First Results of the Crome Experiment

arXiv:1108.0588v2 [hep-ex] 4 Aug 2011 rmEShv ensatd[]btasga eeto has detection signal a but [4] started been have emission EAS microwave from measuring at aiming projects Several bands Ku and available. C commonly the is commercial for receivers Moreover, low-noise for equipment [2]. made interference low human frequency very negligible radio by and radiation characterized background are natural par- they are as communication attractive and satellite GHz) ticularly (3.7–4.2 for C bands (10.7–12.7GHz) frequency Ku presence two the The in clouds. even small of signal very the the and of on-time attenuation 100% atmospheric the are [3]) e.g. (see fluorescence light of observation an to microwave respect a with of measurement advantages The pri- particles. the cosmic-ray EAS of mary composition chemical of and energy development the hence, longitudinal and, the provide about could information EAS from GHz) (1–10 ob- [1]. radiation the Microwave (UHECRs) of rays way cosmic energy promising ultra-high and of new instru- servation a GHz-radio provide standard will thi it by If ments, measured be molecules. air can neutral the radiation with to electrons due of at- radiation interaction been bremsstrahlung has molecular The to signal tributed microwave [1]. signal isotropic microwave and first the a unpolarized of provided intensity process the this of estimate of measurements frequen- Beam microwave at cies. are radiation radio (EAS) produce showers to air expected extensive in electrons Low-energy Introduction 1 2 3 [email protected] 4 1 is eut fteCOEexperiment CROME the of results First .S J. .K O. 32 R. egsh Universit Bergische Universit nttt fNcerPyisPN rkw Poland Krakow, PAN, Physics Nuclear of Institute alrh nttt fTcnlg KT,Krsue Germa Karlsruhe, (KIT), Technology of Institute Karlsruhe ND S ˇ TASIELAK M I R ihdfeetmtos is eut fe afaya fda of Keywords: year a half el after read-out results fast First and methods. different by antennas with detected parabolic showers several Ra with of coincidence signal. consists in microwave GHz) this (3.4–4.2 CRO for band search The C to built showers. was air experiment extensive by initiated bremsstrahlung Abstract: ´ IDA NTERNATIONAL OMER ¨ elAul n NN ’qia Italy L’Aquila, INFN, and dell’Aquila a 1 ` .B H. , 1 4 .M S. , .U M. , ti xetdta ai inli h irwv ag spr is range microwave the in signal radio a that expected is It omcry,dtco,rdoeiso,microwave emission, radio detector, rays, Cosmic L UMER ¨ tWpetl upra,Germany Wuppertal, Wuppertal, at ¨ C NGER ATHYS OSMIC 1 .E R. , 1 .W M. , 2 R .R J. , AY NGEL C ONFERENCE EBER AUTENBERG 1 .H A. , 1 .W F. , AUNGS B , ERNER EIJING 2 .R M. , 1 .H T. , s 1 atkn r presented. are taking ta 2011 .W H. , crnc.Tesniiiyo h eetrhsbe measure been has detector the of sensitivity The ectronics. ny UEGE IEGEL ito rmteamshr smntrdi h extended the in monitored is atmosphere the from diation aeawt adrcies(e iue2 n small a and 2) a Figure with (see receivers each band dishes C m 9 3.4 with with two dish camera GHz, m 1–1.8 2.3 for a receiver of consists one CROME of setup current The upwards. ori- vertically are ented antennas All com- low (LNBs). are block-downconverters with antennas noise equipped other reflectors the parabolic line, available observ mercially hydrogen for cm 21 built an- and the originally GHz 1–1.8 instrument ing band), scientific the a (C While is 3.4–4.2 tenna band). Ku 1–1.8, (low ranges 10.7–11.7GHz frequency receivers the microwave several for of consists setup antenna The array. showers scintillator high-energy the all with for detected stored is signal the Us- 1, GHz KASCADE-Grande measured by array. continuously provided trigger KASCADE-Grande shower to a the ing used above air are the antennas monitor Commer- GHz mi- available emission. of cially Cherenkov and molec- detection from bremsstrahlung expected the ular as showers at air from aims signals crowave experiment CROME The setup Detector 2 near [5]. array Germany shower Karlsruhe, air sta- up (KG) set KASCADE-Grande the been the has discuss within Observa- that detector Ray we Emission) (Cosmic Microwave work CROME via this tion the of In calibration and reported. tus been yet not E(omcRyOsrainvaMcoaeEmission) Microwave via Observation (Cosmic-Ray ME h ACD-rneeprmn.Tedtco setup detector The experiment. KASCADE-Grande the ILCZY 1 1 .H K K.-H. , .R M. , NSKI ´ dcdi h topeedet molecular to due atmosphere the in oduced OTH 4 AMPERT .W J. , 1 .S F. , OCHELE 2 .K H. , ALAMIDA 1 LAGES 3 .S H. , 1 .K M. , CHIELER LEIFGES d 1 1 - , , R. Sˇ MÍDA et al. FIRST RESULTS OF THE CROME EXPERIMENT

