13348( 2) - 27-Jun-2013 16:42:27 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13348 Version: 2 Check-in Time: 27-Jun-2013 16:42:27 STScI Edit Number: 0 Title Imaging the Crab nebula when it is flaring in gamma-rays ------------------------------------------------------------------------------------ Type Cycle GO 21 ------------------------------------------------------------------------------------ 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: 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. 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 13348( 2) - 27-Jun-2013 16:42:27 - [ 2] 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. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 13348( 2) - 27-Jun-2013 16:42:27 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 13348( 2) - 27-Jun-2013 16:42:27 - [ 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 to rejecting CR hits ------------------------------------------------------------------------------------------------------------------------------------ 13348( 2) - 27-Jun-2013 16:42:27 - [ 5] Visit: 01 Visit Requirements: SCHED 80%; ON HOLD ; TOO RESPONSE TIME 1.0D On Hold Comments: 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. Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CRAB ACS/WFC ACCUM WFC1 F550M 1 500 S PATTERN 1 1 (2000 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 13348( 2) - 27-Jun-2013 16:42:27 - [ 6] Visit: 02 Visit Requirements: SCHED 80%; AFTER 01 BY 8 D TO 12 D 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CRAB ACS/WFC ACCUM WFC1 F550M 1 500 S PATTERN 1 1 (2000 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 13348( 2) - 27-Jun-2013 16:42:27 - [ 7] Summary Form for Proposal 13348 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 8 D TO 12 D, ON HOLD , PATTERN 1 1, SCHED 80%, TOO RESPONSE TIME 1.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F550M ------------------------------------------------------------------------------------------------------------------------------------ Target Names CRAB ------------------------------------------------------------------------------------------------------------------------------------