[vsnet-campaign-xray 460] ASASSN-18ey: shortening of superhump period?

[Taichi Kato]

ASASSN-18ey (MAXI J1820+070): shortening of superhump period?

   My analysis suggests decreasing tendency in
the O-C diagram.  PDM analysis of two intervals
June 3-7 and after June 7 yielded periods of
0.7071(2) d (close to ATEL 11756) and 0.6928(8) d
(close to vsnet-alert 22264).  The amplitudes
of superhumps became significantly larger in
the later epoch.  The current profile is very
similar to that of SU UMa-type superhumps.
The variation in the period and phase suggests
that these variations are indeed superhumps
(rather than the orbital modulation as the most
likely candidate listed in in ATEL 11756).

   If the superhump evolution is analogous to
SU UMa-type dwarf novae, we may have observed
the first-ever stage A-B transition of superhumps
in a black-hole transient.
Further observations to confirm the period change
are strongly encouraged.