Isolated Neutron Stars and Black Holes. Intro. Sergei Popov (SAI MSU)

Plan 1. Isolated Young Neutron Stars 2. Isolated Black Holes 3. Old Accreting Neutron Stars

Part 1. Neutron stars

Prediction... Neutron stars have been predicted in 30s: L.D. Landau: Star-nuclei (1932) + anecdote Baade and Zwicky: neutron stars and supernovae (1934) (Landau) (Baade) (Zwicky)

Good old classics The pulsar in the Crab nebula A binary system For years two main types of NSs have been discussed: radio pulsars and accreting NSs in close binary systems

The old zoo of neutron stars In 60s the first X-ray sources have been discovered. They were neutron stars in close binary systems, BUT they were «not recognized».... Now we know hundreds of X-ray binaries with neutron stars in the Milky Way and in other galaxies.

Rocket experiments Sco X-1 Giacconi, Gursky, Hendel 1962 In 2002 R. Giacconi was awarded with the Nobel prize.

UHURU The satellite was launched on December 12, The program was ended in March The other name SAS keV The first full sky survey. 339 sources.

Close binary systems About ½ of massive stars Are members of close binary systems. Now we know hundreds of close binary systems with neutron stars. L=Mηc 2 The accretion rate can be up to g/s; Accretion efficiency – up to 10%; Luminosity –thousands of hundreds of the solar.

Discovery !!!! 1967: Jocelyn Bell. Radio pulsars. Seredipitous discovery.

The old Zoo: young pulsars & old accretors

During last >10 years it became clear that neutron stars can be born very different. In particular, absolutely non-similar to the Crab pulsar. o Compact central X-ray sources in supernova remnants. o Anomalous X-ray pulsars o Soft gamma repeaters o The Magnificent Seven o Unidentified EGRET sources o Transient radio sources (RRATs) o Calvera …. The new zoo of neutron stars

Compact central X-ray sources in supernova remnants Cas ARCW 103 Problem: 6.7 hour period (de Luca et al. 2006) Problem: small emitting area

Puppis A One of the most famous central compact X-ray sources in supernova remnants. Age about 3700 years. Probably the progenitor was a very massive star (mass about 30 solar). V kick =1500 km/s WinklerWinkler, Petre 2006 Petre (astro-ph/ )

CCOs in SNRs Age Distance J Cas A –3.7 J − G266.1−1.2 1–3 1–2 J − Pup A 1–3 1.6–3.3 J − G –20 1.3–3.9 J Kes 79 ~9 ~10 J − G347.3−0.5 ~10 ~6 [Pavlov, Sanwal, Teter: astro-ph/ , de Luca: arxiv: ]arxiv: For two sources there are strong indications for small initial spin periods and low magnetic fields: 1E in PKS /52 and PSR J in Kesteven 79 [see Halpern et al. arxiv: ]arxiv:

Magnetars dE/dt > dE rot /dt By definition: The energy of the magnetic field is released P-Pdot Direct measurements of the field (Ibrahim et al.) Magnetic fields –10 15 G

Known magnetars SGRs – Aug.2008! (?) AXPs CXO U E CXO J RXS J XTE J E AX J E E (СТВ 109)

The newest SGR The most recent SGR candidate was discovered in Aug (GCN 8112 Holland et al.) It is named SGR Several reccurent bursts have been detected by several experiments (see, for example, GCN 8132 by Golenetskii et al.). Spin period sec. Optical and IR counterparts. SWIFT

Extragalactic SGRs [D. Frederiks et al. astro-ph/ ]astro-ph/ It was suggested long ago (Mazets et al. 1982) that present-day detectors could alredy detect giant flares from extragalactic magnetars. However, all searches in, for example, BATSE databse did not provide clear candidates (Lazzati et al. 2006, Popov & Stern 2006, etc.). Finally, recently several good candidates have been proposed by different groups (Mazets et al., Frederiks et al., Golenetskii et al., Ofek et al, Crider...., see arxiv: and references therein, for example).arxiv:

