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SLAC’s First Step into Space: Status of the USA experiment 5-years after launch

SLAC’s First Step into Space: Status of the USA experiment 5-years after launch. Larry Wai SLAC / Group K. The beginning of particle astrophysics at SLAC. Experimental struggles and the rewards of science. Outline of talk. The life and times of the USA experiment The people who made it work

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SLAC’s First Step into Space: Status of the USA experiment 5-years after launch

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  1. SLAC’s First Step into Space: Status of the USA experiment 5-years after launch Larry Wai SLAC / Group K

  2. The beginning of particle astrophysics at SLAC Experimental struggles and the rewards of science

  3. Outline of talk • The life and times of the USA experiment • The people who made it work • On-orbit adventures • The detector and its calibration • Science from the USA experiment • Tests of general relativity in black hole systems • The high frequency power spectrum of Cygnus X-1 • A search for x-ray bursts from ~10 solar mass compact objects • Physics of “jets” in black hole systems • Flares In BL LAC object 1ES1959+65 • Summary and plans Larry Wai, SLAC seminar

  4. Part 1: The life and times of the USA detector • 1991-1998. Design, manufacturing, integration, testing, calibration, storage (satellite late) • T0 = February 23, 1999; Delta-II launch from Vandenberg AFB, CA • End of USA mission at T0+21months (3 months shy of design lifetime of 24 months) Larry Wai, SLAC seminar

  5. The people who made it work How SLAC students and staff got their hands into a space based experiment and made it fly

  6. USA Collaboration USA X-ray Telescope (1-16keV) USA NRL: R. Bandyopadhyay, G. Fritz, P. Hertz, M. Kowalski, M. Lovellette (P.S.), P. Ray, L. Titarchuk (& GMU), M. Wolff, K. Wood (P.I.), D. Yentis, W.N. Johnson SLAC/Stanford: E. Bloom (S.U. Lead Co-I), W. Focke, B. Giebels, G. Godfrey, P. Michelson, K. Reilly, M. Roberts, P. Saz Parkinson, J. Scargle ( & NASA Ames), G. Shabad, D. Tournear Larry Wai, SLAC seminar

  7. The USA project - pushing the limits SLAC contributions: • SLAC mechanical and thermal design, validation - John Hanson (Ph.D. Aero-Astro), Alex Leubke (M.S./Engineering Aero-Astro) • SLAC manufacturing of mechanical framework, collimators – John Hanson, John Broeder • Flight software – SLAC contributions ~1/5 the manpower of GLAST in ~½ the time! • Detector calibration - Gary Godfrey, Ganya Shabad (Ph.D. Physics), Pablo Saz-Parkinson (Ph.D. Physics) , Berrie Giebels • Ground software - Kaice Reilly (Ph.D. App.Physics), Derek Tournear (Ph.D. Physics), Warren Focke • Science operations - Student & post-doc involvement on a weekly basis deciding what sources should be observed (many students defined the subject of their Ph.D. science in this way); heavy involvement in all the publications Larry Wai, SLAC seminar

  8. On-orbit adventures How USA did it the hard way and made it work

  9. Celestial source ARGOS USA Celestial source USA ARGOS Yaw Earth’s center Celestial source USA Pitch Earth’s center ARGOS Earth’s center The pointing challenge • The USA innovation: • Use mechanical rotation system to point detector at celestial sources by setting yaw (X-axis rotation), following source in pitch (Y-axis rotation) The challenge: • Spacecraft (ARGOS) axis was continuously oriented normal to earth’s surface throughout the orbit – need to keep USA pointed on a celestial point source to ~0.05 degrees Larry Wai, SLAC seminar

  10. 10,000 orbits • The polar orbit challenge • Unusual USA characteristic - equatorial orbits are preferable for astronomy (backgrounds are better) • Orbit was divided into segments by passage through earth’s radiation belts and the South Atlantic Anomaly • Two 20min (equatorial) and two 10min (polar) observations segments per orbit USA reached 87% of design lifetime on-orbit During lifetime of detector on-orbit • 10% time used for satellite calibration • 14% time used solving pointing problems (due to satellite misinformation on orientation; USA diagnosed the problem) • 76% time had good pointing Larry Wai, SLAC seminar