Figure 1: Location of CROME antennas in the Figure 2: Photo of segmented parabolic dish (Prodelin KASCADE-Grande array. Full squares indicate the scin- 1344) of 335cm diameter and 119cm focal length. The tillator stations that provide the trigger for CROME. The camera of 9 linearly polarized C band receivers, each con- information from the smaller but much denser KASCADE sisting of a feed matched to the antenna size and a Norsat array [6] (upper right corner) with separate electron and 8215F LNB, is supported by four struts. muon counters is used for estimating the number of muons. 3 Expected event rate 0.9m dish with one receiver for the Ku band. The field of view of a single C band receiver in the 3.4m antenna The calculation of the number of showers measurable by ◦ corresponds to an opening angle of 1.6 for a dropin the the CROME antennas is based on a detailed simulation of ∼ signal by 3dB (for more details see Section 4). air showers detected by KASCADE-Grande together with The layout of the setup is shown in Figure 1. Twelve scin- the estimated microwave signal according to [1]. tillator stations in the center of the KASCADE-Grande ar- KASCADE-Grande is optimized to detect air showers in ray, indicated by full squares in the figure, provides the the range from 1015.5 to 1018 eV. On average, one shower trigger with a rate of a few hundred events per day. Only above 1017 eV per day is measured by KASCADE-Grande showers with the core position reconstructed inside the area and successfully reconstructed. Details can be found in [5]. marked by the dashed lines in Fig. 1, corresponding to The energy range of KASCADE-Grande includes also the 2.0 105 m2, are used in the data analysis. energy of 3.4 1017 eV for which Gorham et al. [1] made × × A fast logarithmic power detector (Analog Devices the accelerator measurement. AD8318) is used to measure the envelope of the antenna Lacking a detailed microscopic model for microwave emis- signals. Measurements show that the exponential time con- sion in air showers, we assume that a fixed fraction of the stant of the whole chain of electronics together with the energy Edep deposited by a shower in the atmosphere is ra- LNB is 4ns (i.e. 9ns for 10-to-90% risetime). The diated off in the microwave frequency band ∆ν. This frac- ∼ ∼ measured signal is readout by five 4-channel digitizers (Pi- tion, in the following called microwave yield YMW, is de- coScope 6402 and 6403) with a sampling time of 0.8ns termined by comparing the simulation results for air show- and 8-bit dynamic range. All channels are readout in a ers with the expected signal given in [1] time window of 10µbefore and after the trigger delivered 1 by KASCADE-Grande. = EMW 1 2 10−18 Hz−1 YMW ∆ . . (1) Particular attention has been paid to the time synchroniza- ν Edep ≈ × tion between the CROME and KASCADE-Grande DAQs Using a 3-d simulation of the showers [7] with iron nu- since the radio signal is expected to be as short as 20ns for clei as primary particle and neglecting attenuation in the at- nearly vertical showers. A GPS clock identical to the one mosphere, which is lower than 0.01dB/km below 10GHz, of KASCADE-Grande is used (Meinberg 167 lcd) and, in we get 2 showers per 9 C band receivers in a 335cm addition, the trigger time from one scintillator station of dish per∼ month with a microwave signal above the mini- KASCADE-Grande is stored for each event. The recon- mum detectable flux. The minimum detectable flux is given structed arrival direction, core position, and energy of the by kBTsys/Aeff /√τ∆ν, where kB is the Boltzmann con- showers recorded by the KASCADE-Grande array are used stant, T =80K the system temperature, A =6.4m2 the in the further analysis. sys eff effective area of a dish, ∆ν=600MHz the bandwidth, and τ=10ns the integrationtime. It should be noted that the pa- 32ND INTERNATIONAL COSMIC RAY CONFERENCE,BEIJING 2011 rameters of the calculation were chosen to obtain a robust lower limit to the expected rate for the given microwave LNB yield. Absorber Vacuum Feed 4 Calibration and radiation pattern

