30TH INTERNATIONAL COSMIC RAY CONFERENCE

Ashra Mauna Loa Observatory and Slow Control System

Y. A ITA1, T. AOKI1, Y. ASAOKA1, T. BROWDER2, T. CHONAN1, S. DYE2, M. EGUCHI1, R. FOX3,J. HAMILTON 3, Y. HIGASHI1, T. KIMURA4, N. KOHTA5, H. KUZE6, J. LEARNED2, M. MASUDA7,S. MATSUNO2, Y. MORIMOTO5, K. NODA1, S. OGAWA5, A. OKUMURA1, S. OLSEN2, M. SASAKI1,H. SHIBUYA 5, K. SHINOMIYA 6, N. SUGIYAMA 8, Y. YAMAGUCHI6, M. YASUDA9, G. VARNER2,Y. WATANABE10, Y. WATANABE5

1Institute for Cosmic Ray Research, University of Tokyo, Kashiwa 277-8582, Japan2Department of Physics and Astronomy, University of Hawaii Manoa, Hawaii 96822, USA3Physics and Astronomy Department, University of Hawaii Hilo, Hawaii 96720, USA4Department of Systems Engineering, Ibaraki University, Hitachi 316-8511, Japan5Department of Physics, Toho University, Funabashi 274-8510, Japan6Center for Environmental Remote Sensing, Chiba University, Chiba 263-8522, Japan7High-Tech Research Center, Kanagawa University, Yokohama 221-8686, Japan8Department of Physics and Astrophysics, Nagoya University, Nagoya 464-8602, Japan9Department of Physics, Tokyo Institute of Technology, Meguro 152-8551, Japan10Institute of Physics, Kanagawa University, Yokohama 221-8686, Japan

oxon@icrr.u-tokyo.ac.jp (Akira Okumura)

Abstract: The observation site of Ashra (All-sky Survey High Resolution Air-shower detector) is locatedon Mauna Loa in Hawaii. A part of the Ashra detectors have already beenconstructed, and pilot runs ofoptical GRB observation and atmospheric Cherenkov light detection havebeen operated using them.Slow control system including Cloud Monitor have also been tested during thepilot runs. We report thecurrent status of the Ashra Mauna Loa Obaservatory.

Ashra

Ashra is a new experiment which has an abilityto detect air fluorescence light and atmosphericCherenkov light yielded by high-energy cosmicrays[1]. In addition to cosmic ray detection, itis able to observe stars and transient objects op-tically. As the name shows, Ashra covers 80 % ofthe sky (80 % of2π [str]) with light collectors of42◦ field of view (FOV) and of a few arcmin opti-cal resolution[2].

Air-shower events and star images in the FOV areobtained using Image Pipeline which consists of20 inch electro-static image intensifier (I.I.), prox-imity I.I.s, trigger sensors and an imaging CMOSsensor[3].

The major gain from such very wide FOV de-tector is the ability to monitor the almost wholesky continuously for an extended period, makingan unprecedented search for new point sourcessuch as gamma-ray bursts (GRBs), supernovae andunidentified sources of other energy ranges.

Ashra Mauna Loa Observatory

Ashra Mauna Loa Observatory, the observationsite of Ashra phase 1, is located at an elevationof 3,300 m of Mauna Loa on the Island of Hawaii(N19.54◦, W155.57◦). Mauna Kea can be viewedon the north side about 35 km far from Mauna Loaand it can be used as a huge target mass for earthskimming tau neutrinos.

Proceedings of the 30th International Cosmic Ray ConferenceRogelio Caballero, Juan Carlos D’Olivo, Gustavo Medina-Tanco,Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.)Universidad Nacional Autónoma de México,Mexico City, Mexico, 2008

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ASHRA MAUNA LOA OBSERVATORY AND SLOW CONTROL SYSTEM

Figure 1: Ashra Mauna Loa Observatory in Dec2006. The mountain in the center of the picture isMauna Kea. A∼E are light collectors which mon-itor around the zenith of30◦. F monitors tau neu-trinos coming through Mauna Kea.

We have been conducting construction of lightcollectors and pilot observations since September2005. Fig. 1 shows the current (December 2006)view of the site. 6 of 28 light collectors have al-ready been constructed by the end of 2006. TheOptical System and Image Pipeline have been in-stalled in part of them. Construction of light col-lectors totaling 28 is scheduled to be finished insummer of 2007.

Pilot Runs

Using part of completed light collectors, pilot runsof atmospheric Cherenkov light detection and op-tical GRB observation were conducted betweenMay 2006 and March 2007 following the earliesttest on Haleakala, Maui[4].

One of the unique features of Ashra is that ithas three different time scales:∼ 100 [ns] forCherenkov light,∼ 10− 100 [µs] for fluorescencelight and∼ 10 [s] for star light[5][4]. These threemodes work simultaneously with only one ImagePipeline. Same image is split to three different sen-sors using half mirrors and optical fibers.

Event images of these three modes are obtainedwith the resolution of a few arcmin. This resolutionand wide FOV are achieved by modified Baker-

Figure 2: Ray trace of the Optics of Ashra.

Nunn optics which consists of three acrylic lensesand seven segment mirrors. The photocathode of20” I.I.s work as a focal plane. Fig. 2 is a ray traceof the optics.

