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Swift Observations of Swift J1933.9+3258: a probable radio-quiet AGN

ATel #859; D. Grupe (PSU), J. Tueller (NASA/GSFC), C. Markwardt (U Md, NASA/GSFC), J. A. Kennea (PSU), A. Falcone (PSU), R. Mushotzky (NASA/GSFC), S. Barthelmy (NASA/GSFC), H. Krimm (NASA/GSFC), W. N. Brandt (PSU), D. Schneider (PSU), M. Ajello (MPE Garching), V. Beckmann (UMBC/NASA/GSFC), T. Belloni (INAF/OAB), O. Godet (U Leicester) , S. Holland (USRA/NASA/GSFC), K. Mukai (USRA/NASA/GSFC), T. Okajima (JHU/NASA/GSFC), R. Sambruna (NASA/GSFC)
on 18 Jul 2006; 15:53 UT
Credential Certification: Dirk Grupe (grupe@astro.psu.edu)

Subjects: Optical, Ultra-Violet, X-ray, AGN, Black Hole, Quasar

Referred to by ATel #: 862, 4151

We report on the Swift observations of the Swift BAT survey source Swift J1933.9+3258. The source was detected in our ongoing Swift Burst Alert Telescope (BAT) hard X-ray survey (Tueller et al. ATEL #668 and #669, Kennea et al. ATEL #677, Ajello et al. ATEL #697). In 9 months of the BAT survey it was detected with a significance of 6 sigma with a flux in the 10-100 keV band of 2.7e-11 ergs/s/cm2. The spectrum is fitted by a single power law with an energy spectral slope of 1.6. Swift observed this source on 2006-July-07 04:53 UT to 2006-July-07 19:23 UT for a total of 1256s with the X-ray telescope (XRT) and the UV-optical telescope UVOT. The UVOT observed it in all six filters with the following observing times: V: 109s, B: 107s, U: 117s, UVW1: 226s, UVM2: 235s, and UVW2: 573s. We found a bright X-ray source, Swift J193347.3+325425 at RA (2000) = 19 33 47.26 Dec (2000) = +32 54 25.4 with a position error of 3.7". Swift J193347.3+325425 was discovered as a bright X-ray source during the ROSAT All-Sky Survey (RASS) as 1RXS J193347.6+325422. It was re-observed by ROSAT serendipitously during a PSPC pointed observation at a far off-axis position. Due to its low Galactic latitude (6 degrees), the ROSAT X-ray spectrum is highly absorbed with a absorption column density of NH=3.4e21 cm^-2. The Swift XRT data confirm this result. The X-ray spectrum is well fitted by a broken power law with energy spectral index alpha_x,soft = 1.98+0.50-0.49, E-break = 1.35+0.52-0.80 keV, alpha_x, hard = 1.02+0.41-0.37 which is in good agreement with the ROSAT spectrum. The source does show some variability on long timescales. The absorbed 0.2-2.0 keV flux during the ROSAT pointed observation was 5.1e-12 ergs/s/cm2 while during the XRT observation this was 8.0e-12 ergs/s/cm2. We do not find however any significant variability over the time period of the XRT observation. A combined fit to the XRT and BAT data results in a hard X-ray spectral slope alpha-X, hard = 1.12+0.20-0.32. The UVOT photometry gives the following magnitudes in all 6 filters: V: 14.82+/-0.03 B: 15.35+/-0.03 U: 14.44+/-0.03 UV W1: 14.81+/-0.02 UV M2: 15.77+/-0.04 UV W2: 15.66+/-0.02 Corrected for reddening (using the value of the Galactic column density NH=2.26e21 1/cm2 given by Dickey & Lockman 1990) the magnitudes are: Vcorr = 13.33 Bcorr = 13.40 Ucorr = 12.00 UVW1corr = 11.75 UVM2corr = 11.40 UVW2corr = 11.99 The X-ray to optical flux ratio fx/fopt=2.7 places it in Diagram Figure 1 of Maccacaro et al. (1998, A&A, 326, 680) and Figure 2 of Beuermann et al. (1999, A&A, 347, 47) as an AGN. Also the very blue optical/UV spectrum argues for this identification. Swift J193347.3+325425 is also associated with the NVSS radio source NVSS 193347+325426. The radio loudness of this AGN is R=1.5. Following the definition by Kellermann et al. (1989) this is a radio-quiet AGN.