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G. Tsarevsky 1,2 , G. Bisnovaty-Kogan 3 , A. Pozanenko 3 , G. Popov 4 et al.

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G. Tsarevsky 1,2 , G. Bisnovaty-Kogan 3 , A. Pozanenko 3 , G. Popov 4 et al.

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  1. 10/10/2002 FedSat-II

  2. . . . . . . . . . . . BigJinnina smallbottle. . . . . . . . . . . .. or. . . . . . . MegaSciencebya microSatellite. . . . . . . . . . .ASTRAL:All-sky Space Telescope to Record Afterglow Locations G. Tsarevsky1,2, G. Bisnovaty-Kogan3, A. Pozanenko3 , G. Popov4 et al. 1. Australia Telescope National Facility, CSIRO, Sydney 2. Astro SpaceCentre, RAS, Moscow 3. Space Research Institute, Moscow 4. Crimean Astrophysical Observatory, Ukraine 10/10/2002 FedSat-II

  3. A b s t r a c t:ASTRAL is a project incorporating wide-field optical telescopes on board a small satellite dedicated to the whole-sky detection of a variety of rapid astronomical phenomena, particularly optical flashes associated with gamma ray bursts (GRB). Those flashes only visible optically (so called "orphans"), as well as those preceding associated GRBs, cannot be detected in the current triggering mode of the world wide GRB Coordinates Network (GCN). Hence ASTRAL would have a unique opportunity to trigger a follow-up multi-frequency study via GCN. ASTRAL consists of a set of 13 wide-field cameras (each with FOV = 70o) equipped with 4096x4096 CCDs. The detection method is based on the Digital Blink Comparator mode, with a template of a complete sample of ~2 million stars down to 12m, precisely measured in the HIPPARCOS and TYCHO-2 missions. Supernovae, novae and nova-like explosions, fast variable AGNs, flare stars, and even new comets would be promptly detected as well. Monitoring of Near-Earth objects (NEO) is of special interest. Thus ASTRAL would be an original working prototype of the prospective major space mission to monitor on-line all the sky down to 25m - a high priority instrument of 21st century astrophysics.

  4. The GRB Coordinates Network (GCN) to be triggered by ASTRAL

  5. CONTENTS: Part I: MOTIVATIONS & SCIENTIFIC OBJECTIVES Part II: PAYLOAD DESCRIPTION - OPTICAL DESIGN: ‘A HEDGEHOG’ - METHOD OF DETECTION - OBSERVATION MODES - PAYLOAD SPECIFICATION 4

  6. MOTIVATION No.1: • Gamma-ray bursts(GRBs) remain one ofthe great mysteries inastrophysics. Although there havebeen measurementsof the energetics ofsome bursts through redshiftdetermination (e.g., Kulkarni etal. 1998), there islittle firm knowledge ofhow the energy isproduced. In fact, thetotal energy production is stilluncertain by approximately 2or 3 orders ofmagnitude because of theunknown level of postulatedcollimated jets. Additionally, the totalnumber of GRBs studiedoptically remains small. 6

  7. MOTIVATION No.1: • Gamma-ray bursts(GRBs) remain one ofthe great mysteries inastrophysics. Although there havebeen measurementsof the energetics ofsome bursts through redshiftdetermination (e.g., Kulkarni etal. 1998), there islittle firm knowledge ofhow the energy isproduced. In fact, thetotal production is stilluncertain by approximately 2or 3 orders ofmagnitude because of theunknown level of postulatedcollimated jets. Additionally, the totalnumber of GRBs studiedoptically remains small. B. Paczynski (Prinston University): “There is only one detection, the only positive result of several man-centuries of effort: the truly spectacular optical flash detected by the ROTSE team (Akerlof et al., 1999). “ ↓ see illustration 7

  8. ` Compare time resolution in gamma [pretty good] and in optics [very bad] .

  9. ` GRB 990123: A unique detection by BATSE + ROTSE missions: Delay 22 sec. Initial detection: V=11.7m Maximum: V= 8.9m Power law decline down to limit: V=14.3m . Thus we have the only case of registered optical flash associated with GRB. Another 32 are with upper limits only. NB: A catch of optical transient (OT) at ~12m by ROTSE: ↓ ↓ ↓ ↓ ↓ ↓ Compare time resolution in gamma [pretty good] and in optics [very bad] .

