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.