On-ground and on-orbit time calibrations of GECAM

Abstract

High time resolution and accuracy are of critical importance in the studies of timing analysis and time delay localization of Gamma-Ray Bursts (GRBs), Soft Gamma-ray Repeaters (SGRs) and pulsars. The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) consisting of two micro-satellites, GECAM-A and GECAM-B, launched on Dec. 10, 2020, is aimed at monitoring and locating X-ray and gamma-ray bursts all over the sky. To achieve its scientific goals, GECAM is designed to have the highest time resolution (0.1 $\mu {\rm s}$) among all GRB detectors ever flown. Here, we make a comprehensive time calibration campaign including both on-ground and on-orbit tests to derive not only the relative time accuracy of GECAM satellites and detectors, but also the absolute time accuracy of GECAM-B. Using the on-ground calibration with a $\rm ^{22}Na$ radioactive source, we find that the relative time accuracy between GECAM-A and GECAM-B is about 0.15 $\mu {\rm s}$ (1σ). To measure the relative time accuracy between all detectors of a single GECAM satellite, cosmic ray events detected on orbit are utilized since they could produce many secondary particles simultaneously record by multiple detectors. We find that the relative time accuracy among all detectors onboard GECAM-B is about 0.12 $\mu {\rm s}$ (1σ). Finally, we use the novel Li-CCF method to perform the absolute time calibration with Crab pulsar and SGR J1935+2154, both of which were jointly observed by GECAM-B and Fermi/GBM, and obtain that the time difference between GECAM-B and Fermi/GBM is 3.06 ± 6.04 $\mu {\rm s}$ (1σ).

Search for Quasiperiodic Oscillations in Precursors of Short and Long Gamma-Ray Bursts

“…On the other hand, although some magnetar theories predict the possible existence of QPOs of tens of Hz in an SGRB precursor (e.g., Sotani et al 2007;Tews 2017;Zhang et al 2022), the duration of the precursors of SGRBs is just about ∼0.1 s (see Table 1), which means that only a few cycles of oscillations could possibly exist in a precursor, making the QPO search even more difficult. A definitive answer may come from sufficient statistics observed by more advanced detectors and higher detection signal-to-noise ratios, or a joined analysis using the light curves obtained by multiple GRB detectors, such as Fermi/GBM (Meegan et al 2009), Insight-HXMT/HE (Liu et al 2020;Zhang et al 2020), Swift/BAT (Barthelmy et al 2005), and GECAM (Li et al 2021;Xiao et al 2022c). Detectors with a similar energy response will be more advantageous, such as GECAM and GBM (Xiao et al 2022d), as will combining the information from theoretical models and the QPO evolution with time as a template in searching for QPOs (Dichiara et al 2013).…”

Flare quasi-periodic pulsation associated with recurrent jets

“…On 2022 July 14, a solar flare occurred in the active region NOAA 13058 (N15E81), which was close to the solar limb and erupted after a group of recurrent jets. It was simultaneously observed by several space-based telescopes, such as the Geostationary Operational Environmental Satellite X-ray Sensor (GOES/XRS; Hanser and Sellers, 1996), the Fermi Gamma-ray Burst Monitor (GBM; Meegan et al, 2009), the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM; Xiao et al, 2022), the Atmospheric Imaging Assembly (AIA; Lemen et al, 2012) and the Extreme Ultraviolet Variability Experiment (EVE; Woods et al, 2012) on board the Solar Dynamics Observatory (SDO; Pesnell et al, 2012), and the ground-based radio telescope, i.e., the Nobeyama Radio Polarimeters (NoRP; Nakajima et al, 1985), as seen in Table 1 and Figure 1. It should be pointed out that all light curves expected for GOES have been multiplied by a factor, so that they can be well displayed in a same window.…”

“…GECAM is designed to detect and localize high-energy transients, such as Gamma-ray bursts and solar flares. It consists of 25 gamma-ray detectors (GRDs), which are used to detect the X-ray and γ-ray radiation (Xiao et al, 2022). Figure 1 (A) shows the solar flux at 25−120 keV (blue) during the M1.2 flare with an uniform temporal cadence of 0.5 s, the GRD numbers and their averaged incident angles for each GRD used in this study are listed in Table 2.…”

The First GECAM Observation Results on Terrestrial Gamma-ray Flashes and Terrestrial Electron Beams

“…Thanks to the high time resolution of GECAM, i.e. 100 ns (Xiao et al, 2022), GECAM can effectively distinguish between cosmic-ray events and TGFs. Indeed, a dedicated data product called Simultaneous Events is designed for GECAM.…”

“…Indeed, a dedicated data product called Simultaneous Events is designed for GECAM. The Simultaneous Events Number (SimEvt-Num) is defined as the number of events from different detectors registered in the same 300 ns time window (Xiao et al, 2022). As the SimEvtNum increases, the probability of these events caused by cosmic-rays surges.…”