17314( 5) - 01-Jun-2023 15:56:41 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17314 Version: 5 Check-in Time: 01-Jun-2023 15:56:41 STScI Edit Number: 3 Title HST/STIS spectroscopy of AT2020vdq: diagnosing fast outflows in a remarkably energetic partial tidal disruption event ------------------------------------------------------------------------------------ Type Cycle GO/DD 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Jean Somalwar California Institute of Technology Y CoI: Dr. Vikram Ravi California Institute of Technology N ------------------------------------------------------------------------------------ Abstract When a star ventures close to a supermassive black hole, it is shredded and consumed in a tidal disruption event (TDE). In a poorly understood fraction of TDEs, the star is not fully consumed, but instead is only partially disrupted and continues orbiting the star. It is repeatedly partially disrupted each time it reaches pericenter, causing a periodic transient. Partial disruption events are key for understanding SMBH growth and feeding and the rate of tidal disruption events, among other subjects. However, only a handful of candidate partial TDEs are known. In the last few days, we have discovered a bonafide partial TDE, AT2020vdq. This event is remarkably energetic, with potential super-Eddington accretion during the present flare and evidence for fast wind launching. We propose two orbits of HST/STIS observations to obtain NUV and FUV spectra for this partial TDE. UV spectra of TDE are sensitive to the presence of outflows near the SMBH and will allow us to make the first strong statements on the evolution and dynamics of partial TDEs. ------------------------------------------------------------------------------------ Observations Description ------------------------ We aim to obtain FUV and NUV spectra for a UV-bright TDE. We were allocated two orbits for this program. We require that the observations occur before June 21 so that the TDE is sufficiently UV bright. We do not expect the TDE to be so UV bright as to require bright target acquisition procedures. Our observation begins with a 20 sec acquisition using the diffuse target procedure, as we aim to acquire a point source on top of diffuse emission from a galaxy. We then obtain a FUV spectrum of the source, split into to exposures so as to ensure no unused orbital visibility. We finally obtain a NUV of the source. ------------------------------------------------------------------------------------ 17314( 5) - 01-Jun-2023 15:56:41 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AT2020VDQ GALAXY, ACCRETION DISK, RA=10H08M53.4570S +/- 0.3", J2000 V = 18.2 +/- 0.2 BLR, NUCLEUS, WIND DEC=+42D43'0.20" +/- 0.3" Reference Frame: ICRS Comments: These coordinates are from TNS as reported by the ZTF survey and are the location of the transient optical flare. They are coincident with the location of the galactic nucleus from public optical imaging (e.g., Legacy survey; the offset from the reported coordinates of the galaxy nucleus is ~0.1"). We assume a uncertainty of 0.3" in both the ra and dec because this is the largest typical uncertainty reported by ZTF, although we expect that this estimate is conservative. ------------------------------------------------------------------------------------------------------------------------------------ 17314( 5) - 01-Jun-2023 15:56:41 - [ 3] Visit: 01 Visit Requirements: BEFORE 21-JUN-2023:00:00:00; TOO RESPONSE TIME 14.0D 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 AT2020VDQ STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 20 S (20 S) Comments: Acquisition of TDE. ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2020VDQ STIS/FUV ACCUM 52X0.2 G140L 1425 1 2296 S -MAMA see below (2296 S) Comments: FUV spectrum of UV-bright TDE. The ETC uses the most recent UV flux of this source from the Swift telescope, assuming that the source has faded according to typical TDE fade timescales. We have split this exposure into two exposures to optimally fill our two orbits. ------------------------------------------------------------------------------------------------------------------------------------ 3 AT2020VDQ STIS/FUV ACCUM 52X0.2 G140L 1425 1 1264 S -MAMA see below (1264 S) Comments: FUV spectrum of UV-bright TDE. The ETC uses the most recent UV flux of this source from the Swift telescope, assuming that the source has faded according to typical TDE fade timescales. We have split this exposure into two exposures to optimally fill our two orbits. ------------------------------------------------------------------------------------------------------------------------------------ 4 AT2020VDQ STIS/NUV ACCUM 52X0.2 G230L 2376 1 1082 S -MAMA see below (1082 S) Comments: NUV spectrum of UV-bright TDE. The ETC uses the most recent UV flux of this source from the Swift telescope, assuming that the source has faded according to typical TDE fade timescales. ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2020VDQ 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A 17314( 5) - 01-Jun-2023 15:56:41 - [ 4] 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2020VDQ 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 1 2296 S -MAMA AT2020VDQ 3 STIS/FUV ACCUM 52X0.2 G140L 1425 none none none none 2 1264 S -MAMA AT2020VDQ 4 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 2 1082 S -MAMA 17314( 5) - 01-Jun-2023 15:56:41 - [ 5] Summary Form for Proposal 17314 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 21-JUN-2023:00:00:00, TOO RESPONSE TIME 14.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names AT2020VDQ ------------------------------------------------------------------------------------------------------------------------------------