American Association of Variable Star Observers (AAVSO)
Mon, 10/17/2022 - 15:53

     As can be seen in recent AAVSO data, the classic blazar BL Lac has become active again.  As recently as Sep 25 it was down at V ~14.2, but is now bouncing around V ~12.5.  Two recent ATels report activity in the visible and at gamma-rays:

This activity is not unusual, but a potential precursor to an outburst.

I note that the AAVSO sequence here is relatively 'soft', with large uncertainties in the photometry.  I recommend instead adopting the much better controlled data summarized by Cameron Pace et al in:

...where there is a finder chart and BVRI data, specifically Table 2 in the paper.  Notice that the uncertainties are 5x to 10x smaller than those shown in the AAVSO sequence for the same stars.  It is best not to use Pace star 1, the very red star close to BL Lac:  it is not variable, but is much too red (B-V~1.7) compared to BL Lac (B-V ~0.9 or so).  Although V-filter photometry is convenient (and useful in my opinion), it is usual in the active galaxy community worldwide to get Cousins R photometry over the long term --- the first ATel cited above is an example.

     Note also that Peter Stetson has posted B,V photometry for fainter stars in the field:

...which complements the Pace et al data.