17449( 11) - 22-Sep-2025 17:49:14 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17449 Version: 11 Check-in Time: 22-Sep-2025 17:49:14 STScI Edit Number: 6 Title Early spectroscopy of tidal disruption events: outflow signatures or chemical composition ? ------------------------------------------------------------------------------------ Type Cycle GO 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Giorgos Leloudas Technical University of Denmark-DTU Space Y CoI: Dr. Matt Nicholl Queen's University Belfast N CoI: Dr. Thomas Wevers Space Telescope Science Institute N CoI: Dr. Iair Arcavi Tel Aviv University - Wise Observatory N CoI: Dr. Panos Charalampopoulos University of Turku N CoI: Dr. Miika Pursiainen University of Warwick N CoI: Prof. Peter G. Jonker Radboud University Nijmegen N CoI: Dr. Francesca Onori INAF - Osservatorio Astronomico d'Abruzzo N CoI: Prof. Ilya Mandel Monash University N CoI: Dr. Mariusz Gromadzki Warsaw University Observatory N CoI: Dr. Suvi Gezari Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract Tidal Disruption Events (TDEs) happen when stars get tidally disrupted by the gravitational field of a supermassive black hole. TDEs are bright panchromatic events and evolve on human-friendly time scales, which makes them prime tools to study accretion physics and black holes in all types of galaxies. Despite considerable progress achieved in the last few years, and the increasing number of TDEs discovered in the optical/UV wavelengths, we still do not know what powers the optical/UV emission of these events, with reprocessed accretion and debris stream collisions being the leading candidates. Important clues to their nature can be derived from spectroscopy, including the presence of Bowen fluorescent emission and the study of kinematical offsets. A growing number of optical TDEs show transient blueshifted line profiles, which are particularly prominent at the He + Bowen blend and at early phases. These have been interpreted as signatures of outflows, which are an inherent prediction of super-Eddington accretion models. However, the blended nature of optical lines makes it hard to disentangle outflows (measured by blueshifts) from chemical composition (the relative contributions of He II and N III). Early UV spectroscopy is required to break this degeneracy by observing the profiles of isolated He II and high-ionisation lines before maximum light, something which has never been possible to achieve before. We therefore propose a ToO program to obtain the first pre-max spectrum of a TDE in the UV and solve this outstanding question. In addition, our proposed COS-STIS observations will contribute to slowly increasing a small legacy sample of TDEs with UV spectroscopy. ------------------------------------------------------------------------------------ Observations Description ------------------------ This is a target of opportunity program. We propose to obtain spectra of a TDE with STIS + COS in order to cover both the NUV and FUV wavelength range, and study a range of spectral lines at different wavelengths. In total, we request for observations at three separate epochs: the first spectrum should be 17449( 11) - 22-Sep-2025 17:49:14 - [ 2] obtained as soon as possible after the early discovery and spectroscopic classification (by means of an optical spectrum) of a TDE showing blueshifted features. Hence, this is a disruptive ToO. Two more epochs will be obtained around the peak of the light curve (or a bit after the peak) and at a few weeks after the peak. These observations will allow us to monitor the evolution of the line profiles, strengths and offsets. These two observations will be linked to be separated by ~3 and ~6 weeks from the first trigger and they will therefore be nondisruptive for the telescope schedule. At the same time, this is an adequate time scale for probing TDE evolution. We will apply strict selection criteria in order to ensure that the data will be adequate to address our goals. We will only trigger our program on a TDE which i) is discovered and spectroscopically classified before peak and ii) shows a blueshifted broad emission line of He II (possibly blended with N III) and iii) is sufficiently bright. Based on our S/N calculations we have set our brightness cut-off to UVM2 < 15.5 mag (Vega) at peak, corresponding to a typical TDE at z < 0.05. During the rise (time of first trigger) and decay, this translates to UVM2 < 16.5 mag. To obtain a quick estimate of the UV magnitude, we will request for a Swift visit within 24 hours from spectroscopic classification and identification as a potential target. However, this is not required and it will not be part of our triggering criteria. If Swift observations are not available or possible within a fast time scale, we will estimate the UV color, using typical TDE optical - UV colors (g-UVW2 = 2.1+/-0.46 based on a large number of TDEs), where the optical color will be provided by the discovery survey. Prior to triggering, a safety control will be performed for nearby bright objects, in compliance with the COS + STIS regulations. Disruptive nature of ToO and justification: As explained, we request a disruptive ToO. This is the only way to obtain a spectrum of a TDE prior to maximum light. TDEs have typical rise times of 20-25 days and the earliest available classifications (i.e. spectroscopic confirmation of their nature) are 1-2 weeks before peak. In addition, spectroscopic evolution is fast at these phases and the line profiles we wish to observe are of transient nature. We can therefore not afford waiting 3 weeks for a non-disruptive trigger but we request a turnaround of 2-5 days. The two follow-up observations will not be disruptive but will be linked to be ~3 and ~6 weeks after the first trigger. ------------------------------------------------------------------------------------ 17449( 11) - 22-Sep-2025 17:49:14 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AT2022DBL EXT-STAR, ACCRETION RA=12H20M45.0500S +/- 0.1", J2000 V = 18.3 +/- 0.2 UV (2000 AA): 16.1 mag DISK, UNDESIGNATED, DEC=+49D33'4.61" +/- 0.1" (Vega) X-RAY TRANSIENT Reference Frame: ICRS Extended: NO Comments: The V-magnitude is a difference magnitude provided