0 Assigned ID: 1611 ----- Attempting Submission 1 (Fri Mar 01 18:19:15 GMT 2013) ----- 0 ----- Attempting Submission 1 (Thu Jun 27 16:37:45 GMT 2013) ----- Imaging the Crab nebula when it is flaring in gamma-rays One of the most intriguing results of the gamma-ray instruments currently in orbit has been the detection of powerful flares from the Crab Nebula. Such events, detected roughly once per year, can be very spectacular. Indeed, in April 2011, for a few days the Crab was by far the brightest source in the gamma-ray sky. Such a dramatic variability challenges our understanding of how pulsar wind nebulae work and defies current astrophysical models for particle acceleration. With the aim of locating the site(s) of the flares, an ad hoc HST strategy must be put in place to be prepared and react promptly in case of a new brightening in gamma rays. We ask here for a triggered TOO observation of the Crab Nebula with ACS/WFC in case a gamma-ray flare is announced by the Agile and/or Fermi missions. This is a crucial part of a multiwavelength program that we are organizing, based on lessons learnt from our follow-up observations of previous flares, including a regular (monthly) monitoring of the source both in X-ray and optical through a joint Chandra-HST proposal. We ask to perform two-epoch imaging of the Crab Pulsar and Nebula, reacting with the fastest possible response time to a trigger provided by the detection of a new gamma-ray flare from the Crab nebula by Fermi-LAT and/or AGILE. The first-epoch observation should be performed as soon as possible after the trigger, the second-epoch observation about 10 days after the first one. For each epoch, we will use the same setup we adopted in our ongoing HST monitoring campaign of the Crab. We will use the ACS/WFC with the WFC1 aperture, with 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. A box dithering pattern will be implemented to fill the inter-chip gap as well as to reject cosmic ray hits. Setting an exposure of 500 s for each position of the dithering pattern results in 2000 s exposure time per visit, which is well suited to achieve our goals and allows for an optimal use of the orbital visibility window. The images collected under the proposed ToO will be completed and compared with images acquired with an identical instrument setup within a monthly multiwavelength X-ray and optical monitoring campaign. Thanks to the sharp angular resolution of HST, the proposed fast TOO observation will be crucial to pinpoint the region responsible for the puzzling gamma-ray flare. HOT STARS 12 false false 0.0 0.0 false false false SUPPORTED STAR NEUTRON STAR PULSAR J2000 J2000 Timing link suitability includes constraints ([002 After 001 by 6.0 to 10.0 days]) The scheduling data was generated by CASM 21.0. CASM was run in Phase I mode. ACS/WFC Imaging No No F550M Timing link suitability includes constraints ([002 After 001 by 6.0 to 10.0 days]) The scheduling data was generated by CASM 21.0. CASM was run in Phase I mode. ACS/WFC Imaging No No F550M POS-TARG DITHER 3.5 Dithering is aimed at filling the inter-chip gap as well as to rejecting CR hits LINE 0.5 false false 85.28 4 85.28 ACS-WFC-DITHER-BOX 1 false /castor/deluca/cave/OP-cache/13348-phaseII-v01.xml Timing link suitability includes constraints ([02 After 01 by 8.0 to 12.0 days]) The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13348 :visit-id "01" :proposal-version -1 :trans-version "20130502" :date "27-Jun-2013 18:16:32.0" :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 13348 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13348 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2704 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3092 :pcs-gap 0 ) true 1 0 This is a target of opportunity observation. The trigger will be provided by the detection of a new gamma-ray flare from the Crab nebula by Fermi-LAT and/or AGILE. /castor/deluca/cave/OP-cache/13348-phaseII-v02.xml Timing link suitability includes constraints ([02 After 01 by 8.0 to 12.0 days]) The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13348 :visit-id "02" :proposal-version -1 :trans-version "20130502" :date "27-Jun-2013 18:31:00.0" :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 13348 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13348 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2704 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3092 :pcs-gap 0 ) true 1 0