0 Assigned ID: 1794 ----- Attempting Submission 1 (Fri Apr 09 02:37:45 GMT 2021) ----- HST Phase I Proposal 1794 successfully submitted. Receipt: # 1794-1 ----- Attempting Submission 2 (Fri Apr 09 22:34:33 GMT 2021) ----- HST Phase I Proposal 1794 successfully submitted. Receipt: # 1794-2 ----- Attempting Submission 3 (Fri Apr 09 23:52:10 GMT 2021) ----- 0 ----- Attempting Submission 1 (Thu Jul 29 16:54:31 GMT 2021) ----- We propose UV spectroscopy of the supermassive black hole binary (SBHB) candidate J095036+512838 (J0950) to test the alternative scenario that it harbors a perturbed accretion disk around a single black hole. By analogy to spectroscopic binary stars, this object was originally selected as a SBHB candidate by virtue of the ~1300 km/s blueshift of its broad Balmer lines relative to the rest frame set by the narrow lines. According to new spectroscopic monitoring of the radial velocity curve, J0950 recently passed conjunction and is consistent with a SBHB with a period of order decades. This is an extremely strong indication of binary motion that no other candidate has shown before, making J095036 the strongest candidate of its class. The radial velocity curve also conclusively rules out the hypothesis that this is a recoiling black hole. We will observe the Ly-alpha and C IV broad lines to discriminate between the SBHB hypothesis and the single, perturbed accretion disk hypothesis. In the former scenario the UV lines are expected to be offset in velocity just as the optical Balmer lines while in the latter they are expected to be centered at the redshift of the narrow optical emission lines. The target has a redshift of 0.2144, galactic E(B-V) value of 0.149, and GALEX FUV and NUV AB magnitudes of 20.25 and 19.67, respectively. We will observe it for 5 orbits with COS/G140L to detect the broad Ly-alpha and CIV emission lines and determine whether they have velocity offsets relative to the rest frame set by narrow lines in a ground-based optical spectrum. The A segment covers 1281-2148 Angstroms, which includes both Ly-alpha and C IV at the target redshift. We obtained the target coordinates from the SDSS DR16 SkyServer. These coordinates are in the ICRS coordinate system. We computed astrometric errors by following the prescription described in the SDSS DR16 web pages. In summary, the uncertainties in the astrometric solution of each plate are combined in quadrature with the uncertainties in the centroid of the object. The final uncertainties are listed in the target forms and are better than 0.1 arcsec. We will acquire the target with COS using ACQ/IMAGE in the NUV. This approach is recommended for targets with coordinate uncertainties <0.4 arcsec even if the science observations to follow are in the FUV. This is advantageous, because the acquisition exposure time to reach S/N 20 given the GALEX NUV magnitude is much shorter than using ACQ/PEAKXD+ACQ/PEAKD in the FUV. We will carry out the ACQ/IMAGE procedure with MIRRORA because the target is faint. Science observations will be conducted with COS/G140L. As recommended to preserve the life of the detector and improve S/N in the FUV, we will use all FP-POS positions. In order to minimize overheads associated with these small movements, we will observe different positions in different orbits. We aim to keep exposure times in each position similar, but prioritized changing positions during occultation so that no time is lost. Buffer times for each exposure are set to the exposure time for that orbit, because the buffer fill time is extremely long for this target. This approach is advantageous because no data will be lost if the target is brighter than expected from the GALEX magnitudes, which is possible because it is a quasar. We have configured the exposures into a single visit. The science goal of this program is to compare the Ly-alpha and CIV broad line profiles to the H-beta profile in the optical. The orbit allocation is needed to reach high enough S/N ratio in the UV line profiles to measure properties of the broad lines (namely, their velocity offset and shape). The target is a quasar, so it is variable and changes in the broad-line profiles are common on week to month timescales. Importantly, if we were to split the program into 2 visits and the shape of the line profile changed between them, we would not be able to combine the resulting spectra to reach our target S/N. Given our science goal of comparing the H-beta and UV line profiles, we need to observe them at the same time to rule out differences due to variability. Coordinated observations with ground-based observatories place very loose scheduling constraints on the HST observations. We determined that the optical and UV observations need to be taken within one month of each other. Given the coordinates of the target, we can obtain a ground-based spectrum during the period between the start of November and the end of May. Given the need for observations within 1 month, we require the HST observations be scheduled between October and June, inclusive. This constraint does not substantially impact schedulability, it only removes two small windows in September 2022. Is the supermassive black hole binary candidate J0950+5128 actually a single perturbed accretion disk? Cycle 29 Proposal J. Runnoe, T. Bogdanovic, M. Charisi, M. Eracleous, J. Lazio, J. Simon, D. Stern All of the investigators have extensive expertise in the observation and physics of supermassive black hole binaries (SBHBs). J. Runnoe, M. Eracleous, and T. Bogdanovic are conducting the observational search that provides the motivation and targets for this proposal (Eracleous et al. 2012, Runnoe et al. 2015, Nguyen et al. 2016, Runnoe et al. 2017, Pflueger et al. 2018, Nguyen et al. 2018, 2019, 2020a,b). J. Runnoe and M. Eracleous have a scientific background in the physics and observations of active galactic nuclei and they are the principal authors of many papers on quasar central engines, which are the main interlopers into SBHB candidate samples. M. Eracleous is also an expert on the physics and spectra of double-peaked emitters (e.g., Eracleous & Halpern 1994, Eracleous et al. 1997, Eracleous & Halpern 2003, Eracleous et al. 2009). T. Bogdanovic's background is in the theory of accreting supermassive black holes and gravitational wave astrophysics. M. Charisi is an expert on the physics and observations associated with periodic variations in the brightness of quasars as signatures of a SBHB (Charisi et al. 2015, Charisi et al. 2016, Charisi et al. 2018). J. Lazio and J. Simon have expertise in developing and exploring links between electromagnetic and gravitational wave signatures of supermassive black hole binaries (Burke-Spolaor et al. 2019). J. Lazio was one of the leads for the GO Cycle 22 project to search for electromagnetic signatures of a candidate SMBH in the cluster Abell 2261. He has been involved in several other efforts to test candidate supermassive black hole binary systems with electromagnetic observations. J. Simon has extensive expertise on the gravitational wave background and its connection to observational astrophysics (Simon & Burke-Spolaor 2016). He is the PI of the Palomar program with long-term status that obtained the new spectrum of the target for this proposal. D. Stern is an expert on the multi-wavelength physics and properties of active galaxies, particularly their variability (Stern et al. 2017, Stern et al. 2018). This collaboration has access to the Hobby-Eberly (co-I Eracleous) and Keck and Palomar (co-I Stern) telescopes and regularly obtain time on them at the level of one night per month or better. We guarantee the time needed to obtain a ground-based optical spectrum in coordination with HST. Supermassive Black Holes and Active Galaxies Galaxies 6 false true true false false false false false SUPPORTED GALAXY SEYFERT NO The coordinates were updated in phase 2 to SDSS DR16 (ICRS) with uncertainties. Target radius in SDSS u-band is <0.35". Spectral classification is QSO. No relevant proper motion. J2000 J2000 GALEX_NUV_MAG=19.67, GALEX_FUV_MAG=20.25 COS/FUV Spectroscopic No No G140L 1280 1626907898590 /Users/runnojc1/Dropbox/Research/proposals/2021_HST/BBH_UVspec/phase2/OP-cache/APTform_phase2_BBH_UVspec-v01.xml The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. 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