Atmospheric pressure dependance of HAWC scaler system

TL;DR

This paper presents a method to estimate and correct for atmospheric pressure effects on HAWC scalar data, enabling more accurate solar modulation studies by isolating pressure-induced variations from cosmic ray flux measurements.

Contribution

The paper introduces a novel approach to accurately estimate pressure coefficients using the periodic behavior of atmospheric pressure at HAWC, improving data correction for solar studies.

Findings

Pressure coefficients estimated with high accuracy.

Method helps identify malfunctioning PMTs.

Corrected data enhances solar modulation analysis.

Abstract

The variation in atmospheric pressure is due to changes in mass of the air column above, which in turn resembles the density variation of atmosphere and will affect the decay of secondary particles of cosmic rays. The ground based cosmic ray detectors observe pressure dependent variation in their flux. The High Altitude Water Cherenkov (HAWC) gamma ray observatory is a great detector of secondary particles because of its high altitude, high uptime, and large area (including total photo-cathode area), which makes the HAWC scaler system an ideal instrument for solar modulation studies. Although, in order to perform these studies it is necessary to isolate and remove the atmospheric modulations. The observed rate in each PMT has signatures of both the solar and atmospheric modulations, which makes it difficult to measure the pressure coefficient ($\beta_P$ ). The pressure at the HAWC site shows a periodic behavior ($\sim$ 12 hours), which also reflects in the scalar rates. This periodic property was used to isolate the pressure modulation and $\beta_P$ were estimated with accuracy. Since the pressure dependence is a physical phenomenon, the estimated coefficients for PMTs should be identical, any deviation from this can be due to malfunction of the PMT. This make this method a useful tool to identify the malfunctioning PMTs and help us to isolate them from the analysis. In this analysis we are presenting the method of estimation of the pressure coefficients and its usage to correct the HAWC scalar data to make it suitable for the solar modulations studies.