Simulations of expected signal and background of gamma-ray sources by large field-of-view detectors aboard CubeSats

Abstract

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.

In-orbit background for X-ray detectors

“…The SPENVIS platform allows to compute the cosmic-ray spectrum for a given orbit with more complex models, such as the ISO-15390 standard and the CREME96 model [14], taking into account also the short-time variations of the magnetosphere (geomagnetic storms) and employ a more accurate numerical calculation of the cutoff rigidity. Usually, results are compatible within a factor of few [15,16] with respect to the simplified approach presented here.…”

Detection of Low-Energy X-rays Using YSO Scintillation Crystal Arrays for GRB Experiments

“…The cosmic X-ray background is well described by two power laws in the range of 2 keV-2 MeV [40]. For an overview of the different background components in low-Earth orbit, see [39]. Figure 8 shows the CXB spectrum multiplied by the FOV of the UBAT, which was 1.85 sr, and by a factor of 0.5, taking into account the blockage by the coded mask.…”

“…We adopted the CPL model for a typical long GRB for the fluence spectrum, that is, the time-integrated spectrum over the entire duration of the burst. Such a spectrum was derived using the Fermi GBM Burst Catalog (FERMIGBRST) [38] in [39]. For the differential photon flux N E in photons cm −2 s −1 keV −1 it holds:…”

“…where E peak is the peak energy; A is a normalization constant; E piv is the pivot energy, which is typically maintained at 100 keV; α is the spectral index; and E is in keV. The values for the typical long GRB are A = 8.9 × 10 −3 photons cm −2 s −1 keV −1 , E peak = 183 keV, and α = −0.96 [39]. Figure 8 shows the differential photon flux for a typical long GRB, where the function N E is multiplied by a factor of 0.5, which approximately corresponds to the fraction of photons blocked by the UBAT's coded mask.…”

A compact instrument for gamma-ray burst detection on a CubeSat platform I: Design drivers and expected performance

“…A recent summary of various background components and models can be found in [61]. According to simulations [62], the count rate of a scintillator detector in low Earth orbit outside the Van Allen radiation belts is dominated by the extragalactic gamma-ray background and atmospheric (albedo) gamma-ray emission. This is consistent with a background model for Fermi GBM based on real data [63].…”