22 Natalucci WFMi

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A Wide-Field-Monitor for EDGE L. Natalucci (1), M. Feroci (1), L. Piro (1), P. Ubertini (1), E. Quadrini (2), D. Barret (3), C. Budtz-Jorgensen (4), L. Amati (5), E.Caroli (5), C. Labanti (5), J.W. Den Herder (6) and collaborators (1) INAF/IASF Rome, (2) INAF/IASF Milan, (3) CESR Toulouse, (4) DSRI Copenaghen, (5) INAF/IASF Bologna, (6) SRON Uthrecht Talk summary instrument concept derived from science requirements and constraints optical design of the units and baseline proposal description design characteristics of detectors budgets performance A concept proposal for hunting and localizing GRBs … and much more

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GRBs are used as beacons for WHIM in absorption. How many GRBs do we need? How much bright? Basic requirement is to detect and localize ~100 GRB per year having prompt fluence greater than ~10-6 erg cm-2 translates to an effective area > ~350 cm2 in the energy range 15-150 keV, omnidirectional within a FOV of ~3 sr. Low energy extension (E < 10 keV) helps to increase trigger sensitivity and is a benefit for GRB prompt science: significant increase in number of afterglows due to detection of XRFs and high-z (>5) GRBs better determination of spectral parameters (advantage over SWIFT/BAT) A Wide-Field Monitor for EDGE Main scientific Requirements: GRB detection [1/2]

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A Wide-Field Monitor for EDGE Main Scientific Requirements: GRB detection [2/2] Threshold @10 keV Threshold @5 keV (study by A. Galli and L. Piro) The number of XRF detections doubles by varying LE threshold from 10 to 5 keV which is also a benefit for type-I bursts detections (SNR is a factor ~3 better) *another key science goal*

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A Wide-Field Monitor for EDGE Overall Design Requirements

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CZT technology (well know, space proven, reliable) Angular resolution similar to IBIS and BAT, to ensure the required location accuracy FOV as large as possible to match the required 3 sr, for bright burst detections detection area large enough for good SNR and transient science Instrument axis slightly tilted respect to the X-ray telescopes, in order to preserve efficient coverage on axis while ensuring a large sky coverage Instrument configuration Detector pixel size in the range of 2-3mm, thickness 2mm Coded masks placed at ~0.5m from detector planes, Tungsten plates 1mm thick, close to 50% open fraction. Yield an angular resolution of 30’. Light detector concept, passive shielding only (cosmic background dominating for E<100 keV) Design Considerations A Wide-Field Monitor for EDGE

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A Wide-Field Monitor for EDGE Payload Accomodation Accomodation of the two WFM units (red shapes) on the PLM platform.

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A Wide-Field Monitor for EDGE 9 CZT modules (200 cm2 each) Coded Mask b a Basic Configuration and Volumes [1/2] GRB detector

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A Wide-Field Monitor for EDGE Basic Configuration and Volumes [2/2] Schematic of detector assembly for one WFM unit (9 modules, 200 cm2 each). Small pink squares are the CZT crystals (12x12 mm2) . Pixels are 3x3 mm2 Modules are assembled on spider structure, mechanical housing with egg-crate, 4x4 crystals each cell Basic crystal egg-crate cell

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A Wide-Field Monitor for EDGE Detector Design 18 modules, each controlled at a single module level by a single DFEE unit (signal acquisition and conditioning). At unit level (9 modules) is performed ADC conversion, background rejection, event reconstruction A single Instrument Control Unit (ICU) is serving the two WFM units (Monitor System level) for target  acknowledgement, position evaluation, fast repointing procedure management.

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A Wide-Field Monitor for EDGE Instrument Control Unit (ICU) Functional Block Diagram A single ICU is serving the two detector units. The S/C  Interfaces for both  data/commands and Power supply are also indicated. (study supported by Thales-Alenia Milano)

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eV-Products multipixel (10.6x10.6x5 mm): 4x4 pixel Am241 source: ΔE/E (FWHM): ~5 % @ 60 keV Energy Threshold: <8 keV (the cut on the spectrum is above the effective low energy threshold) A Wide-Field Monitor for EDGE Low Energy Threshold (basic detector scheme)

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DNSC: 10 mm x 10 mm x 5 mm size CZT/CT (4X4) pixel detectors (REDLEN, Canada) tested with conventional charge sensitive preamplifier and NIM-units. Energy Threshold: <5 keV By C. Budtz-Jørgensen, DNSC (Denmark) A Wide-Field Monitor for EDGE

CZT response improvement by new electrode design (DFTER-INAF/IASF-PA): 

