9680( 2) - 08/07/02 13:40 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9680 Version: 2 Check-in Date: 07-Aug-2002 13:39:56 1.Proposal Title: The X-Ray Emission Mechanism from Optical Jets: 3C 78 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Mark Birkinshaw University of Bristol CoI: Diana Worrall University of Bristol N CoI: Sarah Nolan University of Bristol N CoI: Eric Perlman University of Maryland, Baltimore County Y ------------------------------------------------------------------------------------ 5. Abstract Radio to X-ray spectral coverage and sub-arcsec imaging provide powerful diagnostics of the electron energy distribution and electron acceleration in jets. 3C 78 is the longest optical jet not to have been adequately observed with Chandra, although it is one of only three jets with HST polarimetry. Our 5-ks exploratory ACIS-S3 observation of 3C 78 in A0-3 demonstrated that the jet is detectable in the X-ray, lying outside the PRF of the core and above any diffuse emission from the host galaxy. Here we request a 55 ks ACIS-S observation to complete X-ray work on this jet, and two HST NICMOS near-IR exposures. These data will investigate electron acceleration mechanisms both in the diffuse regions of the jet and in the anomalous x-ray/optical knot 1.5 arcsec from the core. ------------------------------------------------------------------------------------ 9680( 2) - 08/07/02 13:40 - [ 2] Observations Description ------------------------ The purpose of this proposal is a deep investigation of the X-ray emission, optical emission and radio to X-ray spectrum of the jet of the nearby radio galaxy 3C 78. 3C 78 is the longest optical jet source not to have been adequately observed with Chandra, although it is one of only three jets with HST polarimetry. Our 5 ks exploratory ACIS-S observation of 3C 78 in A03 demonstrated that the jet is also detectable in the X-rays, lying outside the PRF of the core and above any diffuse emission from the host galaxy. Comparison of the exploratory Chandra image with our HST polarimetry shows that the X-ray brightest region of the jet is associated with a diffuse optical knot 1.5 arcsec northeast of the core. In the optical, this region is the faintest knot in the optically-visible portion of the jet. Thus the preliminary indication from the first 5ks of data is that 3C78 has an anomalous X-ray morphology, quite different from other X-ray/optical jet sources. Thus 3C 78 has the potential to provide important new insights on jet physics. The differences between the X-ray to optical spectral morphology of (for example) 3C 78 and M 87 may indicate that in 3C 78 different electron acceleration mechanisms are at work in different parts of the jet. With this program we will add a further 55 ks observation with ACIS-S, as well as two HST NICMOS near-IR exposures, each 1 orbit long. Along with already-obtained HST and VLA polarimetry and earlier HST multi-band imaging observations in the optical, this will give us information on 3C 78's emission and particle spectrum equalled by only two other extragalactic jets: the prototypes M87 and 3C 273. By studying together the X- ray and near-IR to optical morphology and spectrum as well as the broadband SED and radio and optical polarimetry, we will investigate deeply the underlying physics behind the emission mechanisms both in the diffuse regions of the jet and in the anomalous X-ray/optical knot 1.5 arcsec from the core, including electron acceleration mechanisms, magnetic field strength and configuration, and any contribution from Comptonized emission. In the HST part of this program we will obtain two NICMOS near-IR exposures, 1 orbit each, on 3C78. The bands chosen, F110W (corresponding to J) and F205W (corresponding to K) fill important gaps in our knowledge of the spectrum of the 3C 78 jet. We will obtain images of 3C~78 in two near-infrared bands (J = F110W and K = F205W) with NICMOS. With two near-IR bands, we will have a total of 8~bands of HST data, covering more than a decade in frequency. This will be enough to spot spectral curvature of the types that are seen in knots~B and~C of the M~87 jet (Perlman et al. 2001) or knot~A of the 3C~273 jet (Jester et al. 2002). A simple extrapolation of the optical-UV spectra shows that the 3C~78 jet is quite bright in the near-IR; our experience with the M~87 jet (Perlman et al. 2001) suggests that one orbit will suffice for each band. Only one pointing is