16943( 3) - 24-Jun-2022 13:58:37 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16943 Version: 3 Check-in Time: 24-Jun-2022 13:58:37 STScI Edit Number: 0 Title Exploring the Nature of the Recurring Flare in ULIRG F01004-2237 with UV spectroscopic Diagnosis ------------------------------------------------------------------------------------ Type Cycle GO/DD 29 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Ning Jiang University of Science & Technology of Y China CoI: Dr. Stephen Bradley Cenko NASA Goddard Space Flight Center Y CoI: Dr. Luming Sun Anhui Normal University N CoI: Mr. Subo Dong Peking University N CoI: Dr. Liming Dou Guangzhou University N CoI: Dr. Zhu Liu Max-Planck-Institut fur extraterrestrische N Physik ------------------------------------------------------------------------------------ Abstract An unexpected luminous optical flare (peak Mg=-21.4) turns up in ULIRG F01004-2237 since 2021 September, revealed by its ATLAS and ASASSN light curves. This nearby galaxy once held a candidate tidal disruption event (TDE) because a luminous flare occurred in 2010, and now it brightens up again. The Gaia has also detected the new flare and pinpointed it at the galaxy's center. The flare is now UV bright yet X-ray weak, and its optical spectrum shows extremely broad Balmer emission lines. These observations have ruled out a supernova as its origin, and therefore the flare is likely to be associated with the central supermassive black hole (SMBH). Such recurrent flares are rare as only few reported recurrent flares in other galaxies with diverse time intervals. Their nature are still ambiguous. They may be caused by repeated TDEs, partial TDE, SMBH binary or peculiar accretion disk instabilities. The timely discovery of the ongoing recurring flare in F01004-2237 offers a unique opportunity to acquire useful clues. Aiming to further explore the mechanism that drives the second flare as well as its connection with the first one, we here propose to conduct STIS UV spectroscopic observations on F01004-2237 with 5 orbits time. Because the flare is darkening, we require the observation to be done as early as possible within the upcoming two visbility windows. The immediate objectives are mainly in three folds: 1) to better map the flare's SED and thus distinguish between the powerlaw (AGN) and blackbody (TDE) scenarios; 2) to detect possible characteristic UV emission lines of either TDEs or AGNs; 3) to detect possible UV absorption lines which might address the X-ray weakness. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request a single epoch (that could be split into multiple visits, if necessary) of UV spectroscopy of the recurring TDE candidate in IRAS F01004-2237, over the wavelength range from 1200-3000A. HST, with its sensitive UV spectrographs and exquisite angular resolution, is the only facility that can conduct such observations. We assume a spectrum proportional to lambda^(-2.2) and an AB magnitude of 18.4 in UVW1 band as suggested by the latest Swift observation. We assume that our targets are visible for 53 minutes 16943( 3) - 24-Jun-2022 13:58:37 - [ 2] each orbit. After including overheads for guide-star acquisition (6 min for the first orbit, 4 min for the subsequent orbits), target acquisition (~ 8 min for an extended source, no peak-up required for 0.2" slit width), and wavelength calibration (4 min per orbit), we find that we can obtain 35 min of exposure in the first orbit (43 in subsequent orbits). We request to allocate three-orbit time for G230L and two-orbit time for G140L, which will result in 7260 and 4680 second exposure time, respectively. According to the exposure time calculator by inputting our assumed SED, we would expect a SNR per resolution element >=10 for the range from 1650-3100 A. In addition, we use the actual data of iPTF16fnl on +51 day (Brown et al. 2018) as a reference. During this observation, iPTF16fnl had a UVW1 magnitude of 18.1 and a UV spectrum consistent with a blackbody curve with TBB ~32000 K, indicating that it is ~30% brighter than our target in the FUV band. The exposure time of iPTF16fnl is 4785 seconds and 5500 seconds for the G140L and G230L gratings, respectively, similar to our requested time. The SNR of the actual spectrum of iPTF16fnl meets our requirements. To