PolKa a tunable polarimeter for (sub)mm bolometer arrays Giorgio Siringo Bolometer Development Millimeter & Submillimeter Astronomy Group Max-Planck-Institut für Radioastronomie (MPIfR) BPol Workshop - October 25-27, 2006 PolKa = Polarimeter für Bolometer Kameras

Bolometer Development MPIfR Walter Esch Hans-Peter Gemünd Ernst Kreysa (group leader) Gundula Lundershausen Giorgio Siringo PolKa team Giorgio Siringo Ernst Kreysa Lothar A. Reichertz Collaboration Giuseppe Cimò Thomas Krichbaum IPHT, Jena PolKa a tunable polarimeter for (sub)mm bolometer arrays PolKa = Polarimeter für Bolometer Kameras

MPIfR Bolometer Arrays HUMBA: Hundred Millikelvin Bolometer Array (discontinued) 19 NTD bolos, DC biased, AC coupled, = 2 mm (150 GHz), 100 mK (dilution fridge) Used at the HHT and IRAM 30 m to observe SZ effect HHT 19-channel Array: (discontinued) 19 NTD bolos, DC biased, AC coupled = 850 m (350 GHz), 300 mK Facility instrument at the Heinrich Hertz Telescope (HHT) SIMBA: SEST Imaging Bolometer Array (discontinued) 37 NTD bolos, DC biased, AC coupled + 5 AC biased and DC coupled = 1.2 mm (250 GHz), 300 mK Used in fast scanning without chopping secondary Facility instrument at the Swedish-ESO Submillimeter Telescope (SEST)

MPIfR Bolometer Arrays MAMBO (Max-Planck Millimeter Bolometer) NTD bolos, DC biased, AC coupled, = 1.2 mm (250 GHz), 300 mK MAMBO-1: 37 elements MAMBO-2: 117 elements Facility instruments on the IRAM 30 m telescope, Pico Veleta, Spain LABOCA (Large APEX Bolometer Camera) 295 NTD bolos, AC biased, DC coupled, = 850 m (350 GHz), 300 mK Facility instrument on the APEX telescope (Atacama Pathfinder Experiment, Llano de Chajnantor, Chile) SABOCA (Submillimeter APEX Bolometer Camera) 37 TES bolos + SQUIDs multiplexing and amplification = 350 m (860 GHz), 300 mK To be installed as facility instrument on the APEX telescope in early 2007 LABOCA-2 (Large APEX Bolometer Camera) 288 TES bolos + SQUIDs multiplexing and amplification Will replace LABOCA at the end of 2007 TES development in collaboration with IPHT (Institute for Physical High Technology) of Jena

LABOCA-2 Wafer (IPHT, Jena) 288 TES bolometers with integrated SQUIDs on a 4-inch wafer

Polarimeter using a half-wave plate (HWP) modulation: a rotating half-wave plate analyzer: a fixed wire-grid polarizer demodulation: a lock-in amplifier

The modulation frequency is four times the mechanical one Unpolarized radiation is not modulated (in theory…) Polarimeter using a HWP analyzer horizontalanalyzer vertical

The PolKa polarimeter PolKa is designed to be used with any of the MPIfR bolometer arrays (large diameter, wide range of wavelengths) It uses a reflection-type HWP to modulate the polarization (crystal-type have stronger absorption and it is difficult to produce large diameters) The HWP is rotated continuously by a precision motorized air-bearing: no chopping secondary mirror Raw data (not demodulated) are acquired (fast data acquisition) Demodulation made offline via a “software lock-in” algorithm

The reflection-type HWP (RHWP) The RHWP is made of two parts: a wire-grid polarizer a flat metallic mirror By tuning the distance t between the two parts it is possible to produce a 180° phase shift between the two components of polarization for any operating wavelength This device uses metallic reflections and absorption is negligible mirror polarizer

but: large wire-grid polarizers are needed they are produced only in a few labs in the world have very long delivery time (order of years) are expensive (in the range $) We decided to produce them in our labs mirror polarizer The reflection-type HWP (RHWP)

~4000 tungsten wires wire size: 20  m step: 63  m position error: ~ 15  m rms clear aperture: 246 mm market price: ~ 10,000 $ Wire-grid production