  10. MOTIVATION No. 2: • Gamma-ray bursts arebelieved to emit synchrotronor inverse Compton radiationfrom material moving atultrarelativistic velocities. The resultantstrong Lorentz beaming of the emission will decreaseas the shocked materialslows down. If theultrarelativistic bulk flow isa collimated jet, radiationat wavelengths longer thangamma rays, believed tobe produced by thisslower material, will beemitted through a largersolid angle (Rhoads 1998). 10

  11. MOTIVATION No. 2: • Gamma-ray bursts arebelieved to emit synchrotronor inverse Compton radiationfrom material moving atultrarelativistic velocities. The resultantstrong Lorentz beaming of the emission will decreaseas the shocked materialslows down. If theultrarelativistic bulk flow isa collimated jet, radiationat wavelengths longer thangamma rays, believed tobe produced by thisslower material, will beemitted through a largersolid angle (Rhodes 1998). This suggests a populationofo r p h a n optical burstswith timescales similar toGRBs but more frequent and with no gamma-raysignature. 11

  12. MOTIVATION No.3: B. Paczynski’s prediction: “Optical flashes preceding GRBs” [ ! ] (astro-ph/0108522): “A search for optical flashes independent of GRB triggers would provide important diagnostics for the GRBs and their environments”. See also a basic theoretical consideration by A. Beloborodov, ApJ 565, 808, 2001 with the following conclusion: “GRB afterglows should start in optical and evolve fast (< 1 min) to a normal X-ray afterglow”. ↓

  13. MOTIVATION No.3 (cont.): B. Paczynski’s prediction: “Optical flashes preceding GRBs”(atro-ph/9908522), and his suggestion to build up corresponding detection system: “The only way to learn about such phenomena is by developing an all-sky optical monitoring system with CCD detectors, ~1 minute time resolution, real time data processing with instant recognition of a rapid variability, the on-line verification of the event with larger robotic instrument”.

  14. It looks like a brief description of the ASTRAL project !

  15. Technical problems to be solved:1)How to squeeze a sensitive all- sky optical telescope into the FedSat-II payload provided ?

  16. Technical problems to be solved:1)How to squeeze a sensitive all- sky optical telescope into the FedSat-II payload provided ?2)How to get 1 min time resolution with a small telescope of reasonable sensitivity ?

  17. Technical problems to be solved:1)How to squeeze a sensitive all- sky optical telescope into the FedSat-II payload provided ?2)How to get 1 min time resolution with a small telescope of reasonable sensitivity ?3)How to record all the sky with a CCD ? and 4)How to process it on-line at the rate of 1 Sky/min ?

  18. Technical problems to be solved:1)How to squeeze a sensitive all- sky optical telescope into the FedSat-II payload provided ?2)How to get 1 min time resolution with a small telescope of reasonable sensitivity ?3)How to record all the sky with a CCD ? and 4) How to process it on-line at the rate of 1 Sky/min ?5)How to recognize rapid variability in real time in one of millions of objects around the sky ?

  19. Technical problems to be solved:1)How to squeeze a sensitive all- sky optical telescope into the FedSat-II payload provided ?2)How to get 1 min time resolution with a small telescope of reasonable sensitivity ?3)How to record all the sky with a CCD ? and 4) How to process it on-line at the rate of 1 Sky/min ?5)How to recognize rapid variability in real time in one of millions of objects around the sky ?6)How to deliver that recognition to a larger robotic instrument for its instant verification ?7) How to guide the telescope and maintain its monitoring mode ?

  20. Technical problems to be solved:1)How to squeeze a sensitive all- sky optical telescope into the FedSat-II payload provided ?2)How to get 1 min time resolution with a small telescope of reasonable sensitivity ?3)How to record all the sky with a CCD ? and 4) How to process it on-line at the rate of 1 Sky/min ?5)How to recognize rapid variability in real time in one of millions of objects around the sky ?6) How to deliver that recognition to a larger robotic instrument for its instant verification ?7) How to guide the telescope and maintain its monitoring mode ?All these questions have been positively answered in the proposal [except of Q6 and Q7, to be resolved by the FedSat specialists].

  21. In brief, the scientific objectives of ASTRALare to detect promptly and monitor in the whole sky a wide varietyofrapid astronomical phenomena: = fast transients= optical outbursts that last from less than a day to as short as a second.↓Go to the list of objects achievable byASTRAL

  22. SCIENTIFIC OBJECTIVES (complete list):Gamma-ray bursts (GRB):ØGRB afterglows ØGRBs visible only in optics (‘orphans’) [NB: Impossible to detect in current ALERT mode of GCN]Ø‘Pre-glows’, i.e. optical flashes preceding the GRB event [NB: Impossible to detect in current ALERT mode of GCN]Ø GRB afterglows accompanied with associated SN bursts ↓ 22.