TI A end-to-end system temperature of 60K is estimated for the C band system by comparing the measurement for clear CU sky with the measurement with a microwave absorber (ra- diating as black body at ambient temperature) placed in front of the camera. 520 The calibration of the individual receivers (LNBs with 265 LN2 feeds) has been measured with a microwave absorber at room and liquid nitrogen temperature of 77K. The setup is shown in Figure 3. The flat 5cm thick microwave absorber is placed along a steel wall, in the bottom and also upper 200 part of a cryostat which is covered by a copper lid. The feed can be mounted in stable position and its entrance is below the copper plate. The liquid nitrogen has been filled Figure 3: Cryostat built for the calibration of feeds with inside the cryostat and also in the upper part above the cop- LNBs. The copper plate (CU) supports the feed, closes the per lid. The temperature has been kept uniform and stable inner part of the cryostat and holds temperature insulation in the whole inner part of the cryostat. The difference in material (TI). Liquid nitrogen (LN2) is filled in the upper the measured voltage corresponds to the system tempera- part above the copper lid and also inside the cryostat which ture ranging from 40 up to 50K for the tested LNBs. is fully covered by microwave absorber material. The antennas do not have an astronomical mount and are kept in stable positions. Therefore a flying radio source has been developed to study the sensitivity pattern of the antennas. The radio transmitter is mounted to a remote- controlled copter together with differential GPS for the pre- cise measurement of the position. A two-element Yagi antenna with a one-sided main lobe (about 4.1dBi) and high backward attenuation (-10dB) to avoid reflections of the copter is used as the radio transmitter. The Yagi antenna consists of a half-wavelength dipole with a radiation coupled reflector in quarter-wavelength distance. The maximum power generated by the stabilized transmitter is 8dBm (6mW) and covers the frequency range between 2970 and 3950MHz. Six operating modes with different Figure 4: Two-dimensional radiation pattern of the central modulation patterns are implemented, which may be trig- and two off-center receivers measured by the airborne radio gered by an external source or internal 3Hz clock. The an- source. Points indicate measured values and curves show tenna provides a wide main lobe with -3dB beamwidth of ◦ simulated far field radiation patterns. The gain pattern has 110 on average. Moreover, a logarithmic-periodic dipole been normalized separately for each feed. antenna is being prepared for wideband sweep operating modes. Preliminary results in the transition zone between the near 5 Performance and data analysis and far field of the CROME antennas allow us to determine the radiation pattern of the whole system. Relative radi- CROME is taking data since September 2010. The initial ation patterns for the central and two off-center receivers C band configuration has been enlarged from a single an- are shown in Figure 4. The obtained results are consistent tenna with 4 receivers to two antennas with 18 receivers. with simulations for the far field zone obtained with the The second antenna has been installed in April 2011. A software package GRASP [8]. The main lobes are clearly few important changes have been made during the mea- visible and the -3dB beam-widths are less than 2◦ for all surement apart from the installation of new receivers and channels. An effect of aberration has been measured for read-out electronics. The first was an implementation of in- off-center receivers. The first side lobe is down by more line filters for the measurement of the average power (fluc- than 10dB relative to the peak of the main beam and is tuations of frequencies less than 100kHz) together with pointed towards the main lobe of the central receiver. fast fluctuations. Later on high pass filters (MiniCircuits R. Sˇ MÍDA et al. FIRST RESULTS OF THE CROME EXPERIMENT

