

Transcription

1 Towads the all-paticle enegy spectum of cosmic ays measued with LORA an ai showe aay fo LOFAR J.R. Höandel, A. Costanje, L. Bähen, H. Falcke, A. Honeffe, C.W. James, J.L. Kelley, M. Mevius, P. Schellat, O. Scholten, S. Thoudam, S. Te Veen, M. van den Akke Jög R. Höandel Radboud Univesity Nijmegen, The Nethelands

2 Towads the all-paticle enegy spectum of cosmic ays measued with LORA an ai showe aay fo LOFAR J.R. Höandel, A. Costanje, L. Bähen, H. Falcke, A. Honeffe, C.W. James, J.L. Kelley, M. Mevius, P. Schellat, O. Scholten, S. Thoudam, S. Te Veen, M. van den Akke Jög R. Höandel Radboud Univesity Nijmegen, The Nethelands

3 Towads the all-paticle enegy spectum of cosmic ays measued with LORA an ai showe aay fo LOFAR J.R. Höandel, A. Costanje, L. Bähen, H. Falcke, A. Honeffe, C.W. James, J.L. Kelley, M. Mevius, P. Schellat, O. Scholten, S. Thoudam, S. Te Veen, M. van den Akke 76m ca. 400m Jög R. Höandel Radboud Univesity Nijmegen, The Nethelands

4 LOFAR Radboud Ai Showe Aay 505 Methods in Physics Reseach A 513 (2003) d t detecto box 125 cm scintillato wavelength shifte PM 1.5 F 98 cm Fig. Sketch of a detecto box with two scintillation countes scintillation detectos of the tigge 2 laye and top cluste. (~1 m each) ead out by wavelength shifte ba and PMT [%] into 12-bit ADCdeviation (2.5 fom nsaveage sampling ate) y (South-Noth) [cm] s s e o J.R. H O RA Figue 1: Location of the LORA detectos (ed boxes) in the coe of LOFAR. signals in eal time. To assist with the development of the tigge algoithm and to measue basic ai showe paametes, a field of conventional paticle detectos has been installed in the coe of LOFAR. The LOFAR Radboud Ai Showe Aay (LORA) is an aay of scintillation countes located in the compact cente of LOFAR, the supe-tep, which compises six LOFAR stations. In the following, we descibe the set-up of LORA, its pop- 12-b time ge s a tim Fou HISP cont PC a two high we u ingly typic sign ead The cent PC. ceta

5 LOFAR Radboud Ai Showe Aay

6 Measued signals in single detecto ADC tace enegy deposition in single detecto ADC counts Time (nsecs) ead-out window 10 µs stat 2 µs befoe tigge 12-bit ADC (2.5 ns sampling ate) Total ADC count fit of Landau distibution to data calibation: single-muon peak

7 A measued ai showe aival time enegy depositions ')) &(( () '( *+,$-% & ) () )$% ( '( ')) &(( '() &'( '() ')) () ) () ')) '() $% & &'( &(( '( ( '( &(( &'( $% econstuct fo each showe: position & diection of showe axis lateal distibution numbe of (chaged) paticles enegy estimato

8 The measued aival diections of cosmic ays ae d Fit of NKG function to data in Fig. 3. They eflect, as expected, the angula dist of ai showes poduced fom an isotopic distibu pimay cosmic ays, afte the showes ae attenu the atmosphee of the Eath. The zenith angle dist can be descibed by a function dn (Θ)/dΘ = sin Θ single ai showe #######'*+++",%'##$%&'(() with n = 9.25 ± $%& -.####### #$0*0+##$$*'/ 1######## #$*2+)##%*$2+ 4 Lateal distibution To obtain the lateal distibution of the signals in the plane, the measued signals ae coected fo the co fects of tack length and vaying detecto size. Th sued aveage lateal distibution fo showes with angles Θ < 30 ae pesented in Fig. 4. A NKG f [15, 16] of the fom $%( $% Ne Γ(4.5 s) 2 2πΓ(s)Γ(4.5 2s) M "s 2 "s M M ρ(, s, Ne ) = % (% /% '% 2% $%% $(% $/% $'% $2% (%% ((% (/% has been fitted to the data. It descibes the paticle :;#1<:="-#6>41#?;@ as function of the distance to the showe axis fo s with a total numbe of electons (paticles) Ne. s is

9 ./ Reconstuction accuacies (fom data) using chess-boad method (1/2 aay vs. 1/2 aay) position of showe axis +# "' < 5 m ' # '() '(* ) )(+ )(, )() )(* - $%&

10 ./ Reconstuction accuacies (fom data) using chess-boad method (1/2 aay vs. 1/2 aay) position of showe axis diection of showe axis +# "' < 5 m./01& (' 5 +(' < "(' ' " # '() '(* ) )(+ )(, )() )(* - $%& #(' '() '(* ) )(+ )(, )() )(* - $%&

