! Proposal 6573, submission 2 ! PI: Jeff Hester ! Received Thu Feb 15 17:41:54 EST 1996 ! From: scowen@tycho.la.asu.edu Proposal_Information Title: Continuation of Temporal Monitoring of the Crab Synchrotron Nebula Proposal_Category: GO Scientific_Category: INTERSTELLAR MEDIUM Cycle: 6 Investigators PI_name: Jeff Hester PI_Institution: Arizona State University CoI_Name: Paul Scowen CoI_Institution: Arizona State University Contact: CoI_Name: Curt Michel CoI_Institution: Rice University Contact: CoI_Name: James Graham CoI_Institution: University of California at Berkeley Contact: CoI_Name: John Gallagher CoI_Institution: University of Wisconsin-Madison Contact: CoI_Name: Alan Watson CoI_Institution: New Mexico State University Contact: CoI_Name: Ravi Sankrit CoI_Institution: Arizona State University Contact: Abstract: The synchrotron nebula surrounding the Crab pulsar has been the subject of intensive study for decades. It is generally accepted that the structure and activity in this region are due to wave phenomena near the termination shock of the pulsar wind, observations of which hold unique promise of leading to more complete models of the pulsar and its magnetosphere. Unfortunately, this promise has not been fulfilled, largely because of the low spatial resolution and uneven temporal coverage of existing studies. Recent HST WFPC2 observations of the Crab synchrotron nebula (Hester et al. 1995a,b) offer new hope in this quest. These data, which reach the natural size scale defined by the Larmor radius of energetic electrons, resolve the majority of the the known features in the Crab. For the first time it is possible to reliably establish the physical conditions (e.g., emissivities, equipartition fields, and pressures) of features associated with the wind and its termination shock. In addition the HST has probed the structure of the nebula very close to the pulsar itself, leading to the exciting discovery of a bright knot located only 1300 AU above the SE pole of the pulsar. It is clear, however, that the Crab is essentially dynamical in character, and to capitalize fully on the promise of HST observations will require temporal monitoring over several years. In Cycle 5 we have begun such a program. Here we propose to continue it through Cycle 6. Questions Observing_Description: The program is a temporal monitor of the dynamical structure near the center of the Crab Nebula. F547M will be used to image the Crab on each of 9 1-orbit visits. Five of these visits will be separated from each other by three months. If these five visits are referred to as A through E, then four additional visits will be scheduled at C minus 1 month, C minus 1 week, C plus 1 week, and C plus one month. This set of observations will provide a full year's monitor of the Crab at 3 month resolution, in the middle of which the four additional observations will sample changes in the nebula over logarithmically stepped 1 week, 2 week, 1 month, and 2 month time scales. For these observations, the pulsar will be centered in the FOV of the Planetary Camera, providing the full resolution of the HST at 5500Angstrom. A full orbit CR- SPLIT F547M exposure will be taken on each visit. F547M is chosen because it offers both a broad passband and minimal contamination from emission lines. The existing WFPC2 have a minimum signal in the field of ~ 100 e^- per PC pixel in each of the two exposures, so the images will be photon noise limited everywhere. In addition to the PC1 observations of the center of the nebula, we will obtain ``serendipitous'' WFC images of much of the nebula located within ~ 90" of the pulsar as the orientation of the HST changes through the year. Real_Time_Justification: This program is a temporal study of the evolution of the Crab Nebula, so scheduling is important. This study is built around 5 visits to the Crab, each separated from its neighbors by as close to 3 months as possible. The Crab emerges from the Sun avoidance zone on 96.217 and will remain accessible until 97.117, again emerging from the zone on 97.217. Meeting the timing requirements for these 5 visits then requires that observations be scheduled as soon as possible after emergence from the Sun avoidance zone on 96.217 and 97.217, and as late as possible prior to the Crab's entry into the avoidance zone on 97.117. Uniform temporal sampling then requires that the other two observations take place 1/3 and 2/3 of the way though the 96.217 to 97.117 window. The five orbits above provide a one- year monitor of what is going on in the nebula. The four additional temporal monitor exposures should be taken 1 month before, 1 week before, 1 week after, and 1 month after the ~ 97.26 visit. These will provide a sample of the behavior of the Crab on time scales as short as a week. It may appear that scheduling this