GRBAlpha and VZLUSAT-2: GRB observations with CubeSats after 3 years of operations

TL;DR

This paper reports on three years of gamma-ray burst observations using CubeSats GRBAlpha and VZLUSAT-2, demonstrating their capability to detect and characterize high-energy transient events in low Earth orbit.

Contribution

It presents the successful deployment and operation of gamma-ray detectors on CubeSats, including detection statistics, event characterization, and system optimization over three years.

Findings

Detected 140 transients, including 100 gamma-ray bursts.

Confirmed bright GRBs like 221009A and 230307A.

Characterized SiPM degradation and optimized detector duty cycle.

Abstract

GRBAlpha is a 1U CubeSat launched in March 2021 to a sun-synchronous LEO at an altitude of 550 km to perform an in-orbit demonstration of a novel gamma-ray burst detector developed for CubeSats. VZLUSAT-2 followed ten months later in a similar orbit carrying as a secondary payload a pair of identical detectors as used on the first mission. These instruments detecting gamma-rays in the range of 30-900 keV consist of a 56 cm2 5 mm thin CsI(Tl) scintillator read-out by a row of multi-pixel photon counters (MPPC or SiPM). The scientific motivation is to detect gamma-ray bursts and other HE transient events and serve as a pathfinder for a larger constellation of nanosatellites that could localize these events via triangulation. At the beginning of July 2024, GRBAlpha detected 140 such transients, while VZLUSAT-2 had 83 positive detections, confirmed by larger GRB missions. Almost a hundred of them are identified as gamma-ray bursts, including extremely bright GRB 221009A and GRB 230307A, detected by both satellites. We were able to characterize the degradation of SiPMs in polar orbit and optimize the duty cycle of the detector system also by using SatNOGS radio network for downlink.