11 ./ Reconstuction accuacies (fom data) using chess-boad method (1/2 aay vs. 1/2 aay) position of showe axis diection of showe axis +# "' < 5 m./01& (' 5 +(' < "(' ' " # '() '(* ) )(+ )(, )() )(* "(, - $%& numbe of (chaged) paticles./012345%6.%0.7 "(+ " #(* #() #(' '() '(* ) )(+ )(, )() )(* - $%& < 25% #(, #(+ '() '(* ) )(+ )(, )() )(* - $%&

12 side of the distibution tal index of β = 2.63 ± months measuing time Using a simple Heitle m =,:84@ opment [18], the enegy Ne Γ(4.5 s) ABA4ïAB6A ρ(, s, Ne ) = 2 (1) mass numbe A) can be M 2πΓ(s)Γ(4.5 2s) AB6AïAB74 numbe of paticles Ne "s 2 "s 4.5 AB74ïABCA ABCAï6B84 1+ E N 6B84ï6B3A 0 M M 6B3Aï6B54 1 PeV 5.95 has been fitted to the data. It descibes the paticle density 6B54ï6BAA 6BAAï6BD4 as function of the distance to the axis fo showes Fo the convesion to e s = showe 1.5 (fixed) 6BD4ï6B7A with a total numbe of electons (paticles) may paticles ae poto M ~ 50 m Ne. s is the age 6B7AïDB44 paamete and M a scale adius. The latte is classically clei (A = 56) yields a DB44ïDB8A the Molie e adius of about 0.25 adiation lengths in ai. mixed composition, the In ou analysis we teat Ne, s, and M as fee paametes. undeestimated. We pla Best fit values ae s = 1.63±0.10 and M = (110±20) m. enegy convesion based These values descibe the lateal distibution fo all chaged CORSIKA code [20] at paticles. The KASCADE goup obtained sepaate lateal The peak position in F distibutions fo electons and muons [17]. Fo electons a about Eth 1014 ev scale adius M = 20 to 30 m and an age paamete s be- theshold of a sub-aa tween 1.6 and 1.8 has been obtained. The muon lateal dis- out of 4 tigge. The tibution is descibed best by M = 420 m. Ou value fo Ne 107 ) coespond t fects of tack length and vaying detecto size. The measued aveage lateal distibution fo showes with zenith angles Θ < 30 ae pesented in Fig. 4. A NKG function [15, 16] of the fom 9.%+:(;)<%+$"'=();(&#"$>)1-ï3 2 Aveage lateal distibutions 84? $%&'()*+,-)#.,/(+)%0)1-2

13 9.%+:(;)<%+$"'=();(&#"$>)1-3 2? Aveage lateal distibutions 84 ABA4 AB6A AB6A AB74 AB74 ABCA ABCA 6B84 6B84 6B3A 6B3A 6B54 6B54 6BAA 6BAA 6BD4 6BD4 6B7A 6B7A DB44 DB44 DB8A $%&'()*+,-)#.,/(+)%0)1-2 compaison to KASCADE data T. Antoni et al., Astopat. Phys. 14 (2001) 245

14 Measued showe size spectum s is simila to the paamete obtained by KASCA 4 <=0%=310>'4.<?.%5@#ï;'3&ï7'3ï7: showe axis is defined as the cente of gavity of the enegy depositions in the individual detectos. The measued aival diections of cosmic ays ae depicted n Fig. 3. They eflect, as expected, the angula distibution of ai showes poduced fom an isotopic distibution of pimay cosmic ays, afte the showes ae attenuated in he atmosphee of the Eath. The zenith angle distibution n can be descibed by a function dn (Θ)/dΘ = sin Θ cos Θ with n = 9.25 ± ï7d ï7c ï7b ou scale adius fo all chaged paticles is in betw values~obtained 33 daysby KASCADE fo electons and m The values fo sshowes and M detemined fom the ave ~ eal distibution been fixed tigge to fit individual s 4 detectohave coincidence An example of the lateal distibution obtained fo < 45 vidual showe is shown in Fig. 5. The only fee fit te is the total numbe of electons (o paticles) N we obtain Ne fo each individual showe. ï76 5 Lateal distibution ï79 Showe size spectum To obtain the lateal distibution of the signals in the showe The measued showe size spectum, obtained by d plane, the measued signals ae coected fo the cosine ef- ing Ne event by event is depicted in Fig. 6. The ig ects of tack length and vaying detecto size. The mea- side of the distibution follows a powe law with sued aveage lateal distibution fo showes with zenith tal index of β = 2.63 ± The data coespon $%&'()'*+,&-%.'/,&01*2%3'4%5 angles Θ < 30 ae pesented in Fig. 4. A NKG function months measuing time with one sub-aay (fou de 15, 16]NKG of thefunction fom Using a simple Heitle model to descibe the showe opment [18], the enegy E0 of the pimay patic Ne Γ(4.5 s) ρ(, s, Ne ) = 2 (1) mass numbe A) can be estimated fom the measu M 2πΓ(s)Γ(4.5 2s) numbe of paticles Ne using the appoximation [1 "s 2 "s 4.5 "1/ E0 Ne M M 0.046/1.046 A 1 PeV ï7a 6 9

