What's New with the �Expanded Owens Valley Solar Array?

Dale E. Gary, Bin Chen, Gregory D. Fleishman,

Gelu M. Nita, Sijie Yu, Surajit Mondal

Center for Solar-Terrestrial Research

New Jersey Institute of Technology

Sphere Meeting 2022, Boulder, CO

07/12/2022

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Outline

• Science Highlights
• Recent Observations of Interest
• Current Status
• New Observing Mode
• Get Involved

Sphere Meeting 2022, Boulder, CO

07/12/2022

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EOVSA is operating well—now as a Geosciences Facility!

Sphere Meeting 2022, Boulder, CO

07/12/2022

13-antenna interferometer array operating over frequency range 1-18 GHz

Provides dynamic (1 s) “imaging spectroscopy” (>100 frequencies)

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Scary Fire Started February 16, 2022

Sphere Meeting 2022, Boulder, CO

07/12/2022

No telescope or building damage, but the power outage caused three computers to have disk failures.

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Science Highlights

• Recall earlier results on magnetic field measurements
• Fleishman et al. (2020) Science
• Chen et al.(2020) Nature Astronomy

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• Latest paper in Nature (Fleishman et al. 2022) follows up with electron energy distribution

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Sphere Meeting 2022, Boulder, CO

07/12/2022

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Region of ~100% Acceleration

Sphere Meeting 2022, Boulder, CO

07/12/2022

Fleishman et al. (2020) Science

Fleishman et al. (2022) Nature

The same region with the rapid decrease in B (rapid release of magnetic energy) is able to accelerate ~all electrons in this large region. This is a second, and dominant, location for energy release.

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X1.3 Event of 2022 Mar 30

Sphere Meeting 2022, Boulder, CO

07/12/2022

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Peak Timing and Peak-to-Peak Delay

• The time between peaks is clearly increasing, from about 5 to 15 s.

Sphere Meeting 2022, Boulder, CO

07/12/2022

T_b at 9 GHz from pixel at (491", 325")

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Location of Oscillation

• The 9 GHz source is essentially stationary all during the oscillations.
• This shows 98% contours on the left, and 50% contours on the right, with the colors time-coded from blue to red, of 80 maps (80 s of time corresponding to the red box).

Sphere Meeting 2022, Boulder, CO

07/12/2022

98% contours 50% contours

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Peak Location vs. Frequency

• There is a significant shift of position with frequency, with a clear shift to the north (toward higher B field).
• These are 70% contours ranging from 3.8 GHz (red) to 14.6 GHz (blue).
• Conclusion, oscillations are from a single loop, and they involve the entire loop length.

Sphere Meeting 2022, Boulder, CO

07/12/2022

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Another Interesting Event (2022-03-31 M9 Flare)

• Coherent emission in the 4-6 GHz range. 6 GHz => n_e = 10¹¹ (2^nd harmonic) or 4x10¹¹ cm^-3 (fundamental)
• Frequency oscillations in some of the short-lived features => zebra pattern burst(?) at 6+ GHz!

Sphere Meeting 2022, Boulder, CO

07/12/2022

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Interpretation (rough!)

• The frequency separation between peaks is very regular.

Sphere Meeting 2022, Boulder, CO

07/12/2022

Kuznetsov & Tsap (2007)

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Current Status

• We are observing every day. Daily coverage can be quickly seen at our browser: http://ovsa.njit.edu/browser.
• Aging infrastructure impact
• The code for accessing raw data and performing the calibrations has been ported to Python 3, and we are in the process of making the calibration database available via a cloud-based service, so that calibration can be done from anywhere.
• We have a flare pipeline under development that can do a decent job of automated self-calibration and flare imaging.
• We have a "user forum" slack workspace. If anyone is not already on it and would like to be, please email me (dgary@njit.edu).

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Sphere Meeting 2022, Boulder, CO

07/12/2022

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New "Fast" Observing Mode (Thanks Jim McTiernan)

• The normal EOVSA observing mode is to sample each of our 50 bands (325 MHz) for 20 ms in frequency order, taking 1 s to cover the entire 1-18 GHz range.
• We now have a "fast" mode where we can dwell on one band and take data at 20 ms rate.
• We caught one flare in an early test run.

Sphere Meeting 2022, Boulder, CO

07/12/2022

Switch to fast mode here

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New "Fast" Observing Mode

• Total power in band 1 (lowest)

Sphere Meeting 2022, Boulder, CO

07/12/2022

30 "science bands"

30000 time samples in 10 min

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Current Fast Mode Capabilities

• The example I showed was a test. We now have additional capabilities:
• Not limited to 30 frequencies but can sample up to 128 frequencies (in a 325 MHz band).
• Can dwell for the entire 1-s cycle on a given band, or dwell on one band for part of the 1-s cycle and sample other frequencies at "normal" cadence (but entire sequence must finish in 1 s).
• Example: sample 128 frequencies in one band for 0.8 s and sample 10 other frequencies at normal 20 ms each to characterize the broader spectrum.
• Control software allows switching to fast mode within 10 s of "flare trigger."
• We can, of course, image each individual frequency-time bin to image rapid frequency/time structure.
• We have NOT worked out calibration strategies yet, however: We are looking for people to propose observations in this mode, who will take "ownership" of the data and help us work out calibration and imaging strategies.

Sphere Meeting 2022, Boulder, CO

07/12/2022

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Get Involved

• EOVSA is really revolutionizing our access to information on the high-energy component of flares and the flaring environment.
• Our biggest impediment by far is the small number of people working with it!
• Our data are completely open, and we STRONGLY encourage everyone to start working with the data. There is a learning curve, but the more people work on it the easier it becomes for everyone. Please come to the EOVSA tutorial this afternoon (3:30-5:00 pm MT).
• EOVSA is a tiny taste of the true capabilities of radio imaging spectroscopy. We are currently engaged in refreshing the design of the future Frequency Agile Solar Radiotelescope (FASR), and we invite you all to join and endorse our decadal survey white papers. See Bin Chen's talk on Thursday.

Sphere Meeting 2022, Boulder, CO

07/12/2022

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OVRO Long Wavelength Array (new capabilities)

Sphere Meeting 2022, Boulder, CO

07/12/2022

Typical type III storm on the left, but at 25 ms resolution (right), we can see amazing detail. Imaging is coming!

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