17208( 4) - 11-Aug-2022 20:26:07 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17208 Version: 4 Check-in Time: 11-Aug-2022 20:26:07 STScI Edit Number: 0 Title Tick Tock, Time's Up: An Alternative to the Supermassive Black Hole Binary Scenario in J1430 ------------------------------------------------------------------------------------ Type Cycle GO 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Jessie Caye Runnoe Vanderbilt University Y CoI: Prof. Michael Eracleous The Pennsylvania State University N CoI: Prof. Tamara Bogdanovic Georgia Tech Research Corp. N CoI: Dr. Benny Trakhtenbrot Tel Aviv University N CoI: Muryel Guolo The Johns Hopkins University N CoI: Dr. Suvi Gezari Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract We propose 3 orbits of optical+UV spectroscopy to test the nature of the "Tick Tock" binary supermassive black hole candidate. J143016+230344 (hereafter J1430) was recently selected based on a rapidly evolving periodicity in its multi-band photometric light curve and is predicted to coalesce within the next 3 years. J1430 is an active galactic nucleus (AGN) and its broad H-alpha line has changed from single peaked with a -2400 km/s velocity offset to double peaked at the systemic velocity. In the binary scenario, this could indicate that the broad line initially traced bulk orbital motion of the secondary and now the newly formed circumbinary broad-line region. We will test the alternative scenario that J1430 is actually a variable single AGN with a perturbed accretion disk. By nearly-simultaneously observing the Ly-alpha, CIV, H-beta, and H-alpha broad emission lines and comparing the shapes of their profiles we can discriminate between (i) bulk orbital motion of the secondary in a binary, (ii) a newly formed circumbinary broad-line region, and (iii) a single black hole with dramatic photometric variability and an emissivity enhancement like a spiral arm in the outer disk where broad lines are produced. This test will arbitrate on the binary nature of J1430. ------------------------------------------------------------------------------------ Observations Description ------------------------ SCIENTIFIC GOALS AND GENERAL STRATEGY This program will use quasi-simultaneous optical and UV spectroscopy to test the nature of the binary supermassive black hole candidate J143016+230344 (hereafter J1430). The practical aim is to compare the Ly-alpha, CIV1549, H-beta, and H-alpha broad-line profiles to rule out the single disk alternative. We will observe J1430 for 2 orbits with COS/G140L to detect the broad Ly-alpha and CIV emission lines and determine their shape and velocity offsets relative to the emission lines in a quasi-simultaneous optical spectrum. We will follow with one STIS orbit to obtain coverage of the optical spectrum. This requires three setups: G430L to cover H-beta, and G750M at tilts of 6768A and 7283A to cover H-alpha. We will also obtain complementary ground-based optical spectra in order to look for changes in the broad H-alpha line before and after the HST observations. 17208( 4) - 11-Aug-2022 20:26:07 - [ 2] TARGET PROPERTIES AND COORDINATES The target has a redshift of 0.081, galactic E(B-V) value of 0.1, and current ZTF g-band and Swift UVW1 AB magnitudes of 17.466 and 18.8, respectively. Notably, the target brightened substantially since Sloan Digital Sky Survey (SDSS) imaging was taken in 2004. Though J1430 is nominally extended (the SDSS u-band exponential model radius is 0.4") in SDSS, the quasar continuum dominates recent spectra. Therefore, we anticipate that the AGN dominates in imaging in the UV and the morphology has a bright point source (i.e., it is not extended). 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. SCHEDULING CONSIDERATIONS We schedule this program as two visits so that no unnecessary constraints are imposed that might impact scheduling. Given the science requirement that the STIS spectrum be observed immediately before or after COS, we adopt the GROUP WITHIN scheduling constraint set to 1 orbit. This will automatically trigger the minimum time possible between orbits, and they will be taken consecutively. Coordinated ground-based observations are needed in order to characterize the longer-term trends in the optical spectrum. This places very loose scheduling constraints on the HST observations. Given the coordinates of the target, we can obtain a ground-based spectrum during the period between the start of January and the middle of August. COS INSTRUMENT SETUP 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 current magnitude is much shorter than using ACQ/PEAKXD+ACQ/PEAKD in the FUV. We will carry out the ACQ/IMAGE procedure with PSA+MIRRORB, a conservative choice that prioritizes detector safety if the target is brighter than expected (see below). 