The HEROES Mission: High Energy Replicated Optics to Explore the Sun

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Revision as of 19:13, 27 October 2013

Introduction

The High Energy Replicated Optics to Explore the Sun (HEROES) mission is a collaborative effort between the NASA Marshall Space Flight Center and the Goddard Space Flight Center to upgrade an existing payload, the High Energy Replicated Optics (HERO) balloon-borne telescope, to make unique scientific measurements of the Sun and astrophysical targets during the same flight. On September 22nd, 2013, HEROES was launched successfully from Fort Sumner, NM. HEROES remained at float altitudes for a total of 21 hours and spent a total of 7 consecutive hours observing the Sun. This nugget is a summary of the flight. A future nugget will discuss the science results from this flight.

HEROES was funded by the NASA HOPE (Hands On Project Experience) Training Opportunity awarded by the NASA Academy of Program/Project and Engineering Leadership, in partnership with NASA's Science Mission Directorate, Office of the Chief Engineer and Office of the Chief Technologist. HOPE is a one-year program to provide early-career NASA civil servants experience on a flight program from conception to actual flight. In practice, HOPE participants develop, build, and fly an instrument on a sub-orbital program while maintaining similar standards and reviews to a large scale flight mission.

Background

The HEROES science payload is a hard X-ray telescope. Similar to FOXSI, HEROES uses MSFC-developped grazing incidence optics. The telescopes consists of 8 mirror modules, housing a total of 109 grazing-incidence optics. These modules are mounted on a carbon-fiber and Aluminum optical bench 6 m from a matching array of high pressure xenon gas scintillation proportional counters, which serve as the focal-plane detectors. The HEROES gondola utilizes a differential GPS system (backed by a magnetometer) for coarse pointing in the azimuth and a shaft angle encoder plus inclinometer provides the coarse elevation. The HEROES payload will incorporate a new solar aspect system to supplement the existing star camera, for fine pointing during both the day and night. The overall payload will be discussed as well as the new solar aspect system.

Science Goals

The solar science objectives for this flight were

• Investigate electron acceleration in the non-flaring solar corona by searching for the hard X-ray signature of energetic electrons.
• Investigate the acceleration and transport of energetic electrons in solar flares.

Since the Sun does eventually set, HEROES also had astrophysical science objectives.

• Investigate the scale of high energy processes in a pulsar wind nebula.
• Investigate the hard X-ray properties of astrophysical targets such as X-ray binaries and active galactic nuclei.

Solar Aspect System

The original HERO payload has flown several times already, most recently in 2011 from Alice Springs, Australia to observe the Crab Nebula under the leadership of Dr. B. Ramsey. To point to astrophysical targets, the HEROES payload makes use of a sensitive star camera which identifies star fields in real-time with sub-arcminute accuracy. Unfortunately this aspect system cannot be used to point to the Sun because it would be blinded, possibly damaged, and confused by the bright and resolved Sun. We therefore developed a solar aspect system (SAS) to add to the HEROES payload to provide solar pointing ability and knowledge. The original conception of the SAS must credit the aspect system being developed for the The Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) another balloon payload. The HEROES SAS consists of the

Solar Observations

Time scales and Correlations

In our conventional view of the sources of flare energy, we turn to the magnetic field in the corona. But it is the low corona, in active regions, that contains the bulk of the energy, and this appears above the photosphere only when flux emerges from the interior. Now we need to consider characteristic scales of space and time on the Sun. In the photosphere, the convective motions are organized into granulation and supergranulation, the latter also the source of the chromospheric network. The time/distance scales for these features are roughly 10 min/1000 km and 1 day/30,000 km respectively.

Now consider the occurrence pattern of the Halloween flares of 2003 and 2013, as illustrated in Figure 1. The major flares occur in each case on spatial and temporal scales quite inconsistent with what we see in the photosphere. Therefore it seems likely that some slowly-developing, large-scale structure in the deep interior - the legendary solar dynamo process - must be responsible.

Fig. 1: The active regions responsible for the major flares of October 2003 and 2013, respectively, obtained from SolarMonitor. In 2003 three regions independently produced X-class flares, and in 2013 one did; the other circle in the right shows the source of an M9.3 almost-X flare, again in an independent region.

These flaring patterns suggest that clues to the nature of the dynamo could come from an assessment of its time/space structure as an eigenmode problem, based on patterns like these. Note that the organization of the coordinated eruptions crosses the equator in the case of the 2003 Halloween flares. This had been suggested in Ref. [1], but so far as we're aware there is no parallel work on the flare distributions. Patterns of coherence have also been remarked upon in terms of Svalgaard's "Hale sector" pattern; were the 2003 Halloween flares - though in both hemispheres - within the same sector?

The October flares themselves are shown here as GOES records in Figure 2. The dashed line shows the X-flare threshold. Note that appearances on a logarithmic plot can be a bit misleading; the mean flux level in 2003 was a factor of 4-5 higher than in 2013..

Fig. 2: Month-long plots of solar X-ray flux from the GOES soft X-ray measurements. The 2003 data (blue) have been translated in time to match. The horizontal dotted line shows the X-class level; the 2003 activity went on beyond November, for example producing the colossal flare SOL2003-11-04.

Conclusions

We have pointed out another feature of the large-scale organization of the solar magnetic field, namely the intense energy it transports and delivers to solar flares. These have extremely short time scales, and yet they occur in structured patterns across space and time, something known since the sunspot cycle and butterfly diagram were first recognized (see also a Yohkoh Science Nugget on a related topic.

References

[1] "Global Wave Patterns in the Sun's Magnetic Field"