E-Print Archive

There are 4291 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
* News 04/04/20 * The archive is using a new backend database. This has thrown up a few SQL errors in the last few days. If you have any issues please email adavey@nso.edu with either the number of eprint you are trying to edit or a link to your preprint.

Radio and X-ray Observations of Short-lived Episodes of Electron Acceleration in a Solar Microflare  

Rohit Sharma   Submitted: 2020-10-01 05:48

Solar flares are sudden energy release events in the solar corona, resulting from magnetic reconnection, that accelerates particles and heats the ambient plasma. During a flare, there are often multiple, temporally and spatially separated individual energy release episodes that can be difficult to resolve depending on the observing instrument. We present multi-wavelength imaging and spectroscopy observations of multiple electron acceleration episodes during a GOES B1.7-class two-ribbon flare on 2012 February 25, observed simultaneously with the Karl G. Jansky Very Large Array (VLA) at 1-2 GHz, the Reuven Ramatay High Energy Solar Spectroscopic Imager (RHESSI) in X-rays, and the Solar Dynamics Observatory in extreme ultraviolet (EUV). During the initial phase of the flare, five radio bursts were observed. A nonthermal X-ray source was seen co-temporal, but not co-spatial, with the first three radio bursts. Their radio spectra are interpreted as optically thick gyrosynchrotron emission. By fitting the radio spectra with a gyrosynchrotron model, we derive the magnetic field strength and nonthermal electron spectral parameters in each acceleration episode. Notably, the nonthermal parameters derived from X-rays differ considerably from the nonthermal parameters inferred from the radio. The observations are indicative of multiple, co-temporal acceleration episodes during the impulsive phase of a solar microflare. The X-ray and radio burst sources likely originate from separate electron distributions in different magnetic loops.

Authors: Rohit Sharma, Marina Battaglia, Yingjie Luo, Bin Chen, Sijie Yu
Projects: None

Publication Status: Accepted in ApJ 29th September 2020
Last Modified: 2020-10-07 10:17
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Propagation Effects in Quiet Sun Observations at Meter Wavelengths  

Rohit Sharma   Submitted: 2020-09-23 00:38

Quiet sun meterwave emission arises from thermal bremsstrahlung in the MK corona, and can potentially be a rich source of coronal diagnostics. On its way to the observer, it gets modified substantially due to the propagation effects - primarily refraction and scattering - through the magnetized and turbulent coronal medium, leading to the redistribution of the intensity in the image plane. By comparing the full-disk meterwave solar maps during a quiet solar period and the modelled thermal bremsstrahlung emission, we characterise these propagation effects. The solar radio maps between 100 and 240 MHz come from the Murchison Widefield Array. FORWARD package is used to simulate thermal bremsstrahlung images using the self-consistent Magnetohydrodynamic Algorithm outside a Sphere coronal model. The FORWARD model does not include propagation effects. The differences between the observed and modelled maps are interpreted to arise due to scattering and refraction. There is a good general correspondence between the predicted and observed brightness distributions, though significant differences are also observed. We find clear evidence for the presence of significant propagation effects, including anisotropic scattering. The observed radio size of the Sun is 25-30% larger in area. The emission peak corresponding to the only visible active region shifts by 8'-11' and its size increases by 35-40%. Our simple models suggest that the fraction of scattered flux density is always larger than a few tens of percent, and varies significantly between different regions. We estimate density inhomogeneities to be in the range 1-10%.

Authors: Rohit Sharma and Divya Oberoi
Projects: None

Publication Status: Accepted in ApJ 15th September 2020
Last Modified: 2020-09-23 13:11
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Estimating Solar Flux Density at Low Radio Frequencies Using a Sky Brightness Model  

Rohit Sharma   Submitted: 2017-05-31 09:59

Sky models have been used in the past to calibrate individual low radio frequency telescopes. In this article, we generalize this approach from a single antenna to a two element interferometer, and formulate the problem in a way that allows us to estimate the flux density of the Sun using the normalized cross-correlations (visibilities) measured on a low resolution interferometric baseline. For wide field-of-view instruments, typically the case at low radio frequencies, this approach can provide robust absolute solar flux calibration for well characterized antennas and receiver systems. It can provide a reliable and computationally lean method for extracting parameters of physical interest using a small fraction of the voluminous interferometric data, which can be computationally prohibitively expensive to calibrate and image using conventional approaches. We demonstrate this technique by applying it to data from the Murchison Widefield Array and assess its reliability.

Authors: Divya Oberoi, Rohit Sharma and Alan E.E. Rogers
Projects: None

Publication Status: Published in Solar Physics, 30th May 2017
Last Modified: 2017-05-31 13:49
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

On the Bright Loop Top Emission in Post Eruption Arcades  

Rohit Sharma   Submitted: 2016-03-16 21:26

The observations of post eruption arcades (PEAs) in X-rays and EUV reveal strong localised brightenings at the loop top regions. The origin of these brightenings and their dynamics is not well understood to date. Here, we study the dynamics of PEAs using one-dimensional hydrodynamic modelling with the focus on the the understanding of the formation of localised brightening.Our findings suggest that these brightenings are the result of collisions between the counter-streaming chromospheric evaporation from both the foot points. We further perform forward modelling of the emission observed in simulated results in various spectral lines observed by the Extreme-Ultraviolet Imaging Telescope aboard Hinode. The forward modelled intensities in various spectral lines are in close agreement with a flare observed in December 17, 2006 by EIS.

Authors: Rohit Sharma, Durgesh Tripathi, Hiroaki Isobe, Avyarthana Ghosh
Projects: None

Publication Status: Accepted by ApJ
Last Modified: 2016-03-21 15:33
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 


Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
Radio and X-ray Observations of Short-lived Episodes of Electron Acceleration in a Solar Microflare
Propagation Effects in Quiet Sun Observations at Meter Wavelengths
Estimating Solar Flux Density at Low Radio Frequencies Using a Sky Brightness Model
On the Bright Loop Top Emission in Post Eruption Arcades

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2000-2020 Solar Physics Group - Montana State University