  11. Celestial source observations Source Name ksec comments Crab_Pulsar 1220. pulsar X1630-472 716.6 black hole Cyg_X-1 706.0 black hole Cyg_X-2 626.6 neutron star XTE_J1118+480 601.1 black hole SMC_X-1 415.4 pulsar E_2259+586_SNR 397.4 pulsar Cas_A 370.0 supernova remnant Circinus X-1 345.3 neutron star Mkn_421 278.2 active galactic nucleus Cen_X-3 265.7 pulsar X0614+091 249.0 neutron star GRS_1915+105 243.6 black hole GX_349+2 232.9 neutron star X0142+614 224.9 pulsar • Strategy: accumulate long object observing times ~fraction of a month • About 90 Sources Observed by USA • Top sources in observing time had 0.1-0.5 months each! Larry Wai, SLAC seminar

  12. The detector and its calibration A story of careful work on the ground, an on-orbit surprise, and a lesson learned

  13. Detector design goals • Low energy threshold (~1 keV) • Large collecting area (~2000 sq.cm) • High time resolution (~1 microsecond) • Sustained high data rates (40-128kbps) Larry Wai, SLAC seminar

  14. X-ray detection technique: collimator + standard multiwire proportional chamber  X-ray photon Collimator ~ 1.3o FWHM ~10% of 1KeV photons pass through pressure window Gas Volume (P10) 90%Argon 10%Methane Initial Ionization 2 sec time resolution (typical ~ 32 sec res) E/E ~ 17% at 6 keV 40-600 e-ion pairs 50 mm wire anode ~105 electrons/event Larry Wai, SLAC seminar

  15. 2 interleaved wires running serpentine through each layer x 2 layers + 1 wire around the outside for anticoincidence USA detector details Larry Wai, SLAC seminar

  16. Transmission of 5.0 mm Mylar + 2.5 mm Kapton Absorption edge of Argon Effective area determination • ~200’ long tube w/ 55Fe source at one end, collimator on rotation fixture at other; ~1Hz count rate through collimator • Measure acceptance vs angle of incidence (point spread function, collimator effective area ~1000 sq. cm) • Energy dependence of effective area derived from Livermore x-ray cross-section formulae for various detector materials • Superior effective area below 4 keV as compared to PCA (proportional counter array aboard RXTE – NASA mission up since Dec. 1995) Larry Wai, SLAC seminar

  17. 16.5 ms Detector 1 1035 cts/sec c2 / dof = 0.979 DOF = 493 55Fe source mounted to yoke T-Vac high rate tests 55Fe source fastened to yoke, scan in yaw Ganya fitted histograms of time difference between events with event time domain model including deadtime and other electronics effects Extraction of deadtime as a function of rate Larry Wai, SLAC seminar

  18. Good agreement between deadtime model and data using all energy channels! Rate = 4075 cts/sec Pj=P1+P2cos(2pj/N) P1=1.763, P2=-0.0245 c2 / dof = 1.08 DOF = 2046 Leahy normalized power spectrum Purely Poisson process 2 power 0 Frequency 0 5200 Hz Power spectrum tests General procedure for power spectrum: • Break down all data into equal length time segments (T), each with N equal length bins • For each segment calculate the “Leahy normalized” power spectrum Pj=2|Xj|2/Ncounts where Xj is the amplitude of the discrete Fourier transform: xk (k=0,1,…,N-1) is the number of counts in the kth time bin • Average segments to get mean and RMS • Power spectrum: convert the time series of counts into the frequency domain • Basic idea for the test: check for subtle systematic effects in the calibration data USA calibration data: deadtime introduces correlations between photon times Good agreement between calibration data and Ganya’s deadtime model – when using all energy channels combined Larry Wai, SLAC seminar

