[vsnet-alert 23525] The 1898 and 1934 outbursts of ASASSN-18ey (= MAXI J1820+070) (Atel #13066)

[Kojiguchi Naoto]

The 1898 and 1934 outbursts of ASASSN-18ey (= MAXI J1820+070)

ATel #13066; Naoto Kojiguchi (Kyoto University), Taichi Kato (Kyoto University), Keisuke Isogai (Kyoto University), Daisaku Nogami (Kyoto University)
on 2 Sep 2019; 16:21 UT
Credential Certification: Daisaku Nogami (nogami.daisaku.5z at kyoto-u.ac.jp)
Subjects: Optical, Binary, Black Hole, Transient

     We report on two past outbursts of the low-mass X-ray binary ASASSN-18ey (= MAXI J1820+070) detected via Digital Access to a Sky Century @ Harvard (DASCH;http://dasch.rc.fas.harvard.edu<http://dasch.rc.fas.harvard.edu/>).
The large outburst of ASASSN-18ey was discovered in March 2018 and lasted for about 8 months (ATel #11399 <http://www.astronomerstelegram.org/?read=11399>, #11400 <http://www.astronomerstelegram.org/?read=11400>). Then, this object showed two rebrightenings in March and August 2019
(ATel #12567 <http://www.astronomerstelegram.org/?read=12567>, #12573 <http://www.astronomerstelegram.org/?read=12573>, #12577 <http://www.astronomerstelegram.org/?read=12577>, #12596 <http://www.astronomerstelegram.org/?read=12596>, #13014 <http://www.astronomerstelegram.org/?read=13014>, #13025 <http://www.astronomerstelegram.org/?read=13025>). We checked the public data of the photographic plates provided by DASCH and discovered two historical outbursts in 1898 and 1934.
ASASSN-18ey (= DASCH_N020311310706)

#yyyymmdd mag band observer
18981017.979 12.73 B DASCH
18990928.020 14.47 B DASCH
19340713.107 14.05 B DASCH
19340717.102 14.20 B DASCH
*DASCH data are photographic plate data converted to APASS B-band magnitude.

     By using these data, we could approximately estimate the outburst-recurrence time of ASASSN-18ey to be 40 years. As a similar example, it is known that the 1917 outburst of V616 Mon (= Mon X-1)
was found in Harvard photographic plates (Eachus, Wright & Liller 1976 <http://adsabs.harvard.edu/abs/1976ApJ...203L..17E>).