  23. SCIENTIFIC OBJECTIVES (cont.)Supernova explosions(SN):ØSN in our Galaxy [NB: at least 10 have been missed since Kepler’s SN 1604] ØSN in the nearest galaxies, e.g., in Magellanic Clouds ØSN in distant galaxiesNovae and nova-like stars(N):ØN in our Galaxy ØN in Magellanic Clouds↓23

  24. SCIENTIFIC OBJECTIVES (cont.)Flare stars:Ø  Flares of the UV Ceti, U Gem and RS CVn type variables. ↓See example24

  25. Flare stars:flare of the UV Ceti as a representative exampleBernard LOWELL et al.,‘Large flare on the red dwarf star UV Ceti’, Nature, vol. 250, p. 124, 1974 Note a sharp leading optical flare (still not adequately resolved):

  26. SCIENTIFIC OBJECTIVES (cont.)Active galactic nuclei (AGN):Ø Fast violent variability of the BL Lac related sources (like SDSS J124602.5+011318.8) ↓26

  27. SCIENTIFIC OBJECTIVES (cont.)In the Solar System:Ø 1)  Detection of new comets (as well as their bursts)↓ see example27

  28. In the Solar System: See spectacular burst of comet↓

  29. SCIENTIFIC OBJECTIVES (cont.)In the Solar System:Ø 1)  Detection of new cometsØ 2) Fireballs (at the low orbit of perigee) Ø 3) Monitoring of approaching near-Earth asteroids (to be coordinated with the Spaceguard [NEO] Program)Ø 4) Experimental Satellite Tracking29

  30. Part II. PAYLOAD DESCRIPTION: WHAT IT IS and HOW IT WORKS

  31. Part II. PAYLOAD DESCRIPTION:1. Detection concept2. Optical system design3. Optical unit 3.1. Wide-field camera 3.2. CCD unit 4. Modes of observations5. Limiting magnitude 6. Timing resolution7. Orbit8. Stabilisation/Pointing9. On-board computer 10. Software required11. Telemetry 12. Power budget13. Weight budget 14. Cost15. Synergy

  32. Basic Detection Concept:An automated digital version of classic Blink Comparator (BC),a powerful tool to find variable objects in crowded field. Optical flare appears in the digital BC mode as a new or considerably brightened source above the noise limited level, NLL (~0m.5). All other (constant) sources in the field will be suppressed (i.e. deducted against thetemplateprovided). Template: A sample of the objects in the whole sky down to a certain threshold magnitude. Must be: complete; precision photometry provisioned; variable stars content to be very well known; compatible with optical unit (by FoV + CCD), see below.32

  33. 1. Detection Concept (cont.):An adequate template already exists asthe All Sky Compiled Catalogue(ASCC-2.5) [ I/280 in CDS ]:consists of2,041,518 stars as a compilation of the HIPPARCOS, TYCHO-2, and other space and ground missions;complete to V = 12m.0;capacity: 200 Mb (i.e. ~20 Mb per each Optical Unit, see below); average on-sky density: 1 star per 60 sq. arcmin, or < 1 star per 5 sq. arcmin in a crowded field (e.g., Milky Way).Hence 1' resolution of ASTRALseems to be an adequate solution. Such coordinate precision is good enough to identify ASTRAL’sdetection in the triggered follow-up. It is considerably better than the error boxes of the current high energy triggers (like HETE-2). The template will probably be steadily improved in limiting magnitude (up to 13-14m) via further astrometry/photometry studies, along ground based missions like ASAS, and, possibly, space missions like FAME, GAIA or DIVA.33

  34. 2. Optical System design: A set of 13 optical units (OUs) to cover a whole sky (a ‘hedgehog’ like design). Each OU consists of a wide–field camera (see Sec. 3.1) and a CCD unit as recording device (see Sec. 3.2). Blind spot on the sky: 50owide, possibly directed to the Sun (hence only 5% of the sky not covered at the time of observation). Illumination from the Earth/Moon to be prevented mechanically/electronically.34

  35. ROTSE’s ‘hedgehog’-like design as a prototype 10/10/2002 FedSat-II

  36. Another hedgehog like design prototype: The all-sky 7-camerapatrol of the Odessa University Observatory, Ukraine Very primitive and extremely effective instrumentation for the variable star study covering 30 deg. wide belt on the sky from Dec = -30 deg. to zenith.

