Alert Notice 625: ASASSN-18ey = MAXI J1820+070 coverage needed for VLT and XMM

March 21, 2018: Dr. Tom Maccarone (Texas Tech University) has requested AAVSO observers' assistance in monitoring the outbursting black hole X-ray binary ASASSN-18ey = MAXI J1820+070 in support of VLT and XMM observations scheduled for:

2018 22 March 08-09:30 UT  and  29 March 08-09:30 UT

V time series are requested, with as short a cadence as possible (ideally, a time resolution of 0.1 second or better).

Please see AAVSO Alert Notice 624 for more information about this object.

ASASSN-18ey = MAXI J1820+070 has a published optical range of 12.5 CV - 18.3: V. The most recent observations submitted to the AAVSO International Database are:
2018 Mar. 20.38034 UT, 12.557 CV +/-0.015 (F.-J. Hambsch, Mol, Belgium);
20.38014, 12.341 CV +/-0.014 (Hambsch);
20.37994, 12.511 CV +/-0.016 (Hambsch);
20.37973, 12.426 CV +/-0.015 (Hambsch);
20.37953, 12.413 CV +/-0.015 (Hambsch);
20.37934, 12.535 CV +/-0.016 (Hambsch);
20.37913, 12.485 CV +/-0.016 (Hambsch);
Coordinates (2000.0):  R.A. 18 20 21.95   Dec. +07 11 07.3

Charts with a comparison star sequence for ASASSN-18ey may be created using the AAVSO Variable Star Plotter (VSP). You may use either ASASSN-18ey or MAXI J1820+070 as the name when creating a chart.

Please submit observations to the AAVSO International Database using the name ASASSN-18ey.

This observing campaign is being followed on the AAVSO Time Sensitive Alerts online forum at

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.

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