  19. Energy channel 2 Energy channel 1 An on-orbit surprise • Pablo notices recurring patterns of distortions in the power spectrum of celestial sources when selecting energy bins Larry Wai, SLAC seminar

  20. Going back to the calibration data • Ganya goes back to calibration data and confirms an energy dependent instrumental effect (a.k.a. EDIE) on power spectrum • Positive vs negative spectral slope (as measured in detector) inverts shape in frequency domain • Effect cancels out when all energy channels are combined; that’s why it was missed during T-Vac testing • Working hypothesis is pulse tail oscillations; phenomenological corrections used at present Larry Wai, SLAC seminar

  21. A lesson for space-based detectors • More manpower and time in analysis of data during detector testing on the ground could have unearthed EDIE before launch and allowed us to characterize the effect more carefully than was possible on-orbit • The lesson learned: let’s check the data carefully during testing of the GLAST large area telescope at SLAC! (2004-2005!) Larry Wai, SLAC seminar

  22. Part 2: Science from the USA experiment Selected Astrophysical Journal papers: • USA and RXTE Observations of a Variable Low-Frequency QPO in XTE J1118+480, K. S. Wood et.al. , ApJ (2000) • Disk Diffusion Propagation Model for the Outburst of XTE J1118+480, Kent S. Wood et al., ApJ (2001) • USA Observation of Spectral and Timing Evolution During the 2000 Outburst of XTE J1550-564, K. T. Reilly et.al., ApJ (2001) • Eclipse Timing of the Low Mass X-ray Binary EXO0748-676 III. An apparent Orbital Period Glitch Observed with USA and RXTE, M. T. Wolff et.al., ApJ (2002) • Observation of X-ray variability in the BL Lac object 1ES1959+65, Berrie Giebels et.al., ApJ (2002) • X-ray Bursts in Neutron Star and Black Hole Binaries from USA and RXTE, D. Tournear et.al., ApJ (2003) • High frequency power spectrum of Cygnus X-1 from the USA experiment, W. Focke and L. Wai et.al., (in progress) Larry Wai, SLAC seminar

  23. High frequency power spectrum of Cygnus X-1 Testing a prediction of General Relativity: the innermost stable circular orbit

  24. An innermost stable orbit Relativistic Effective Potential Stable circular orbit • Innermost stable circular orbit (ISCO) at slightly more than a x (M/Msolar)3km, 2<a<4.5 Distance from center of black hole Larry Wai, SLAC seminar

  25. Mass-Donor Companion Star ~106 km ~103 km Accretion Disk Black hole Looking for the innermost stable orbit in Cygnus X-1 • Non-uniform orbiting matter in the disk will produce variations in observed flux at orbital frequency • Models, e.g. Bao and Ostgaard (1995), predict power spectrum P~f-1 up to the frequency of the innermost stable orbit fISCO= (Msolar/M)2.2kHz • Cygnus X-1: a ~10 solar mass black hole candidate with a companion star donating matter to an accretion disk around the black hole • X-ray luminosity from Cygnus X-1 originates in ~10KeV plasma upscattering “seed photons” from orbiting matter in the disk • Signature of the innermost stable circular orbit is a sharp drop-off in the power spectrum at ~220Hz Larry Wai, SLAC seminar

  26. Extracting the power spectrum • For each time segment (~1sec) calculate the power spectrum and subtract the noise including deadtime distortion (from Ganya’s results) • Average all the resulting power spectra over all segments (~400k) • Fit in region above 2kHz to correct for residual noise/deadtime • Fit in region above 300Hz to correct for residual EDIE Larry Wai, SLAC seminar

  27. f-1.6 Cygnus X-1 Power Spectrum • Model the “drop-off” as a broken power law • Best fit broken power law has c2=1457 for 1437 DOF • Best fit single power law has c2=1465 for 1439 DOF • Dc2=8 with 2 additional degrees of freedom • 2.5 sigma effect – marginal evidence for a dropoff Focke, Wai, Bloom, et.al. Residual EDIE Residual deadtime Larry Wai, SLAC seminar

  28. A search for x-ray bursts from 10 solar mass compact objects Testing another prediction of General Relativity: the event horizon

