14272( 2) - 23-Jul-2015 20:42:49 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14272 Version: 2 Check-in Time: 23-Jul-2015 20:42:49 STScI Edit Number: 0 Title Long-Term Ultraviolet Spectroscopy of a Tidal Disruption Event at only 90 Mpc ------------------------------------------------------------------------------------ Type Cycle GO 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Walter Peter Maksym III Smithsonian Institution Astrophysical Y Observatory CoI: Dr. Stephen Bradley Cenko NASA Goddard Space Flight Center N CoI: Prof. Michael Eracleous The Pennsylvania State University N CoI: Dr. William C. Keel University of Alabama N CoI: Prof. Jimmy A. Irwin University of Alabama N CoI: Prof. Steinn Sigurdsson The Pennsylvania State University N CoI: Dr. Andrew S. Fruchter Space Telescope Science Institute N CoI: Prof. Suvi Gezari University of Maryland N CoI: Dr. Tamara Bogdanovic University of Maryland N CoI: Dr. Katherine C. Roth Gemini Observatory, Northern Operations N ------------------------------------------------------------------------------------ Abstract We propose multi-epoch ultraviolet spectroscopy of ASASSN-14li, a stellar tidal disruption event (TDE) at ~90 Mpc. Such very nearby stellar TDEs have been thus far only observed about once per decade and provides an exceptional opportunity to study broad emission lines which describe the abundances and accretion flow of the stellar debris in one of the most important physical regimes for understanding basic TDE behavior. We also request brief XMM observations to constrain the high-energy spectral evolution on similar timescales. These observations will build upon surprising new results, and will provide an important foundation for follow-up of more ambiguous TDE candidates subsequently identified by LSST and WFIRST at higher redshifts. ------------------------------------------------------------------------------------ Observations Description ------------------------ This is the first cycle of a two-cycle program to spectroscopically monitor the decay of transient ASASSN-14li at the nucleus of galaxy PGC 043234/LEDA 43234. This transient appears to be due to the tidal disruption of a star by a supermassive black hole, and has been observed as a TOO in Cycle 22 by Cenko et al. To first order, we expect the host-subtracted transient spectrum to look like a quasar in the UV with some significant differences in terms of broad line strength. For this program, we will be observing two UV STIS spectroscopic epochs in each of cycles 23 and 24. Since we are expecting joint time from a recently-successful Chandra program (#17700613) as well, we expect to coordinate two similar epochs from the Chandra program in order to improve temporal coverage of the transient. For HST program 14272, we expect two 6.5-ks observations from XMM-Newton joint time. Our Chandra program will also contain 145 ks of XMM-Newton joint time over the next two Chandra cycles, including one 14272( 2) - 23-Jul-2015 20:42:49 - [ 2] long 95-ks XMM observation and two short 5-ks XMM-Newton observations over Chandra cycles 17 and 18. We hope to coordinate Chandra or XMM-Newton observations as close to the HST epochs as possible, but given the narrow available observing windows for early HST cycle 23, the X-ray observatories may have better relative scheduling flexibility. With our successful Chandra program, we also anticipate additional UV HST spectroscopy with STIS as Chandra joint time. In Cycle 23 (roughly), we therefore expect four UV STIS spectroscopic epochs total: two from HST program 14272 and two from Chandra program 17700613. We have therefore selected timing windows for HST program 14272 to allow maximal temporal spacing in Cycle 23, expecting that the remaining windows outside our requested range for HST program 14272 would be used for the two UV STIS epochs from Chandra program 17700613. For epochs 1 and 2 (both in Cycle 23), we are acquiring on the nucleus of PGC 043234 which is also the site of the target transient. Since the galaxy has good elliptical symmetry and the transient is well-centered (to within ~0.02 arcsec, vs 0.2 arcsec slit width for all spectroscopic observations), we are acquiring for a diffuse object, using the diffuse centroid with a 13-pixel checkbox. Since we are interested in weighting the acquisition on the UV-bright transient, we are using the CLEAR filter (F25ND3 was used by Cenko et al, but we expect exposure times for F25ND3 to be prohibitive by Cycle 23). As a conservative estimate for minimum acquisition exposure, we subtract the transient from Keck AO K-band images to estimate the fractional flux in the checkbox relative to the whole galaxy, then rescale to the host r-band magnitude. We find S/N in 3.7 seconds, but request 12 seconds per acquisition to be conservative. Saturation should not be a major issue since readout is along the direction of the slit, but to be conservative we model the central point source as a quasar normalized at the host r-band magnitude (though we actually expect the UV flux to be much lower than for a quasar at such a late epoch, as low as GALEX NUV~20). The ETC expects saturation at about 22 seconds for a QSO with r~15.5. In epoch 1, we plan 4 NUV G230L exposures with the 52x0.2 arcsec slit in 2 orbits, followed by 4 FUV G140L exposures with the 52x0.2 arcsec slit in 2 orbits. This