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 current magnitudes, which is possible because it is a variable quasar. The bright object tool (BOT) reveals one unsafe exposure which we investigate further. The culprit is the acquisition exposure of the target itself. The 17208( 4) - 11-Aug-2022 20:26:07 - [ 3] Guide Star Catalog 2 (GSC2) lists the target at V(Vega)=13.89 mag and adopts a stellar spectrum of type OV5 to yield a high count rate per pixel, which triggers the warning. We verify the safety of our acquisition strategy via recent photometry and with further exposure time calculations. Given recent ZTF g(AB)=17.145 and r(AB)=16.369 magnitudes, the inferred V(Vega)=16.71 is fainter than expected based on the BOT. However, we conservatively adopt MIRRORB for acquisition. This increases the required exposure time, but even if the target does have V(Vega)=13.89 the count rate per pixel will still be acceptable with the exposure time required to reach S/N=20 at g(AB)=17.466 (the latest magnitude from ZTF). This still triggers a warning from the BOT, which is due to the use of the incorrect stellar OV5 spectral shape. We verify in the ETC that usage of the correct SDSS quasar spectrum mitigates this issue. STIS INSTRUMENT SETUP To acquire the targets with STIS we will use the standard point-source acquisition sequence with the CCD. Since we are using the 52x0.5 arcsec slit, we will not need an ACQ/PEAK sequence. We adopt a 3-step dither pattern along the slit (step size 0.35 arcsec or 7 pix) to mitigate the effects of hot pixels and cosmic rays. To mitigate the effects of charge-transfer inefficiency, we will place the target at the recommended E1 (or E2 for exposures requiring Fringe Flats) aperture position. For the 52x0.5 slit, the E1 and E2 positions have similar throughput. We schedule calibration observations to reduce overheads and prioritize science observations during the orbit. For the first STIS/CCD observation we select WAVECAL=NO, which turns off automatic wavelength calibration exposures for the entire visit. We manually include wavelength calibration for each of the G430L, G750M-6768, and G750M-7283 setups, pushing the final wavelength calibration into occultation. Additionally, G750M experiences substantial fringing at wavelengths longer than 7000 A, which could impact the G750M-7283 observations. We schedule the G750M-7283 science observation at the end of the orbit and include a contemporaneous fringe flat exposure during occultation (after the wavelength calibration) to correct fringing effects. All calibration exposures use the 52x0.1 arcsec slit recommended for science with the 52x0.5 arcsec slit. IMPACT OF REDUCED-GYRO OPERATIONS Reduced-gyro operations should not have a major impact specific to this program. A potential issue is that reduced gyro observations can impact COS observations if roll angle constraints are present in order to avoid putting the secondary aperture on a bright source when the primary aperture is on the target. No such constraints are required for this program according to the BOT. Other common impacts include the reduction of observing windows (especially for programs with constrains that reduce observability) and difficulty completing coordinated time-domain observations. Neither of these issues apply because we have only one 3-orbit visit with only very loose observing constraints. ------------------------------------------------------------------------------------ 17208( 4) - 11-Aug-2022 20:26:07 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 2MASS-J14301 GALAXY, SEYFERT RA=14H30M16.0538S +/- J2000 Z = V = 16.7115 +/- 0.01 603+2303445 0.0386877", DEC=+23D03'44.43" 0.081 ZTF_g(MJD=59769)=17.466+/-0.023, +/- 0.0485025" Swift_UVW1(MJD~59300)~18.8 Reference Frame: ICRS Extended: NO Comments: Target is variable AGN, latest magnitudes estimated from ZTF and Swift in 2022. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016 -1.638996561623503E-4 0.002044207925416694 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17208( 4) - 11-Aug-2022 20:26:07 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.35 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 90.0 Angle_Between_Sides Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 17208( 4) - 11-Aug-2022 20:26:07 - [ 6] Visit: 01 Visit Requirements: BETWEEN 01-JAN-2022:00:00:00 AND 15-AUG-2022:00:00:00; BETWEEN 01-JAN-2023:00:00:00 AND 15-AUG-2023:00:00:00; BETWEEN 01-JAN-2024:00:00:00 AND 15-AUG-2024:00:00:00; GROUP 01, 02 WITHIN 1 Orbits On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 2MASS-J1430 COS/NUV ACQ/IMA PSA MIRRORB 1 33 S (33 1603+230344 GE S) 5 ------------------------------------------------------------------------------------------------------------------------------------ 2 2MASS-J1430 