Spectroscopic Classification of WISE J061647.01-402142.8 (Fermi J0617-4026) as a Blazar

ATel #6937; J. Strader (Michigan State University), L. Chomiuk (Michigan State University), M. Landoni (INAF, Brera Observatory), D. Kocevski (GSFC/NASA), C. C. Cheung (Naval Research Laboratory)
on 16 Jan 2015; 21:39 UT
Credential Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)

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The bright X-ray detected infrared source WISE J061647.01-402142.8 was found within the LAT localization of the recently reported unidentified transient gamma-ray source Fermi J0617-4026 (ATel #6912). We obtained a spectrum of the optical counterpart of WISE J061647.01-402142.8 with the Goodman High Throughput Spectrograph on the SOAR 4.1m telescope on January 14, 2015, with wavelength coverage of ~ 3500-7000 Angstrom. A bright broad emission line is clearly detected which we associate with Mg II (lambda 2800) at a redshift, z=0.67. We further note that the WISE source does not have a counterpart listed in the SUMSS 843 MHz catalog. Inspecting the SUMSS image, we found a possible radio source at the WISE position with a peak of only 6.3 mJy/beam, which is close to the catalog threshold (Mauch et al. 2003 MNRAS, 342, 1117). We conclude the broad line detection is consistent with the flat-spectrum radio quasar (FSRQ) classification based on the infrared colors of WISE J061647.01-402142.8 but the radio emission is unusually faint for a FSRQ.