16714( 5) - 21-May-2023 23:51:56 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16714 Version: 5 Check-in Time: 21-May-2023 23:51:56 STScI Edit Number: 1 Title HST Spectroscopy of a Fast-Rising Luminous Ultraviolet Transient ------------------------------------------------------------------------------------ Type Cycle GO 29 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Daniel Perley Liverpool John Moores University Y CoI: Dr. Lin Yan California Institute of Technology N CoI: Anna Yen Qin Ho Cornell University N CoI: Ms. Yuhan Yao California Institute of Technology N CoI: Prof. Shrinivas R. Kulkarni California Institute of Technology N CoI: Dr. Christoffer Fremling California Institute of Technology N CoI: Dr. Ragnhild Lunnan Stockholm University N ------------------------------------------------------------------------------------ Abstract High-cadence time-domain surveys have unveiled a population of fast-evolving, luminous extragalactic transients with SEDs that remain dominated by ultraviolet emission for long after peak and also exhibit luminous X-ray and radio counterparts. While they show some observational similarities with strongly-interacting supernovae, optical follow-up has failed to identify any recognizable supernova features and the extreme properties of these events strain theoretical models for what is possible in a supernova explosion. Ultraviolet spectroscopy has the power to reveal similarities or differences betwen this event and other supernova classes not apparent from optical observations alone, and offers a means of identifying the progenitor star via transmission spectroscopy of the dense stellar wind before the explosion sweeps it up. We propose to obtain target-of-opportunity UV spectroscopy of a new event of this type in Cycle 29 to secure the physical origins of this class while HST's unique UV spectroscopic resource is still available. ------------------------------------------------------------------------------------ Observations Description ------------------------ Our objective is to carry out low-resolution FUV and NUV spectroscopy of a fast-luminous UV transient with COS (G140L) and STIS (G230L). Fast turnaround is helpful for many reasons - both to optimize the S/N (the target will not be bright) and to decrease the risk of acquisition failure if the target's UV flux evolution is different than expected. A turnaround of up to 1 week is acceptable, although for a sufficiently nearby event we may accept a longer delay. Using fewer guide stars may be acceptable to achieve faster turnaround. It is desirable in principle to obtain the COS and STIS observations close in time to each other but observing sooner in one band will almost always be preferred if the option is available. Rapid two-way communication with STScI will be necessary to correctly configure the observations and perform all safety checks to ensure a successful acquisition. The PI's mobile number is +44 745 6339330 and can be contacted 24 hours a day. ------------------------------------------------------------------------------------ 16714( 5) - 21-May-2023 23:51:56 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2023IUC STAR, SUPERNOVA RA=14H38M55.6500S +/- 0.3", J2000 Z = V = 19 +/- 1 DEC=+02D17'14.14" +/- 0.3" 0.07676 Reference Frame: ICRS Extended: NO Comments: Estimated magnitude is that in one week. The current (2023 May 21) magnitudes (AB) are ~18.0 in the UV bands, ~18.2 in u/g/r, and ~18.5 in i/z. The source is not currently fading significantly, although we expect it to begin fading soon. ------------------------------------------------------------------------------------------------------------------------------------ 16714( 5) - 21-May-2023 23:51:56 - [ 3] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 1 TOO STAR, SUPERNOVA FAST RISE (<3 DAYS) TO HIGH V = 19 +/- 2 LUMINOSITY (M ~ -20) WITHOUT COOLING Comments: The target will be identified from ZTF or potentially another high-cadence optical survey. The trigger will be submitted at or after peak and there will be a clear upper limit on the flux of the target based on this. The source will probably be close to V=18.5, UV=17.5 mag at peak (AB). The source is expected to fade rapidly after peak, but this is difficult to project. The target is a point source and we expect it will be brighter than its host galaxy (in UV) but will confirm at the time of triggering. ------------------------------------------------------------------------------------------------------------------------------------ 16714( 5) - 21-May-2023 23:51:56 - [ 4] Visit: 01 (COS FUV spectrum) Visit Requirements: BEFORE 01-JUN-2023:00:00:00; TOO RESPONSE TIME 4.0D 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 AT2023IUC COS/NUV ACQ/IMA PSA MIRRORB 1 180 S (180 GE S) Comments: The target is currently ~18 mag in the UV and ~18.3 mag in r-band. Over the past two nights its flux has not changed significantly in either band, although based on past similar objects fading is expected to set in soon. We are able to supply up-to-date magnitudes on request as needed. ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2023IUC COS/FUV TIME-TA PSA G140L 1105 FLASH=YES, BUFFER-TIME=6400, 1 1000 S G FP-POS=ALL see below (4516 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2023IUC 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE AT2023IUC 2 COS/FUV TIME-TA PSA G140L 1105 none none none 1 1 973.0 S G AT2023IUC 2 COS/FUV TIME-TA PSA G140L 1105 none none none 2 1 973.0 S G AT2023IUC 2 COS/FUV TIME-TA PSA G140L 1105 none none none 3 2 1285.0 S G AT2023IUC 2 COS/FUV TIME-TA PSA G140L 1105 none none none 4 2 1285.0 S G 16714( 5) - 21-May-2023 23:51:56 - [ 5] Visit: 02 (COS FUV spectrum) Visit Requirements: BEFORE 01-JUN-2023:00:00:00; TOO RESPONSE TIME 4.0D On Hold Comments: Additional Comments: If the target remains bright we may request a time constraint on the second visit to delay the observation for a few days to study time evolution. (For now, we are not requesting this.) 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 AT2023IUC COS/NUV ACQ/IMA PSA MIRRORB 1 180 S (180 GE S) Comments: The target is currently ~18 mag in the UV and ~18.3 mag in r-band. Over the past two nights its flux has not changed significantly in either band, although based on past similar objects fading is expected to set in soon. We are able to supply up-to-date magnitudes on request as needed. As the target is bright, it is not essential that this observation be executed alongside the other COS visit, and we may indeed prefer a gap of a few days or more between them. But, please schedule the observations as is most convenient for the schedulers. ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2023IUC COS/FUV TIME-TA PSA G140L 1105 FLASH=YES, BUFFER-TIME=6400, 1 1000 S G FP-POS=ALL see below (4516 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2023IUC 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE AT2023IUC 2 COS/FUV TIME-TA PSA G140L 1105 none none none 1 1 973.0 S G AT2023IUC 2 COS/FUV TIME-TA PSA G140L 1105 none none none 2 1 973.0 S G AT2023IUC 2 COS/FUV TIME-TA PSA G140L 1105 none none none 3 2 1285.0 S G AT2023IUC 2 COS/FUV TIME-TA PSA G140L 1105 none none none 4 2 1285.0 S G 16714( 5) - 21-May-2023 23:51:56 - [ 6] Visit: 03 (STIS NUV spectrum) Visit Requirements: BEFORE 01-JUN-2023:00:00:00; TOO RESPONSE TIME 4.0D On Hold Comments: Additional Comments: It is preferable, but not required, to execute this close in time with the COS observations. 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 AT2023IUC STIS/CCD ACQ F28X50LP MIRROR 1 60 S (60 S) Comments: The target is currently ~18 mag in the UV and ~18.3 mag in r-band. Over the past two nights its flux has not changed significantly in either band, although based on past similar objects fading is expected to set in soon. We are able to supply up-to-date magnitudes on request as needed. ------------------------------------------------------------------------------------------------------------------------------------ 2 AT2023IUC STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=663 1 2100 S -MAMA G see below (1982 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 AT2023IUC STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=663 1 2100 S -MAMA G see below (2722 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 | ------------------------------------------------------------------------------------------------------------------------------------ AT2023IUC 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A AT2023IUC 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 1982.0 S -MAMA G AT2023IUC 3 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 2 2722.0 S -MAMA G 16714( 5) - 21-May-2023 23:51:56 - [ 7] Summary Form for Proposal 16714 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV, STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=6400, BUFFER-TIME=663, FLASH=YES, FP-POS=ALL ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 01-JUN-2023:00:00:00, TOO RESPONSE TIME 4.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names AT2023IUC ------------------------------------------------------------------------------------------------------------------------------------