15 Measued showe size spectum s is simila to the paamete obtained by KASCA ï7d ï7c ï7b ï76 Lateal distibution ï79 % ='4.<=.%5'>#ï;'3&ï7'3ï7: 4 <=0%=310>'4.<?.%5@#ï;'3&ï7'3ï7: showe axis is defined as the cente of gavity of the enegy depositions in the individual detectos. The measued aival diections of cosmic ays ae depicted n Fig. 3. They eflect, as expected, the angula distibution of ai showes poduced fom an isotopic distibution of pimay cosmic ays, afte the showes ae attenuated in he atmosphee of the Eath. The zenith angle distibution n can be descibed by a function dn (Θ)/dΘ = sin Θ cos Θ with n = 9.25 ± ou scale adius fo all chaged paticles is in betw values~obtained 33 daysby KASCADE fo electons and m The values fo sshowes and M detemined fom the ave ~ eal distibution been fixed tigge to fit individual s 4 detectohave coincidence An example of the lateal distibution obtained fo < 45 vidual showe is shown in Fig. 5. The only fee fit te is the total numbe of electons (o paticles) N we obtain Ne fo each individual showe. x Ne2.5 5 Showe size spectum ï7a 6 9 ;?@ To obtain the lateal distibution of the signals in the showe The measued showe size spectum, obtained by d plane, the measued signals ae coected fo the cosine ef- ing Ne event by event is depicted in Fig. 6. The ig ects of tack length and vaying detecto size. The mea- side of the distibution follows a powe law with sued aveage lateal distibution fo showes with zenith tal index of β = 2.63 ± The data coespon $%&'()'*+,&-%.'/,&01*2%3'4%5 angles Θ < 30 ae pesented in Fig. 4. A NKG function months measuing time with one sub-aay (fou de 15, 16]NKG of thefunction fom Using a simple Heitle model to descibe the showe opment [18], the enegy E0 of the pimay patic Ne Γ(4.5 s) ρ(, s, Ne ) = 2 (1) mass numbe A) can be estimated fom the measu M 2πΓ(s)Γ(4.5 2s) numbe of paticles Ne using the appoximation [1 "s 2 "s 4.5 "1/ E0 Ne M M 0.046/1.046 $%&'()'*+,&-%.'/,&01*2%3'4%5 A 1 PeV

16 Using a simple Heitle model to descibe the showe development [18], the enegy E0 of the pimay paticle (with mass numbe A) can be estimated fom the measued total numbe of paticles Ne using thetoappoximation [19] spectum use simple Heitle model estimate enegy "1/1.046 J. Matthews, Astopat. Phys. 22 (2005) 387 E0 Ne 0.046/1.046 J.R. Höandel, Mod. Phys. Lett. A 22 (2007) 1533 A. (2) 5 1 PeV Reconstucted enegy spectum 3#4$#154'(6376"+89ï21%ï-1ï-)$*ï-0 The peak position in ï-;fig. 6 coesponds to an enegy of about Eth eV. This coesponds to the tigge theshold of a sub-aay of fou detectos, equiing a 4 out of 4 tigge. The ï-, biggest measued showes (with -. Ne 107 ) coespond to enegies above 1016 ev. y a in im el p Fo the convesion to enegy, it is assumed that all pimay paticles ae potons (A = 1). Assuming ion nuï-= clei (A = 56) yields -. a 20% highe enegy. Hence, fo a mixed composition, the econstucted enegies ae slightly undeestimated. We plan to establish a moe sophisticated enegy convesion based -.ï-< on ai showe simulations with the ~ CORSIKA code [20] at a late time. -.ï-/ ï-: -., -. -./ $%&'()$*+

17 A measued ai showe paticle detectos & adio > =. $* > $* $* ###### #&($%$")*+# #$%$&'&,-####### #'+(/%# #.($' see also: August 17th, 15:36-17:00, Hall 3, J. Kelley: LOFAR: Detecting cosmic ays with a adio telescope $ * '* $** $'* >** >'* #2879",#4:12#;<= ai showe egisteed by LORA used to tigge LOFAR adio antennas Jög R. Höandel Radboud Univesity Nijmegen, The Nethelands