  37. 3. Optical Unit (OU) 3.1. Wide-field camera:Optical design: Super-Schmidt camera, simplified (not fully achromatic). Aperture: Ø 100 mm Flat field: angular 70o; linear 60 x 60 mmPart of the sky covered by each camera: ~1/10 Overlap with the neighboring camera: ~10o (which means an overlap of 20% of the sky area).Number of stars above 12min the field of the unit: ~250,000 (stored as a template in the on-board unit’s memory).Angular resolution: 5 arcsec in optics; 1 arcmin on CCD (depending of number of pixels, and of pixel size). Weight: Optics 1.0 kg (net) [foam glass to be used]Framework 1.3 kg Total: 2.3 kg

  38. 3.2. CCD unit (as a part of Optical Unit, Sec. 3.1): CCD device: Lockheed-Martin 4096x4096, low DC, low blemished (16 mln pixels; ~1 arcmin/px at the focal plane, >10 pxs per star) Pixel size: 15 x 15 m Die size: 60 x 60 mm QE: 60-80% around 550-800 nm Cooling: Passive, 100 K (of outer space) Prototype: LNA cooling system of ‘Radioastron’. Wavelength Range: 400 – 900 nm Filter: Unfiltered Dynamic Range: 104 - 105 Readout time: 1 s Unit weight: 0.4 kg Number of units: 13

  39. 4. Modes of Observations:Detection mode: An early detection of various optical flares above 12m around the sky, ( = basic ALERT mode)Post-detection mode: On-source, with possibly better time resolution (to be chosen automatically depending of the detected source brightness)Monitoring mode: Continuous on-source monitoring, with better sensitivity/time resolution. Fireball-like detection mode of moving object.39

  40. 5. Limiting Magnitude: Detection mode: 12m (due to the template provisioned). To be steadily improved along further photometric/astrometric studies. Post-detection mode: Variable (depending of integration time). Monitoring mode: ~19m in 30 min integration. 40

  41. 6. Timing Resolution: Detection mode: 30 s Post-detection mode: up to 1 s (to be chosen automatically depending on brightness of the detected source) Monitoring mode: arbitrary 41

  42. 7. O r b i t (preliminary): A variety of orbits to be considered, e.g.: - eccentric, with a major axis directed from the Sun; - polar, circular ~1000 km. Easy launchable orbit to be chosen if required by technical circumstances. Example: Perigee altitude: 350 km Apogee altitude: 2000 – 40000 km Period of revolution: 24 h (and more) 42

  43. 8. Stabilisation/Pointing: Calibrated pointing knowledge: 6-10 arcsec ( 1-σ ) Re-pointing Rate: Nil ! 9. On-board computer: CPU, with a direct access via telemetry. 13 microprocessors, one per each Optical Unit (in parallel). Memory: CPU: 2 Gb Mcp Unit: 64 Mb Re-programming and template updating (via telemetry). 43

  44. 10. Software required: Modeling a Blink Comparator mode. Burst localization. ALERT mode. Post-detection mode (an adaptive algorithm of the variable time resolution). Monitoring mode (in a small field around the source specified). Fireball-like detection mode (moving object in the field of view). Two way data exchange between CPU and CCD units. Re-programming (template Star Catalogue updating, etc). Pointing system routine. 44

  45. 11. Telemetry: Uplink: Command line. Rate : 4 kb/s Schedule: ≥ 12 min/day, once per day Downink: Low rate ALERT mode: 4 kb/s Schedule: switch-on by the inner ALERT command Data transfer: 1.0 Mb/s Schedule: ≥ 12 min/day, once per day Possible regime: To be incorporated into and supported by the GCNetwork GTS location: main – Adelaide. Mobile tracking antenna – Sydney (AAO/ATNF/TIP site), or elsewhere in campaign mode. 45

  46. 12. Power budget:: Optical Unit microprocessorsystem: ~1 Wt Total for MCP units: ~15 Wt Payload, total: Low ( < 20 Wt ) NB: Huge power saving due to absence of re-pointings. 13. Weight budget: A set of 13 optical cameras: 30.0 kg [2.3 kg x 13] A set of 13 CCD units: 5.2 kg [0.4 kg x 13] ---------------------------------------------------- Total: ~35.0 kg 46

