is not observed at the expected strength.

Fig. \[fig:literature\] shows a comparison of this work to previous measurements (see also discussion above). The results show conservative limits from the *Chandra* ACIS-S and ACIS-I analysis and the offset shows possible systematics between instruments. The average value of all individual limits is closer to the ACIS-I measurement since the sample has higher exposure in ACIS-I and more clusters have ACIS-I observations. Most detections are consistent with our 95 per cent confidence regions. Reasons for the more conservative limits can be the smaller FOV of *Chandra*, the lower combined exposure compared to some sample studies, the smaller effective area of *Chandra* compared to *XMM-Newton*, and a more conservative modelling approach.

Conclusions {#sec:concl}
===========

This study presents a large sample of deep cluster spectra with limits on the previously detected emission at 3.55keV assuming the line originated from the decay of sterile neutrino DM ($\rm{m_s = 7.1~keV}$). We extend the number of objects previously searched for the line and provide further insight to whether the line only occurs in special observations or objects. This is the first study using a large sample of *Chandra*-observed clusters to constrain the 3.55keV line. The driving cluster property 