I had it at 12.5 visual on March 14.085 UT. It was a tad brighter in April 2020 at 12 4, and then 11.9 in April 2013 – the brightest ‘outburst’ for a number of years. I have a light curve here… https://garypoyner.wix.com/variablestars/markarian-421
Gary
