Science with a Rover-based Low-frequency Dipole Array A multi-configuration rover-borne dipole array for Low-frequency RadioAstronomy from the Moon Ettore Carretti INAF-IRA Bologna On behalf of the Radio WP group in collaboration with CIRANO (PoliMi) E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Why =3-30 MHz astrophysics? Almost unexplored frequency band –next years (2009+) the ground-based array LOFAR will explore the and MHz bands; –< 30 MHz almost impossible from ground (ionosphere) –Only strongest sources and very large scales maps (HPMW = 2°-10°) TO OPEN A NEW ASTROPHYSICS WINDOW ! E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Extragalactic astrophysics Cosmology Physics of Acceleration of high energy particles in the Universe Origin and amplification of magnetic fields in the Universe Physics of Black Holes and Duty cycles Most distant and oldest radio emitting plasma in the Universe New Physics … (coherent emission, serendipity) E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Galactic astrophysics Diffuse Emission from the Galaxy Magnetic field in the Galaxy Acceleration and diffusion of high energy particles in the Galaxy Mapping HII in the Galaxy Supernova Remnants in the Galaxy Physics of Micro-Quasars New Physics … (coherent emission, serendipity) E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

What is possible from ground? Roger et al MHz Ellis MHz Ellis MHz Ellis 1982 Roger et al MHz  = 2°-3° LOW RESOLUTION ! E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Resolution improvement by >10X... Roger et al MHz Ellis 1982 Haslam et al subdegree resolution (at least) down to 3 MHz E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Low frequency: strong signal Low frequencies dominated by synchrotron Synch spectrum: negative slope => strong signal at low frequency –Galactic diffuse emission >10000s K (30MHz) even at high lat. – > 1 MK (2-3MHz) It is not required a huge collecting area to map the sky. Haslam et al MHz Roger et al MHz  = 2°-3° 2.1 MHz Ellis 1982 E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Instrument Need for high resolution => large telescope aperture No need for high sensitivity (strong signal and first survey experiment) => interferometric small antenna array –many separated antenna, whose signals are 2-by-2 correlated –N antennas => N(N-1)/2 independent pairs –resolution  = /D max (D max = maximum baseline – pair distance) 10 Km equivalent aperture:  [MHz]  [m]  [arcmin] E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Array each antenna pair is sensitive to the angular scale   /D several baselines D are necessary to cover from largest to smallest angular scales D from “a few”-m to 10 Km (even 3 Km would be OK) Array “shape” E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Antennas Which antenna? Mirrors not suitable: –need D >> –3 MHz => = 100m –it’d be D = HUGE !?! Dipole antenna: “Natural” choice for a low frequency antenna –. /2 electric dipoles not suitable because of lengths and very narrow frequency band –magnetic dipoles: using coils, much higher efficiency with same length –length: 10s-cm –double dipoles: both polarizations –Large F.o.V.: 90° => optimal for surveys, i.e. full sky mapping –lightweight: just wire E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Antenna (2) Receiver: simple and well developed technologyReceiver: simple and well developed technology Dipole antennas Receiver: sky signal dominated conditions (10-kK to 1-MK) –amplifier sensitivity is not an issue (state-of-the-art technology not necessary); –commercial components can be used; –standard Medium/Short-Wave telecommunication components (well tested in space-enviroment and space-qualified); –standard electronics No “critical” technology to be developed E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Experiment Main requirement: Mass < Kg  antennas: not enough to realize all the baselines from 3-5m throughout 10km solution: reconfigurable array => Rover-Borne antennas (new approach w.r.t. ESA or EADS studies) PROs: –it allows to deploy antennas from the lander to the wanted position with the wanted attitude. –flexibility –it allows to re-deploy the antennas in different configurations of larger and larger sizeLIGHTWEIGHT!!! E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Rover-Borne Stations Station =Station = telescope (dipole + electronics) + rover telescope (dipole + electronics) + rover Mass station: 5-6 kg  10 stations stay within mass requirements E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

A “walking” experiment reconfigurable array: first the 10 antennas realize the most compact core and observe the sky with this configuration;... and so on for a number of steps until the 10km baselines are set so to realize the full array 6 steps: D max = 30m, 100m, 300m, 1km, 3km, 10km then: antennas are moved to longer distances to realize a larger configuration and observe the sky; E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Where Far side of the Moon: Earth is shielded => RFI fully mitigated Lunar latitude: within the range 30°- 60° E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Operations observing frequencies: –3, 6, 12, 25, 50, 100 MHz –3, 4.5, 7, 10, 15, 22, 30 MHz lunar night observations – Sun is too strong ! observations all lunar night long, for optimal angular frequency space coverage 1 array configuration a lunar night 1 lunar day (= 1 month) observing cycle: –6 months to realize D max = 30m, 100m, 300m, 1km, 3km, 10km E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Operations (2) Station data must be correlated for each station pair Data must be collected by one processing station. Two possible solutions: –one master station (central one); –orbiter. Communications to Earth: only once a month (simple and cheap mission control) E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Science with WARP Walking Array Radio Pathfinder (WARP): –subdegree Galactic diffuse emission –relativistic electron age, confinement and diffusion processes, magnetic field –New SNR: oldest visible at low freq only (high res to separate them from diffuse em.) –Micro quasars (e.g. SS433): no lobes. Why? old, or p + ? –Extragalactic sources: all 3C catalogue: spectrum, lowest energy e -, evolution history; free-free absorption: W-IGM synchrotron self-absorption: direct measurement of B, n e –galaxy-cluster halos and relics... but... most important.... it is an unexplored window: hunt for new sources and astrophysical (and physical) processes fully unknown so far. E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Conclusions To open a NEW window in astrophysics.To open a NEW window in astrophysics. High interest of the scientific community (e.g. ESA and EADS studies for experiments in this frequency band). Instrument: a simple, easy, well developed technology: No “critical” developments required FLEXIBILITYNew approach based on a Rover-borne experiment: FLEXIBILITY Safe against failure of one/more stations Many-stations array realized with “few” stations Lightweight payload. E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

Conclusions (2) ESA studies for a lunar experiment in such band WARP: unique opportunity for the italian community (astrophysics + space engineering) to earn experience and be candidate to lead the European mission. A rover colony getting around on the lunar surface: high impact for the Italian System –italian space industry; –italian engineer research; –italian astrophysics research; –visibility; –italian space technology capabilities. E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007