17933( 3) - 29-Apr-2025 14:32:04 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17933 Version: 3 Check-in Time: 29-Apr-2025 14:32:04 STScI Edit Number: 0 Title Turn-on AGN or IMBH-TDE? UV Spectroscopic Observations May Tell ------------------------------------------------------------------------------------ Type Cycle GO/DD 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Ning Jiang University of Science and Technology of Y China CoI: Dr. Tinggui Wang University of Science and Technology of N China CoI: Mr. Jiazheng Zhu University of Science and Technology of N China CoI: Yibo Wang University of Science and Technology of N China CoI: Mr. Wenkai Li University of Science and Technology of N China CoI: Dr. Shifeng Huang University of Science and Technology of N China ------------------------------------------------------------------------------------ Abstract The quasi-periodic eruptions (QPEs) are an intriguing transient phenomenon associated with supermassive balck holes (SMBHs) discovered in the past few years. There is growing observational evidence that some (if not all) QPEs are connected with tidal disruption events (TDEs), which has promoted the "EMRI+TDE=QPE" model. Very recently, another remarkable QPE source has been reported after an optical outburst in the nearby galaxy SDSSJ1335+0728. It is suggested that the QPEs in this galaxy are linked to a turn-on active galactic nuclei (AGN) rather than a TDE as its slow decay and AGN-like variability differ greatly from noraml TDEs. Therefore, this discovery may broaden the possible formation channels for QPEs. However, its blue optical color, soft X-ray emission and lack of broad emissions are unusual for AGNs, but could be consistent with a TDE scenario. In fact, such a long, blue and faint optical outburst can be a strong evidence for TDEs by intermediate-mass black holes (IMBHs). To further explore the nature of the intriguing outburst (turn-on AGN or IMBH-TDE), we propose to conduct STIS UV spectroscopic observations on SDSSJ1335+0728 with 4 orbits time. The immediate objectives are mainly in two folds: 1) to detect possible characteristic UV emission lines; 2) to better characterize the outburst SED down to 1000 A, both of which may help to distinguish between the AGN and TDE scenarios. If it is indeed an IMBH-TDE, it provides another representative example of QPE-TDE associations in a rare IMBH-TDE system while in the case of a turn-on AGN, it also provides valuable, yet rarely studied, SED information for a newly formed AGN disk. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to observe the UV spectrum of SDSSJ1335+0728 with STIS. We require to use G140L and G230L gratings to obtain a continuous wavelength coverage from 1120 to 3100 A in the rest frame. A slit width of 0.2" is preferred to cover 17933( 3) - 29-Apr-2025 14:32:04 - [ 2] the galactic nucleus and minimize the starlight contamination. The magnitudes in UVW1, UVM2, UVW2 bands measured from the latest Swift/UVOT observations on March 12 are 17.91+-0.05, 18.17+-0.05 and 18.05+-0.10, respectively. After subtracting the host contribution from the host galaxy, the UVM2 (with a central wavelength of 2246A) magnitude is around 18.9. We expect the magnitude to be comparable after a few months, since its evolution is rather slow. We try to estimate the needed exposure time using the Exposure Time Calculator (ETC) of HST/STIS. We assume a blackbody spectrum with a temperature of 30, 000K, and an AB magnitude of 18.9 in the UVM2 band. To reliably detect a possible N III]1750 line, a continuum signal-to-noise ratio (SNR) of 10 at 1792A is required. This requires an exposure time of about 5000 seconds (~2 orbits) with the G230L grating. Based on our previous experience in analyzing the STIS data, a similar time is required in G140L. Therefore, a total of 4 orbits is sufficient for both gratings, including overheads. ------------------------------------------------------------------------------------ 17933( 3) - 29-Apr-2025 14:32:04 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SDSSJ1335+07 GALAXY, SEYFERT RA=13H35M19.9356S, J2000 V = 19 28 DEC=+07D28'7.74" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 17933( 3) - 29-Apr-2025 14:32:04 - [ 4] Visit: 01 Visit Requirements: BEFORE 01-JUN-2025:00:00:00 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 SDSSJ1335+0 STIS/CCD ACQ 50CCD MIRROR 1 40 S (40 728 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SDSSJ1335+0 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1337 1 1926 S 728 -MAMA G (1926 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SDSSJ1335+0 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=1337 1 2602 S 728 -MAMA G (2602 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 | ------------------------------------------------------------------------------------------------------------------------------------ SDSSJ1335+0728 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A SDSSJ1335+0728 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 N/A -MAMA G SDSSJ1335+0728 3 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 2 N/A -MAMA G 17933( 3) - 29-Apr-2025 14:32:04 - [ 5] Visit: 02 Visit Requirements: BEFORE 01-JUN-2025:00:00:00 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 SDSSJ1335+0 STIS/CCD ACQ 50CCD MIRROR 1 40 S (40 728 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SDSSJ1335+0 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=6996 1 1926 S 728 -MAMA G (1926 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SDSSJ1335+0 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=6996 1 2602 S 728 -MAMA G (2602 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 | ------------------------------------------------------------------------------------------------------------------------------------ SDSSJ1335+0728 1 STIS/CCD ACQ 50CCD MIRROR none none none none 1 N/A SDSSJ1335+0728 2 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 1 N/A -MAMA G SDSSJ1335+0728 3 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 2 N/A -MAMA G 17933( 3) - 29-Apr-2025 14:32:04 - [ 6] Summary Form for Proposal 17933 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD, 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1337, BUFFER-TIME=6996 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 01-JUN-2025:00:00:00 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names SDSSJ1335+0728 ------------------------------------------------------------------------------------------------------------------------------------