9139( 2) - 02/14/01 11:20 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9139 Version: 2 Check-in Date: 14-Feb-2001 11:19:03 1.Proposal Title: Variability in the UV Spectrum of 3C 279: Testing Models for the Gamma-Ray Emission in Blazars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle SNAP 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Anuradha Koratkar Space Telescope Science Institute CoI: Dr. C. Megan Urry Space Telescope Science Institute N CoI: Dr. Laura Maraschi Osservatorio di Milano N CoI: Dr. Elena Pian ITESRE-CNR, Bologna N CoI: Mr. Brett S. Blacker Space Telescope Science Institute Y ------------------------------------------------------------------------------------ 5. Abstract Gamma-ray emission dominates the power output of many luminous blazars, yet we do not know the physical scale on which it is produced i.e., where in the jet most of the kinetic power is dissipated. We know the production of Gamma- rays depends critically on the blazar line emission: ambient photons from broad emission lines (primarily LyAlpha) are upscattered to Gamma-ray energies by relativistic electrons in the blazar jet. Rapid large-amplitude Gamma-ray variability implies that both electrons and LyAlpha photons must vary rapidly. This suggests some broad-line clouds are photoionized by synchrotron flares in the jet (the ``mirror model''). We propose a critical test to determine if Gamma- rays are produced on the scale of the broad line region, using multi-epoch STIS UV snapshots of 3C 279 to find and characterize its LyAlpha variability. This will validate the mirror model for generating the intense Gamma-ray emission from blazars, which could then be quantified with (much more resource intensive) coordinated Gamma-ray and HST observations. 3C 279 is the best-studied blazar from radio to Gamma-ray wavelengths, showing frequent large flares over days to months. Variability in the UV continuum and LyAlpha will directly reveal any coupling between the jet ionizing flux and the broad-line region emission, providing clues to the physics and energetics of all radio-loud AGN. ------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 2] Observations Description ------------------------ This is a demonstration proposal, rather than an intensive attempt to ``reverberation map'' the continuum and emission line variations. Our goal is to establish whether for any changes in the UV flux we see changes in the emission line profile, and is this change in a narrow velocity range. Thus, the only constraints on sampling are to obtain 10 -- 20 line spectra in this cycle. The number of observations is similar to the entire IUE historical monitoring, but these STIS observations will have much better SNR and spectral resolution, and will sample more rapid variations. Multiwavelength campaigns on 3C 279 show that large flares occur on timescales of a few months, and even in a very faint, non-flaring state, the UV flux still varies by a factor of 2 (Maraschi et al. 1994, Wehrle et al. 1998). Hence, any likely snapshot sampling is sufficient to ensure detection of significant change both in the line and the continuum. Choice of STIS Configurations. We propose to observe the LyAlpha (1867 Angstrom observed wavelength) emission line region and the nearby UV continuum in 3C 279 with the HST/STIS in the ACCUM mode. The STIS ETC and instrument handbook show that the NUV-MAMA/G230L is the best configuration to use to maximize SNR. But, the MAMA detectors are restricted to operate only in SAA free orbits which reduces the scheduling probability of a snapshot observation by a factor of nearly 3. To increase our scheduling probability we will also obtain some of the proposed snapshots using the CCD/G230LB configuration which has no SAA restriction and only slightly worse SNR. Therefore, we ask for 10 snapshots with the NUV-MAMA/G230L (1570 - 3180 Angstrom) and 10 snapshots with the CCD/G230LB (1680 - 3060) STIS configurations. This combination of two STIS configurations will maximize the scheduling of observations as well as the SNR in some of the spectra. With the two STIS configurations we will obtain wavelength coverage from ~1020 Angstrom to ~2070 Angstrom in the rest frame of 3C 279, with a resolution of ~500 km s^- 1. Because of this wavelength coverage and the proposed SNR, if observations are at low flux levels we will also be able to investigate for evidence of thermal emission from a disk. Our exposure time calculations are such that we will get a minimum SNR of 10 per resolution element in the LyAlpha emission line. We have used HST/FOS observations of 3C 279 to determine exposure times using the STIS ETC. The FOS spectrum was obtained in 1992 and extends from 1600 -- 