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Pulsars… Neutron Star Astrophysics Pulsar Sounds Pulsars I. Pulsars I. The Why and How of Searching for Exotic Pulsars The Why and How of Searching for Exotic Pulsars Jim Cordes, Cornell University Jim Cordes, Cornell University • Why would you want to know about pulsars and • The forefront of neutron star science why would you like to discover more? • Extreme states of matter • Science, the big questions • Gravitational laboratories • How do I find new pulsars? • Probing core collapse supernovae • Galactic structure • How do I estimate pulsar distances? • Issues in pulsar survey optimization • What can I learn about … • Dedispersion • the inside of a NS? • Periodicity searches • the magnetosphere of a NS? • Single pulse searches • the orbit of a binary pulsar? • Simulations of pulsar surveys • the space velocity of a pulsar? • ALFA: A massive pulsar survey at Arecibo • the ISM along the path to a pulsar? • SKA: toward a full Galactic census of pulsars Pulsars… Neutron Star Astrophysics • Embody physics of the EXTREME – surface speed ~0.1c – 10x nuclear density in center 13 – some have B > Bq = 4.4 x 10 G – Voltage drops ~ 10 12 volts 9 9 11 –FEM = 10 Fg = 10 x 10 FgEarth 6 –Tsurf ~ 10 K • Relativistic plasma physics in action ( γ ~ 10 6) • Probes of turbulent and magnetized ISM Surface quantities: • Precision tools, e.g. B ≈≈≈ 10 12 Gauss - Period of B1937+21 (the fastest millisecond pulsar) ≈≈≈ 11 gNS 10 g⊕⊕⊕ P = 0.0015578064924327 ±0.0000000000000004 s F ≈≈≈ 10 9 g m Orbital eccentricity of J1012+5307: e<0.0000008 EM NS p • Laboratories for extreme states of matter and as clocks for ΦΦΦ≈≈≈ 10 12 volts probing space-time and Galactic material Pulsar Sounds Radio signals demodulated into audio signals P f=1/P sound file Pulsar (ms) (Hz) B0329+54 714 1.4 B0950+08 253 3.9 B0833-45 89 11.2 (Vela) B0531+21 33 30.2 (Crab) J0437-4715 5.7 174 B1937+21 1.56 642 J0437 -4715 profile 1 Pulsar Populations: diagram Pulsar Populations: diagram • Canonical • Canonical • P~ 20ms – 5s • P~ 20ms – 5s • B ~ 10 12±1 G • B ~ 10 12±1 G ) ) • Millisecond pulsars (MSPs) -1 • Millisecond pulsars (MSPs) -1 • P ~ 1.5 – 20ms • P ~ 1.5 – 20ms • B ~ 10 8 – 10 9 ms • B ~ 10 8 – 10 9 ms • High field • High field • P ~ 5 – 8 s • P ~ 5 – 8 s • B ~ few x 10 13 G • B ~ few x 10 13 G • Braking index n: • Braking index n: • • logPeriod derivative(ss logPeriod derivative(ss • n=3 magnetic dipole radiation • n=3 magnetic dipole radiation • Death line • Death line • Strong selection effects • Strong selection effects Period (sec) Period (sec) Manifestations of NS: Spindown • Rotation driven: • “radio” pulsars (radio → γ rays) • magnetic torque • γγ → e+ e- + plasma instability ⇒ coherent radio • Accretion driven: • X-rays • LMXB, HMXB • Magnetic driven: Crustquakes? • Magnetars (AXPs, SGRs) • Spindown … but • Gravitational catastrophes? • Gamma-ray bursts, G.wave sources, hypernovae? Spinup Quarks to Cosmos: Relevant Questions • Did Einstein have the last word on Gravity? • How do cosmic accelerators work and what are they accelerating? • What are the new states of matter at exceedingly high density and temperature? • Is a new theory of light and matter needed at the highest energies? 2 First Double Pulsar: J0737-3939 Lyne et al.(2004) ω • Pb=2.4 hrs, d /dt=17 deg/yr Testing GR: •MA=1.337(5)M , M B=1.250(5)M obs s = ± Now to 0.1% exp .1 000 .0 002 s Kramer et al.(2004) Double Neutron Star Binary: What are the Big Questions? J0737-0939A,B • Formation and Evolution: • What determines if a NS is born as a magnetar vs a canonical pulsar? • How fast do NS spin at birth? • How fast can recycled pulsars spin? • What is the role of instabilities and gravitational radiation in determining the spin state? • How do momentum thrusts during core collapse affect the resulting spin state and translational motion of the NS? • What processes determine the high space velocities of NS? » Neutrino emission » Matter rocket effects » Electromagnetic rocket effect (Harrison-Tademaru) » Gravitational-wave rocket effect • Are orbital spiral-in events at all related to high-energy bursts? (GRBs? Other transients?) Palomar Bow Shocks Bow Shocks H image MSPs Guitar Nebula: Low V • Ordinary pulsar High • P = 0.68 s Edot • B = 2.6 x 10 12 G J2124-3358 B1957+20 (Kulkarni & Hester; Gaensler et al. J0437-47 • = 1.1 Myr HST Gaensler et al WFPC2 (Fruchter et al.) 33.1 -1 • E = I 10 erg s H • D 1.9 kpc (from DM) Mouse Duck • 1600 km s -1 at nominal distance • Will escape the Milky Way 1994 Radius of curvature of bowshock RXJ1856 nose increased from 1994 to 2001, corresponding to a 33% B0740-28 decrease in ISM density Canonical pulsars J0617 The pulsar is emerging from a 2001 High V, low to high Edot region of enhanced density Chatterjee & Cordes 2004 3 What are the Big Questions? What are the Big Questions? • NS Structure: • NS as Laboratories: • Are neutron stars really neutron stars? • Can departures from General Relativity be identified in the orbits of compact binary pulsars? • What comprises