necessary for each band, since the 3C~78 jet is only about $2$~arcsec long, considerably smaller than the NICMOS field-of-view. We will utilize the NIC2 chip in each band, in order to obtain images with matched pixellation. We will dither the NICMOS images in a four-position pattern, by fractional-pixel amounts. This strategy is recommended by the STScI NICMOS team to eliminate image defects and maximize resolution. Using this observing mode, one orbit in J will provide an exposure of 2500~s and which will reach a limiting sensitivity (at $5\sigma$) of $\rm 20.9 \ mag \, arcsec^{-2}$, which is far below the expected peak J-band surface brightness of the X-ray bright knot (extrapolated from existing HST data) of $19.3 \ \rm mag \, arcsec^{-2}$, so that we will obtain a high signal/noise image. At K~band we must use a different procedure. F205W images are dominated by the thermal background signal, which must be subtracted by chopping. We will employ a 2~arcmin chop to an off-source field, using a background exposure of $4 \times 100 \ \rm s$ (dithered to eliminate image defects), and a science exposure of 2000~s, as was successful in the F205W NICMOS observation of M~87 (Perlman et al. 2001). The 9680( 2) - 08/07/02 13:40 - [ 3] chop direction will be chosen to avoid companion galaxies on the basis of our existing optical imges. In 2000~s we will reach a limiting surface brightness sensitivity (at $5\sigma$) of $18.5 \ \rm mag \, arcsec^{-2}$, which is the predicted peak surface brightness of the X-ray bright knot. These near-IR observations with NICMOS should therefore detect the outer jet with high sensitivity in J beyond the X-ray bright knot, and provide a good enough spectral index measurement for this knot in the near-IR for us to check for spectral curvature. Real Time Justification ----------------------- There are no special POS TARG or ORIENT requirements for this observation, since the jet is only 2 arcseconds long. We also do not have tight schedule time requirements. The only important restrictions are that: (1) The dither pattern be carried out as requested to maximize resolution and minimize instrumental effects (see Description of Observation). (2) Both orbits in the visit must be carried out sequentially - this is necessary since we have split up the dithered pattern for the background observations between the two orbits. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9680( 2) - 08/07/02 13:40 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 3C78 GALAXY, JET, GALAXY, RA=03H 08M 26.22S +/- 1", J2000 V = 12.5 ELLIPTICAL, RADIO DEC=04D 06' 39.5" +/- 1", PLATE- GALAXY ID=04YJ Coordinate Source: IMAGE_TIED_TO_GSC_FRAME 2 3C78-THROW CALIBRATION, SKY RA=03H 08M 22S +/- 1", DEC=04D J2000 SURF-BKG(K) = 21+/-2 BACKGROUND, GALAXY, JET 06' 27" +/- 1", PLATE-ID=04YJ Coordinate Source: GSC_SURVEY_PLATE 9680( 2) - 08/07/02 13:40 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type NIC-SPIRAL-DITH Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.4125 Coordinate_Frame POS-TARG Pattern_Orient 0 Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 9680( 2) - 08/07/02 13:40 - [ 6] 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 3C78 NIC2 MULTIAC NIC2 F110W NSAMP=12,SAMP-SEQ=SPARS64 1 DEF PATTERN 1 10 CUM ------------------------------------------------------------------------------------------------------------------------------------ 15 3C78-THROW NIC2 MULTIAC NIC2 F205W NSAMP=9,SAMP-SEQ=STEP64 1 DEF PATTERN 1 15 CUM Comments: OFFSET FIELD ------------------------------------------------------------------------------------------------------------------------------------ 20 3C78 NIC2 MULTIAC NIC2 F205W SAMP-SEQ=SPARS64,NSAMP=11 1 DEF PATTERN 1 20 CUM ------------------------------------------------------------------------------------------------------------------------------------ 9680( 2) - 08/07/02 13:40 - [ 7] Summary Form for Proposal 9680 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=12 SAMP-SEQ=SPARS64 SAMP-SEQ=STEP64 NSAMP=11 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 10 PATTERN 1 15 PATTERN 1 20 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W F205W ------------------------------------------------------------------------------------------------------------------------------------ Target Names 3C78 3C78-THROW ------------------------------------------------------------------------------------------------------------------------------------