summarize, we request a single epoch of STIS spectroscopy of F01004-2237, for a total of 5 orbits (2 FUV + 3 NUV). ------------------------------------------------------------------------------------ 16943( 3) - 24-Jun-2022 13:58:37 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 F01004-2237 GALAXY, ACCRETION DISK, RA=01H02M50.0088S +/- 0.02", J2000 Z = V = 17.3 +/- 0.2 NUCLEUS, SEYFERT DEC=-22D21'57.20" +/- 0.02" 0.11797 Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the NED database.This object was generated by the targetselector and retrieved from the NED database. ------------------------------------------------------------------------------------------------------------------------------------ 16943( 3) - 24-Jun-2022 13:58:37 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.4165 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 90.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 16943( 3) - 24-Jun-2022 13:58:37 - [ 5] Visit: 01 Visit Requirements: BEFORE 01-AUG-2022:00:00:00 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 F01004-2237 STIS/CCD ACQ F28X50LP MIRROR 1 60 S (60 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 F01004-2237 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=676 1 528 S PATTERN 1 2 -MAMA G (1584 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 F01004-2237 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=676 1 727 S PATTERN 1 3 -MAMA G (2181 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 F01004-2237 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=676 1 727 S PATTERN 1 4 -MAMA G (2181 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 | ------------------------------------------------------------------------------------------------------------------------------------ F01004-2237 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A F01004-2237 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 1 none none none 1 N/A -MAMA G F01004-2237 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 2 none none none 1 N/A -MAMA G F01004-2237 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 3 none none none 1 N/A -MAMA G F01004-2237 3 STIS/NUV TIME-TA 52X0.2 G230L 2376 1 none none none 2 N/A -MAMA G F01004-2237 3 STIS/NUV TIME-TA 52X0.2 G230L 2376 2 none none none 2 N/A -MAMA G F01004-2237 3 STIS/NUV TIME-TA 52X0.2 G230L 2376 3 none none none 2 N/A -MAMA G F01004-2237 4 STIS/NUV TIME-TA 52X0.2 G230L 2376 1 none none none 3 N/A -MAMA G F01004-2237 4 STIS/NUV TIME-TA 52X0.2 G230L 2376 2 none none none 3 N/A -MAMA G F01004-2237 4 STIS/NUV TIME-TA 52X0.2 G230L 2376 3 none none none 3 N/A -MAMA G 16943( 3) - 24-Jun-2022 13:58:37 - [ 6] Visit: 02 Visit Requirements: BEFORE 01-AUG-2022:00:00:00 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 F01004-2237 STIS/CCD ACQ F28X50LP MIRROR 1 60 S (60 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 F01004-2237 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=676 1 528 S PATTERN 1 2 -MAMA G (1584 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 F01004-2237 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=676 1 727 S PATTERN 1 3 -MAMA G (2181 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 | ------------------------------------------------------------------------------------------------------------------------------------ F01004-2237 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A F01004-2237 2 STIS/FUV TIME-TA 52X0.2 G140L 1425 1 none none none 1 N/A -MAMA G F01004-2237 2 STIS/FUV TIME-TA 52X0.2 G140L 1425 2 none none none 1 N/A -MAMA G F01004-2237 2 STIS/FUV TIME-TA 52X0.2 G140L 1425 3 none none none 1 N/A -MAMA G F01004-2237 3 STIS/FUV TIME-TA 52X0.2 G140L 1425 1 none none none 2 N/A -MAMA G F01004-2237 3 STIS/FUV TIME-TA 52X0.2 G140L 1425 2 none none none 2 N/A -MAMA G F01004-2237 3 STIS/FUV TIME-TA 52X0.2 G140L 1425 3 none none none 2 N/A -MAMA G 16943( 3) - 24-Jun-2022 13:58:37 - [ 7] Summary Form for Proposal 16943 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=676 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 01-AUG-2022:00:00:00, PATTERN 1 2, PATTERN 1 3, PATTERN 1 4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names F01004-2237 ------------------------------------------------------------------------------------------------------------------------------------