A recent X-ray spectrum of the Seyfert 1.5 Mrk 279 shows a remarkable, unprecedented change - a previously strong narrow Fe K line has disappeared. The X-ray continuum spectrum is otherwise normal in brightness and shape. If the narrow line is formed at distances of ~1 pc, around the obscuring torus, it is difficult for the flux to disappear from such an extended structure, either via obscuration or photoionization changes. This suggests that the line may be formed in the broad line region. However, recent ground-based optical spectra show that the broad Balmer lines have normal widths and intensity. The accretion flow must have changed dramatically at smaller radii, potentially signaling a torn or disrupted disk. Clues to such a disruption could be apparent in the shape of the UV/optical continuum or the structure of the inner parts of the BLR. To test this possibility, we propose to obtain a UV through optical spectrum to examine the continuum shape and to probe the high-ionization UV broad lines (Ly alpha, NV, C IV, He II) which are formed 2-10 times closer to the central engine than the Balmer lines. The narrow Fe K emission line in the Seyfert galaxy Mrk 279 has recently disappeared in X-ray spectra obtained with NuSTAR. We will obtain spectra with a S/N of ~15 covering the wavelength range from the far-UV to the optical, encompassing the major broad lines visible in a typical AGN spectrum: Ly alpha, N V 1240, Si IV 1400, C IV 1550, He II 1640, C III] 1909, Mg II 2798, H beta, and [O III] 4959,5007. We will acquire the target using an imaging target acq with the STIS CCD in the long-pass filter. Using the gratings G430L (with the CCD), G140L (FUV MAMA) and G230L (NUV MAMA), we will cover the full wavelength range. Current ground-based observations show a continuum flux level near H beta at 4900 A of 1e-15 erg/cm2/s/A. Our calculations using the STIS ETC use the SDSS-based QSO spectrum as a model, z=0.03045, and E(B-V)=0.014. All observations fit in a single orbit. Bright object checking shows a violation with GSC2, but this is due to the host galaxy, which is extended and has an integrated brightness of V=10.4. GALEX shows that the nucleus and surrounding field are safe for STIS. Dr. Ed Cackett, Wayne State University is an expert on multi-wavelength observations of AGN. Cackett has previous experience of HST/STIS spectroscopy of Seyfert 1s. He analyzed the recent LCO ground-based spectrum of Mrk 279. He is a co-I on the NuSTAR Mrk 279 analysis. Dr. Jon Miller, University of Michigan is the PI of the NuSTAR observations of Mrk 279 and an expert on X-ray spectroscopy of black holes. Dr. Elias Kammoun & Dr. Abdu Zoghbi are experts on X-ray spectroscopy of AGN, and are co-Is on the Mrk 279 NuSTAR project. Dr. Gerard Kriss & Dr. Elisa Costantini are experts on UV and X-ray spectroscopy of AGN, and have both worked on previous HST spectra of Mrk 279. Supermassive Black Holes and Active Galaxies 0 false SUPPORTED GALAXY ACCRETION DISK BLR NLR NUCLEUS SEYFERT This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 5.5E-15 erg/cm^2/s/A at 2246A from recent Swift/UVM2 observations STIS/CCD Spectroscopic No No G430L 4300 STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/NUV-MAMA Spectroscopic No No G230L 2376 POS-TARG DITHER 0.2 LINE false false 3 90.0 STIS-ALONG-SLIT 1 false 1600880633002 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16433 :visit-id "01" :proposal-version -1 :trans-version "20200619" :date "23-Sep-2020 13:03:52.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 248080 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16433 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16433 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2565 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2970 :pcs-gap 0 ) false 1 0 In case the target is fainter than expected, we use a 5 s exposure instead of the 1 s exposure from the ETC calculation at the current brightnesss level of 1e-15 at 4900 A.