0 Assigned ID: 2692 ----- Attempting Submission 1 (Mon Jan 31 22:22:41 GMT 2022) ----- HST Phase I Proposal 2692 successfully submitted. Receipt: # 2692-1 ----- Attempting Submission 2 (Mon Jan 31 22:33:38 GMT 2022) ----- --Submission 3: 1. Switched to the UVIS2-C1K1C-SUB aperture to improve CTE-loss mitigation and to reduce risk of scattered light from the nearby bright source. 2. Switched to RAPID with NSAMP=11 to improve the fit-up-the ramp and CR rejection and to reduce read noise. --Submission 2: 1. The STIS ACQ type has been fixed to be more appropriate for the extended host galaxy, although the science target is the flare from the central nucleus. The ETC/exposure has been updated to ensure a SNR for the ACQ of ~100. 2. TIME-TAG mode is adopated for the MAMA observation for legacy value. 3. The point_spacing of Patterns 3 and 4 has been decreased to better cover the target. 1216246242 ----- Attempting Submission 1 (Tue Mar 29 15:00:43 GMT 2022) ----- ----- Attempting Submission 2 (Mon Apr 11 22:49:03 GMT 2022) ----- ----- Attempting Submission 3 (Thu Apr 14 20:20:24 GMT 2022) ----- UV Spectroscopy and Host Galaxy Imaging of a Possibly Coalescing Binary Supermassive Black Hole Binary supermassive black holes (SMBHs) are expected to be common from galaxy mergers. Their final inspirals and coalescences should produce gravitational waves detectable by pulsar-timing arrays and future space interferometers, making them exciting targets for multi-messenger astronomy. Subsequent to the most recent proposal deadline, the first candidate coalescing binary SMBH has just been discovered with rapidly decaying periods revealed by the remarkable optical and X-ray light curves (with the periods decreasing from ~one year to ~one month in the past three years). Multiple lines of evidence suggest that the system may be an uneven mass-ratio, highly eccentric binary SMBH that will likely merge within ~one to three years, presenting an exciting opportunity for multi-wavelength and potentially multi-messenger observations to witness the first ever binary SMBH merger event, justifying the mid-cycle request. New STIS UV spectroscopy may reveal evidence (or lack thereof) for a cutoff or notch in the NUV spectrum, which may arise from gap opening in the circumbinary accretion disk, and to measure the UV emission lines as tracers of accretion disk winds. Multi-band high-resolution WFC3 imaging is proposed to quantify the structural properties of the host galaxy, enabling bulge stellar mass measurement through robust bulge-disk decomposition for better (total) SMBH mass estimation, and to search for morphological evidence of a past merger. The program will independently test the binary hypothesis and provide the anchor for future follow-up campaigns. It has broad implications for multi-messenger astronomy and for understanding the cosmic formation and evolution of SMBHs. The target is a redshift z=0.081 Serfect 1 AGN (i.e., the nuclear point source) hosted by an extended galaxy with an effective radius of ~10" (5") along the semi-major (semi-minor) axis. It has been found to host an unusual nuclear transient flare whose period and amplitude are both decreasing rapidly. While the leading hypothesis is a coalescing binary SMBH, complementary observations are needed to fully test the binary hypothesis as well as alternative scenarios. This program will conduct STIS NUV-MAMA first-order spectroscopy with the G230L grating (3 orbits) and the CCD first-order spectroscopy with the G430L grating (1 orbit) for the nuclear transient flare (point source). This setup will obtain a low-resolution (R~500) spectrum of the AGN flare covering the observed wavelengths ~1570--5700 Anstrom (rest-frame 1452--5272 Angstrom). It will test if there is any NUV flux deficit as expected from circumbinary accretion disk gap opening assuming the fiducial binary model parameters. The secondary goal with the STIS UV/optical spectroscopy is to measure the UV broad emission line (C IV and Mg II) profiles to test accretion disk wind models. The MAMA G230L grating is preferred over the CCD G230LB grating for its better throughput at the bluer end to measure C IV. The tertiary goal is to identify any spectroscopic post-starburst signatures in the circumnuclear emission as independent evidence for a past galaxy merger (e.g., the Balmer break and strong high-order Balmer absorption). We use the 0.2" wide slit as a good compromise between resolution and throughput. We do not require any specific PA for the slit to minimize scheduling constraints. This program will also conduct WFC3 three-band (UVIS F336W and F606W, and IR F105W) imaging (3 orbits in total at 1 orbit per filter) of the host galaxy of the unusual transient flare. The goal is to perform AGN-host and bulge-disk decompositions, enabling robust bulge stellar mass and total galaxy stellar mass estimates from three-band imaging to independently infer an estimate of the (total) SMBH mass, complementary to the broad-emission-line-based virial mass estimate. The deep, high-resolution imaging will also be used to search for morphological evidence of ongoing nuclear starbursts (with F336W