  47. 14. Cost: Optical Unit: A$ 100 K CCD Unit : A$ 120 K ---------------------------------------------- Total per Unit: A$ 220 K ---------------------------------------------- Total per Optical System: A$ 2.9 M (13 units) Hardware Modeling & Software: A$ 4.0 M -------------------------------------------------------- Total Cost of the payload (estimated): A$ 7.0 M 15. Synergy: - ASTRAL Mission accomplished with multi-mission GCNetwork already in action and steady development. - ASTRAL to improve all over ability and scientific output of the GCN. - ASTRAL to catch other than GRB astrophysical phenomena, including early detection of Supernova in our Galaxy waited from 1604 Kepler’s SN.

  48. Acknowledgements I am very grateful to many colleagues for help, advice and encouragement. It is a pleasure to acknowledge Bruce Slee and Bob Duncan for multiple comments; G. Beskin and S. Bondar for the ground based prototyping of ASTRAL; Francois Mignard for valuable comments; Nikolay Samus for the General Catalogue of Variable Stars statistics; Holger Pedersen for early GRB all-sky monitoring ideas; Roald Gershberg for discussion of the flare stars behavior; Raylee Stathakis for the SN data; Brian Embleton for providing the relevant FedSat satellite parameters; Andrew Parfitt for leading advice of some communication issues; Grzegorz Pojmanski and Grzegorz Wrochna for some ideas of ASTRAL development; Bohdan Pazcynski for discussion of basic issues of ASTRAL and stimulating enthusiasm.

  49. R e f e r e n c e s : Akerlof C., et al. 1999, Nature 398, 400 (GRB 990123: A unique BATSE+ROTSE flash of OT V=9m) Barthelmy S. D., et al., GRB Coordinates Network Description [ http://gcn.gsfc.nasa.gov/gcn/ ] Beloborodov A. M. 2001, ApJ 565, 808 (First principles physics of GRBs) Connors A., et al. 1986, ApJ 303, 769 (Up to 200,000 flashes a year missing) Galama T., et al., 1998, Nature 395, 670 (Discovery of SN associated with GRB afterglow) Gamma-ray Burst Mystery Solved. In: CRCSS Space Industry News, No.94, 2002(Editorial Review) Hessman F. V. Links to the Robotic Telescopes Projects(List of ASTRAL’s prototipes) [http://www.uni-sw.gwdg.de/~hessman/MONET/links.html ]Greiner J., et al. 2000, A&A 353, 998 (X-ray bursts and GRB/flare stars connection) Kehoe R., et al. 2002, ApJ 577, 845 (ROTSE search for ‘orphans’) Kharchenko N. V. 2002, The All-Sky Compilation Catalogof 2.5 million stars (Template of ASTRAL) Kronk G.W. 1984. Comets: A Descriptive Catalog(Discovery magnitudes of comets) Kulkarni S., et al. 1998, Nature 393, 35 (Cosmological origin of GRB) Lowell B., et al. 1974, Nature 250, 124 (Optical flash of UV Ceti) Mikhelson N. N. 1995. Astronomical Optics (Wide-field camera design) Paczynski B. 2000, PASP 112, 1281 (Monitoring all sky for variability) Paczynski B. 2001, astro-ph/0108522 (Prediction of optical flashes preceding GRBs) Pozanenko A., et al. 2002. In: ADASS XII Conference (Synchronous optical and γ-ray observations) Rhodes J. 1998. In Gamma-Ray Bursts, 4th Huntsville Symp., 699 (Physics of ‘orphans’) Pojmanski G., ASAS: The All-Sky Automated Survey(A source of ASTRAL’s template development) [http://www.astrouw.edu.pl/~gp/asas/ and AcA 47, 467, 1997 ] Tsarevsky G.S. 2002, Project ASTRAL. In: An Australian Astronomical Payload for FedSat-II [www.atnf.csiro.au/people/norris/fedsat&www.atnf.csiro.au/people/gregory.tsarevsky] van Paradijs J., et al. 2000, ARAA 38, 379 (Review of the GRB afterglows) Wrochna G., et al. 2002, Project ’Project Pie of the Sky’ (ASTRAL’s ground based prototype ) [http://hep.fuw.edu.pl/~wrochna/pi/ ]

  50. ASTRAL mission: To be incorporated into the GCNetworkas a triggering component.

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