the core of a NS? • Does the Strong-Equivalence Principle hold to high precision in • What is the mass distribution of NS? pulsars with WD or BH companions? • In what regions are the neutrons in a superfluid • NS as Gravitational Wave Detectors: state? • Use pulsars to detect long-period gravitational waves • How large are interior magnetic fields? » Early universe » Mergers of supermassive black holes • Magnetosphere and Emission Physics: » Topological defects (cosmic strings) • What QED processes are relevant for • Pulsars as Probes of Galactic Structure electromagnetic emissions? • What kind of spiral structure does the Galaxy have? • What is the nature of interstellar turbulence? Forefronts in NS Science Forefronts in NS Science • Finding compact relativistic binary pulsars for • Understanding NS populations and their use as laboratories physical differences • Gravity • Radio pulsars and their progenitors • Relativistic plasma physics in strong B • Magnetars • Radio quiet/Gamma-ray loud objects • Finding spin-stable MSPs for use as • Branching ratios in supernovae gravitational wave detectors ( λ ~ light years) • h ~ σ T-1 (T = data span length) • The physics of NS runaway velocities TOA • Are “neutron stars” neutron stars? • Complete surveys of the transient radio sky • pulsars as prototype coherent radio emission Currently about 1700 pulsars known Galactic birth rate ~ 1/100 yr × 10 Myr lifetime for canonical pulsars Fulfilling the Promise of NS Physics ⇒10 5 active pulsars × 20% beaming fraction and Astrophysics ⇒ 2×10 4 detectable pulsars + 10% more MSPs + NS-NS, NS-BH etc. • Find more pulsars • Time them with maximal precision • Phase-resolved polarimetry • VLBI them to get high astrometric precision Step 1: conduct surveys that optimize the detection of faint, pulsed emission that is dispersed and that may or may not be periodic. 4 Arecibo + SKA Surveys Pulsar Search Domains Region/Direction Kind of Pulsar Telescope Arecibo, Young pulsars Effelsburg, GBT, Galactic Plane (< 1 Myr) Jodrell, Parkes, WSRT Young, recycled, Galactic Center GBT, SKA binary, circum-SgrA* Moderate Galactic MSPs, binary, Arecibo, GBT, latitudes runaway Parkes Arecibo, GBT, Globular clusters MSPs, binary Parkes Local Group Young (probably) Arecibo, GBT, Galaxies Giant pulses SKA A Single Dispersed Pulse from the Crab Pulsar Refractive indices for cold, magnetized plasma Arecibo WAPP ν 2 ν 2 − ν 2 ν ν 3 nl,r ~ 1 - p / 2 + p B 2 ν ν ν ν >> p ~ 2 kHz >> B ~ 3 Hz ∆ S ~ 160 x Crab Nebula Group velocity ⇒ group delay = (time of arrival) ~ 200 kJy Detectable to ~ 1.5 Mpc t = t DM ± t RM birefringence with Arecibo ν -2 t DM = 4.15 ms DM ν -3 t RM = 0.18 ns RM -3 Dispersion Measure DM = ∫ ds ne pc cm -2 Rotation Measure RM = 0.81 ∫ ds ne B rad m Refractive indices for cold, magnetized plasma Basic data unit = a dynamic spectrum 2 2 2 3 nl,r ~ 1 - np / 2n m np n B 2n 10 6 – 10 8 samples x 64 µs n >> np ~ 2 kHz n >> n B ~ 3 Hz Fast-dump spectrometers: ⇒ ∆ Group velocity group delay = (time of arrival) • Analog filter banks • Correlators t = t DM ± t RM P • FFT (hardware) ν -2 • FFT (software) t DM = 4.15 ms DM • Polyphase filter bank ν -3 Frequency t RM = 0.18 ns RM 64 to64 1024 channels ∫ -3 E.g. WAPP, GBT DM = ds ne pc cm time correlator + spigot card, new PALFA -2 RM = 0.81 ∫ ds ne B rad m correlator 5 P P Frequency Frequency Time Time Interstellar Scintillation RFI New Pulsars Known Pulsars Periodicity Single-pulse search Arrival time Polarization Scintillation Search Monitoring Analysis Studies (matched filtering) (FFT) Astrophysical effects are typically buried in noise and RFI Issues In Pulsar Survey Optimization P Frequency • Broad luminosity function for pulsars • Beam luminosity Time • Geometric beaming • Pulse sharpness • Intrinsic pulse width W • Smearing from propagation effects » Dispersion across finite bandwidth (correctable) New Pulsars Known Pulsars » Multipath propagation (scattering in the ISM) • Smearing from orbital acceleration Periodicity Single-pulse search Arrival time Polarization Scintillation Search Monitoring Analysis Studies (matched filtering) • Intermittency of the pulsar signal (FFT) • Nulling, giant pulses, precession, eclipsing • Interstellar scintillation Issues In Pulsar Survey Optimization Dedispersion Two methods: • Combine the signal over time and frequency while Coherent : maximizing S/N through matched filtering: • operates on the voltage proportional to the electric • Dedispersion : sum over frequency while removing the dispersive field accepted by the antenna, feed and receiver time delays • computationally intensive because it requires • Single pulses : match the shape and width of the pulse sampling at the rate of the total bandwidth • Periodic pulses : match the period as well as the pulse shape and width • “exact” • Orbital motion : match the change in pulse arrival times related to Post-detection : the changing Doppler effect 2 ⇒ Single-pulse searches: • operates on intensity = |voltage| Search vs.
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