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Spectroscopic observations of a major flare in QSO TXS0917+624.

ATel #11187; L. Wyrzykowski, M. Gromadzki, Sz. Kozlowski, P. Mroz(Warsaw Observatory),M. Shahbandeh, E. Hsiao(Florida State University),M. Berton, S. Ciroi, A. Pastorello, S. Chen, A. Reguitti(Padova)
on 17 Jan 2018; 15:45 UT
Credential Certification: Lukasz Wyrzykowski (wyrzykow@astrouw.edu.pl)

Subjects: Infra-Red, Optical, Blazar, Quasar, Transient

We report on optical and near-IR spectroscopy of QSO TXS0917+624 (radio and gamma source) which showed a major 2 magnitude flare on 9th of December 2017 (Spiridonova, Moskvitin and Vlasyuk 2017, ATEL #11048).

Near-IR spectrum was taken on 2017-12-11 with IRTF telescope in Hawaii, in Prism and SXD mode. The spectrum is rather featureless and shows marginal Halpha in emission at z=1.446.

A low resolution optical spectrum was also taken on 2017-12-19 with Asiago 1.82m Copernico Telescope with AFOSC instrument (range 340-820 nm; resolution 1.4 nm), showed a featureless continuum in rest-frame ultraviolet. The new spectrum was compared to the archival SDSS spectrum from 2014-03-06, which showed broad emission lines of MgII, CIII and CIV. These lines disappeared in the new spectrum because of a significant increase of synchrotron continuum most likely connected with jet ejection. The behavior of this blazar is consistent with the anti-correlation between jet continuum and lines EW as shown for 3C345 in Berton et al. 2017, but in a more extreme fashion. The series of intergalactic absorption lines did not change their intensity.

Further spectroscopic and photometric monitoring of this source is strongly encouraged.