# The X-ray variable sky as seen by MAXI: the future of dust echo tomography with bright Galactic X-ray bursts

## TL;DR

This study analyzes MAXI X-ray data to predict the future of dust echo tomography, estimating the number of observable dust rings from Galactic X-ray flares with upcoming more sensitive telescopes.

## Contribution

It provides a statistical analysis of X-ray flare properties and predicts the increased detection rate of dust echo rings with future X-ray observatories.

## Key findings

- Power law distribution of dust echo fluences with slope -2.3
- Future telescopes will detect 10-30 dust rings annually
- Next-generation telescopes will be 30 times more sensitive than current ones

## Abstract

Bright, short duration X-ray flares from accreting compact objects produce thin, dust scattering rings that enable dust echo tomography: high precision distance measurements and mapping of the line-of-sight distribution of dust. This work looks to the past activity of X-ray transient outbursts in order to predict the number of sight lines available for dust echo tomography. We search for and measure the properties of 3$\sigma$ significant flares in the 2-4 keV light curves of all objects available in the public MAXI archive. We derive a fluence sensitivity limit of $10^{-3}$ erg cm$^{-2}$ for the techniques used to analyze the light curves. This limits the study mainly to flares from Galactic X-ray sources. We obtain the number density of flares and estimate the total fluence of the corresponding dust echoes. However, the sharpness of a dust echo ring depends on the duration of a flare relative to quiescence. We select flares that are shorter than their corresponding quiescent period to calculate a number density distribution for dust echo rings as a function of fluence. The results are fit with a power law of slope $-2.3 \pm 0.1$. Extrapolating this to dimmer flares, we estimate that the next generation of X-ray telescopes will be 30 times more sensitive than current observatories, resulting in 10-30 dust ring echoes per year. The new telescopes will also be 10-100 times more sensitive than Chandra to dust ring echoes from the intergalactic medium.