6309( 5) - 04/18/96 17:35 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6309 Version: 5 Check-in Date: 18-Apr-1996 17:29:44 1.Proposal Title: DETERMINING THE SED OF AN ULTRAVIOLET FLARE AT THE CENTRE OF THE ELLIPTICAL GALAXY NGC 4552 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle AGN GO/DD 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Francesco Bertola Department of Astronomy Padova CoI: David Burstein Arizona State University N CoI: Michele Cappellari Department of Astronomy Padova Y CoI: Sperello Di Serego Alighieri Osservatorio Astrofisico di Arcetri N CoI: Laura Greggio Department of Astronomy Bologna N CoI: Alvio Renzini Department of Astronomy Bologna N CoI: Rodolfo Viezzer Department of Astronomy Bologna N ------------------------------------------------------------------------------------ 6. Abstract Previous HST observations show that the otherwise normal elliptical galaxy NGC 4552, has a UV-bright flare in its nucleus that brightened in luminosity from 1991 to 1993 by over a factor of 7. The UV spectral energy distribution of the spike in 1993 is consistent either with a thermal source or a wavelength-independent source of UV flux. While we believe the best fitting model for this flare is that of a star encountering the central black hole in a close fly-by, other models (including that of a supernova) are possible. To distinguish among the available models, we need data only HST can provide: a) What is the true SED of the flare? We require 0.25" angular resolution spectra, which we can only get by taking HST/FOS spectra. b) What is our best estimate of the spatial extent of the flare? HST/FOC observations give us the highest possible spatial resolution images. ------------------------------------------------------------------------------------ 6309( 5) - 04/18/96 17:35 - [ 2] Observations Description ------------------------ Using our previous FOC observations we've computed a flux from the 1993 flare in NGC 4552 of 2.2*10^-17 erg/(cm^2 s A) over the galaxy background. The SED is consistent with a flat spectrum in the range 1700-3500 Angstrom. We've estimated a count rate comparable to the dark rate through the G270H grating and under these conditions we've computed the exposure time to reach a S/N about 20 after rebinning in 50 Angstrom intervals. In the G270H grating and the 0.25-PAIR aperture, after subtraction of the dark counts, we'll get about half counts from the galaxy background and we will eliminate this contamination using our IUE spectra of the galaxy. Through the G780H grating we hope to be able to detect H-alpha emission, as already detected by Eracleous et al. at the 7*10^-16 erg/(cm^2 s A) level in the nucleus of NGC 1097 (at the same distance from us as NGC 4552), and attributed to accretion about a massive blackhole in that galaxy. The G650L grating permits us to complete the full SED of the spike little time overhead. Our FOS observations are supplemented by contemporary FOC imaging, primarily to try to determine the spatial extent of the spike in NGC 4552. We are taking FOC observations with three filters as: a) The F175W filter permits extension of the SED of the spike from 2200A down to 1500A, using known sensitivity curves and our FOS spectra. b) The F275W and F342W permit direct comparison with the 1991 and 1993 observations of the spike. This permits us to contruct a 3-point light curve for this spike, which is variable in luminosity. c) If there is any spatially-extended structure around the spike (as suggested by Crane et al.'s 1991 FOC image), imaging in multiple filters permits us to estimate the SEDs of these structures. d) All FOC obsevations nicely fit into one orbit, maximizing the science output of this program. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6309( 5) - 04/18/96 17:35 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4552-NUC GALAXY, Elliptical RA=12H 35M 39.81S +/- 0.1S, 2000 Z=0.0008 F(1750)=2.2+/-0.5e-17 DEC=+12D 33' 23.0" +/- 1", PLATE F(2750)=2.2+/-0.5e-17 -ID=00IY F(3400)=2.2+/-0.5e-17 W-LINE(6600)=200+/-100 F-LINE(6600)=6+/-3e-16 Comments: The target luminosity is irregularly variable. The fluxes at specified wavelength refer to the last values measured with FOC in october 1993. The line flux is a very uncertain extrapolation based on theoretical considerations. The coordinate position was measured by the observers thus: The coordinate position is averaged between those of the pre-COSTAR FOC data of both Crane and Bertola, and the only possible GS plate ID to be used is PLATE-ID=00IY because the target is not close enough to the edge of the GSSS plate for any FGS to be positioned in an overlap region. 6309( 5) - 04/18/96 17:35 - [ 4] Visit: 01 Visit Requirements: SEQ 1-2 WITHIN 24H On Hold Comments: Additional Comments: FOC photometry will be used in conjunction with FOS spectra to determine the Spectral Energy Distribution of the variable flare. Do both visits in sequence within a 24-hour period. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4552-NUC FOC/96 IMAGE 512X512 F342W 3410 1 300S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4552-NUC FOC/96 IMAGE 512X512 F275W 2770 1 388S SAME POS AS 1 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4552-NUC FOC/96 IMAGE 512X512 F175W 1730 1 1000S SAME POS AS 1; EXPAND; END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 6309( 5) - 04/18/96 17:35 - [ 5] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4552-NUC FOS/RD ACQ/PEA 4.3 MIRROR SCAN-STEP- 1 1S ONBOARD ACQ FOR 2 K Y=1.204,SEARCH- SIZE-X=1,SEARCH -SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4552-NUC FOS/RD ACQ/PEA 1.0- MIRROR SCAN-STEP- 1 1S ONBOARD ACQ FOR 3 K PAIR-A X=.602,SCAN- STEP- Y=.602,SEARCH- SIZE-X=6,SEARCH Comments: -SIZE-Y=2,STEP- PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4552-NUC FOS/RD ACQ/PEA 0.25- MIRROR SCAN-STEP- 1 1S ONBOARD ACQ FOR 4 K PAIR-A X=.172,SCAN- STEP- Y=.172,SEARCH- SIZE-X=5,SEARCH Comments: -SIZE-Y=5,STEP- PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4552-NUC FOS/RD ACQ/PEA 0.25- MIRROR SCAN-STEP- 1 10S ONBOARD ACQ FOR 5 K PAIR-A X=.05,SCAN-STEP -Y=.05,SEARCH- SIZE-X=5,SEARCH -SIZE-Y=5,STEP- Comments: Critical ACQ/PEAK stage PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC4552-NUC FOS/RD ACCUM 0.25- G270H STEP- 1 2340S EXPAND END ORBIT PAIR-A PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC4552-NUC FOS/RD ACCUM 0.25- G650L STEP- 1 400S SAME POS AS 5 PAIR-A PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC4552-NUC FOS/RD ACCUM 0.25- G780H STEP- 1 1670S SAME POS AS 5 EXPAND END ORBIT PAIR-A PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 6309( 5) - 04/18/96 17:35 - [ 6] Summary Form for Proposal 6309 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCAN-STEP-Y=1.204 SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 STEP-PATT=SINGLE SEARCH-SIZE-Y=5 SEARCH-SIZE-X=5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category AGN ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SEQ 1-2 WITHIN 24H SAME POS AS 1 SAME POS AS 1; EXPAND; END ORBIT ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3 ONBOARD ACQ FOR 4 ONBOARD ACQ FOR 5 EXPAND END ORBIT SAME POS AS 5 SAME POS AS 5 EXPAND END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F342W F275W F175W MIRROR G270H G650L G780H ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4552-NUC ------------------------------------------------------------------------------------------------------------------------------------