12912( 3) - 04-Mar-2013 14:22:28 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12912 Version: 3 Check-in Time: 04-Mar-2013 14:22:28 STScI Edit Number: 1 Title Imaging the Crab nebula when it is flaring in gamma-rays ------------------------------------------------------------------------------------ Type Cycle GO 20 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Andrea De Luca INAF, Instituto di Astrofisica Spaziale e Y Fisica CoI: Dr. Patrizia A. Caraveo INAF, Instituto di Astrofisica Spaziale e N Fisica CoI: Dr. Fabio Pizzolato INAF, Instituto di Astrofisica Spaziale e N Fisica CoI: Prof. Giovanni F. Bignami Instituto Universitario de Studi Superiori N Pavia CoI: Dr. Marco Tavani INAF, Instituto di Astrofisica Spaziale e N Fisica CoI: Dr. Roberto Mignani Mullard Space Science Laboratory N CoI: Dr. Martin C. Weisskopf NASA Marshall Space Flight Center N CoI: Dr. Stefan Funk Stanford University N CoI: Dr. Andrea Belfiore University of California - Santa Cruz N ------------------------------------------------------------------------------------ Abstract 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 in September 2010. In April 2011 a similar flare, lasting several days, made the nebula the brightest source in the gamma-ray sky. A critical reassessment of long term behavior of the Crab flux clearly showed that both Agile and Fermi had already detected similar events in October 2007 and February 2009, pointing to a recurrence time of once per year. A HST observing strategy must be set up to react promptly to any possible new brightening of the Crab in gamma rays. In September 2010 we requested a DD observation which was promptly accepted and carried out. However, the lack of a suitable reference image hampered our efforts to pinpoint the sites of possible variability inside the nebula. Thus, while now we ask 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, we are also organizing a regular (monthly) monitoring of the source both in X-ray and optical through a joint Chandra-HST proposal. ------------------------------------------------------------------------------------ Observations Description ------------------------ We ask to perform simple 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. 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 12912( 3) - 04-Mar-2013 14:22:28 - [ 2] 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 new image will be compared to the most recent reference one, acquired with an identical instrument setup within a monthly multiwavelength X-ray and optical monitoring campaign proposed as a joint Chandra-HST program. 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. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12912( 3) - 04-Mar-2013 14:22:28 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CRAB STAR, NEUTRON STAR, RA=05H34M31.9500S +/- 0.1", J2000 V = 16.5 +/- 0.1 PULSAR DEC=+22D00'52.10" +/- 0.1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 12912( 3) - 04-Mar-2013 14:22:28 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 3.5 Line_Spacing 0.5 Coordinate_Frame POS-TARG Pattern_Orient 85.28 Angle_Between_Sides 85.28 Center_Pattern NO Pattern_Comments: Dithering is aimed at filling the inter-chip gap as well as at rejecting CR hits ------------------------------------------------------------------------------------------------------------------------------------ 12912( 3) - 04-Mar-2013 14:22:28 - [ 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 ACS/WFC ACCUM WFC1 F550M 1 500 S PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 1 ACS/WFC ACCUM WFC1 F550M 1 none none none 1 N/A CRAB 1 ACS/WFC ACCUM WFC1 F550M 2 none none none 1 N/A CRAB 1 ACS/WFC ACCUM WFC1 F550M 3 none none none 1 N/A CRAB 1 ACS/WFC ACCUM WFC1 F550M 4 none none none 1 N/A 12912( 3) - 04-Mar-2013 14:22:28 - [ 6] Summary Form for Proposal 12912 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F550M ------------------------------------------------------------------------------------------------------------------------------------ Target Names CRAB ------------------------------------------------------------------------------------------------------------------------------------