Heinrich Hertz submillimeter Telescope (HHT), Mount Graham, ~120 Km north-east of Tucson, Arizona 3,186 m above the see level diameter: 10 m surface accuracy: 15  m rms At the telescope

the 246 mm version of PolKa was tested at the HHT on Jan 2002 receiver: MPIfR 19 channel  m rotation frequency: 3.5 Hz polarization modulation: 14 Hz full size HWP: full 19 channel array on the sky improved analyzer system and... we had excellent weather! At the telescope

Observing modes We had two main observational strategies: Polarization On-Off : to perform polarized flux measurements or detection experiments. Used on point sources. NEFD ~ 1650 mJy t (1/2) /(20” beam) Polarization On-the-Fly maps: to map the polarization pattern of extended sources. NEFD ~ 380 mJy/(20” beam) per coverage (6’x6’, t~0.5 h) complemented by Total power measurements: to get I and for point, focus, skydip At the telescope

Polarization OO results an example: 3C279 The signal is strong enough to be fitted using a sine! OO data NOT demodulated AC coupling

Linear polarization was detected on the two quasars 3C279 and Polarization OO results

HHT: –3186 m above the see level –10 m telescope –850  m –Reflection type HWP –Continuous spinning & no wobbler A comparison: SCUBA-Pol JCMT: –4092 m above the see level –15 m telescope –850  m –Crystal type HWP –Step & integrate + wobbler SCUBA-Pol map Length = pol. degree Vectors rotated by 90° Ori OMC-1 Coppin & al., A&A 356 (2000) Polarization OtF results

pol. degree map Length = pol. degree Vectors rotated by 90° 12 maps co-added: ~ 6 h Coppin & al., A&A 356 (2000) Siringo & al., A&A 422 (2004)

Orion OMC-3 MMS3-4 PolKa map / 1.5 h int. time (3 scans) SCUBA-Pol / ~7 h int.time B.C.Matthews & al., ApJ, 562 (2001) pol.intensity map

Contours = CO(6-5) Grey-scale = 1.2 mm continuum IRAS ~ 3 h int. time (6 scans) pol. degree map H.Beuther & al., A&A, 387 (2002)

Summary The good points of PolKa are: – tunable over a wide range of wavelengths – low insertion loss (RHWP) – easy changeover between polarimetry and photometry – high modulation efficiency – high imaging quality (no chopping mirror) We proposed a new concept of polarimeter for mm/submm wavelengths: RHWP + continuous spinning - wobbler Results: –polarization detection on 3C279 and –polarization variability of 3C279 –high resolution polarization maps of Orion OMC-1, MMS3/4 in Orion OMC-3, IRAS These results confirm that the new concept is valid

Ongoing experiments We have 2 new RHWP units for our active experiments: MAMBO-1 on the IRAM 30m telescope Pico Veleta, Spain (3000 m amsl) larger telescope: 30 m dish longer wavelength: receiver 1.2 mm more sensitivity: MAMBO-1 has 37 bolometers higher resolution: 11” beam LABOCA on APEX better site: Llano de Chajnantor, Chile (5,100 m amsl) submillimeter telescope: 12 m dish, 15 m rms wavelength: 850 m large array: 295 bolometers high resolution: 18” beam larger array: 11’ fast mapping speed: 2’/s higher sensitivity: 1 square degree in 1.5 hour, 125 mJy rms noise level

Hints for discussion Contributions to BPol from ground based polarimeters: Foreground observations (dust) Instrument calibrations Complications: Small angular scale Limitations due to the atmosphere Available ground based polarimeters with bolometers: QUaD, South Pole (optimized for CMB), GHz PolKa + MAMBO-1, Pico Veleta, Spain, 250 GHz PolKa + LABOCA, APEX, Chile, 350 GHz SHARP + SHARC-II, CSO, Hawaii, 860 GHz

PolKa a tunable polarimeter for (sub)mm bolometer arrays Giorgio Siringo Bolometer Development Millimeter & Submillimeter Astronomy Group Max-Planck-Institut für Radioastronomie (MPIfR) BPol Workshop - October 25-27, 2006 PolKa = Polarimeter für Bolometer Kameras