by the ATLAS survey (in the orange filter) The UV magnitude is measured by Swift UVOT in the UVM2 filter on 2024-02-03 ------------------------------------------------------------------------------------------------------------------------------------ 17449( 11) - 22-Sep-2025 17:49:14 - [ 4] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 2 TDE EXT-STAR, ACCRETION BRIGHT TIDAL DISRUPTION EVENT V = 16 +/- 1 UV (2000 AA): 14-16.5 mag (Vega) DISK, UNDESIGNATED, (TDE), DISCOVERED PRE-PEAK X-RAY TRANSIENT Comments: The target will be a TDE satisfying the following criteria: i) it will be discovered and spectroscopically classified before peak AND ii) the optical spectrum will show a blueshifted broad emission line of He II (possibly blended with N III) AND iii) it will be sufficiently nearby/bright. We have set our brightness cut-off to UVM2 < 15.5 mag (Vega) at peak, corresponding to a typical TDE at z < 0.05. During the rise (time of first trigger), this translates to UVM2 < 16.5 mag (where UVM2 is the Swift band). The target will be by definition found in the nucleus of a host galaxy that could be of similar brightness as the transient in the optical (V band). However, in the UV wavelengths we do not expect significant contamination from the host. ------------------------------------------------------------------------------------------------------------------------------------ 17449( 11) - 22-Sep-2025 17:49:14 - [ 5] Visit: 01 (COS - epoch 1) Visit Requirements: SCHED 70%; TOO RESPONSE TIME 5.0D 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 AT2022DBL COS/NUV ACQ/IMA BOA MIRRORA 1 37 S (37 GS ACQ SCENARIO BASE1B3 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2022DBL COS/FUV TIME-TA PSA G140L 800 FP-POS=ALL, FLASH=YES, 1 500 S G BUFFER-TIME=320 see below (1784 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2022DBL 1 COS/NUV ACQ/IMA BOA MIRRORA none none none none 1 N/A GE AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 1 1 446.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 2 1 446.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 3 1 446.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 4 1 446.0 S G 17449( 11) - 22-Sep-2025 17:49:14 - [ 6] Visit: 02 (STIS - epoch 1) Visit Requirements: SCHED 70%; AFTER 01 BY 0.9 Orbits TO 1.1 Orbits; TOO RESPONSE TIME 5.0D 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 AT2022DBL STIS/CCD ACQ F28X50LP MIRROR 1 40 S (40 GS ACQ SCENARIO BASE1B3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2022DBL STIS/NUV ACCUM 52X0.2 G230L 2376 1 2000 S -MAMA see below (2050 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2022DBL 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A AT2022DBL 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 1 2050.0 S -MAMA 17449( 11) - 22-Sep-2025 17:49:14 - [ 7] Visit: 03 (COS - epoch 2) Visit Requirements: SCHED 100%; AFTER 01 BY 11 D TO 30 D 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 AT2022DBL COS/NUV ACQ/IMA BOA MIRRORA 1 37 S (37 GS ACQ SCENARIO BASE1B3 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2022DBL COS/FUV TIME-TA PSA G140L 800 FP-POS=ALL, FLASH=YES, 1 500 S G BUFFER-TIME=320 see below (1672 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2022DBL 1 COS/NUV ACQ/IMA BOA MIRRORA none none none none 1 N/A GE AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 1 1 418.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 2 1 418.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 3 1 418.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 4 1 418.0 S G 17449( 11) - 22-Sep-2025 17:49:14 - [ 8] Visit: 04 (STIS - epoch 2) Visit Requirements: SCHED 100%; AFTER 03 BY 0.9 Orbits TO 1.1 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 AT2022DBL STIS/CCD ACQ F28X50LP MIRROR 1 40 S (40 GS ACQ SCENARIO BASE1B3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2022DBL STIS/NUV ACCUM 52X0.2 G230L 2376 1 2000 S -MAMA see below (1591 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2022DBL 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A AT2022DBL 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 1 1591.0 S -MAMA 17449( 11) - 22-Sep-2025 17:49:14 - [ 9] Visit: 05 (COS - epoch 3) Visit Requirements: AFTER 03 BY 15 D TO 27 D 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 AT2022DBL COS/NUV ACQ/IMA BOA MIRRORA 1 37 S (37 GS ACQ SCENARIO BASE1B3 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2022DBL COS/FUV TIME-TA PSA G140L 800 FP-POS=ALL, FLASH=YES, 1 500 S G BUFFER-TIME=320 see below (1844 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2022DBL 1 COS/NUV ACQ/IMA BOA MIRRORA none none none none 1 N/A GE AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 1 1 461.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 2 1 461.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 3 1 461.0 S G AT2022DBL 2 COS/FUV TIME-TA PSA G140L 800 none none none 4 1 461.0 S G 17449( 11) - 22-Sep-2025 17:49:14 - [ 10] Visit: 06 (STIS - epoch 3) Visit Requirements: AFTER 05 BY 0.9 Orbits TO 1.1 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 AT2022DBL STIS/CCD ACQ F28X50LP MIRROR 1 40 S (40 GS ACQ SCENARIO BASE1B3 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2022DBL STIS/NUV ACCUM 52X0.2 G230L 2376 1 2000 S -MAMA see below (2167 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2022DBL 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A AT2022DBL 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 1 2167.0 S -MAMA 17449( 11) - 22-Sep-2025 17:49:14 - [ 11] Summary Form for Proposal 17449 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, BOA, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV, STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=320, FLASH=YES, FP-POS=ALL ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 0.9 Orbits TO 1.1 Orbits, AFTER 01 BY 11 D TO 30 D, AFTER 03 BY 0.9 Orbits TO 1.1 Orbits, AFTER 03 BY 15 D TO 27 D, AFTER 05 BY 0.9 Orbits TO 1.1 Orbits, GS ACQ SCENARIO BASE1B3, SCHED 100%, SCHED 70%, TOO RESPONSE TIME 5.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names AT2022DBL ------------------------------------------------------------------------------------------------------------------------------------