In spite of its resolution and FOV, alignment of op-tical components (segment mirrors, acrylic lensesand focal plane) is simpler than other cosmic raydetectors or astronomer’s telescopes. Because itdoes not need any online adjustment nor active ac-tuators. It always views a fixed area. Thus theorder of alignment accuracy is sub-millimeter thatcan be adjusted by hand. This is very importantto reduce the cost of construction of a few tens oflight collectors.

Fig. 3 shows an image example of untriggeredmode during the pilot runs. We achieved a few ar-cmin resolution in the FOV.

We confirmed that the optics could be well aligned,data flow worked smoothly. Data acquisition ofun-triggered images was conducted in two monthswithout any major problems. Unfortunately, noGRB has occurred in our FOV during the obser-vations. However time zero of GRBs will be ob-served by Ashra after the start of official run inSeptember 2007.

Slow Control System

We also operated our slow control system dur-ing the pilot runs. It includes Cloud Moni-tor, Weather Monitor, power control, tempera-

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Figure 3: Sky image in the area within the radius of21◦ from the point of(zenith = 30◦, azimuth =0◦). The exposure time is 4 [s]. The seven brightstars are the Big Dipper. Note that saturated starsare not good indicators of resolution.

ture/humidity control and so on. We focus onCloud Monitor in this section.

Operators have to be careful of the weather con-ditions during observations in cosmic ray exper-iments. Because optical thickness of the atmo-sphere depends on the quantity of clouds, and oper-ations should be shut down before it rains. Humid-ity can be an indicator of rain but it is not enoughfor a rain shower forecast on the mountain. Thesimplest way to know signs of rain is to grasp con-ditions of clouds. However clouds are not visibleto human eyes on moon-less nights.

We have developed Cloud Monitor which visual-izes near-infrared radiation from clouds. Therehave already been some cloud monitors utilizingnear-infrared (for example [6]). However we needoriginal system which has wider FOV and bettercost performance. Because the FOV of Ashra cov-ers even beneath the horizon.

We used mainly two products: IR-U300M1 (Mit-subishi Electronics) and ETX-90/EC (MEADE).The former is a CCD camera which is sensitive tonear-infrared, and the latter is an altazimuth tele-scope for amateur astronomers. The telescope isused as just a camera platform. Since the camerahas only29◦×21◦ FOV, composite images are cre-ated from 54 images of different directions. Con-trol of the instruments is executed from a Linux PCthrough RS232C, and each image is stored in FITS

Figure 4: Near-infrared cloud images. Left: Clearsky. Right: Cloudy sky. The center of each im-age is the point ofzenith = 0◦. The area of0 ≤ zenith ≤ 100◦ and0 ≤ azimuth ≤ 360◦ isdrawn in one image. Each solid line shows zenithof 30◦, 60◦ and90◦ respectively. Dashed lines areFOVs of light collectors. Top is the north side andleft is the west side.

format. Fig. 4 shows image examples of CloudMonitor.

Weather Monitor is also equipped at the site tomeasure temperature, humidity, wind speed and at-mospheric pressure. It monitors external condi-tions of the light collectors. Collaborating withCloud Monitor, it helps operators to decide tostart/stop observations.

Since day-by-day variation of internal conditionsof light collectors may cause degradation of opti-cal system, internal temperature and humidity arealso being monitored by small chip sensors SHT71(Sensirion).

Summary

The status of Ashra is changing from the develop-mental phase to observation phase. Most parts ofthe detector system are ready and have been testedin pilot runs. After completing construction oflight collectors, untriggered observation and searchfor transient objects are scheduled to be startedfrom September 2007, and TeVγ-ray observationwill follow it.

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Acknowledgments

This study was supported mainly by the Coordina-tion Fund for Promoting Science and Technology(157-20004100) and by a Grant-in-Aid for Scien-tific Research (16740130) from the Ministry of Ed-ucation, Science, Sports and Culture of Japan. A.Okumura and K. Noda were supported by Grant-in-Aid for JSPS Fellows.

References

[1] M. Sasaki, Very high energy particle astron-omy with All-sky Survey High Resolution Air-shower detector (ASHRA), Progress of The-oretical Physics Supplement 151 (2003) 192–200.

[2] M. Sasaki, A. Kusaka, Y. Asaoka, Design ofUHECR telescope with 1 arcmin resolutionand 50◦ field of view, Nuclear Instruments andMethods in Physics Research A 492 (2002)49–56.

[3] M. Sasaki, Y. Asaoka, M. Jobashi, Self-triggered image intensifier tube for high-resolution UHECR imaging detector, NuclearInstruments and Methods in Physics ResearchA 501 (2003) 359–366.

[4] M. Sasaki, et al., Observation of optical tran-sients with the Ashra prototype, in: Proceed-ings of the 29th International Cosmic RayConference Pune, Vol. 5, 2005, pp. 319–322.

[5] Y. Arai, et al., ASHRA trigger and readoutpixel sensors, in: 28th International CosmicRay Conference, 2003, pp. 961–964.

[6] M. Suganuma, et al., The infrared cloud mon-itor for the MAGNUM robotic telescope atHaleakala, astro-ph/0704.2270 accepted forpublication in PASP.

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