SRG/eROSITA prospects for detection of GRB afterglows

TL;DR

eROSITA's all-sky survey is expected to detect 4-8 long-duration GRB afterglows annually, offering an unbiased sample for statistical analysis and insights into relativistic jets from massive star collapses.

Contribution

This study predicts eROSITA's capability to detect and analyze GRB afterglows unbiased by triggering, providing new data for understanding GRB populations and jet properties.

Findings

Expected 4-8 long GRB afterglows per year

Potential detection of up to 40 afterglows in total

Early localization within a day for follow-up observations

Abstract

We discuss the potential of the eROSITA telescope on board the \emph{Spectrum-X-Gamma} observatory to detect gamma-ray burst (GRB) X-ray afterglows during its 4-year all-sky survey. The expected rate of afterglows associated with long-duration GRBs without any information on the bursts proper that can be identified by a characteristic power-law light curve in the eROSITA data is 4--8 events per year. An additional small number, $\lesssim 2$ per year, of afterglows may be associated with short GRBs, ultra hard (GeV) GRBs and X-ray flashes. eROSITA can thus provide the first unbiased (unaffected by GRB triggering) sample of $\lesssim 40$ X-ray afterglows, which can be used for statistical studies of GRB afterglows and for constraining the shape of the GRB $\log N$--$\log S$ distribution at its low-fluence end. The total number of afterglows detected by eROSITA may be yet higher due to orphan afterglows and failed GRBs. The actual detection rate could thus provide interesting constraints on the properties of relativistic jets associated with collapse of massive stars. Finally, eROSITA can provide accurate ($\lesssim 30"$) coordinates of newly discovered afterglows within a day after the event, early enough for scheduling further follow-up observations.