SH043-0002
Limits on the X-ray emission of the quiet Sun from the FOXSI sounding rockets
Tuesday, 15 December 2020
Poster
Juan Camilo Buitrago-Casas1, Lindsay Glesener2, Steven Christe3, Sam Krucker4, Juliana Therese Vievering5, P. S. Athiray5, Sophie Musset6, Daniel Ryan3, Shin-nosuke Ishikawa7, Noriyuki Narukage8, Stephen Bongiorno9, Kento Furukawa10, Brian Ramsey9, Lance Davis11, Sasha Courtade12, Gregory Dalton13, Paul Turin13, Zoe Turin14, Tadayuki Takahashi15, Shin Watanabe15, Ikuyuki Mitsuishi16, Kouichi Hagino17 and Jessie McBrayer Duncan11, (1)University of California Berkeley, Berkeley, CA, United States, (2)University of Minnesota, Twin Cities, MN, United States, (3)NASA GSFC, Solar Physics Lab, Greenbelt, MD, United States, (4)UC Berkeley, Space Science Lab, Berkeley, CA, United States, (5)University of Minnesota, Minneapolis, MN, United States, (6)University of Minnesota, Minneapolis, United States, (7)National Astronomical Observatory, Mitaka, Japan, (8)Washington, DC, United States, (9)NASA Marshall Space Flight Center, Huntsville, AL, United States, (10)University of Tokyo, Tokyo, Japan, (11)University of Minnesota Twin Cities, Minneapolis, MN, United States, (12)University of California, Berkeley, Space Sciences Laboratory, Berkeley, CA, United States, (13)University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, United States, (14)Georgia Tech Research Institute, Atlanta, GA, United States, (15)ISAS Institute of Space and Astronautical Science, Kanagawa, Japan, (16)Nagoya University, Nagoya, Japan, (17)Tokyo University of Science, Tokyo, Japan
Abstract:
Nanoflares are a potential solution for the coronal heating problem. In the quiet Sun, nanoflares should exhibit hard X-ray (HXR) signatures manifested to an observer via either i) a single HXR kernel or ii) HXRs from many flares spread all over the Sun. In both cases, detecting nanoflare HXRs requires an instrument with superior dynamic range and sensitivity in the ~4 to 15 keV energy range over previous solar dedicated HXR telescopes, like RHESSI. The Focusing Optics X-ray Solar Imager (FOXSI) fulfills these requirements. FOXSI has successfully flown on three sounding rocket campaigns; the last two (FOXSI-2 and -3) included the observation of quiet areas of the solar disk. For FOXSI-3, several techniques were tested and developed to minimize a background effect unique to hard X-ray focusing optics, frequently referred to as ghost rays.
In this presentation, we provide, for the first time, a FOXSI sounding rocket assessment of the HXR flux from the quiet Sun. To fully characterize the sensitivity of FOXSI, we assessed ghost rays generated by sources outside of the field of view via a ray-tracing algorithm. This is particularly important for observations from FOXSI-2 when techniques to minimize ghost rays were not implemented yet. Using the ray tracing tool, we identify areas free of ghost rays that contribute to the background and therefore have maximum sensitivity to quiet Sun HXR emission. We use a bayesian approach to provide upper thresholds of quiet Sun HXR emission and probability distributions for the expected flux when a quiet-Sun HXR source is assumed to exist. We compare this result with prior constraints such as that made by RHESSI (Hannah et al. 2010).
