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Register a new userFlame-like Ellerman Bombs and Their Connection to Solar UV Bursts
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Ellerman bombs (EBs) are small-scale intense brightenings in H$alpha$ wing images, which are generally believed to be signatures of magnetic reconnection events around the temperature minimum region of the solar atmosphere. They have a flame-like morphology when observed near the solar limb. Recent observations from the Interface Region Imaging Spectrograph (IRIS) reveal another type of small-scale reconnection events, termed UV bursts, in the lower atmosphere. Though previous observations have shown a clear coincidence of some UV bursts and EBs, the exact relationship between these two phenomena is still under debate. We investigate the spatial and temporal relationship between flame-like EBs and UV bursts using joint near-limb observations between the 1.6--meter Goode Solar Telescope (GST) and IRIS. In total 161 EBs have been identified from the GST observations, and 20 of them reveal signatures of UV bursts in the IRIS images. Interestingly, we find that these UV bursts have a tendency to appear at the upper parts of their associated flame-like EBs. The intensity variations of most EB-related UV bursts and their corresponding EBs match well. Our results suggest that these UV bursts and EBs are likely formed at different heights during a common reconnection process.
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Ellerman bombs (EBs) and UV bursts are both brightenings related to flux emergence regions and specifically to magnetic flux of opposite polarity that meet in the photosphere. These two reconnection-related phenomena, nominally formed far apart, occasionally occur in the same location and at the same time, thus challenging our understanding of reconnection and heating of the lower solar atmosphere. We consider the formation of an active region, including long fibrils and hot and dense coronal plasma. The emergence of a untwisted magnetic flux sheet, injected $2.5$~Mm below the photosphere, is studied as it pierces the photosphere and interacts with the preexisting ambient field. Specifically, we aim to study whether EBs and UV bursts are generated as a result of such flux emergence and examine their physical relationship. The Bifrost radiative magnetohydrodynamics code was used to model flux emerging into a model atmosphere that contained a fairly strong ambient field, constraining the emerging field to a limited volume wherein multiple reconnection events occur as the field breaks through the photosphere and expands into the outer atmosphere. Synthetic spectra of the different reconnection events were computed using the $1.5$D RH code and the fully 3D MULTI3D code. The formation of UV bursts and EBs at intensities and with line profiles that are highly reminiscent of observed spectra are understood to be a result of the reconnection of emerging flux with itself in a long-lasting current sheet that extends over several scale heights through the chromosphere. Synthetic diagnostics suggest that there are no compelling reasons to assume that UV bursts occur in the photosphere. Instead, EBs and UV bursts are occasionally formed at opposite ends of a long current sheet that resides in an extended bubble of cool gas.
Ellerman bombs (EBs) and UV bursts are both small-scale solar activities that occur in active regions. They are now believed to form at different heights in the lower atmosphere. In this paper, we use one-dimensional radiative hydrodynamic simulations to calculate various line profiles in response to heating in different atmospheric layers. We confirm that heating in the upper photosphere to the lower chromosphere can generate spectral features of typical EBs, while heating in the mid to upper chromosphere can generate spectral features of typical UV bursts. The intensity evolution of the H$alpha$ line wing in EBs shows a rise--plateau pattern, while that of the Si IV 1403 r{A} line center in UV bursts shows a rise--fall pattern. However, the predicted enhancement of FUV continuum near 1400 r{A} for EBs is rarely reported and requires further observations to check it. With two heating sources or an extended heating source in the atmosphere, both EB and UV burst features could be reproduced simultaneously.
Recent observations from the Interface Region Imaging Spectrograph (IRIS) appear to show impulsive brightenings in high temperature lines, which when combined with simultaneous ground based observations in H$alpha$, appear co-spatial to Ellerman Bombs (EBs). We use the RADYN 1-dimensional radiative transfer code in an attempt to try and reproduce the observed line profiles and simulate the atmospheric conditions of these events. Combined with the MULTI/RH line synthesis codes, we compute the H$alpha$, Ca II 8542~AA, and Mg II h & k lines for these simulated events and compare them to previous observations. Our findings hint that the presence of superheated regions in the photosphere ($>$10,000 K) is not a plausible explanation for the production of EB signatures. While we are able to recreate EB-like line profiles in H$alpha$, Ca II 8542~AA, and Mg II h & k, we cannot achieve agreement with all of these simultaneously.
Ellerman Bombs (EBs) are often found co-spatial with bipolar photospheric magnetic fields. We use H$alpha$ imaging spectroscopy along with Fe I 6302.5 AA spectro-polarimetry from the Swedish 1-m Solar Telescope (SST), combined with data from the Solar Dynamic Observatory (SDO) to study EBs and the evolution of the local magnetic fields at EB locations. The EBs are found via an EB detection and tracking algorithm. We find, using NICOLE
The presence of photospheric magnetic reconnection has long been thought to give rise to short and impulsive events, such as Ellerman bombs (EBs) and Type II spicules. In this article, we combine high-resolution, high-cadence observations from the Interferometric BIdimensional Spectrometer (IBIS) and Rapid Oscillations in the Solar Atmosphere (ROSA) instruments at the Dunn Solar Telescope, National Solar Observatory, New Mexico with co-aligned Atmospheric Imaging Assembly (SDO/AIA) and Solar Optical Telescope (Hinode/SOT) data to observe small-scale events situated within an active region. These data are then compared with state-of-the-art numerical simulations of the lower atmosphere made using the MURaM code. It is found that brightenings, in both the observations and the simulations, of the wings of the H alpha line profile, interpreted as EBs, are often spatially correlated with increases in the intensity of the FeI 6302.5A line core. Bi-polar regions inferred from Hinode/SOT magnetic field data show evidence of flux cancellation associated, co-spatially, with these EBs, suggesting magnetic reconnection could be a driver of these high-energy events. Through the analysis of similar events in the simulated lower atmosphere, we are able to infer that line profiles analogous to the observations occur co-spatially with regions of strong opposite polarity magnetic flux. These observed events and their simulated counterparts are interpreted as evidence of photospheric magnetic reconnection at scales observable using current observational instrumentation.
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