On the Nova Rate in M87

TL;DR

This paper reanalyzes HST data to estimate the nova rate in M87, finding it remains uncertain but possibly as low as 200 per year, highlighting challenges in nova identification and rate extrapolation.

Contribution

It provides an independent analysis of HST data, questioning the previously reported high nova rate in M87 and emphasizing uncertainties in such estimates.

Findings

Broad agreement with previous high nova rate estimates

Uncertainty in nova rate due to incomplete lightcurves

Possible nova rate as low as 200 per year

Abstract

Recently, Shara and collaborators searched for novae in M87 in a series of images originally acquired in HST program #10543 (PI: Baltz), finding a surprisingly high nova rate of $363_{-45}^{+33}$ per year. In an attempt to reconcile this rate with previous ground-based estimates, we have undertaken an independent analysis of the HST data. Our results are in broad agreement with those of Shara et al., although we argue that the global nova rate in M87 remains uncertain, both due to the difficulty in identifying bona fide novae from incomplete lightcurves, and in extrapolating observations near the center of M87 to the entire galaxy. We conclude that nova rates as low as ~200 per year remain plausible.