program is difficult, and in fact doing so requires working in close cooperation with the scheduling branch at the STScI. However, we note that we have both a good understanding of what is possible and a good long-term working relationship with the relevant personnel at the STScI. We also note that we have been successful so far in scheduling the even more difficult Cycle 5 program of which this program is a continuation. While not specifically tagged as a long term proposal, we anticipate that on the basis of the extent, type, and time scales of evolution observed during Cycle 5, we will propose to continue the monitoring program in Cycle 7. Keck: An informal monitoring program has been in effect at the W. M. Keck telescope since November, 1993. Observations have been, and will continue to be, obtained at 2.3 Mum in seeing of typically ~ 0arcs6. These data will provide a long wavelength baseline for keeping track of spectral index variations. (Graham has access to Keck as Co-I of the team that developed the Keck NIRC.) Steward / Lowell: We have initiated a program of ground based monitoring of the Crab. This program was begun at Lowell, then moved to Steward Observatory this fall when Watson left Lowell. This ground based monitoring includes photometric and polarimetric observations. It is intended both to tie the HST observations to a ground based data set that can be longer term, and to provide additional data (e.g., polarization and spectral index monitoring) that will not be routinely obtained with HST. Calibration_Justification: Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: CRAB-PULSAR Alternate_Names: Description: STAR, PULSAR, HALO Position: RA=5H 34M 31.856S +/- 0.010S, DEC= 22D 0' 54.30" +/- 0.10" Equinox: J2000 Rv_or_z: Flux: V=15.9+/-0.5 Comments: Visits Visit_Number: 01 Visit_Requirements: AFTER 6-AUG-96 Visit_Comments: FIRST MONITOR EXPOSURE. Exposure_number: 10 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-TOLERANCE=0.0, CR-SPLIT=0.5, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 2400S Special_Requirements: Visit_Number: 02 Visit_Requirements: AFTER 01 BY 70D TO 80D ORIENT 294D TO 298D Visit_Comments: SECOND MONITOR EXPOSURE. Exposure_number: 20 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-TOLERANCE=0.0, CR-SPLIT=0.5, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 2400S Special_Requirements: Visit_Number: 03 Visit_Requirements: AFTER 02 BY 6D TO 8D SAME ORIENT AS 02 Visit_Comments: THIRD MONITOR EXPOSURE Exposure_number: 30 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-TOLERANCE=0.0, CR-SPLIT=0.5, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 2400S Special_Requirements: Visit_Number: 04 Visit_Requirements: AFTER 03 BY 6D TO 8D SCHED 70% SAME ORIENT AS 02 Visit_Comments: FOURTH MONITOR EXPOSURE Exposure_number: 40 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1200S Special_Requirements: Exposure_number: 45 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1100S Special_Requirements: Visit_Number: 05 Visit_Requirements: AFTER 04 BY 6D TO 8D SCHED 70% SAME ORIENT AS 02 Visit_Comments: FIFTH MONITOR EXPOSURE Exposure_number: 50 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1200S Special_Requirements: Exposure_number: 55 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1100S Special_Requirements: Visit_Number: 06 Visit_Requirements: AFTER 05 BY 6D TO 8D SCHED 70% SAME ORIENT AS 02 Visit_Comments: SIXTH MONITOR EXPOSURE Exposure_number: 60 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1200S Special_Requirements: Exposure_number: 65 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1100S Special_Requirements: Visit_Number: 07 Visit_Requirements: AFTER 06 BY 6D TO 8D SCHED 70% SAME ORIENT AS 02 Visit_Comments: SEVENTH MONITOR EXPOSURE Exposure_number: 70 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1200S Special_Requirements: Exposure_number: 75 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1100S Special_Requirements: Visit_Number: 08 Visit_Requirements: AFTER 07 BY 6D TO 8D SCHED 70% SAME ORIENT AS 02 Visit_Comments: EIGHTH MONTIOR EXPOSURE Exposure_number: 80 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1200S Special_Requirements: Exposure_number: 85 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-SPLIT=NO, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 1100S Special_Requirements: Visit_Number: 09 Visit_Requirements: AFTER 08 BY 110D TO 120D Visit_Comments: NINTH MONITOR EXPOSURE Exposure_number: 90 Target_Name: CRAB-PULSAR Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F547M Optional_Parameters: CLOCKS=NO, CR-TOLERANCE=0.0, CR-SPLIT=0.5, ATD-GAIN=7 Number_of_iterations:1 Time_Per_Exposure: 2400S Special_Requirements: Data_Distribution Medium: 8MM Blocking_Factor: 10 Ship_To: PI_Address Ship_Via: UPS Recipient_Email: