Parks et al. (1981) and McCarthy and Parks (1985) captured a phenomenon of X-ray intensification during a passage of a thundercloud using an aircraft-mounted X-ray detector for the first time. Balloon experiments by Eack et al. (1996) observed similar X-ray emissions. These observations were followed by further aircraft (e.g.,

GRBAlpha is a 1U CubeSat mission with an expected launch date in the first half of 2021. It carries a 75 × 75 × 5 mm CsI(Tl) scintillator, read out by a dual-channel multi-pixel photon counter (MPPC) setup, to detect gamma-ray bursts (GRBs). The GRB detector is an in-orbit demonstration for the detector system on the Cubesats Applied for MEasuring and LOcalising Transients (CAMELOT) mission. While GRBAlpha provides 1/8th of the expected effective area of CAMELOT, the comparison of the observed light curves with other existing GRB monitoring satellites will allow us to validate the core idea of CAMELOT, i.e. the feasibility of timing-based localization.

In recent years the number of CubeSats (U-class spacecrafts) launched into space has increased exponentially marking the dawn of the nanosatellite technology. In general these satellites have a much smaller mass budget compared to conventional scientific satellites which limits shielding of scientific instruments against direct and indirect radiation in space.In this paper we present a simulation framework to quantify the signal in large field-of-view gamma-ray scintillation detectors of satellites induced by X-ray/gamma-ray transients, by taking into account the response of the detector. Furthermore, we quantify the signal induced by X-ray and particle background sources at a Low-Earth Orbit outside South Atlantic Anomaly and polar regions. Finally, we calculate the signal-to-noise ratio taking into account different energy threshold levels. Our simulation can be used to optimize material composition and predict detectability of various astrophysical sources by CubeSats.We apply the developed simulation to a satellite belonging to a planned CAMELOT CubeSat constellation. This project mainly aims to detect short and long gamma-ray bursts (GRBs) and as a secondary science objective, to detect soft gamma-ray repeaters (SGRs) and terrestrial gamma-ray flashes (TGFs). The simulation includes a detailed computer-aided design (CAD) model of the satellite to take into account the interaction of particles with the material of the satellite as accurately as possible.Results of our simulations predict that CubeSats can complement the large space observatories in high-energy astrophysics for observations of GRBs, SGRs and TGFs. For the detectors planned to be on board of the CAMELOT CubeSats the simulations show that detections with signal-to-noise ratio of at least 9 for median GRB and SGR fluxes are achievable.

This study presents a background estimation for the CubeSats Applied for MEasuring and LOcalising Transients (CAMELOT), which is a proposed fleet of nanosatellites for the all-sky monitoring and timing-based localization of gamma ray transients with precise localization capability at low Earth orbits. CAMELOT will allow us to observe and precisely localize short gamma ray bursts (GRBs) associated with kilonovae, long GRBs associated with core-collapse massive stars, magnetar outbursts, terrestrial gamma ray flashes, and gamma ray counterparts to gravitational wave sources. A fleet of at least nine 3U CubeSats is proposed to be equipped with large and thin CsI(Tl) scintillators read out by multipixel photon counters (MPPC). A careful study of the radiation environment in space is necessary to optimize the detector casing, estimate the duty cycle due to the crossing of the South Atlantic Anomaly and polar regions, and minimize the effect of the radiation damage of MPPCs. K E Y W O R D S(ISM:) cosmic rays, gamma rays: bursts, instrumentation: detectors, X-rays: diffuse background This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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