Maurizio Falanga

Millisecond X-ray pulsars: 10 years of progress

History I

Radio Astronomy in the 30’s-60’s Radio Astronomy in the 30’s-60’s

Discovery (1961-63) Quasi-Stellar Radio Sources as the most energetic and distant members of a class of objects

3C273

Karl Jansky 1933

1967

Radio Signals from the Sky

Jocelyn Bell (1943-)

- 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!

Period of 1.337 s 1.3372866576 s

LGM-1 (Little Green Men)

- It could originate from extra terrestrial intelligence?

History II

M. Falanga

A massive star can collapse into something denser (1930). He was awarded the 1983 Nobel Prize in Physics for this fundamental prediction!

M. Falanga

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.

S. Chandrasekhar (1910-1995)

Fritz Zwicky (1898 –1974)

In 1932, James Chadwick, then at the Cavendish Laboratory in Cambridge, England, discovers the neutron. He got the Nobel physics prize in 1935.

James Chadwick (1891-1974)

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.

PULSARS are NEUTRON STARS Anthony Hewish, won the Nobel Prize in Physics for the discovery in 1974.

R ~ 10 km ! ~1014g/cm3 M ~ 1.4 Msun -! Magnetic dipole -! Electromagnetic radiation -! Pulsar slowdown

Properties of neutron stars:

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.

1968: The discovery of PSR B0531+21 (Crab Pulsar)

1968: The discovery of PSR B0531+21 (Crab Pulsar) PSR B0531+21 (Crab Pulsar) PSR B0531+21 (Crab Pulsar) These extremely short bursts (~33 ms) proved the

existence of a pulsar at the center of the Nebula. (This is the compact radio source detected by

Hewish and Okoye in 1964)

PSR 0531+21

Crab Nebula

1968: The discovery of 1968: The discovery of 1968: The discovery of In 1968, at the height of the “pulsar fever”, giant radio pulses originating in the Crab Nebula were detected.

1054

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

Data from ATNF Pulsar Catalogue, V1.33

ms Pulsars

Pulsars as Clocks

Pspin ~ incredibly stable but not constant

R ~ 10 km ! ~1014g/cm3 M ~ 1.4 Msun

Pulsars lose energy and slow down

Pspin < µs/yr #

Rotation-Powered Pulsars

5.757451831072007 ± 0.000000000000008 ms

e.g., PSR J0437-4715 has a period of :

(www.atnf.csiro.au/research/pulsar/psrcat)

..

.

Stellar Evolution &

Predictions

Recycling model for MSPs

LMXB phase preceding the MSP stage; "! mass transfer stops; "!the radio MSP switches on

Most binary MSPs have short orbital periods and mass function identifying the companions as low mass evolved dwarfs

X-ray transients can be the missing link between LMXBs and MSPs!

Old Neutron stars spin up by accretion from a companion

Accreting NS in LMXBs are conventionally thought to be the progenitors of millisecond or „recycled“ radio pulsars (Alpar et al. 1982)

birth

Spin up by

accretion

Young Pulsars

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

20

!! 14 MSP

!! Ps 180-600 Hz !! Porb 40 min. - few hrs. (e.g., Wijnands 2004)

L ~ 1031-1032 erg/s L ~ 1036-1038 erg/s Recurence time 2-5yr

Close X-ray binaries:

Companion: M << Msun

NS: B~108-9 G

20

21

Source Name PSpin POrbit MC,Min Discovered

SAX J1808.4-3658 (ms) (min) (M$)

2.5 120 Apr. 1998 0.043

XTE J1751-306 2.3 42 0.014 Apr. 2002

XTE J0929-314 Apr. 2002 5.4 44 0.083

XTE J1807-294

IGR J00291+5934

HETE J1900.1-2455

Swift J1756.9-2508

Swift J1749.4-2807

XTE J1814-338

Feb. 2003

Jun. 2003

Dec. 2004

Jun. 2005

Jun. 2007

Sep. 2009

Apr. 2010

IGR J17511-3057

40

258

150

84

54

208

530

0.0066

0.17 0.039

0.016

0.007

5.2

3.2

1.67

2.6

5.5

+ Two Intermittent Pulsars

4.1

1.9 0.13 0.6

21 21

IGR J18245-2452 660 Apr. 2013 3.9 0.204

IGR J00291+5934

SAX J1808.4-3658

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

23

(NASA, D. Barry)