CZT response improvement by new electrode design (DFTER-INAF/IASF-PA) Peaking time: 2.2 μs Main Bias: 200 V, Threshold = 7.7 keV FWHM @ 122 keV = 1.37 keV (1.1%) FWHM @ 136 keV = 1.51 keV (1.1%) FWHM @ 60 keV = 1.1 keV (1.8%) CZT detector: 5x5x1 mm3 Central anode: 80 μm Guard rings: 100 μm Peltier cooled at -5 ºC A Wide-Field Monitor for EDGE

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A Wide-Field Monitor for EDGE Coded Mask Design A design similar to the SWIFT/BAT mask (e.g. random pattern) is taken as reference, with the mask shape adapted to be fit into the VEGA fairing envelope. Material: tungsten is assumed with a typical open area of 50% and a thickness of 1mm. Detailed simulations are required to calculate the optimum open fraction and absorber material (small effect on the overall mass) A low energy threshold close to 5 keV could suggest the use of a dual layer mask, with reduced transparency of 1 layer. In this case the mask itself can be eventually composed by an assembly of self-supporting, smaller plates mounted on a rigid structure. This structure will hide a very small (negligible) part of the coding area. an example: a coded mask design for ECLAIR/SVOM with an open fraction of ~ 30% to be able to work down to 2 keV energy threshold (courtesy P.Mandrou)

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A Wide-Field Monitor for EDGE Detailed Hardware Tree

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A Wide-Field Monitor for EDGE Budgets: Mass

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A Wide-Field Monitor for EDGE Budgets: Power

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A Wide-Field Monitor for EDGE Budgets: Telemetry The long time averaged telemetry rate is dominated by the continuous datarate when observing with the galactic plane in the FOV (up to ~5000 c/s per camera). Tables below describe the TLM demand in case no onboard data selection or compression scheme are considered. Data compression can eventually reduce the TLM rate by a factor ~3 (as required –currently 1.4 Mbits/s-). This will demand signal shape processing on board for each event to perform computation of additional parameters, so implying reduced flexibility and more complex design, testing and operability.

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A Wide-Field Monitor for EDGE TRL and Redundancy Philosophy Redundancy: Single point failures are removed through the monitor segmentation obtained by the 18 indipendent modules  and  the duplication  in cold redundancy of critical parts (like microprocessors and OBDH interfaces).

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SDC coupled to CsI(Tl) X-rays in Si produce a fast pulse (< 10 ns) while g ‘s interacting in CsI result in a slow pulse un impulso lento: (few ms) Pulse Shape Discrimination (PSD) to identify event type Main characteristics: Extended range (~2-1000 keV) Excellent energy resolution Design solutions alternative to CZT A Wide-Field Monitor for EDGE Technology under development (lead by IASF-Bologna)

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A Wide-Field Monitor for EDGE Performances: effective area, sky coverage The field of view of one WFM unit, represented as the detection area exposed to given offset direction (contour levels are in cm2). For reference, the red circle represents a 3sr region. Effective Area vs. Energy (1unit)

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A CZT Imager for EDGE/WFM Assuming 0.2 ph cm-2 s-1 for BAT Sensitivity on axis: 0.28 ph cm-2 s-1 (15-150 keV) @50%coding: 0.45 ph cm-2 s-1 Background estimates based on scaling from BAT and IBIS FOV (50% coding): BAT 1.4sr, IBIS 0.1sr, WFM 0.9sr for M2D = 45cm Assuming 10000 c/s for BAT, we obtain 300 c/s for IBIS, 1300 c/s on each WFMI unit (15-150 keV) Performances: Background and Sensitivity [1/2]

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A Wide-Field Monitor for EDGE Performances: Background and Sensitivity [2/2] Continuum Sensitivity of the WFMonitor in comparison with IBIS/ISGRI.

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A Wide-Field Monitor for EDGE Conclusions the WFM has been currently designed to perform transient localization in a limited energy band (5-200 keV). Imaging capability not required at higher E the CZT (or CdTe) technology is actually regarded as the best one to achieve a balance between performance and technical readyness (really flight proven technology) CZT as baseline design the WFM will be able to detect all GRBs with prompt fluence > ~10-6 erg/cm2 within a region as large as ~2sr. Also, a high fraction (50 to 100%, depending on low energy threshold) of XRFs occuring in the FOV will be followed up, and the instrument has good capability of detecting type-I X-ray bursts and other fast X-ray transients resources have been evaluated and checked versus the overall payload budgets and accomodation constraints Items, still open for optimization (next days work): location accuracy is limited by power budget (need to implement a two-step re-pointing procedure, using the WFI Field-Of-View) The FOV can possibly be improved to better match ~3sr