The high energy gamma-ray flux from the Crab nebula doubled in a couple of days (from September 19 to September 21). Such enhancement, never seen before, is clearly detected both by Agile and Fermi, the two gamma-ray telescopes currently in operation. While such huge brightening is exciting the entire astrophysical community, TOOs are being scheduled by high energy space observatories such as Integral, Swift and Chandra. By imaging the status of the knots and wisps in the inner Crab nebula, HST could provide a unique piece of information, which may yield a clue to understand the source behavior.

We ask for straight imaging of the Crab Nebula. We will use the HST/ACS instrument in its WFC configuration (which will cover the entire field of interest). We propose to use the large-band F550M filter, well suited to sample the continuum emission from the system, with almost no contamination from line emission from the SNR filaments. Such a choice will also allow for an easy comparison of the new image with the large available database of HST images of the Crab collected with the WFPC2 instrument through the F547M filter, having a very similar bandpass to the F550M selected here. The observation (2200s integration; one single orbit) must be split in 4 frames (550s each) with a standard 4-point BOX dithering pattern (few pixel spacing). The observation has to be performed as soon as possible (within 2 days maximum) to observe the target as close as possible to the peak of its variability HOT STARS 0 false 0.0 0.0 false false false false false false SUPPORTED STAR NEUTRON STAR PULSAR SUPERNOVA This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 05 34 31.9500 +22 00 52.10 J2000 ACS/WFC Imaging No No F550M ACS/WFC Imaging No No F550M ACS/WFC Imaging No No F550M POS-TARG DITHER 0.265 LINE 0.187 false false 69.05 4 20.67 ACS-WFC-DITHER-BOX 1 false The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 1285723901000 267.72065284387213 (Tic-Visit :proposal-id 12381 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "24-Sep-2010 21:03:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12381 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12381 :visit-id "01" :orbit-number 1 :pcs-time 0 :si-vis-utilization 720 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) true 1 0 (Tic-Visit :proposal-id 12381 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "24-Sep-2010 21:03:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12381 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12381 :visit-id "01" :orbit-number 1 :pcs-time 0 :si-vis-utilization 720 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) false 1 0