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Swift detection of the rapidly flaring FSRQ SDSSJ002829.81+200026.7

ATel #12094; S. Komossa (MPIfR), D. Grupe (Morehead State University), K. Z. Stanek (OSU)
on 10 Oct 2018; 16:10 UT
Credential Certification: St. Komossa (stefanie.komossa@gmx.de)

Subjects: Optical, Ultra-Violet, X-ray, AGN, Blazar, Quasar

Referred to by ATel #: 12120, 12193

We have observed the flaring flat-spectrum radio quasar (FSRQ) SDSSJ002829.81+200026.7 (87GB 002553.4+194347; Gregory & Condon 1991) at redshift z=1.55 with the Neil Gehrels Swift observatory on 2018 October 09 in all filters in the optical and UV, and in the X-ray band. SDSSJ002829.81+200026.7 was detected in a rapid, unprecedented factor ~100 outburst with the All Sky Automated Survey for SuperNovae (ASAS-SN; ATEL #12082) with peak on 2018 October 05. It is now fading, and was accompanied by a gamma-ray flare (ATEL #12084). With Swift, we detect the FSRQ at an X-ray countrate of (4.1+1.3-1.1)e-3 counts/s, marginally fainter than during an earlier Swift observation carried out on 2018 October 08 at (5.5+1.5-1.3)e-3 counts/s. Merging both observations, we estimate a rather flat X-ray spectrum with photon index Gamma_x=1.3+/-0.3 (absorption fixed at the Galactic value), and an average unabsorbed X-ray flux of 3.81e-13 erg/cm2/s in the observed (0.3-10) keV band. The X-ray position of RA-2000: 00h 28m 29.77s, Dec-2000: +20deg 00' 24.7'' (90% confidence error radius of 4.4'', based on Evans et al. 2009) is consistent with the optical SDSS position of this broad emission-line quasar. SDSSJ002829.81+200026.7 was detected in all optical/UV bands with Swift at magnitudes in the Vega system of UVW2: 19.88+/-0.20 (19.21), UVM2: 18.99+/-0.11 (18.19), UVW1: 18.96+/-0.13 (18.40), U: 18.42+/-0.12 (17.97), B: 19.21+/-0.19 (18.86), and V: 18.52+/-0.23 (18.25) (uncorrected and corrected for Galactic extinction, respectively) on 2018 October 09. This implies a decline by 0.6 mag in the filter UVW1 which was chosen during the earlier, independent Swift observation of October 08, and shows that the flare is rapidly fading in the UV as well.