# Solar Ultraviolet Bursts in a Coordinated Observation of IRIS, Hinode and SDO

## TL;DR

This study investigates small-scale solar UV bursts using coordinated IRIS, Hinode, and SDO observations, revealing their spectral, magnetic, and plasma flow properties with no significant coronal signatures.

## Contribution

It provides the first detailed analysis of UV burst properties combining multi-instrument observations and magnetic field modeling.

## Key findings

- Most UV bursts show small blueshifts in Ni II lines.
- One UV burst exhibits redshifts indicating cold plasma downflows.
- UV bursts are associated with magnetic null points or bald patches.

## Abstract

Solar ultraviolet (UV) bursts are small-scale compact brightenings in transition region images. The spectral profiles of transition region lines in these bursts are significantly enhanced and broadened, often with chromospheric absorption lines such as Ni~{\sc{ii}} 1335.203 and 1393.330 {\AA} superimposed. We investigate the properties of several UV bursts using a coordinated observation of the Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory (SDO), and \textit{Hinode} on 2015 February 7. We have identified 12 UV bursts, and 11 of them reveal small blueshifts of the Ni~{\sc{ii}} absorption lines. However, the Ni~{\sc{ii}} lines in one UV burst exhibit obvious redshifts of $\sim$20 km s$^{-1}$, which appear to be related to the cold plasma downflows observed in the IRIS slit-jaw images. We also examine the three-dimensional magnetic field topology using a magnetohydrostatic model, and find that some UV bursts are associated with magnetic null points or bald patches. In addition, we find that these UV bursts reveal no obvious coronal signatures from the observations of the Atmospheric Imaging Assembly (AIA) on board SDO and the EUV Imaging Spectrometer (EIS) on board \textit{Hinode}.