Millisecond X-ray pulsars: 10 years of progress Maurizio Falanga
History I
Radio Astronomy in the 30 s-60 s Karl Jansky 1933 3C273 Discovery (1961-63) Quasi-Stellar Radio Sources as the most energetic and distant members of a class of objects
1967 Radio Signals from the Sky
Period of 1.337 s 1.3372866576 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-)
History II
S. Chandrasekhar (1910-1995) A massive star can collapse into something denser (1930). He was awarded the 1983 Nobel Prize in Physics for this fundamental prediction! James Chadwick (1891-1974) In 1932, James Chadwick, then at the Cavendish Laboratory in Cambridge, England, discovers the neutron. He got the Nobel physics prize in 1935. Fritz Zwicky (1898 1974) 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
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 1974. 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
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.
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 B0531+21 (Crab Pulsar) (This is the compact radio source detected by Hewish and Okoye in 1964) 1054 PSR 0531+21
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
Pulsars as Clocks R ~ 10 km! ~10 14 g/cm 3 M ~ 1.4 M sun Rotation-Powered Pulsars e.g., PSR J0437-4715 has a period of : 5.757451831072007 ± 0.000000000000008 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
... (www.atnf.csiro.au/research/pulsar/psrcat)
Stellar Evolution & Predictions
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!
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
1998 the first Accreting Millisecond X-ray Pulsar & The growing family of the X-ray millisecond pulsars
Close X-ray binaries: Companion: M << M sun NS: B~10 8-9 G!! 14 MSP!! P s 180-600 Hz!! P orb 40 min. - few hrs. (e.g., Wijnands 2004) L ~ 10 31-10 32 erg/s L ~ 10 36-10 38 erg/s Recurence time 2-5yr 20
+ Two Intermittent Pulsars Source Name P Spin P Orbit M C,Min Discovered (ms) (min) (M $ ) SAX J1808.4-3658 2.5 120 0.043 Apr. 1998 XTE J1751-306 2.3 42 0.014 Apr. 2002 XTE J0929-314 5.4 44 0.083 Apr. 2002 XTE J1807-294 XTE J1814-338 IGR J00291+5934 HETE J1900.1-2455 Swift J1756.9-2508 IGR J17511-3057 Swift J1749.4-2807 5.2 3.2 1.67 2.6 5.5 4.1 1.9 40 258 150 84 54 208 530 0.0066 0.17 0.039 0.016 0.007 0.13 0.6 Feb. 2003 Jun. 2003 Dec. 2004 Jun. 2005 Jun. 2007 Sep. 2009 Apr. 2010 IGR J18245-2452 3.9 660 0.204 Apr. 2013 21
2005 the first Accreting Millisecond X-ray Pulsar spinning-up
Pulsar spin-up Animation (NASA, D. Barry) 23
" Geometry of the emission region Thermal Comptonization in plasma of Temperature ~ 40 kev Seed photons from the hotspot XTE J1807-294 B ~ 10 8-9 G R m Thermal disk emission (Falanga et al. 2005, A&A)
PULSE PROFILE IGR J00291+5934 Mag. # Porbit = 2.457 hr Ps = 1.67 ms Pdot = +8.4 x 10-13 Hz/s (Falanga, Kuiper, Poutanen et al. 2005) 25
We measured for the first time a spin-up for an accreting X-ray millisecond Pulsar IGR J00291+5934 $ = + 8.4 % 10-13 Hz s -1 (Falanga et al. 2005, A&A) $ = + 3.7 % 10-13 (L 37 /& -1 I 45 ) (R m /R co ) 1/2 (M/1.4M sun ) ($ spin /600) -1/3 Hz s -1 26
Cannibalism in Space: A Star Eats its Companion «Star eats companion» 27
2013 the first Accreting Millisecond X-ray Pulsar Swinging between rotation and accretion power in a binary millisecond pulsar
Accreting Millisecond X-ray Pulsar in General
Flux oscillations are observed in the tails of some bursts Mag. 4U 1728-34; 363 Hz ( 2.7 ms) X-ray Flux Frequency SAX J1808.4-3658 # Time (Strohmayer et al, 1996 ApJ) Burst oscillations reflect the NS spin frequency (D. Chakrabarty, Nature, 2003
X-ray bursts Bursts with Photosphere Radius Expansion Standard Candle to determine the Source Distance: L Edd ' 3 % 10 38 erg s -1 (e.g. Kuulkers 2004, ApJ) (Falanga et al, 2007, A&A) (Falanga et al, 2011, A&A)
Trec "M = # M (t)dt $ 0 M T rec $ cont % T rec & M '1 & F '1 <F bol,pers > -1.1
OUTBURST PROFILE Distinct knee (Falanga, Kuiper, Poutanen et al. 2005) (For a review Wijnands 2005, astro-ph/0403409) Outburst are extended as a consequence of X-ray irradiation of the disk? 36
Outburst are extended as a consequence of X-ray irradiation of the disk Theory: dwarf novae, SXT XTE J1751-305 R h < R disc (King & Ritter 1998) SAX J1808.4-3658 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)
Thank You 38
Pulsed fraction and Time lag : IGR J00291+5934 (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 ) *
Time/Phase Lag Model (Falanga & Titarchuk 2007) +t(c ill,! ref,! hot,n e ref,n e hot ) = upscattering lag + downscattering lag 40
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 J0929-314 XTE J1751-305 XTE J1807-294 Companion mass Mc/Msun IGR J00291+5934 SAX J1808..4-3658 XTE J1814-338!!Brown dwarf models at different ages (Chabrier et al. 2000)!!Cold low-mass white dwarfs with pure-helium composition!! IGR J00291+5934!! SAX J1808.4-3658 H-rich donor, brown dwarf!! XTE J1814-338!! XTE J0292-314!! XTE J1751-305 H-poor, highly evolved dwarf!! XTE J1807-294
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 $
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