The Imaging Magnetograph eXperiment (IMaX) is one of the post-focus instruments of the one-meter solar telescope aboard the Sunrise mission. The latter is a stratospheric balloon mission that has been studying the Sun while flying above the Arctic (from Kiruna in Sweeden all the way to Canada). The mission is a collaboration between Germany (through its space agency, DLR and the Max Planck Institut für Sonnensystemforschung [MPS], which acts as the leader institution, and the Kiepenheuer Institut für Sonnenphysik [KIS]), the USA (through its space agency, NASA, the High Altitude Observatory [HAO-NCAR], and the Lockheed-Martin Solar and Astrophysics Laboratory [LMSAL]), and Spain (through its national space program, PNE, the Instituto de Astrofísica de Canarias [IAC], the Instituto Nacional de Técnica Aerospacial [INTA], the Grupo de Astronomía y Ciencias del Espacio [GACE], and the Instituto de Astrofísica de Andalucía [IAA-CSIC]). The Spanish contribution to the project is the IMaX magnetograph. This instrument has provided information about the solar magnetic fields with unprecedented quality: it has combined high temporal cadence and polarimetric precision while preserving the bidimensional integrity of high-resolution images.

IMaX uses liquid crystal variable retarders (LCVRs) as a polarization modulator, a Fabry-Pérot étalon as a spectrum analyzer, and two CCD cameras as detectors. The four Stokes parameters I, Q, U, and V (full vector polarimetry) or just two (I and V; longitudinal magnetography) of the Fe I line at 525.02 nm has typically measured at four (two) wavelength samples plus one in the continuum nearby but other modes were also available. This spectropolarimetric information is interpreted in terms of the magnetic and dynamic properties of the Sun.

Science drivers for IMaX

Sunrise (and IMaX as part of the whole experiment) studied the solar magnetism, with the aim of helping to answer the following key questions:

• What are the origin and the properties of the intermittent magnetic structure?  
• How does the magnetic field provide energy to the upper solar atmosphere?
• How is the magnetic field brought up and removed from the solar surface?
• How does the variable magnetic field modify the solar brightness?

IMaX, among all the instruments aboard SUNRISE, provides the best temporal resolution (the vector magnetic field will be determined every few tens of a second). This high temporal cadence is needed to study phenomena occurring on the Sun at very short temporal scales (for instance, the formation of kG flux tubes) and the propagation of MHD waves. Also important is the fact that the Sun was observed during ~ 5 days during the two flights, under conditions which are far more stable than at the ground. Only after these long observational sequences, the natural temporal scales of magnetic field appearance and disappearance will become clear.

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