Anamparambu N. Ramaprakash

Imaging through a turbulent medium like atmosphere has always been a difficult challenge. The random variations of the refractive index prevent the formation of diffraction-limited images; instead, we get a speckle image. In this work, we have given our analysis as to how we can exploit the inherent ’memory effect principle’ present in the atmosphere to produce diffraction-limited results for amplitude recovery. This paper includes obtaining accurate speckle images through a simulated imaging system in the presence of atmospheric turbulence and its validation. For amplitude and phase recovery, an accurate approach been developed and implemented using hybrid Bispectrum- Fienup algorithm and tested against different sky background, read noise, telescope reflectivity. Polychromatic effect of limited bandwidth source been introduced into simulation and tested against different sky background and detector noises.

The Solar Ultraviolet Imaging Telescope (SUIT) observes the Sun in the near-ultraviolet regime on board the Aditya-L1 satellite, India’s dedicated mission to study the Sun. SUIT will image the Sun in the wavelength range of 200 to 400 nm using 11 science bandpasses with varying spectral bandwidths between 0.1 and 58 nm. Within this range, the Sun provides huge incoming solar flux to the telescope that also varies by a factor of ≈20 from the lower end to the upper end of the wavelength band of interest. The thermal filter assembly (TFA) is an optical component at the SUIT entrance aperture, directly facing the Sun. The TFA is used to control the heat load entering the telescope cavity and also to reduce the signal reaching the SUIT camera system and the charge-coupled device sensor, which is limited in full-well capacity and the linear operational regime. The TFA is designed to allow only 0.1% to 0.45% of the incoming flux to pass within 200 to 400 nm. The choice of materials for substrate and coating for the filter poses several challenges in terms of contamination, corrosion/oxidation, and durability during the manufacturing process. In addition, long-term exposure to harsh space environments and the formation of pinholes are other concerns. Direct exposure to the sun leads to a strong temperature gradient along the thickness of the filter. The design and assembly of the TFA are performed to avoid any thermo-elastic stress affecting optical performance. Different levels of qualification tests and the operation of SUIT in orbit for more than 14 months have confirmed the perfect working of the TFA. To the best of our knowledge, the design, development, and testing of such a rejection filter is the first of its kind for space telescopes in the near ultraviolet range.

The WALOPControl software is designed to facilitate comprehensive control and operation of the Wide Area Linear Optical Polarimeter (WALOP) polarimeters, ensuring safe and concurrent management of various instrument components and functionalities. This software encompasses several critical requirements, including control of the filter wheel, calibration half-wave plate, calibration polarizer, guider positioning, focusers, and four concurrent charge-coupled device cameras. It also manages the host telescope and dome operations while logging operational parameters, user commands, and environmental conditions for troubleshooting and stability. It provides a user-friendly graphical user interface and secure access control, a notification system for errors, and a modular configuration for troubleshooting that are integral to the software’s architecture. It is accessible over the internet with the backend developed using NodeJS and ExpressJS, featuring a RESTful API that interacts with a MongoDB database, facilitating real-time status updates and data logging. The frontend utilizes the React.JS framework, with Redux for state management and Material UI for the graphical components. The system also allows for automatic observations based on user-defined schedules. A continuous integration and continuous deployment pipeline ensures the software’s reliability through automated testing and streamlined deployment. The WALOPControl software is a key component of the Polar-Areas Stellar Imaging in Polarimetry High Accuracy Experiment project, which aims to study the dust and magnetic field of the Milky Way by observing the polarization of starlight.

We present the multi-wavelength study of the ejection of a plasma blob from the limb flare SOL2023-12-31T21:36:00 from NOAA 13536 observed by the Solar Ultraviolet Imaging Telescope (SUIT) on board Aditya-L1. We use SUIT observations along with those from Atmospheric Imaging Assembly (AIA) on board SDO and Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter to infer the kinematics and thermal nature of the ejected blob and its connection to the associated flare. The observations show that the flare was comprised of two eruptions. The blob was ejected during the first eruption and later accelerated to velocities over 1500 km/s measured at a maximum projected height of ~ 178 Mm from the Sun's surface. The acceleration of the ejected plasma blob is co-temporal with the bursty appearance of the hard X-ray light curve recorded by STIX. Radio spectrogram observations from STEREO-A/WAVES and RSTN reveal type III bursts at the same time, indicative of magnetic reconnection. DEM analysis using AIA observations suggests the plasma blob is comprised of cooler and denser plasma in comparison to the ambient corona. To the best of our knowledge, this is the first observation of such a plasma blob in the NUV, providing crucial measurements for eruption thermodynamics.