4750Angstrom. Over 8 years of UV observations of 3C 279 has been known to vary between ~0.6* 10^-15 and 31.6* 10^-15 erg s^-1 cm^-2 AA^-1 at 1750 Angstrom. At a low continuum flux level of 2.0 * 10^-15 erg cm^-2 s^-1 AA^-1 at 1750Angstrom, the ETC shows that 1200s gives 85 and 50 source counts at 1750 Angstrom with the NUV-MAMA/G230L and CCD/G230LB configurations respectively. With the resulting minimum SNR of > 7 per resolution element over the wavelength range from 1800 to 3000 Angstrom, emission line variations of > ~7. The actual SNR in the LyAlpha emission line will be higher than 15 for the typical intensity of 3C 279, but this exposure guarantees we can observe 3C 279 sufficiently well to low flux levels. Depending on the brightness of the target, our proposed observations will have ~6 times the resolution and > 10 times the SNR (per comparable resolution element) of the IUE data. They are also a factor of 2.5 improvement on the FOS data in SNR and hence should allow us to easily investigate emission line profile changes. To minimize target acquisition overheads we will use STIS in the slitless mode (3C 279 is a bright point source). A guide star acquisition will assure good imaging and hence full spectral resolution on this point source. We will also forgo the ``automatic" wavecal that is part of the overhead, saving 4 minutes of overhead per spectrum since the source has a well known redshift. Using Table 6.11 from the Cycle 10 HST Primer, the nominal overheads then total 6m + 8m = 14m (GS Acq + exposure overhead) for the MAMA exposures and 6m + 5m = 11m (GS Acq + exposure overhead) for the CCD exposures. With 20m for science observing, our snapshots total 31 - - 34m, near the center of the distribution for snapshots having a high rate of scheduling and execution. Real Time Justification ----------------------- Our scheduling requirements are very flexible. Any snapshot sampling is sufficient to ensure detection of some change both in the line and the continuum. This is a stand-alone program which will explore the nature of variability of the LyAlpha emission line from the STIS observations. It is a step toward providing crucial estimates of the spatial scale for energy dissipation in jets. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 3C279 GALAXY, BL LAC RA=12H 56M 11.17S +/- 1.0", DEC= J2000 Z = V = 17 -05D 47' 21.52" +/- 1.0", PLATE- 0.5362 ID=024R Coordinate Source: GSC_SURVEY_PLATE Comments: VTT Generated target from DSS image. 9139( 2) - 02/14/01 11:20 - [ 4] Visit: 01 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 5] Visit: 02 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 6] Visit: 03 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 7] Visit: 04 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 8] Visit: 05 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 9] Visit: 06 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 10] Visit: 07 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 11] Visit: 08 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 12] Visit: 09 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 13] Visit: 10 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/N ACCUM 25MAMA G230L 2376 WAVECAL=NO 1 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 14] Visit: 20 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 15] Visit: 21 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 16] Visit: 22 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 17] Visit: 23 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 18] Visit: 24 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 19] Visit: 25 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 20] Visit: 26 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 21] Visit: 27 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 22] Visit: 28 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 23] Visit: 29 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 3C279 STIS/C ACCUM 50CCD G230LB 2375 WAVECAL=NO 1 1200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 9139( 2) - 02/14/01 11:20 - [ 24] Summary Form for Proposal 9139 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 25MAMA 50CCD ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/NUV-MAMA STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category SNAP ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L G230LB ------------------------------------------------------------------------------------------------------------------------------------ Target Names 3C279 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2376 2375 ------------------------------------------------------------------------------------------------------------------------------------