12434( 3) - 29-Nov-2010 19:54:11 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12434 Version: 3 Check-in Time: 29-Nov-2010 19:54:11 STScI Edit Number: 1 Title Deciphering the Flare in the Crab Nebula: ------------------------------------------------------------------------------------ Type Cycle GO/DD 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Andrei Lobanov Max-Planck-Institut fur Radioastronomie CoI: Prof. Dieter Horns Deutsches Elektronen Synchrotron N ------------------------------------------------------------------------------------ Abstract Physics of activity in the "wisps" of the Crab nebula remains poor understood, with shocks, in situ particle acceleration and magnetic field all proposed to be the driving factors. A recent flare in the Crab Nebula discovered with AGILE offers an excellent opportunity to shed the light on this issue. The flare has been successfully observed with Chandra, HST, and VLBI (EVN+MERLIN), with the flaring region (located at ~5" west from the Crab pulsar) remaining in a high state for over two months and showing a brightness temperature of >10^7 . Such a peculiar behavior is difficult to explain with the usual shock scenario. Instead it may imply a magnetic field build up or reconnection, which may turn out a common mechanism driving the activity in the "wisps" inside the Crab nebula. New observations with VLBI (23-24 November) and Chandra (27 November) are aiming at further investigating this possibility. We propose here to image the flaring region concurrently with the HST in order to be able to address radio-optical-X-ray spectral properties and also to study the evolution of the flaring region in all three bands by comparing the new images with the ones made during the previous round of concurrent observations (made about one month ago). ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to use the HST/ASC instrument to image optical continuum emission from the Crab nebula and to attempt detecting the region of enhanced emission resulting from the ongoing flare. In order to cover a sufficiently large area and avoid contamination from line emission, we propose to use the WFC-FIX aperture, observing with the broad-band F550M filter. This choice will, in addition, facilitate the comparison with the image from the previous HST ToO observation of the flare (Project 12381), made on October 2, 2010. We propose to use the default 4-point dither box, allocating 550 seconds per single dither pointing. This choice will result in the total on-target time of 2200 seconds, and it will minimize the amount of unused visibility during the observing run. Real Time Justification ----------------------- The flaring region has been observed recently with VLBI (November 23-24) and Chandra (November 27). Scheduling the HST observation is as closely in time to these observations as possible is desired for improving the accuracy physical modeling and reducing the effect of (likely) emission variability in the flaring region. 12434( 3) - 29-Nov-2010 19:54:11 - [ 2] Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12434( 3) - 29-Nov-2010 19:54:11 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CRAB-PSR-PWN ISM, EJECTA, SNR, WIND RA=05H34M31.9500S +/- 0.1", J2000 V = 16.5 +/- 0.05 DEC=+22D00'52.10" +/- 0.1" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 12434( 3) - 29-Nov-2010 19:54:11 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.265 Line_Spacing 0.187 Coordinate_Frame POS-TARG Pattern_Orient 20.67 Angle_Between_Sides 69.05 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 12434( 3) - 29-Nov-2010 19:54:11 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CRAB-PSR-PW ACS/WFC ACCUM WFC-FIX F550M 1 520 S PATTERN 1 1 N ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CRAB-PSR-PWN 1 ACS/WFC ACCUM WFC-FIX F550M 1 none none none 1 N/A CRAB-PSR-PWN 1 ACS/WFC ACCUM WFC-FIX F550M 2 none none none 1 N/A CRAB-PSR-PWN 1 ACS/WFC ACCUM WFC-FIX F550M 3 none none none 1 N/A CRAB-PSR-PWN 1 ACS/WFC ACCUM WFC-FIX F550M 4 none none none 1 N/A 12434( 3) - 29-Nov-2010 19:54:11 - [ 6] Summary Form for Proposal 12434 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F550M ------------------------------------------------------------------------------------------------------------------------------------ Target Names CRAB-PSR-PWN ------------------------------------------------------------------------------------------------------------------------------------