Millisecond X-ray pulsars: 10 years of progress. Maurizio Falanga

Transcription

1 Millisecond X-ray pulsars: 10 years of progress Maurizio Falanga

2 History I

3 Radio Astronomy in the 30 s-60 s Karl Jansky C273 Discovery ( ) Quasi-Stellar Radio Sources as the most energetic and distant members of a class of objects

4 1967 Radio Signals from the Sky

5 Period of s s - They soon realized that the best clocks of the time were not accurate enough to time the object. It seemed very unnatural to receive such a perfectly regular signal from space! - It could originate from extra terrestrial intelligence? LGM-1 (Little Green Men) Jocelyn Bell (1943-)

6 History II

7 S. Chandrasekhar ( ) A massive star can collapse into something denser (1930). He was awarded the 1983 Nobel Prize in Physics for this fundamental prediction! James Chadwick ( ) In 1932, James Chadwick, then at the Cavendish Laboratory in Cambridge, England, discovers the neutron. He got the Nobel physics prize in Fritz Zwicky ( ) In 1934, F. Zwicky and W. Baade and that a stellar collapse of a heavy star during a supernova event should lead to the formation of a dense core of neutrons (NS) at the center of the SN remnant. M. Falanga

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9 During the course of the next few months, J. Bell discovered 3 more pulsating radio sources (or pulsars). These pulsars were proposed to be rapidly rotating neutron stars. Anthony Hewish, won the Nobel Prize in Physics for the discovery in PULSARS are NEUTRON STARS Properties of neutron stars: R ~ 10 km! ~10 14 g/cm 3 M ~ 1.4 M sun -! Magnetic dipole -! Electromagnetic radiation -! Pulsar slowdown

10 Core collapse of an evolved star! Stellar core collapse => conservation of angular momentum => fast spinning neutron star!! Stellar core collapse => conservation of magnetic flux => highly magnetized neutron star! Pacini (1967) proposed the existence of a highly magnetized, rapidly spinning neutron star as the power source of the nebula. This would radiate a very powerful EM wave with the rotational frequency of the star. This is below the plasma frequency of the nebula, therefore all this energy will be absorbed and re-radiated by the plasma of the nebula.

11 In 1968, at the height of the pulsar fever, giant radio pulses originating in the Crab Nebula were detected. 1968: The discovery of These extremely short bursts (~33 ms) proved the existence of a pulsar at the center of the Nebula. Crab Nebula PSR B (Crab Pulsar) (This is the compact radio source detected by Hewish and Okoye in 1964) 1054 PSR

12 Observational confirmation that:!! Pulsars results from stellar collapse in Supernovae "! W. Baade and F. Zwicky were right!! The rotational Energy loss of the Crab Pulsar is Exactly the same as the emission of the Crab Nebula "! Pacini was right, neutron stars are fast, have large magnetic fields, and one of them powers the Crab Nebula. The basic model of pulsar emission becomes established Pulsars are the radio equivalent of lighthouses on a neutron star

13 Pulsars as Clocks R ~ 10 km! ~10 14 g/cm 3 M ~ 1.4 M sun Rotation-Powered Pulsars e.g., PSR J has a period of : ± ms P spin ~ incredibly stable but not constant ms Pulsars Pulsars lose energy and slow down # P spin < µs/yr Data from ATNF Pulsar Catalogue, V1.33

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15 Stellar Evolution & Predictions

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17 Recycling model for MSPs Young Pulsars birth Old Neutron stars spin up by accretion from a companion LMXB phase preceding the MSP stage; "! mass transfer stops; "!the radio MSP switches on Spin up by accretion Most binary MSPs have short orbital periods and mass function identifying the companions as low mass evolved dwarfs Accreting NS in LMXBs are conventionally thought to be the progenitors of millisecond or recycled radio pulsars (Alpar et al. 1982) X-ray transients can be the missing link between LMXBs and MSPs!

