! Proposal 6309, submission 1 ! PI: Francesco Bertola ! Received Wed May 3 14:04:16 EDT 1995 ! From: lucas@stsci.edu ! $Id: 6309,v 5.1 1996/04/18 21:29:41 pepsa Exp $ ! Bertola Cycle 5 DD Program, submission 1 ! PI: Francesco Bertola ! Received Wed May 3 07:23:09 EDT 1995 ! From: lbuson@eso.org Proposal_Information Title: DETERMINING THE SED OF AN ULTRAVIOLET FLARE AT THE CENTRE OF THE ELLIPTICAL GALAXY NGC 4552 Proposal_Category: GO/DD Scientific_Category: AGN Cycle: 5 Investigators PI_name: Francesco Bertola PI_Institution: Department of Astronomy Padova CoI_Name: David Burstein CoI_Institution: Arizona State University Contact: N CoI_Name: Michele Cappellari CoI_Institution: Department of Astronomy Padova Contact: Y CoI_Name: Sperello Di Serego Alighieri CoI_Institution: Osservatorio Astrofisico di Arcetri Contact: N CoI_Name: Laura Greggio CoI_Institution: Department of Astronomy Bologna Contact: N CoI_Name: Alvio Renzini CoI_Institution: Department of Astronomy Bologna Contact: N CoI_Name: Rodolfo Viezzer CoI_Institution: Department of Astronomy Bologna Contact: N 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. Questions Observing_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. Fixed_Targets Target_Number: 1 Target_Name: NGC4552-NUC Description: GALAXY, Elliptical Position: RA=12H 35M 39.81S +/- 0.1S, DEC=+12D 33' 23.0" +/- 1", PLATE-ID=00IY Equinox: 2000 RV_or_Z: Z=0.0008 Flux: F(1750)=2.2 +/- 0.5 E-17, F(2750)=2.2 +/- 0.5 E-17, F(3400)=2.2 +/- 0.5 E-17, W-LINE(6600)=200 +/- 100, F-LINE(6600)=6 +/- 3 E-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. Visits Visit_Number: 1 Visit_Requirements: SEQ 1-2 WITHIN 24H Visit_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. Exposure_Number: 1 Target_Name: NGC4552-NUC Config: FOC/96 Opmode: IMAGE Aperture: 512x512 Sp_Element: F342W Wavelength: 3410 Number_of_Iterations: 1 Time_Per_Exposure: 300S Exposure_Number: 2 Target_Name: NGC4552-NUC Config: FOC/96 Opmode: IMAGE Aperture: 512x512 Sp_Element: F275W Wavelength: 2770 Number_of_Iterations: 1 Time_Per_Exposure: 388S Special_Requirements: SAME POS AS 1 Exposure_Number: 3 Target_Name: NGC4552-NUC Config: FOC/96 Opmode: IMAGE Aperture: 512x512 Sp_Element: F175W Wavelength: 1730 Number_of_Iterations: 1 Time_Per_Exposure: 1000S Special_Requirements: SAME POS AS 1; EXPAND; END ORBIT Visit_Number: 2 Exposure_Number: 1 Target_Name: NGC4552-NUC Config: FOS/RD Opmode: ACQ/PEAK Aperture: 4.3 Sp_Element: MIRROR Optional_Parameters: SCAN-STEP-Y=1.204, SEARCH-SIZE-X=1, SEARCH-SIZE-Y=3 Number_of_Iterations: 1 Time_Per_Exposure: 1S Special_Requirements: ONBOARD ACQ FOR 2 Exposure_Number: 2 Target_Name: NGC4552-NUC Config: FOS/RD Opmode: ACQ/PEAK Aperture: 1.0-PAIR-A Sp_Element: MIRROR Optional_Parameters: SCAN-STEP-X=.602, SCAN-STEP-Y=.602, SEARCH-SIZE-X=6, SEARCH-SIZE-Y=2 STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 1S Special_Requirements: ONBOARD ACQ FOR 3 Exposure_Number: 3 Target_Name: NGC4552-NUC Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.25-PAIR-A Sp_Element: MIRROR Optional_Parameters: SCAN-STEP-X=.172, SCAN-STEP-Y=.172, SEARCH-SIZE-X=5, SEARCH-SIZE-Y=5 STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 1S Special_Requirements: ONBOARD ACQ FOR 4 Exposure_Number: 4 Target_Name: NGC4552-NUC Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.25-PAIR-A Sp_Element: MIRROR Optional_Parameters: SCAN-STEP-X=.05, SCAN-STEP-Y=.05, SEARCH-SIZE-X=5, SEARCH-SIZE-Y=5 STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 10S Special_Requirements: ONBOARD ACQ FOR 5 Comments: Critical ACQ/PEAK stage Exposure_Number: 5 Target_Name: NGC4552-NUC Config: FOS/RD Opmode: ACCUM Aperture: 0.25-PAIR-A Sp_Element: G270H Optional_Parameters: STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 2340S Special_Requirements: EXPAND END ORBIT Exposure_Number: 6 Target_Name: NGC4552-NUC Config: FOS/RD Opmode: ACCUM Aperture: 0.25-PAIR-A Sp_Element: G650L Optional_Parameters: STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 400S Special_Requirements: SAME POS AS 5 Exposure_Number: 7 Target_Name: NGC4552-NUC Config: FOS/RD Opmode: ACCUM Aperture: 0.25-PAIR-A Sp_Element: G780H Optional_Parameters: STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 1670S Special_Requirements: SAME POS AS 5 EXPAND END ORBIT Data_Distribution Medium: 8MM Blocking_Factor: 10 Ship_To: PI_Address Ship_Via: UPS