eSASS4DR1 introduction

As part of the eROSITA-DE Early Data Release (EDR), the necessary software to reduce and analyse the eROSITA data was made public. Since then, the tasks that made up the eROSITA Science Analysis Software System (eSASS), have evolved. The eROSITA-DE Data Release 1 (DR1) was produced with a new version of eSASS, which is also made public through this site under the name of eSASS4DR1.

The public eRASS1 data processing version is 010.

The EDR data was not reprocessed with this processing version, and these data are not part of DR1.

Data calibration changes with respect to the EDR (001) processing

The eROSITA-DE calibration database experienced minor changes between the EDR and DR1 data processing. The Ancillary Response Files (ARFs) and Response Matrix Files (RMFs) for the different telescope modules (TM) are the same for both processings. The main difference between the EDR and DR1 calibration is the improved suppression of low energy detector noise. This was achieved by extending the definition of invalid patterns to doubles, triples, and quadruples, which are likely to consist of noise events only. Moreover, a few bad pixels were set to bad. Bad pixels usually present an anomalous behavior, e.g., by generating an unusual amount of noise. These pixels can be set to bad on board or on ground: on board, they will not transmit any telemetry to Earth, on ground, they are ignored during the data processing. In eRASS1, some pixels were set bad on ground: two in TM2, seventeen in TM4, three in TM6, and one in TM7. TM1, TM3 and TM5 did not show any bad pixels during this time.

Improvements in the data analysis with respect to the EDR (001) processing

The main improvements of the 010 processing version with respect to the 001 one regarding the production of calibrated event lists are:

• Improved flagging of image artifacts.
• Improvement in the handling of CCD frames split across telemetry frames.
• Correct flagging of neighboring pixels.
• Addition of time filtering of bad pixels.
• Improvement in the treatment of secondary event threshold and bad pixels.
• Stronger telescope module (TM) specific noise suppression in valid >1 pixel patterns.
• Consideration of CCD temperature and long-term degradation.
• Renormalisation of orientation quaternions to increase accuracy.

The upgrades on the different eSASS4DR1 tasks include the following:

• Improvement in the accuracy of the projection.
• Correction on the flagging of pixels next to bad pixels.
• Addition of upper and lower errors of source parameters.
• Increased maximum number of fit iterations and minimum step width for Maximum Likelihood source fitting.
• Improvement in the computation of BACKRATIO.
• Errors and additional columns to lightcurve tables.