epoch should be scheduled before 2016-Feb-01, and the earlier the better. Epoch 2 consists of 6 orbits, and is broken up into two visits for ease of scheduling. We can tolerate 5-day separation, though a smaller interval is preferred to avoid short-timescale object variability. We plan 3 NUV G230L exposures with the 52x0.2 arcsec slit in 3 orbits for the first visit, and 3 FUV G140L exposures with the 52x0.2 arcsec slit in 3 orbits for the second visit. For this epoch we have designated a window in May/June of 2016. We expect to coordinate Cycle 24 observations for this program at a later time according to the normal schedule of Phase II planning, but are happy to develop the Cycle 24 observations in advance, to the extent that this is possible. ------------------------------------------------------------------------------------ 14272( 2) - 23-Jul-2015 20:42:49 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ASASSN-14LI GALAXY, ACCRETION DISK, RA=12H48M15.2300S, J2000 V = 16.1 GALEX NUV is expected to decay BLR, NUCLEUS DEC=+17D46'26.56" from ~19.6 to ~21.5 over the period of interest Reference Frame: ICRS Extended: NO Comments: Coordinates determined from Keck AO imaging matched to SDSS. ------------------------------------------------------------------------------------------------------------------------------------ 14272( 2) - 23-Jul-2015 20:42:49 - [ 4] Visit: 01 Visit Requirements: BETWEEN 01-AUG-2015:00:00:00 AND 01-FEB-2016:00:00:00 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 ASASSN-14LI STIS/CCD ACQ 50CCD MIRROR ACQTYPE=DIFFUSE, CHECKBOX=13, 1 12 S (12 DIFFUSE-CENTER=FLUX-CENTROID S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ASASSN-14LI STIS/NUV ACCUM 52X0.2 G230L 2376 4 1000 S -MAMA see below (4906 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ASASSN-14LI STIS/FUV ACCUM 52X0.2 G140L 1425 4 1000 S -MAMA see below (5784 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 | ------------------------------------------------------------------------------------------------------------------------------------ ASASSN-14LI 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A ASASSN-14LI 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none 1 none 1 1090.0 S -MAMA ASASSN-14LI 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none 2 none 1 1090.0 S -MAMA ASASSN-14LI 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none 3 none 2 1363.0 S -MAMA ASASSN-14LI 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none 4 none 2 1363.0 S -MAMA ASASSN-14LI 3 STIS/FUV ACCUM 52X0.2 G140L 1425 none none 1 none 3 1418.0 S -MAMA ASASSN-14LI 3 STIS/FUV ACCUM 52X0.2 G140L 1425 none none 2 none 3 1418.0 S -MAMA ASASSN-14LI 3 STIS/FUV ACCUM 52X0.2 G140L 1425 none none 3 none 4 1474.0 S -MAMA ASASSN-14LI 3 STIS/FUV ACCUM 52X0.2 G140L 1425 none none 4 none 4 1474.0 S -MAMA 14272( 2) - 23-Jul-2015 20:42:49 - [ 5] Visit: 02 Visit Requirements: BETWEEN 10-MAY-2016:00:00:00 AND 20-JUN-2016:00:00:00; GROUP 02, 03 WITHIN 5D 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 ASASSN-14LI STIS/CCD ACQ 50CCD MIRROR ACQTYPE=DIFFUSE, CHECKBOX=13, 1 12 S (12 DIFFUSE-CENTER=FLUX-CENTROID S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ASASSN-14LI STIS/NUV ACCUM 52X0.2 G230L 2376 3 1000 S -MAMA see below (8258 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 | ------------------------------------------------------------------------------------------------------------------------------------ ASASSN-14LI 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A ASASSN-14LI 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none 1 none 1 2316.0 S -MAMA ASASSN-14LI 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none 2 none 2 2971.0 S -MAMA ASASSN-14LI 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none 3 none 3 2971.0 S -MAMA 14272( 2) - 23-Jul-2015 20:42:49 - [ 6] Visit: 03 Visit Requirements: BETWEEN 10-MAY-2016:00:00:00 AND 20-JUN-2016:00:00:00; GROUP 03, 02 WITHIN 5D 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 ASASSN-14LI STIS/CCD ACQ 50CCD MIRROR ACQTYPE=DIFFUSE, CHECKBOX=13, 1 12 S (12 DIFFUSE-CENTER=FLUX-CENTROID S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ASASSN-14LI STIS/FUV ACCUM 52X0.2 G140L 1425 3 1000 S -MAMA see below (8258 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 | ------------------------------------------------------------------------------------------------------------------------------------ ASASSN-14LI 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A ASASSN-14LI 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none 1 none 1 2316.0 S -MAMA ASASSN-14LI 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none 2 none 2 2971.0 S -MAMA ASASSN-14LI 2 STIS/FUV ACCUM 52X0.2 G140L 1425 none none 3 none 3 2971.0 S -MAMA 14272( 2) - 23-Jul-2015 20:42:49 - [ 7] Summary Form for Proposal 14272 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD, 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE, CHECKBOX=13, DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-AUG-2015:00:00:00 AND 01-FEB-2016:00:00:00, BETWEEN 10-MAY-2016:00:00:00 AND 20-JUN-2016:00:00:00, GROUP 02, 03 WITHIN 5D, GROUP 03, 02 WITHIN 5D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names ASASSN-14LI ------------------------------------------------------------------------------------------------------------------------------------