MASTER optical activity of blazar H 1426+428

ATel #14503; K. Zhirkov, V. Lipunov, V. Kornilov (Lomonosov MSU), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), R. Podesta, F. Podesta, C. Francile (OAFA), D. Buckley (SAAO), , E. Gorbovskoy, O. Gress, N. Tiurina, P. Balanutsa, F. Balakin, V. Vladimirov, A. Kuznetsov, D. Vlasenko, I. Gorbunov, D. Zimnukhov, V. Senik, A. Chasovnikov, A. Pozdnyakov, V. Topolev, D. Cheryasov, V. Shumkov, T. Pogrosheva (Lomonosov Moscow State University, SAI, Physics Department), N. M. Budnev (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V. Yurkov (Blagoveshchensk State Pedagogical University)
on 2 Apr 2021; 06:55 UT
Credential Certification: Nataly Tyurina (tiurina@sai.msu.ru)

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MASTER-Net (Lipunov et al., 2010, MASTER Robotic Net, Advances in Astronomy, vol. 2010, p.30L) reports on an enhanced optical activity of the blazar H 1426+428 during its elevated very-high energy gamma-ray flux(Quinn et al. ATel #14501).

MASTER-IAC observed the source on 2021-04-01 from 04:42UT to 05:21UT in BVRI and unfiltered with exposure time of 180s.
Reference stars for aperture photometry were taken from GSC2.3 catalog for B and V bands, PPMX catalog for R band, LONEOS catalog for I band and from GAIA EDR3 for unfiltered band.
We obtained the following magnitudes:
B=16.80+/-0.04,
V=16.21+/-0.07,
R=16.34+/-0.09,
I=15.67+/-0.04,
W(unfiltered)=16.21+/-0.04.

Variability on a timescale of 10 minutes was not detected.
Since MASTER-Net telescopes usually survey sky with no filter, we can directly compare only W band.
Reference frame was taken on 2020-09-28 by MASTER-Tunka with a source magnitude of W=16.48+/-0.05.
Considering it, we can assume that the blazar has an optical brightening, simultaneous with very-high energy gamma-ray flux (ATel #14501).
We encourage multiwavelength observations.
MASTER-Net will continue observing the blazar in the following nights.

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