23

Pulsar spin-up Animation

Geometry of the emission region

XTE J1807-294

Thermal disk emission

Seed photons from the hotspot

B ~ 108-9 G

Rm

(Falanga et al. 2005, A&A)

"

Thermal Comptonization in plasma of Temperature ~ 40 keV

25 (Falanga, Kuiper, Poutanen et al. 2005)

PULSE PROFILE IGR J00291+5934

Porbit = 2.457 hr

Ps = 1.67 ms

Pdot = +8.4 x 10-13 Hz/s

Mag.

#

25

26

IGR J00291+5934

We measured for the first time a spin-up for an accreting X-ray millisecond Pulsar

$ = + 8.4 % 10-13 Hz s-1

$ = + 3.7 % 10-13 (L37/&-1I45) (Rm/Rco)1/2 (M/1.4Msun) ($spin/600)-1/3 Hz s-1 (Falanga et al. 2005, A&A)

26

27

« Star eats companion »

Cannibalism in Space: A Star Eats its Companion

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

Burst oscillations reflect the NS spin frequency

(D. Chakrabarty, Nature, 2003

Time

X-r

ay F

lux

Freq

uenc

y

Flux oscillations are observed in the tails of some bursts

4U 1728-34; 363 Hz ( 2.7 ms)

(Strohmayer et al, 1996 ApJ)

SAX J1808.4-3658

Mag.

#

X-ray bursts

(Falanga et al, 2007, A&A)

Standard Candle to determine the Source Distance: LEdd ' 3 % 1038 erg s-1 (e.g. Kuulkers 2004, ApJ)

Bursts with Photosphere Radius Expansion

(Falanga et al, 2011, A&A)

<F bol,pers >-1.1

!

"M = M•

(t)dt0

Trec

# $

M•

Trec $ cont%

Trec & M• '1

& F '1

36

OUTBURST PROFILE

(For a review Wijnands 2005, astro-ph/0403409)

Outburst are extended as a consequence of X-ray irradiation of the disk?

Distinct knee

(Falanga, Kuiper, Poutanen et al. 2005)

36

Outburst are extended as a consequence of X-ray irradiation of the disk

(Powell, Haswell & Falanga, 2007)

SAX J1808.4-3658

XTE J1751-305

Central object prevents the disk to cool down due to Irradiation, on a viscous time-scale, accounting for the exponential decay of the outburst on a timescale (~20–40 d.

Theory: dwarf novae, SXT

Rh < Rdisc

(King & Ritter 1998)

38

Thank You

Pulsed fraction and Time lag : IGR J00291+5934

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/Ec]*),Componization photon index )(E) = )0 + !(E/Ec)*

(Falanga, Kuiper, Poutanen et al. 2005)

40

Time/Phase Lag Model (Falanga & Titarchuk 2007)

+t(Cill,!ref,!hot,neref,ne

hot) =

upscattering lag + downscattering lag 40

Companion mass Mc/Msun

Com

pani

on ra

dius

Rc/

Rsu

n

Brown dwarfs 0.1 Gyr

5 Gyr 1 Gyr

White dwarfs

XTE J0929-314 XTE J1751-305 XTE J1807-294

IGR J00291+5934 SAX J1808..4-3658 XTE J1814-338

The companion star should fill ist Roche lobe to

allow sufficient accretion on the compact star

Companion Star

!!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

M. Falanga

Sloa

n D

igita

l Sky

Sur

vey

!! 30 M$ Blue supergiant main-sequence star (optically bright, X-ray dim)

Optical Astronomy

!! 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$

What is it?

Cygnus X-1

!! Can’t be a Neutron star because M > 3 M$

By elimination, we are left with a Black Hole

!! 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$