Spectroscopic confirmation of the AGN nature of Swift J1933.9+3258 (=1RXS J193347.6+325422)
ATel #862; M. A.P. Torres, D. Steeghs, M. R. Garcia, J. E. McClintock, P. Berlind, P. Zhao (CfA), P. G. Jonker (CfA/SRON), P. J. Callanan (UCC)
on 21 Jul 2006; 13:55 UT
Credential Certification: Danny Steeghs (dsteeghs@cfa.harvard.edu)
Subjects: Radio, Optical, X-ray, AGN, Black Hole
Referred to by ATel #: 4151
We report on optical spectroscopy of Swift J1933.9+3258 (=1RXS J193347.6+325422).
This X-ray source has recently been classified as a likely radio-quiet AGN on the
basis of its broad-band (radio, optical, UV, X-ray) properties (Grupe et al.
2006, ATel #859). In order to confirm its nature, a single 7-min spectrum of
the optical counterpart was acquired on June 20 2006 08:53 UT with the
1.5m Tillinghast telescope on Mt.Hopkins using its FAST spectrograph. The resultant
spectrum covered the wavelength range 3480-7420 Angstroms with a
dispersion of 1.5 A/pix and a 6 A FWHM resolution.
The optical spectrum clearly shows redshifted and broad Balmer lines
in emission from Halpha (blended with unresolved [NII]) to
Hepsilon. Also evident is HeI 5876 and narrow [OIII] 4959,5007 in
emission. The spectrum is highly reminiscent of a Seyfert 1 galaxy
given the large broadening of the hydrogen lines compared to the
forbidden lines. The Hbeta profile has FWHM > 3000 km/s and the
strength of Hbeta to [0III] 5007 is 2-3 implying a Seyfert 1.2 galaxy
(Winkler 1992,MNRAS,257,677). Swift J1933.9+3258 is therefore indeed a
radio-quiet AGN as proposed in ATel #859. Using the narrow emission
lines only, we measure a redshift of z=0.0580 +/- 0.0001,
corresponding to a source distance of 256 Mpc (for a Universe with
Ho=71 Km/s/Mpc, Omega=0.27, Lambda=0.73).
