  We studied the transient Galactic black hole candidate MAXI J0637-430 with
data from Insight-HXMT, Swift and XMM-Newton. The broad-band X-ray observations
from Insight-HXMT help us constrain the power-law component. MAXI J0637-430 is
located at unusually high Galactic latitude; if it belongs to the Galactic
thick disk, we suggest a most likely distance <7 kpc. Compared with other black
hole transients, MAXI J0637-430 is also unusual for other reasons: a fast
transition to the thermal dominant state at the start of the outburst; a low
peak temperature and luminosity (we estimate them at ~ 0.7 keV and <0.1 times
Eddington, respectively); a short decline timescale; a low soft-to-hard
transition luminosity (<0.01 times Eddington). We argue that such properties
are consistent with a small binary separation, short binary period (P ~ 2 hr),
and low-mass donor star (M2 ~ 0.2 M_sun). Moreover, spectral modelling shows
that a single disk-blackbody component is not a good fit to the thermal
emission. Soft spectral residuals, and deviations from the standard L_disk ~
T^4 in relation, suggest the need for a second thermal component. We propose
and discuss various scenarios for such component, in addition to those
presented in previous studies of this source. For example, a gap in the
accretion disk between a hotter inner ring near the innermost stable orbit, and
a cooler outer disk. Another possibility is that the second thermal component
is the thermal plasma emission from an ionized outflow.
