The ANtarctic Impulsive Transient Antenna (ANITA) NASA long-duration balloon payload completed its fourth flight in December 2016, after 28 days of flight time. ANITA is sensitive to impulsive broadband radio emission from interactions of ultra-high-energy neutrinos in polar ice (Askaryan emission). We present the results of two separate blind analyses searching for signals from Askaryan emission in the data from the fourth flight of ANITA. The more sensitive analysis, with a better expected limit, has a background estimate of 0.64 +0.69 −0.45 and an analysis efficiency of 82±2%. The second analysis has a background estimate of 0.34 +0.66 −0.16 and an analysis efficiency of 71±6%. Each analysis found one event in the signal region, consistent with the background estimate for each analysis. The resulting limit further tightens the constraints on the diffuse flux of ultra-high-energy neutrinos at energies above 10 19.5 eV.

Aims. The durations of 388 gamma-ray bursts detected by the Swift satellite, are analyzed statistically to search for subgroups. The results are then compared with results obtained earlier for data from the BATSE database. Methods. We apply the standard χ 2 test. Results. As for data in the BATSE database, short and long subgroups are also reliably identified in the Swift data. An intermediate subgroup is also seen in the Swift database.Conclusions. The analysis of the entire sample of 388 GRBs provides a support for the existence of three subgroups.

Aims. We study a sample of 427 gamma-ray bursts (GRBs), measured by the RHESSI satellite, statistically with respect to duration and hardness ratio. Methods. Standard statistical tests were used, such as χ 2 , F-test, and the maximum likelihood ratio test, to compare the number of GRB groups in the RHESSI database with that of the BATSE database. Results. Previous studies based on the BATSE Catalog claim the existence of an intermediate GRB group, besides the long and short groups. Using only the GRB duration T 90 as information and χ 2 or F-test, we do not find any statistically significant intermediate group in the RHESSI data. However, maximum likelihood ratio test reveals a significant intermediate group. Using the 2-dimensional hardness/T 90 plane, the maximum likelihood analysis also reveals a significant intermediate group. In contrast to the BATSE database, the intermediate group in the RHESSI data set is harder than the long one. Conclusions. The existence of an intermediate group follows not only from the BATSE data set, but also from the RHESSI one.

Abstract:We report on design, manufacture, and testing of a Slewing Mirror Telescope (SMT), the first of its kind and a part of Ultra-Fast Flash Observatory-pathfinder (UFFO-p) for space-based prompt measurement of early UV/optical light curves from Gamma-Ray Bursts (GRBs). Using a fast slewing mirror of 150 mm diameter mounted on a 2 axis gimbal stage, SMT can deliver the images of GRB optical counterparts to the intensified CCD detector within 1.5~1.8 s over ± 35 degrees in the slewing field of view. Its Ritchey-Chrétien telescope of 100 mm diameter provides a 17 × 17 arcmin 2 instantaneous field of view. Technical details of design, construction, the laboratory performance tests in space environments for this unique SMT are described in conjunction with the plan for in-orbit operation onboard the Lomonosov satellite in 2013.