17001( 11) - 12-Jun-2024 13:13:06 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17001 Version: 11 Check-in Time: 12-Jun-2024 13:13:06 STScI Edit Number: 5 Title The Last Gasp of the TDE Wind ------------------------------------------------------------------------------------ Type Cycle GO 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Walter Peter Maksym III NASA Marshall Space Flight Center Y CoI: Dr. Martin Elvis Smithsonian Institution Astrophysical N Observatory CoI: Dr. Giuseppina Fabbiano Smithsonian Institution Astrophysical N Observatory ------------------------------------------------------------------------------------ Abstract When a star is tidally disrupted by a supermassive black hole, the rapid accretion of the stellar debris may drive super-Eddington winds which. After a period of accretion rate decay, we expect the winds to "shut off", drastically reducing the production of broad line emission and changing the evolution of the band-specific light curve across the spectrum. Spectroscopic monitoring of new tidal disruption events (TDEs) in the ultraviolet is the best place to observe this transition due to the persistence of a windless disk continuum. the lack of stellar contamination, and the wealth of high-ionization diagnostic lines that probe the relatively small TDE accretion structure. We propose to observe 5 TDEs over 3 epochs with monitoring UV spectroscopy and complementary X-ray and optical observations, in order to observe this transition and investigate its connection to the evolution of the accretion flow. Beyond this primary goal, these observations will also provide an important legacy contribution of HST towards understanding TDE physics in the UV. ------------------------------------------------------------------------------------ Observations Description ------------------------ --- Update for 17001 This is cycle #2 of a 70-orbit 3-cycle program (following 16775). We have used or scheduled 24 orbits in cycle #1 (out of 34 currently allowed) on 3 targets, and anticipate 2-3 additional targets over all cycles of this program . Configurations are forwarded from 16775. AT2022dsb and AT2022hvp were triggered in 16775 with all orbits planned. These visits are useful templates for future triggers in a full 3-epoch monitoring program, and have been assigned new generic target TDE-TOO-6. In practice, we are likely to only use epochs #2-#3 at most for any given target, since 14 orbits are still allocated for triggers in 16775. ---Updated notes from 16775 This program aims to spectroscopically monitor at least 5 tidal disruption events (TDEs) total as TOOs over the course of their Eddington timescales. Like active galactic nuclei, TDEs frequently display broad spectral lines that are 17001( 11) - 12-Jun-2024 13:13:06 - [ 2] likely formed by emission from ionized clouds circulating in a hot accretion-driven outflowing wind. If this wind is powered by the accretion of stellar debris from the tidal disruption, then as the accretion rate declines over time (0.5-2 years), the wind should die down and the broad lines should disappear. Ancillary science depends upon measurement of the broad line strengths and kinematic profiles, and (much less challenging) the SED profile. TIME-TAG observations may be possible for a sufficiently bright TDE, which would could allow intra-observation variability studies (e.g. reverberation mapping). In terms of program strategy, this translates into monitoring each TDE over ~2 years, with a cadence of ~1 year between each of 3 epochs. We will obtain STIS FUV (G140L) and NUV (G230L) MAMA spectra using the 0.2" slit for each target in each epoch. A "typical" number of orbits is 2/2/3 for each grating in epochs #1/#2/#3, totaling 4/4/6 orbits for each epoch. In practice, the cadence depends upon the black hole mass (which can be estimated from pre-flare observations of the host galaxy) and the trajectory of the disrupted star (which may be imprinted in the light curve photometry). As such, each epoch #2 will be "on hold" until we have had a chance to confirm and revise the cadence strategy. Since neither the brightness nor the light cuve evolution is known, we have previously devised sample visit strategies for multiple different combinatons of the two: We assign a different cadence to each target, with plausible example timescales between 0.41 years and 1.25 years. For each target we devise two different alternate setups, each covering epochs #1 and #2: 1) The first setup assumes a very bright target which requires a neutral density filter for acquisition, and therefore a longer acquisition time. For a very bright target, TIME-TAG observations may be possible, and fewer orbits may be efficiently used in epoch #1 (only one orbit per grating, possibly allowing additional targets or improved late-time epochs). 2) The second setup assumes a moderately bright target (fainter, but still bright enough for UV spectroscopy) and uses the 50CCD filter with a reduced acquisition exposure. The second setup does not use TIME-TAG observations and assumes 2 orbits per grating in epoch #1 and epoch #2. We will refine these setups before triggering epoch #1. Epoch #2 is on hold to refine the setup (including cadence) after triggering epoch #1. In any case, these are long baseline observations: the cadence is unlikely to be