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RHESSI and STIX

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Hard X-Ray Imaging of Solar Flares

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Abstract

In this chapter we describe the design features of the RHESSI and STIX instruments, both of which use bi-grid modulation collimators pointed at the Sun to obtain information that can be used to make X-ray images. The difference is that RHESSI is on a rapidly rotating spacecraft while STIX is on a 3-axis stabilized spacecraft. We describe the manner in which imaging information is encoded by the bi-grid collimators and the strengths and limitations of the two imaging concepts necessitated by the different spacecraft motions. We also describe the software that has been developed to transform the raw data collected into higher-level products useful for scientific studies. We illustrate the power of such imaging techniques using an example solar flare.

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Notes

  1. 1.

    Solar flares can be classified in many ways. One of the most common uses the observed flux in the 0.1–0.8 nm “soft” X-ray range, as observed by the series of Geostationary Operational Environmental Satellites (GOES). Similar to the Richter scale for earthquakes, the classification scale is logarithmic: A-class events have fluxes less than 10−7 Watts per square meter (W m−2), B-class events have fluxes between 10−7 and 10−6 W m−2, C-class events have fluxes between 10−6 and 10−5 W m−2, M-class events have fluxes between 10−5 and 10−4 W m−2, and X-class events have fluxes exceeding 10−4 W m−2. Within each class, a number indicates the multiplier of the lowest flux appropriate to that classification; for example, an M5 event has a 0.1–0.8 nm flux of 5 × 10−5 W m−2. The most intense flare recorded by GOES in the RHESSI era was an X28 event (with an 0.1–0.8 nm flux of 28 × 10−4 = 2.8 × 10−3 W m−2) that occurred on 2003 November 4.

  2. 2.

    The above analysis applies when the occulting grids have exactly equal slit and slat widths; then only odd cosine harmonics are present. For unequal slit/slat widths, the Fourier expansion includes even cosine harmonics as well.

  3. 3.

    https://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/RHESSI_Visibilities.

  4. 4.

    https://hesperia.gsfc.nasa.gov/rhessi3/software/spectroscopy/spectral-analysis-software/index.html.

  5. 5.

    Detailed documentation, including instructions for installing SSW, is available online at https://hesperia.gsfc.nasa.gov/rhessi/software/installation/index.html. Information on how to access and use all RHESSI data and software is available at https://hesperia.gsfc.nasa.gov/rhessi/.

  6. 6.

    The original name for RHESSI was HESSI. The leading “R” was added shortly after launch in tribute to Reuven Ramaty, one of the pioneers of gamma-ray astronomy and a major contributor to establishing the scientific justification for RHESSI’s high resolution gamma-ray spectroscopy. Sadly, he died just months before RHESSI was launched.

  7. 7.

    The four pixels in each detector are numbered as −2, −1, 0 and 1, so that the quantity e iπn∕2, used in the sequel, takes on the purely real or imaginary values −1, − i, 1, and i.

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Authors and Affiliations

  1. The MIDA Group, Dipartimento di Matematica, Università di Genova and CNR - SPIN Genova, Genova, Italy

    Michele Piana & Anna Maria Massone

  2. Department of Physics & Astronomy, Western Kentucky University, Bowling Green, KY, USA

    A. Gordon Emslie

  3. Solar Physics Laboratory, Code 671, Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA

    Brian R. Dennis

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  1. Michele Piana
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  3. Anna Maria Massone
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  4. Brian R. Dennis
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Piana, M., Emslie, A.G., Massone, A.M., Dennis, B.R. (2022). RHESSI and STIX . In: Hard X-Ray Imaging of Solar Flares. Springer, Cham. https://doi.org/10.1007/978-3-030-87277-9_3

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  • DOI: https://doi.org/10.1007/978-3-030-87277-9_3

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