Table 1: Performance of the CROME C band setup till May 10th, 2011. The columns show the start dates of measurement with a given setup, the number of receivers used for the measurement, the uptime in days (percent) and the number of well reconstructed events above 5 1016 eV passing through ﬁeld of view. ×

Date Receivers Uptime Events 14/09/2010 4 33.5d (48%) 10 19/11/2010 8 106.7d (82%) 49 01/04/2011 15 26.8d (83%) 17 04/05/2011 18 4.9d (100%) 3 all – 171.8d (73%) 79 Figure 5: Simulated power flux of the most energetic event crossing the field of view of the 4-receiver camera. The VHF-1200) have been installed in the electronic chain to dashed line corresponds to the minimum detectable flux suppress signals from airplane altimeter radars. (see Section 3). The fields of view of the receivers are shown in an inset along with the shower track and its al- The uptime and number of reconstructed events crossing titude above the antenna. the field of view of at least one C band receiver is shown in Table 1 for the given a detector configuration. The uptime of the detector has been affected in particular by the down- crossed the field of view of at least one installed receiver. time of KASCADE-Grande and then by detector upgrades, The analysis of the measured data is in progress, with the calibration or test measurements. Total uptime (i.e. period candidate events being studied in detail. for which CROME and KASCADE-Grande provided data Acknowledgements and full reconstruction of KG events was possible) equals It is our pleasure to thank our colleagues from the Pierre to more than 170 days with 8.6 receivers taking data on Auger and KASCADE-Grande Collaborations for many average. stimulating discussions. This work was partially supported In total 79 events with energy higher than 5 1016 eV were by the Polish Ministry of Science and Higher Education detected by KASCADE-Grande that pass the× quality crite- under grant No. NN 202 2072 38 and in Germany by the ria for reconstruction and have crossed a field of view of at DAAD, project ID 50725595. least one receiver in the C band setup. The most energetic event was measured on September 24th, 2010. Its energy is 7.9 1017 eV with a zenith angle of 10.5◦ and a distance References between× the shower core to the antenna of 159m. The simulated signal for this event is shown in Figure 5. The high- [1] P.W. Gorham et al., Phys. Rev. D, 2008, 78: 032007 est expected signal is about 4dB above noise fluctuations [2] European Radiocommunications Committee, ERC re- and the time width of the signal is about 20ns. port 25, 2009 [3] J. Blümer, R. Engel, J.R. Hörandel, Prog. Part. Nucl. It is worth to mention that we might detect also a Phys., 2009, 63: 293– 338 Cherenkov signal from almost vertical events with recon- [4] P. Privitera, AIP Conference Proceedings, to be pub- structed shower-core distances less than 100m from the an- lished, 1367 tenna (see e.g. [9]). [5] W.D. Apel et al. (KASCADE-Grande Collab.) Nucl. Instrum. Meth., 2010, A 620: 202– 216 6 Conclusion [6] T. Antoni et al. (KASCADE Collab.) Nucl. Instrum. Meth., 2003, A 513: 490– 510 The first results obtained with the CROME antenna array [7] D. Gora et al., Astropart. Phys., 2006, 24: 484 – 494 have been presented. The detector has shown stable perfor- [8] www.ticra.com mance over more than half a year complementedby several [9] N.N. Kalmykov, A.A. Konstantinov, R. Engel, Phys. improvements in the setup or test measurements. We have Atom. Nuc., 2010, 73: 1191– 1202 built an airborne GHz transmitter which has been successfully used for mapping the sensitivity pattern of the antennas and will be used also for absolute calibration. Also the properties of the receivers have been measured with a ded- icated test setup. Many extensive air showers initiated by primary particles with an energy above 5 1016 eV have ×