imaging) and low-surface-brightness tidal features (with F105W imaging) as independent evidence of a past galaxy merger event. The F336W filter is chosen to cover the rest-frame U band, sampling ongoing star formation and potential nuclear starbursts in the host. The F606W filter is chosen to cover the rest-frame B band to probe young stellar populations in the host. The F105W is chosen to sample the rest-frame Y band to probe the old stellar populations in the host. The central AGN is expected to be minimal at this wavelength to facilitate AGN-host decomposition. Subarray is used to avoid saturation of the bright galaxy while covering an enough field of view to include the large host galaxy and nearby sources to register absolute astrometry. The 4-point box dither pattern is used to facilitate cosmic-ray and bad-pixel rejection and to better sample the PSF to achieve the best possible image quality. Dr. Liu has expertise in HST data reduction for STIS and WFC3, the prime instruments used in the proposed observations. She also has extensive experiences in reducing slit spectra and optical/NIR images obtained from various ground-based telescopes (including Gemini, Keck, Subaru, Magellan, and MMT). Dr. Liu is an expert in binary and dual AGNs. She has more than two dozen papers published in the past decade on the general topic of merging supermassive black holes. She has led four past HST observing programs with five papers published based on the HST observations. Supermassive Black Holes and Active Galaxies Galaxies 3 false true true false false true false SUPPORTED GALAXY SEYFERT YES J2000 J2000 SDSS r = 15.63, SDSS u = 18.44, GALEX NUV = 21.0 (pre-flare), GALEX FUV = 23.5 (AB, model magnitudes), Swift UVW1 = 18.8+/-0.2 (flare) STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F606W WFC3/IR Imaging No No F105W POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 2 false POS-TARG DITHER 0.15 LINE false false 2 90.0 STIS-ALONG-SLIT 3 false POS-TARG DITHER 0.15 LINE false false 3 90.0 STIS-ALONG-SLIT 4 false The scheduling data was generated by CASM 30.1. CASM was run in Phase II mode. 1652755064000 161.5 (Tic-Visit :proposal-id 16926 :visit-id "01" :proposal-version -1 :trans-version "20211222" :date "14-Apr-2022 11:43:01.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1017968 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16926 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16926 :visit-id "01" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2772 :al-overhead-at-end 0 :internal-dur-at-end 697 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) true 1 0 HOPR repeat of visit 1 (Tic-Visit :proposal-id 16926 :visit-id "01" :proposal-version -1 :trans-version "20211222" :date "14-Apr-2022 11:43:01.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1017968 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16926 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16926 :visit-id "01" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2772 :al-overhead-at-end 0 :internal-dur-at-end 697 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 30.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16926 :visit-id "02" :proposal-version -1 :trans-version "20211222" :date "14-Apr-2022 11:37:28.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 71312 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16926 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16926 :visit-id "02" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2762 :al-overhead-at-end 83 :internal-dur-at-end 114 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 30.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16926 :visit-id "03" :proposal-version -1 :trans-version "20211222" :date "14-Apr-2022 11:38:01.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 71312 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16926 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16926 :visit-id "03" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2762 :al-overhead-at-end 74 :internal-dur-at-end 114 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 30.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16926 :visit-id "04" :proposal-version -1 :trans-version "20211222" :date "14-Apr-2022 11:39:50.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 997408 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16926 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16926 :visit-id "04" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2761 :al-overhead-at-end 0 :internal-dur-at-end 2225 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16926 :visit-id "04" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2765 :al-overhead-at-end 0 :internal-dur-at-end 320 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16926 :visit-id "04" :orbit-number 3 :pcs-time 392 :si-vis-utilization 2765 :al-overhead-at-end 0 :internal-dur-at-end 320 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16926 :visit-id "04" :orbit-number 4 :pcs-time 392 :si-vis-utilization 2765 :al-overhead-at-end 0 :internal-dur-at-end 582 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3157 :pcs-gap 0 ) true 4 0