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=1083, FLASH=YES, 1 1138 S 1603+230344 G FP-POS=1 see below 5 (1083 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 2MASS-J1430 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=1083, FLASH=YES, 1 1138 S 1603+230344 G FP-POS=2 see below 5 (1083 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 2MASS-J1430 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=1260, FLASH=YES, 1 1279 S 1603+230344 G FP-POS=3 see below 5 (1260 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 2MASS-J1430 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=1260, FLASH=YES, 1 1279 S 1603+230344 G FP-POS=4 see below 5 (1260 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 2MASS-J14301603+230 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A 3445 GE 2MASS-J14301603+230 2 COS/FUV TIME-TA PSA G140L 800 none none none none 1 1083.0 S 3445 G 2MASS-J14301603+230 3 COS/FUV TIME-TA PSA G140L 800 none none none none 1 1083.0 S 3445 G 2MASS-J14301603+230 4 COS/FUV TIME-TA PSA G140L 800 none none none none 2 1260.0 S 3445 G 2MASS-J14301603+230 5 COS/FUV TIME-TA PSA G140L 800 none none none none 2 1260.0 S 3445 G 17208( 4) - 11-Aug-2022 20:26:07 - [ 7] Visit: 02 Visit Requirements: BETWEEN 01-JAN-2022:00:00:00 AND 15-AUG-2022:00:00:00; BETWEEN 01-JAN-2023:00:00:00 AND 15-AUG-2023:00:00:00; BETWEEN 01-JAN-2024:00:00:00 AND 15-AUG-2024:00:00:00; GROUP 02, 01 WITHIN 1 Orbits On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 2MASS-J1430 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 2 S (2 S) 1603+230344 5 ------------------------------------------------------------------------------------------------------------------------------------ 2 WAVE STIS/CCD ACCUM 52X0.1 G430L 4300 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 2MASS-J1430 STIS/CCD ACCUM 52X0.5E1 G430L 4300 CR-SPLIT=NO, WAVECAL=NO 1 67 S PATTERN 1 3 1603+230344 see below 5 (180 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 WAVE STIS/CCD ACCUM 52X0.1 G750M 6768 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 2MASS-J1430 STIS/CCD ACCUM 52X0.5E1 G750M 6768 CR-SPLIT=NO 1 189 S PATTERN 1 5 1603+230344 see below 5 (546 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 2MASS-J1430 STIS/CCD ACCUM 52X0.5E2 G750M 7283 CR-SPLIT=NO 1 209 S PATTERN 1 6 1603+230344 see below 5 (606 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 WAVE STIS/CCD ACCUM 52X0.1 G750M 7283 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 CCDFLAT STIS/CCD ACCUM 52X0.1 G750M 7283 2 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 2MASS-J14301603+230 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 3445 WAVE 2 STIS/CCD ACCUM 52X0.1 G430L 4300 none none none none 1 N/A 2MASS-J14301603+230 3 STIS/CCD ACCUM 52X0.5E1 G430L 4300 1 none none none 1 60.0 S 3445 2MASS-J14301603+230 3 STIS/CCD ACCUM 52X0.5E1 G430L 4300 2 none none none 1 60.0 S 3445 2MASS-J14301603+230 3 STIS/CCD ACCUM 52X0.5E1 G430L 4300 3 none none none 1 60.0 S 3445 WAVE 4 STIS/CCD ACCUM 52X0.1 G750M 6768 none none none none 1 N/A 17208( 4) - 11-Aug-2022 20:26:07 - [ 8] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 2MASS-J14301603+230 5 STIS/CCD ACCUM 52X0.5E1 G750M 6768 1 none none none 1 182.0 S 3445 2MASS-J14301603+230 5 STIS/CCD ACCUM 52X0.5E1 G750M 6768 2 none none none 1 182.0 S 3445 2MASS-J14301603+230 5 STIS/CCD ACCUM 52X0.5E1 G750M 6768 3 none none none 1 182.0 S 3445 2MASS-J14301603+230 6 STIS/CCD ACCUM 52X0.5E2 G750M 7283 1 none none none 1 202.0 S 3445 2MASS-J14301603+230 6 STIS/CCD ACCUM 52X0.5E2 G750M 7283 2 none none none 1 202.0 S 3445 2MASS-J14301603+230 6 STIS/CCD ACCUM 52X0.5E2 G750M 7283 3 none none none 1 202.0 S 3445 WAVE 7 STIS/CCD ACCUM 52X0.1 G750M 7283 none none none none 1 N/A CCDFLAT 8 STIS/CCD ACCUM 52X0.1 G750M 7283 none none 1 none 1 N/A CCDFLAT 8 STIS/CCD ACCUM 52X0.1 G750M 7283 none none 2 none 1 N/A 17208( 4) - 11-Aug-2022 20:26:07 - [ 9] Summary Form for Proposal 17208 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.1, 52X0.5E1, 52X0.5E2, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV, STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT, BUFFER-TIME=1083, BUFFER-TIME=1260, CR-SPLIT=NO, FLASH=YES, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-JAN-2022:00:00:00 AND 15-AUG-2022:00:00:00, BETWEEN 01-JAN-2023:00:00:00 AND 15-AUG-2023:00:00:00, BETWEEN 01-JAN-2024:00:00:00 AND 15-AUG-2024:00:00:00, GROUP 01, 02 WITHIN 1 Orbits, GROUP 02, 01 WITHIN 1 Orbits, PATTERN 1 3, PATTERN 1 5, PATTERN 1 6 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G430L, G750M, MIRROR, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names 2MASS-J14301603+2303445, CCDFLAT, WAVE ------------------------------------------------------------------------------------------------------------------------------------