Improved background model for the Large Area X-ray Proportional Counter (LAXPC) instrument on-board AstroSat

TL;DR

This paper introduces an improved background model for the LAXPC instrument on AstroSat, accounting for a previously unmodeled quasi-diurnal variation caused by charged particle flux changes, based on 5 years of data.

Contribution

The paper presents a novel background model that incorporates a quasi-diurnal variation, significantly enhancing the accuracy of background estimation for LAXPC on AstroSat.

Findings

Identification of an 84495 s quasi-diurnal variation period.

Improved background modeling accuracy during the orbit.

Correlation of variation with charged particle flux changes.

Abstract

We present an improved background model for the Large Area X-ray Proportional Counter (LAXPC) detectors on-board AstroSat. Because of the large collecting area and high pressure, the LAXPC instrument has a large background count rate, which varies during the orbit. Apart from the variation with latitude and longitude during the orbit there is a prominent quasi-diurnal variation which has not been modelled earlier. Using over 5 years of background observations, we determined the period of the quasi-diurnal variation to be 84495 s and using this period, it is possible to account for the variation and also identify time intervals where the fit is not good. These lead to a significant improvement in the background model. The quasi-diurnal variation can be ascribed to the changes in charged particle flux in the near Earth orbit.