  29. Neutron star mass limit The measured masses of compact objects • Maximum neutron star mass is 3.2 solar masses • Sample of observed ~10 solar mass objects are widely believed to be black holes - with an event horizon at (M/Msolar)3km • In a binary system, need orbital period, velocity, partner mass, and angle of inclination to estimate the mass of the compact object • Two populations emerge, one around ~1.4 solar masses, and ~10 solar masses Miller (1998) +Tournear (2003) Larry Wai, SLAC seminar

  30. Using bursts as an event horizon litmus test • Observation of thermonuclear burning on the surface of the black hole candidate would reject the event horizon hypothesis • The signature: type 1 x-ray bursts • These bursts are due to unstable thermonuclear burning on the surface of neutron stars (cooling blackbody temperature, radiating area corresponding to 10-15km radius sphere, and linear correlation between burst flux and time delay) • Narayan-Heyl (2002) prediction for bursting luminosity region for 1.5 and 10 Msolar compact object w/ baryonic surface Larry Wai, SLAC seminar

  31. Black hole candidate burst rate limit Tournear, Bloom, et. al. (2003) • Result: BHC burst rate is less than 5% of that for neutron stars (at 95% C.L.) • Black hole candidates quantitatively don’t have baryonic surfaces! Larry Wai, SLAC seminar

  32. Flares In BL LAC object 1ES1959+65 Testing a prediction about how an AGN jet works

  33. Large! Microquasar • E.g. Cygnus X-1 • E.g. GRS 1915+105 • GLAST bread and butter ~106-9 solar mass black hole ~10 solar mass black hole Black holes, small and large Small! Galactic black hole candidate • ~10 solar mass black hole • ~103 km disk • Jets! Active galactic nuclei (AGN) • ~106-9 solar mass black hole • ~109 km disk • Jets of electrons! • E.g. 1ES1959+65 Larry Wai, SLAC seminar

  34. USA AGN observations We analyzed this one so far… Larry Wai, SLAC seminar

  35. Giebels, Bloom, et.al. (2002) Daily x-ray flux Hardness ratio Holder, et.al. (2003) daily TeV gamma flux Flaring in BL Lac object 1ES1959+65 • 2000 Sept-Nov. observation of variability by USA led to search in TeV • 2002 May-July observations by Whipple of clear TeV gamma ray flaring Larry Wai, SLAC seminar

  36. Confirmation of a prediction • 1ES1959+65 was predicted to be the 3rd brightest extra-galactic TeV source by Stecker et.al. (1996) based upon data from the two known extragalactic TeV sources Mrk 421 and 501 • Prediction based upon “synchrotron self compton” scattering in AGN jets as the mechanism for TeV emission • x-rays come from synchrotron radiation of jet electrons, and TeV gammas are the x-rays Compton upscattered by the same jet electrons • Example of a multiwavelength campaign (which we will need in GLAST to study jet physics) Larry Wai, SLAC seminar

  37. Summary and plans How did we do, and what is left?

  38. How did we do? SLAC’s first step into space • SLAC people contributed to the design, made flight hardware/software, tested and calibrated the detector, helped define the observation schedule, took good data, and published science results • Cranked out 7 Stanford Ph.D.’s • Established an experimental astrophysics presence at SLAC Larry Wai, SLAC seminar

  39. More papers: High frequency power spectrum of Cygnus X-1 High frequency QPO searches (Circinus X-1, XTE J1859+226) AGN studies Another Ph.D. Han Wen (Physics Ph.D.) Andrew Lee (Physics Ph.D.) John Hanson (Aero-Astro Ph.D.) Alex Leubke (Aero-Astro M.S/Engineering) Ganya Shabad (Physics Ph.D.) Kaice Reilly (App. Physics Ph.D.) Derek Tournear (Physics Ph.D.) Pablo Saz-Parkinson (Physics Ph.D.) Daniel Engovatov (Physics Ph.D., in progress) What’s left for USA? Larry Wai, SLAC seminar

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