We present the multiwavelength study of the ejection of a plasma blob from the limb flare SOL2023-12-31T21:36:00 from NOAA 13536 observed by the Solar Ultraviolet Imaging Telescope (SUIT) on board Aditya-L1. We use SUIT observations along with those from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter to infer the kinematics and thermal nature of the ejected blob and its connection to the associated flare. The observations show that the flare was comprised of two eruptions. The blob was ejected during the first eruption and later accelerated to velocities over 1500 km s⁻¹ measured at a maximum projected height of ∼178 Mm from the Sun’s surface. The acceleration of the ejected plasma blob is cotemporal with the bursty appearance of the hard X-ray light curve recorded by STIX. Radio spectrogram observations from STEREO-A/WAVES and RSTN reveal type III bursts at the same time, indicative of magnetic reconnection. DEM analysis using AIA observations suggests the plasma blob is comprised of cooler and denser plasma in comparison to the ambient corona. To the best of our knowledge, this is the first observation of such a plasma blob in the near-ultraviolet providing crucial measurements for eruption thermodynamics.

The Solar Ultraviolet Imaging Telescope (SUIT) is one of the seven payloads on board Aditya-L1 mission of the Indian Space Research Organization (ISRO). SUIT provides full and partial disk images of the Sun in the 200-400 nm wavelength range. This would help us probe the solar atmosphere at different heights and understand the mass and energy transfer process between its layers. For the first time, SUIT will also help us measure spatially resolved solar spectral irradiance at this wavelength band, which is significant for studying the sun-climate relationships. To perform these studies, it is necessary to photometrically calibrate the payload and validate the spectral coverage of the various bandpasses. We perform the photometric calibration and spectral validation of 8 bandpasses using light of known intensity and spectral coverage. For photometric calibration, the telescope throughput is modeled using sun-as-a-star spectrum from SOLSTICE and SOLSPEC. The modeled throughput is compared with in-lab measurements taken with light of known intensity. The ratio of measured photoelectrons gathered with the modeled prediction agree within 20%. For spectral validation, readings are taken across the transmission spectrum of each filter, keeping adjacent readings independent of each other. The relative intensity measured at each wavelength is seen to trace the modeled telescope bandpass for that filter. These tests could not be performed for filters with bandpasses operating below 250 nm (NB01, BB01 and BB02), primarily due to heavy atmospheric attenuation in these wavelengths leading to decreased SNR of the data. The experimentally measured results agree closely with the modeled values, validating SUIT's optical performance and presenting the reliability of the developed throughput model.

Solar flares are regularly observed in extreme-ultraviolet soft X-rays (SXRs) and hard X-rays (HXRs). However, those in near- and mid-ultraviolet are sparse. The Solar Ultraviolet Imaging Telescope (SUIT) on board the Aditya-L1, launched on 2023 September 2, provides regular observations in the 200–400 nm wavelength range through 11 filters. Here, we report the observation of the X6.3 flare on 2024 February 22 using eight narrowband (NB) filters of SUIT. We have also used co-spatiotemporal observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), Solar Orbiter/STIX, GONG Hα, Aditya-L1/SoLEXS, and GOES. We obtained light curves over the flaring region from AIA 1600 and 1700 Å and GONG Hα and compared them with the disk-integrated light curve obtained from GOES and SoLEXS SXRs and STIX HXRs. We find that the flare peaks in SUIT NB01, NB03, NB04, and NB08 filters simultaneously with HXRs 1600 and 1700 Å, along with the peak temperature obtained from SoLEXS. In contrast, in NB02 and NB05, the flare peaks ∼2 min later than the HXR peak, while in NB06 and NB07, the flare peaks ∼3 min after the GOES SXR peak. To the best of our knowledge, this is the first observation of a flare in these wavelengths (except in NB03, NB04, and NB05). Moreover, for the first time, we show the presence of a bright kernel in NB02. These results demonstrate the capabilities of SUIT observations in flare studies.