Search for GRB Optical Prompt Afterglow and Precursor
Search for GRB Optical Prompt Afterglow and Precursor with the Ashra prototype light collector Naohiro Manago and Ashra Collaborators Joint Meeting of Pacific Region Particle Physics Communities Oct, 31, 2006 @Sheraton Waikiki Hotel
Collaboration List Y. Aitaa, T. Aokia, Y. Asaokaa, T. Browderh, T. Chonana, S. Dyeh, M. Eguchia, R. Foxi, S. Fukagawab, V. Garyh, G. Guillianh, J. Hamiltoni, M. Ieirie, T. Kimurac, I. Kogab, H. Kuzeb, J. Learnedh, N. Managoa, N. Masudag, S. Matsunoh, Y. Morimotof, K. Nodaa, S. Ogawaf, A. Okumuraa, S. Olsenh, M. Sasakia, H. Shibuyaf, N. Sugiyamad, M. Yasudag, Y. Watanabeg (a) ICRR, Univ. Tokyo (b) Chiba Univ. (c) Ibaraki Univ. (d) Nagoya Univ. (e) KEK (f) Toho Univ. (g) Tokyo Inst. (h) Univ. Hawaii Manoa (i) Univ. Hawaii Hilo
Introduction / Motivation Ashra Optical System - design l l Wide F. O. V. 50 degrees High Resolution ~arcmin a Suitable for Monitoring Unpredictable Events 2/3 -scale prototype detector l l Ashra Optical System Lens 1 Lens 2 Lens 3 Focal plane Mirror It was constructed and used for R&D. Then, it was dedicated to monitor GRB prompt optical afterglows and optical precursors. 2/3 -scale prototype
Introduction / Prompt Optical Afterglow Reverse Shock with ISM l l Sari & Piran 1999 Nakar & Piran 2004 Fireball model Reverse Shock in wind environment l Kobayashi & Zhang 2003 Others l l l Internal Shock Neutron-Fed GRB Pair Avalanche Lightcurve a Model test Farther constraints can be obtained by cooperating with radio/IR observations T. Piran 2003 Kobayashi & Zhang 2003
Introduction / Optical Precursor Collapsar l Collapsar Supranova model l l Vietri & Stella Supranova explosion followed by BH creation Baryon clean environment Timescale hours-years Merger l NS-NS l l Rosswog & Ramirez-Ruiz n`n explosion followed by BH creation thermal emission ~2. 5× 104 K (Li & Paczynski) Timescale minutes-weeks NASA Merger P. J. T. Leonard (NASA/GSFC)
Contents Introduction Observation Analysis Results Discussion Summary
Observation / Setup Test Observation site was at the summit of Haleakala l l l Latitude 20 o 42’ N Longitude 156 o 15’ W Altitude 3030 m The 2/3 -scale prototype was shipped from NAOJ to Hawaii in Jun, 2004 a arrived in Aug, 2004 It was ready for observation in Sep, 2004, just before the launch of Swift (Nov, 2004) Test Observation Site Maui Oahu We are here! Hawaii Current Observation Site 2/3 -scale prototype
Observation / Operation Result Sep, 2004 ~ Sep, 2005 Operating Condition: l Between astronomical twilights l l Solar altitude < -18 degrees Moonless l l l Operation Result Lunar altitude < 0 or Moon fraction < 0. 1 Good Weather l l Humidity < 75% No visible clouds Operation Result: l l l Total 844 hours 55% of Moonless nights 11% of entire time From Sep, 2004 to Sep, 2005
Observation / GRB Sample 93 GRBs were detected by GRBs detected by satellites We observed locations of SWIFT HETE-II INTEGRAL 9 GRBs preceding the detection (<24 h) GRB Start (hour) End (hour) 041211 -1. 5 +2. 0 050209 -17. 7 -14. 1 050408 -8. 6 -5. 4 050502 B -3. 3 -2. 4 050504 -0. 17 +2. 2 050509 B -21. 8 -18. 3 050607 -21. 3 -18. 8 050716 -23. 2 -22. 6 050803 -7. 6 -4. 9
Observation / GRB 041211 Dec/11/2004 11: 31: 47 UTC Moonless clear midnight HETE-II detected GRB 041211 near the local zenith (q = 4 o) Our first observation coincident with GRB The world’s earliest observation (GCN 2846) l l Continuous data from -1. 4 H to +1. 9 H Delayed GCN alert (80 min) The advantage of the Ashra optical system has been demonstrated GRB 041211
Contents Introduction Observation Analysis Results Discussion Summary
Analysis / Image Correction Analysis procedure l l Image correction Photometry instrumental magnitude limiting magnitude Image correction l l Offset - dark image Gain - flat image Noise Model l l Measured noise after image correction is consistent with the noise model VI = GI + sr 2 l l G = 0. 53 ADU/esr = 4. 3 ADU Noise before/after correction
