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Abstract Even small solar flares can display a surprising level of complexity regarding their morphology and temporal evolution. Many of their properties, such as energy release and electron acceleration can be studied using highly complementary observations at X-ray and radio wavelengths. We present X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager and radio observations from the Karl G. Jansky Very Large Array (VLA) of a series of GOES A3.4–B1.6 class flares observed on 2013 April 23. The flares, as seen in X-ray and extreme ultraviolet, originated from multiple locations within active region NOAA 11726. A veritable zoo of different radio emissions between 1 GHz and 2 GHz was observed cotemporally with the X-ray flares. In addition to broadband continuum emission, broadband short-lived bursts and narrowband spikes, indicative of accelerated electrons, were observed. However, these sources were located up to 150″ away from the flaring X-ray sources but only some of these emissions could be explained as signatures of electrons that were accelerated near the main flare site. For other sources, no obvious magnetic connection to the main flare site could be found. These emissions likely originate from secondary acceleration sites triggered by the flare, but may be due to reconnection and acceleration completely unrelated to the cotemporally observed flare. Thanks to the extremely high sensitivity of the VLA, not achieved with current X-ray instrumentation, it is shown that particle acceleration happens frequently and at multiple locations within a flaring active region.
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Multiple Regions of Nonthermal Quasiperiodic Pulsations during the Impulsive Phase of a Solar Flare
Abstract Flare-associated quasiperiodic pulsations (QPPs) in radio and X-ray wavelengths, particularly those related to nonthermal electrons, contain important information about the energy release and transport processes during flares. However, the paucity of spatially resolved observations of such QPPs with a fast time cadence has been an obstacle for us to further understand their physical nature. Here, we report observations of such a QPP event that occurred during the impulsive phase of a C1.8-class eruptive solar flare using radio imaging spectroscopy data from the Karl G. Jansky Very Large Array (VLA) and complementary X-ray imaging and spectroscopy data. The radio QPPs, observed by the VLA in the 1–2 GHz with a subsecond cadence, are shown as three spatially distinct sources with different physical characteristics. Two radio sources are located near the conjugate footpoints of the erupting magnetic flux rope with opposite senses of polarization. One of the sources displays a QPP behavior with a ∼5 s period. The third radio source, located at the top of the postflare arcade, coincides with the location of an X-ray source and shares a similar period of ∼25–45 s. We show that the two oppositely polarized radio sources are likely due to coherent electron cyclotron maser emission. On the other hand, the looptop QPP source, observed in both radio and X-rays, is consistent with incoherent gyrosynchrotron and bremsstrahlung emission, respectively. We conclude that the concurrent, but spatially distinct QPP sources must involve multiple mechanisms which operate in different magnetic loop systems and at different periods.
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- Award ID(s):
- 1654382
- PAR ID:
- 10382670
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 940
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 137
- Size(s):
- Article No. 137
- Sponsoring Org:
- National Science Foundation
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