This proposal is for mid-cycle consideration (Jan 30 2021 deadline). (Typo fixed #3) 41435715 Assigned ID: 1384 ----- Attempting Submission 1 (Sun Jan 31 04:01:39 GMT 2021) ----- HST Phase I Proposal 1384 successfully submitted. Receipt: # 1384-1 ----- Attempting Submission 2 (Sun Jan 31 04:32:53 GMT 2021) ----- HST Phase I Proposal 1384 successfully submitted. Receipt: # 1384-2 ----- Attempting Submission 3 (Sun Jan 31 04:34:52 GMT 2021) ----- HST Phase I Proposal 1384 successfully submitted. Receipt: # 1384-3 ----- Attempting Submission 4 (Sun Jan 31 04:54:26 GMT 2021) ----- Phase II resubmission corrects an error that was spotted by Amy Jones. (Thank you Amy!) This project is a continuation of HST Proposal 16451. -1545987800 ----- Attempting Submission 1 (Sat Nov 28 21:01:58 GMT 2020) ----- HST Phase II Proposal 16451 successfully submitted. Receipt: # 16451-1 ----- Attempting Submission 2 (Tue Dec 15 20:25:53 GMT 2020) ----- HST Phase II Proposal 16451 successfully submitted. Receipt: # 16451-2 ----- Attempting Submission 3 (Thu Mar 11 03:00:33 GMT 2021) ----- HST Phase II Proposal 16498 successfully submitted. Receipt: # 16498-3 ----- Attempting Submission 4 (Fri Mar 12 22:51:04 GMT 2021) ----- ASASSN-14ko is a recently discovered, periodically flaring, nuclear transient within known AGN ESO 253-G003. The flares have a mean period of ~114 days and a nonzero, negative period derivative. The exact origin of these UV/optical flares is currently unknown. STIS UV observations of the rise, peak, and decline in the UV revealed rapid and dramatic evolution in Dec 2020 showing strong P Cygni profiles in the FUV for C IV and N V that rapidly changed. The UV spectra during all of the epochs substantially differ from any tidal disruption event (TDE) with UV spectroscopic observations and also differ from any AGN/quasar spectrum the proposers are familiar with. The rapid evolution itself is also unprecedented for TDEs which thus far have exhibited static or slowly evolving UV spectra. Most intriguing is that the appearance of the P Cygni profiles appears to correlate with X-ray diminings which are consistent with being due to obscuration. Combining the X-ray and STIS observations for the Dec flare a consistent picture of a rapid outflow, possibly a tidal stream, is emerging. Here we propose for 2 additional early-time STIS spectra covering the earliest phases of ASASSN-14ko's April 2021 outburst. These observations will bring into focus these dramatic spectroscopic and X-rays changes. The impact of reduced-gyro operations on this project are uncertain, but, given that the epochs of these observations are highly constrained it is likely that the effect will be to further constrain or eliminate some of the epochs. This is a proposal by the ASAS-SN team to observe the UV bright, repeating nuclear transient ASASSN-14ko. We believe this source is a repeating TDE although it might be a new form of AGN variability. ASAS-SN has revolutionized the TDE field through its discovery and characterization of bright, nearby TDEs. This includes the discoveries of ASASSN-14ae (Holoien et al. 2014, Brown et al. 2016), ASASSN-14li (Holoien et al. 2016, Brown et al. 2017a), ASASSN-15oi (Holoien et al. 2016, 2018) and ASASSN-18jd (Neustadt et al. 2020). We have also carried out studies of iPTF16fnl (Brown et al. 2017b) and PS18kh (Holoien et al. 2018), which were first identified by iPTF and PanSTARRS, respectively. The paper on iPTF16fnl includes our STIS UV spectra from a previous proposal, although the campaign was halted after three observations because the source faded so rapidly. The paper on ASASSN-18jd contains a sequence of STIS spectra we obtained.We were obtained HST/STIS, NICER, Swift, Chandra, Keck, Magellan, and other ground-based observations of the Dec 2020 flare of ASASSN-14ko. Those observations are currently being analyzed and some are shown in this proposal. The PI and CoIs have extensive experience with both AGN and TDE science. Supermassive Black Holes and Active Galaxies 6 false false true false false false false SUPPORTED GALAXY ACCRETION DISK MULTIPLE NUCLEI NUCLEUS QUASAR Note, this is the nucleaus of a galaxy, but, it is a complex galaxy. Please see submission notes. J2000 J2000 at peak: W1=15.69(0.04), M2=15.66(0.07), and W2=15.64(0.04) STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/FUV-MAMA Spectroscopic No No G140L 1425 POS-TARG DITHER 0.3829 LINE false false 3 90.0 STIS-ALONG-SLIT 2 false 1615588170845 Timing link suitability includes constraints ([02 After 01 by 2.2 to 3.2 days]) The scheduling data was generated by CASM 29.0. CASM was run in Phase II mode. /private/var/folders/bb/9k9k0f9x07d7hbyn05zb3wx40000gn/T/OPVisit12477189524673136213.xml Quiescence before ASASSN-14ko Dec 2020 outburst (Tic-Visit :proposal-id 16498 :visit-id "01" :proposal-version -1 :trans-version "20200619" :date "12-Mar-2021 12:29:30.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 452736 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16498 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16498 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2892 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3285 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16498 :visit-id "01" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2893 :al-overhead-at-end 0 :internal-dur-at-end 450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3285 :pcs-gap 0 ) true 2 0 1615588301876 Timing link suitability includes constraints ([02 After 01 by 2.2 to 3.2 days]) The scheduling data was generated by CASM 29.0. CASM was run in Phase II mode. /private/var/folders/bb/9k9k0f9x07d7hbyn05zb3wx40000gn/T/OPVisit13332605927272714602.xml Rise of ASASSN-14ko Dec 2020 outburst (Tic-Visit :proposal-id 16498 :visit-id "02" :proposal-version -1 :trans-version "20200619" :date "12-Mar-2021 12:31:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 452736 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16498 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16498 :visit-id "02" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2580 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2973 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16498 :visit-id "02" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2581 :al-overhead-at-end 0 :internal-dur-at-end 450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2973 :pcs-gap 0 ) true 2 0