Observations of the low-luminosity Type Iax supernova 2019gsc: a fainter
  clone of SN 2008ha?
  We present optical photometric and spectroscopic observations of the
faint-and-fast evolving type Iax SN 2019gsc, extending from the time of g-band
maximum until about fifty days post maximum, when the object faded to an
apparent r-band magnitude m_r = 22.48+/-0.11 mag. SN 2019gsc reached a peak
luminosity of only M_g = -13.58 +/- 0.15 mag, and is characterised with a
post-maximum decline rate Delta(m_15)_g = 1.08 +/- 0.14 mag. These light curve
parameters are comparable to those measured for SN 2008ha of M_g = -13.89 +/-
0.14 mag at peak and Delta(m_15)_g = 1.80 +/- 0.03 mag. The spectral features
of SN 2019gsc also resemble those of SN 2008ha at similar phases. This includes
both the extremely low ejecta velocity at maximum, about 3,000 km/s, and at
late-time (phase +54 d) strong forbidden iron and cobalt lines as well as both
forbidden and permitted calcium features. Furthermore, akin to SN 2008ha, the
bolometric light curve of SN 2019gsc is consistent with the production of 0.003
+/- 0.001 Msol of nickel. The explosion parameters, M_ej = 0.13 Msol and E_k =
12 x 10E48 erg, are also similar to those inferred for SN 2008ha. We estimate a
sub-solar oxygen abundance for the host galaxy of SN 2019gsc, (12 + log10(O/H)
= 8.10 +/- 0.18 dex), consistent with the equally metal-poor environment of SN
2008ha. Altogether, our dataset of SN 2019gsc indicates that this is a member
of a small but growing group of extreme SN Iax that includes SN 2008ha and SN
2010ae.
