On-Orbit Results and Lessons Learned from the ASTERIA Space Telescope Mission

The Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) was deployed from the International Space Station (ISS) on 20 November 2017, beginning a technology demonstration and opportunistic science mission to advance the state of the art in nanosatellite performance for astrophysical observations. The goal of ASTERIA is to achieve arcsecond-level line-of-sight pointing error and highly stable focal plane temperature control. These capabilities enable precision photometry—i.e. the careful measurement of stellar brightness over time—which in turn allows investigation of astrophysical phenomena such as transiting exoplanets. By the end of the 90-day prime mission, ASTERIA had achieved line-of-sight pointing stability of approximately 0.5 arcseconds root mean square (RMS) over 20-minute observations, pointing repeatability of 1 milliarcsecond RMS from one observation to the next, and focal plane temperature stability better than ±0.01 K over 20-minute observations. This paper presents an overview of the ASTERIA flight and ground system, summarizes the pre-delivery test campaign, and discusses the on-orbit performance obtained by the pointing and thermal control subsystems. We also describe the process for planning opportunistic science observations and present lessons learned from development and operations. Having successfully operated for over 200 days as of this writing, ASTERIA is currently in an extended mission to observe nearby bright stars for transiting exoplanets

Holistic improvement of image acquisition and reconstruction in fluorescence microscopy

Recent developments in microscopic imaging led to a better understanding of intra- and intercellular metabolic processes and, for example, to visualize structural properties of viral pathogens. In this thesis, the imaging process of widefield and confocal scanning microscopy techniques is treated holistically to highlight general strategies and maximise their information content. Poisson or shot noise is assumed to be the fundamental noise process for the given measurements. A stable focus position is a basic condition for e.g. long-term measurements in order to provide reliable information about potential changes inside the Field-of-view. While newer microscopy systems can be equipped with hardware autofocus, this is not yet the widespread standard. For image-based focus analysis, different metrics for ideal, noisy and aberrated, in case of spherical aberration and astigmatism, measurements are presented. A stable focus position is also relevant in the example of 2-photon confocal imaging and at the same time the situation is aggravated in the given example, the measurement of the retina in the living mouse. In addition to the natural drift of the focal position, which can be evaluated by means of previously introduced metrics, rhythmic heartbeat, respiration, unrhythmic muscle twitching and movement of the mouse kept in artificial sleep are added. A dejittering algorithm is presented for the measurement data obtained under these circumstances. Using the additional information about the sample distribution in ISM, a method for reconstructing 3D from 2D image data is presented in the form of thick slice unmixing. This method can further be used for suppression of light generated outside the focal layer of 3D data stacks and is compared to selective layer multi-view deconvolution. To reduce phototoxicity and save valuable measurement time for a 3D stack, the method of zLEAP is presented, by which omitted Z-planes are subsequently calculated and inserted

Detection of short Gamma-Ray Bursts with CTA through real-time analysis

With respect to the current IACTs, CTA will cover a larger energy range (~20 GeV - 300 TeV) with one order of magnitude better sensitivity. The facility will be provided with a real-time analysis (RTA) software that will automatically generate science alerts and analyse data from on-going observations in real-time. The RTA will play a key role in the search and follow-up of transients from external alerts (i.e. from on-space gamma-ray missions, observatories operating at other energy bands or targets of opportunity provided by neutrinos and gravitational waves detectors). The scope of this study was to investigate the ctools software package feasibility for the RTA, adopting a full-field of view maximum likelihood analysis method. A prototype for the RTA was developed, with natively implemented utilities where required. Its performance was extensively tested for very-short exposure times (far below the lower limit of current Cherenkov science) accounting for sensitivity degradation due to the non-optimal working condition expected of the RTA. The latest IRFs, provided by CTA Performance, were degraded via effective area reduction for this purpose. The reliability of the analysis methods was tested by means of the verification of Wilks' theorem. Through statistical studies on the pipeline parameter space (i.e. minimum required exposure time), the performance was evaluated in terms of localization precision, detection significance and detection rates at short-timescales using the latest available GRB afterglow templates for the source simulation. Future improvements involve further tests (i.e. with an updated population synthesis) as well as post-trials correction of the detection significance. Moreover, implementations allowing the pipeline to dynamically adapt to a range of science cases are required. Prospects of forthcoming collaboration may involve the integration of this pipeline within the on-going work of the gamma-ray bursts experts of CTA Consortium