Dimming of MAXI J1820+070 (ASASSN-18ey) in the optical band

ATel #12747; L. Zampieri and U. Munari (INAF Padova), P. Ochner (Univ. Padova), F. Manzini (ANS Collaboration)
on 11 May 2019; 23:03 UT
Credential Certification: Luca Zampieri (luca.zampieri@oapd.inaf.it)

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Recent Swift and NuSTAR observations (ATel #12688, #12732) indicate that MAXI J1820+070 has significantly dimmed in the X-rays after the second prominent rebrightening started in March 2019 and detected in the optical, X-ray and radio bands (ATel #12567, #12573, #12577, #12596, #12608). The rebrightening occurred after the major outburst of the source in 2018 and during its decay to quiescence. We have been monitoring the evolution of the multiwavelength outburst and rebrightening of MAXI J1820+070 with the Asiago 1.22m, 1.82m and Schmidt 67/92 telescopes, and the ANS Collaboration telescope ID 2300, in coordination with the optical timing monitoring carried out by the AQUEYE+IQUEYE Collaboration (ATel #11723, #11824, #11899, #11936, #12157). The recent photometric evolution of MAXI 1820+070 recorded within the framework of our program confirms the dimming detected in the X-rays, with the brightness of the source decreasing to B = 17.84 and V = 17.30 (averaged over intra-night variability) on May 7, 2019, only 0.7-0.8 magnitudes above the minimum flux detected around the beginning of March 2019. Similarly to what observed in the X-rays (ATel #12732), the decay rate in both the B and V bands increased after Apr 29, 2019, passing from 0.06 mag/day between Mar 28 and Apr 29, 2019, to 0.18-0.19 mag/day between Apr 29 and May 7, 2019.