18 1.! We have to discover the first Accreting Millisecond X-ray Pulsar (AMXP) 2. We have to discover an AMXP spinning-up 3. We have to prove that LMXB are the progenitors of radio millisecond pulsar

19 1998 the first Accreting Millisecond X-ray Pulsar & The growing family of the X-ray millisecond pulsars

20 Close X-ray binaries: Companion: M << M sun NS: B~ G!! 14 MSP!! P s Hz!! P orb 40 min. - few hrs. (e.g., Wijnands 2004) L ~ erg/s L ~ erg/s Recurence time 2-5yr 20

21 + Two Intermittent Pulsars Source Name P Spin P Orbit M C,Min Discovered (ms) (min) (M $ ) SAX J Apr XTE J Apr XTE J Apr XTE J XTE J IGR J HETE J Swift J IGR J Swift J Feb Jun Dec Jun Jun Sep Apr IGR J Apr

22 2005 the first Accreting Millisecond X-ray Pulsar spinning-up

23 Pulsar spin-up Animation (NASA, D. Barry) 23

24 " Geometry of the emission region Thermal Comptonization in plasma of Temperature ~ 40 kev Seed photons from the hotspot XTE J B ~ G R m Thermal disk emission (Falanga et al. 2005, A&A)

25 PULSE PROFILE IGR J Mag. # Porbit = hr Ps = 1.67 ms Pdot = +8.4 x Hz/s (Falanga, Kuiper, Poutanen et al. 2005) 25

26 We measured for the first time a spin-up for an accreting X-ray millisecond Pulsar IGR J $ = % Hz s -1 (Falanga et al. 2005, A&A) $ = % (L 37 /& -1 I 45 ) (R m /R co ) 1/2 (M/1.4M sun ) ($ spin /600) -1/3 Hz s -1 26

27 Cannibalism in Space: A Star Eats its Companion «Star eats companion» 27

28 2013 the first Accreting Millisecond X-ray Pulsar Swinging between rotation and accretion power in a binary millisecond pulsar

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32 Accreting Millisecond X-ray Pulsar in General

33 Flux oscillations are observed in the tails of some bursts Mag. 4U ; 363 Hz ( 2.7 ms) X-ray Flux Frequency SAX J # Time (Strohmayer et al, 1996 ApJ) Burst oscillations reflect the NS spin frequency (D. Chakrabarty, Nature, 2003

34 X-ray bursts Bursts with Photosphere Radius Expansion Standard Candle to determine the Source Distance: L Edd ' 3 % erg s -1 (e.g. Kuulkers 2004, ApJ) (Falanga et al, 2007, A&A) (Falanga et al, 2011, A&A)

35 Trec "M = # M (t)dt $ 0 M T rec $ cont % T rec & M '1 & F '1 <F bol,pers > -1.1

36 OUTBURST PROFILE Distinct knee (Falanga, Kuiper, Poutanen et al. 2005) (For a review Wijnands 2005, astro-ph/ ) Outburst are extended as a consequence of X-ray irradiation of the disk? 36

37 Outburst are extended as a consequence of X-ray irradiation of the disk Theory: dwarf novae, SXT XTE J R h < R disc (King & Ritter 1998) SAX J Central object prevents the disk to cool down due to Irradiation, on a viscous timescale, accounting for the exponential decay of the outburst on a timescale (~20 40 d. (Powell, Haswell & Falanga, 2007)

38 Thank You 38

39 Pulsed fraction and Time lag : IGR J (Falanga, Kuiper, Poutanen et al. 2005) If the spectrum has a sharp cutoff, the amplitude of the pulse at energies above the cutoff increases dramatically. F(E) 'E -()-1) exp(-[e/e c ] * ),Componization photon index )(E) = ) 0 +!(E/E c ) *

40 Time/Phase Lag Model (Falanga & Titarchuk 2007) +t(c ill,! ref,! hot,n e ref,n e hot ) = upscattering lag + downscattering lag 40

41 Companion Star The companion star should fill ist Roche lobe to allow sufficient accretion on the compact star M. Falanga Companion radius Rc/ Rsun 0.1 Gyr 1 Gyr 5 Gyr White dwarfs Brown dwarfs XTE J XTE J XTE J Companion mass Mc/Msun IGR J SAX J XTE J !!Brown dwarf models at different ages (Chabrier et al. 2000)!!Cold low-mass white dwarfs with pure-helium composition!! IGR J !! SAX J H-rich donor, brown dwarf!! XTE J !! XTE J !! XTE J H-poor, highly evolved dwarf!! XTE J

42 Optical Astronomy Sloan Digital Sky Survey!! 30 M $ Blue supergiant main-sequence star (optically bright, X-ray dim)!! Orbits, 5.6 days, an unseen optically (but bright X-ray) object X-ray Binary System!! The companion has a mass between of ~ 10 M $

43 Cygnus X-1 What is it?!! A red giant would be easily seen!! A main-sequence star would be seen with a little effort!! Can t be a White Dwarf because M > 1.4 M $!! Can t be a Neutron star because M > 3 M $ By elimination, we are left with a Black Hole