9494( 2) - 01/28/02 08:14 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9494 Version: 2 Check-in Date: 28-Jan-2002 08:14:05 1.Proposal Title: ACS Observations of the Optical Jet of MH 2136-428 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Paolo Padovani Space Telescope Science Institute CoI: Dr. Paolo Giommi ASI Science Data Center N CoI: Hermine Landt Space Telescope Science Institute N CoI: Dr. Eric Perlman University of Maryland, Baltimore County N CoI: Matteo Perri ASI Science Data Center N CoI: Prof. C. Megan Urry Yale University N ------------------------------------------------------------------------------------ 5. Abstract The total number of well-established extragalactic jets is less than twenty, and of these only a handful are blazars. We propose here to use ACS (one orbit) to image in three bands the newly discovered optical jet in the BL Lac object MH 2136-428. This is the first time that an optical jet has been discovered in a completely featureless blazar, that is in an object whose nucleus is particularly highly beamed and/or whose accretion disk power is extremely low. Moreover, our source has a radio flux more than an order of magnitude fainter than those typical of the other blazars with optical jets, allowing us to study an intrinsically weaker jet. Our goals include the study of the jet morphology, its spectral energy distribution, and the relationship between the jet properties in blazar and non-blazar sources, extremely relevant for unified schemes. Only HST can provide the resolution required to study such a faint, narrow feature, close to the bright nucleus. We are also asking for 10ks of Chandra observing time to further constrain the jet spectral energy distribution and its underlying emission processes. ------------------------------------------------------------------------------------ 9494( 2) - 01/28/02 08:14 - [ 2] Observations Description ------------------------ We propose to image MH 2136-428 with HST/ACS in three bands: F475W, F625W, F850LP, i.e., SDSS g, r, z. We need all three bands to derive spectral information within the optical band, extremely useful to constrain the characteristic energy of the radiating electrons. Given the brightness of the feature in question on the ESO 3.6m image (taken with a 30s exposure), just 1 orbit is required for all three images. We have used the ACS ETC to simulate the exposures in each band, assuming a nu^-1 spectral energy distribution, typical of other optical jets (e.g., O'Dea et al. 1999; Perlman et al. 2001). A signal-to-noise (S/N) ratio of 7, more than adequate for our purposes, is reached in 810s, 780s, and 960s, respectively, for a surface brightness in R of 20.5 mag/arcsec^2. Adding the required overheads, obtained from the ACS handbook, our observations sum up to about 55 minutes, i.e. somewhat less than one orbit given the declination of our source. The Chandra exposure time has been determined based on the results of Pesce et al. (2001) on 3C 371. The optical jet of this source has a surface brightness roughly 1.5 magnitudes fainter than that of our source, but the S/N ratio of the Chandra observations was far from optimal. Assuming that the X-ray-to-optical ratio of the jet in MH 2136-428 is similar to that of 3C 371, 10ks should allow us to constrain the presence of an X-ray jet without reasonable doubt. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9494( 2) - 01/28/02 08:14 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MH2136-428 GALAXY, BL LAC, JET RA=21H 39M 24.14S +/- 0.1S, DEC= J2000 B = 17.3+/-0.6 -42D 35' 21.3" +/- 1" Coordinate Source: OTHER_SOURCE 9494( 2) - 01/28/02 08:14 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 30D TO 70D On Hold Comments: Additional Comments: ORIENT is specified so that the suspected optical jet falls along a diagonal of the HRC chip. Other orientations are possible and equally good, i.e., 120-160, 210-250, 300-340 degrees. Any of these four orientations would be acceptable to us if they are preferable for scheduling reasons. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 MH2136-428 ACS/HR ACCUM HRC F475W CR-SPLIT=2,GAIN=2 1 810 S C ------------------------------------------------------------------------------------------------------------------------------------ 20 MH2136-428 ACS/HR ACCUM HRC F625W CR-SPLIT=2,GAIN=2 1 780 S C ------------------------------------------------------------------------------------------------------------------------------------ 30 MH2136-428 ACS/HR ACCUM HRC F850LP CR-SPLIT=2,GAIN=2 1 960 S C ------------------------------------------------------------------------------------------------------------------------------------ 9494( 2) - 01/28/02 08:14 - [ 5] Summary Form for Proposal 9494 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 GAIN=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 30D TO 70D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W F625W F850LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names MH2136-428 ------------------------------------------------------------------------------------------------------------------------------------