Analysis / Notes on the Uniformity Twilight Flat l l l Twilight Flat is NOT uniform within 50 -degree FOV Nonuniformity was estimated using simulation code lib. Radtran Maximum difference ~30% Flat Image Atmospheric Attenuation l l Atmospheric attenuation is a function of zenith angle Optical depth was measured at the site Total optical depth ~ 0. 12@500 nm Rayleigh optical depth ~ 84% Response to uniform light source
Analysis / Photometry Contribution to pixel brightness from stars? a Aperture photometry l Point Spread Function BG-subtracted pixel brightness is integrated within an aperture radius from the center of a PSF Point Spread Function (PSF) l l ~ 2 -dim Gaussian s = 2 arcmin (FOV center) Aperture radius is determined to maximize S/N ratio (SNR) A typical image of a star
Analysis / Instrumental Magnitude Pixel brightness n apparent magnitude? We did NOT use optical filters to maximize sensitivity Sensitive region is BT-VT Color dependence is expressed as 1 st-order (BT-VT) term l l Detector Sensitivity m. APO = m 0 - 2. 5 log 10 F m. APO = BT - k(BT-VT) l l m 0 = 14. 7 k = 0. 41 BT, VT. . . Tycho-2 APO. . . Ashra prototype
Analysis / Limiting Magnitude Limiting magnitude l l l mlim = m. APO + 2. 5 log 10(SNR/3) Signal is measured for Tycho-2 stars Noise is estimated from BG samples around the stars Typical limiting magnitude l m. APO = 10 (4 sec) Image stacking Signal. . . ×N l Random noise. . . ×N 1/2 a SNR. . . ×N 1/2 l Limiting Magnitude. . . +2. 5 log 10 N 1/2 - small loss due to alignment error etc. l m. APO = 12 (4 sec x 40) l
Contents Introduction Observation Analysis Results Discussion Summary
Limiting Magnitudes GRB 041211 050209 050408 050502 B 050504 050509 B 050607 050716 050803 m. APO 10. 0 9. 6 8. 0 8. 4 7. 4 8. 7 7. 4 7. 6 7. 5 m. APO/N 12. 0/40 11. 5/40 10. 0/20 9. 4/40 10. 7/40 9. 4/40 9. 2/20 9. 5/40 Pre lim ina ry m. APO. . . limiting magnitude/frame (4 sec) m. APO/N. . . limiting magnitude/N frames
Contents Introduction Observation Analysis Results Discussion Summary
Discussion / Comparisons with models Extinction factor l l l Distance to the GRB Dust extinction at Host/MW Absorption by neutral H Optical Flash l l Compared with X-ray afterglow Spectrum index -0. 5 Optical Precursor l l z mopf maft MB 041211 3. 29 11. 4 13 -38. 7 Pre lim ina ry 050209 2. 93 - - -38. 1 050408 1. 2 - - -36. 0 050502 B 8. 5 - - -44. 3 - - 15 - 0. 22 - - -29. 6 5 - - -42. 6 050716 8 - - -44. 8 050803 0. 42 - - -32. 7 Compared with GRB 990123 050504 Peak magnitude 8. 9 050509 B Decay slope -2. 4 050607 Optical Afterglow l GRB Compared with SNIa Absolute magnitude -19. 5 z. . . redshift mopf. . . Apparent magnitude of GRB 990123 -like opt. flash at redshift z maft. . . Apparent magnitude of optical afterglow with Fn n-0. 5 MB. . . B band absolute magnitude
Discussion / Future Prospect Ashra detector unit l l Early Lightcurves 4 light collectors Improved sensitivity Upgrading / Degrading Signal larger aperture × 2 proximity I. I. × 100 2 half mirrors × 1/4 4 light collectors Ashra detector station l l (4 sec exposure) × 4 Total × 200 l Assuming Fn n-1 & typical NSB, limiting magnitude is estimated to be 15/4 sec l Ashra sensitivity 12 detector units Total FOV 5 sr 10~12 events/year coincident with Swift GRBs Guidorzi et al. 2006
Summary The Ashra optical system has a wide FOV and suitable for monitoring unpredictable events. The advantage of the Ashra optical system has been demonstrated by the prompt afterglow/precursor search with the Ashra prototype detector (e. g. GRB 041211). Ashra detector units have improved sensitivity and 10~20 events/year coincident with Swift GRBs are expected for an Ashra station.
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