Bright Optical Flare in the flaring gamma-ray BL Lac S5 1803+784
ATel #13711; Tapio Pursimo (NOT), Roopesh Ojha (NASA/GSFC/UMBC), and Haakon Dahle (ITA, U. of Oslo)
on 7 May 2020; 02:40 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)
Subjects: Optical, Gamma Ray, >GeV, VHE, AGN, Blazar, Quasar
We report optical photometry of the BL Lac object S5 1803+784,
obtained with the 2.56m Nordic Optical Telescope in La
Palma, to look for any enhanced optical activity associated with its
enhanced gamma-ray emission state (ATel#13633).
These NOT observations were made using the ALFOSC (Alhambra Faint
Object Spectrograph and Camera) instrument. Standard IRAF data
reduction (de-biasing + flat field correction with twilight flats) was
carried out. The magnitude is obtained using SExtractor MAG_AUTO and
the magnitude zero point was calibrated against PS1 field stars near the target.
The std-dev of the zero point was 0.02 mag.
We find that S5 1803+784 has SDSS r(AB)-magnitude = 14.518+/-0.002 and
14.670+/-0.002 at epochs 2020-04-19T0557 and 2020-04-20T0545, respectively.
This is close to its historical maximum of about R=13.9 (Nesci et al.
2002, AJ, 1234, 53)
and brighter than during the gamma-ray and optical flare in 2011
(ATel#3792, ATel#3323).
It is ~5 times and ~10 times brighter than its survey magnitudes of
16.236 and 17.08 from
PanSTARRS PS1 and SDSS, respectively.
We encourage further multi-wavelength coverage. We will continue to
monitor this source and report future developments using this and
other platforms.