Transient radio emission from AXP (Camilo et al. astro-ph/ ) Radio emission was detected from XTE J during its active state. Clear pulsations have been detected. Large radio luminosity. Strong polarization. Precise Pdot measurement. Important for limting models, better distance and coordinates determination etc. ROSAT and XMM images an X-ray outburst happened in AXP has spin period 5.54 s

Another AXP detected in radio 1E P= 2 sec SNR G (see also arxiv: )arxiv: Pdot changed significantly on the scale of just ~few months Rotation and magnetic axis seem to be aligned Also these AXP demostrated weak SGR-like bursts (Rea et al. 2008, GCN 8313) Radio X-rays [simultaneous]

Transient radiopulsar PSR J P=0.326 sec B= G , Among all rotation powered PSRs it has the largest Edot. Smallest spindown age (884 yrs). The pulsar increased its luminosity in X-rays. Increase of pulsed X-ray flux. Magnetar-like X-ray bursts (RXTE). Timing noise. See additional info about this pulsar at the web-site However, no radio emission detected. Due to beaming?

Bursts from the transient PSR Gavriil et al Chandra: Oct 2000 June 2006

ROSAT ROentgen SATellite Launched 01 June The program was successfully ended on 12 Feb German satellite (with participation of US and UK).

Close-by radioquiet NSs Discovery: Walter et al. (1996) Proper motion and distance: Kaplan et al. No pulsations Thermal spectrum Later on: six brothers RX J

Magnificent Seven NamePeriod, s RX RX RBS RBS ? RX RX RBS Radioquiet (?) Close-by Thermal emission Absorption features Long periods

Unidentified EGRET sources Grenier (2000), Gehrels et al. (2000) Unidentified sources are divided into several groups. One of them has sky distribution similar to the Gould Belt objects. It is suggested that GLAST (and, probably, AGILE) Can help to solve this problem. Actively studied subject (see for example papers by Harding, Gonthier) no radio pulsars in 56 EGRET error boxes (Crawford et al. 2006) However, Keith et al. ( ) found a PSR at high frequency.

Discovery of RRATs 11 sources detected in the Parkes Multibeam survey (McLaughlin et al 2006) Burst duration 2-30 ms, interval 4 min-3 hr Periods in the range s Period derivative measured in 3 sources: B ~ G, age ~ Myr RRAT J detected in the X-rays, spectrum soft and thermal, kT ~ 120 eV (Reynolds et al 2006)

RRATs P, B, ages and X-ray properties of RRATs very similar to those of XDINSs Estimated number of RRATs ~ 3-5 times that of PSRs If τ RRAT ≈ τ PSR, β RRAT ≈ 3-5 β PSR β XDINS > 3 β PSR (Popov et al 2006) Are RRATs far away XDINSs ?

RRAT in X-rays (arXiv: ) X-ray pulses overlaped on radio data of RRAT J Thermally emitting NS kT ~ 120 eV (Reynolds et al 2006)

Calvera et al. Recently, Rutledge et al. reported the discovery of an enigmatic NS candidated dubbed Calvera. It can be an evolved (aged) version of Cas A source, but also it can be a M7-like object, who’s progenitor was a runaway (or, less probably, hypervelocity) star. No radio emission was found.

Resume for Part 1. There are several types of sources: CCOs, M7, SGRs, AXPs, RRATs... Magnetars Significant fraction of all newborn NSs Unsolved problems: 1. Are there links? 2. Reasons for diversity

Part 2. Isolated BHs

Early works Victorij Shvartsman «Halos around black holes» Soviet Astronomy – Astronom. Zhurn (1971) In this paper accretion onto isolated BHs from the ISM was studied for different BH masses (including intermediate). Dynamics of accretion, the role of turbulence, the role of magnetic fields in the ISM, spectrum. Synchrotron radiation of magnetized plasma, which is heated during accretion up to K (here the temperature means the average energy of electrons motion perpendicular to magnetic field lines). (Development of this approach see in astro-ph/ )

Basic formulae Velocity of turbulent motions The critical velocity corresponding to an accretion disc formation. (Fujita et al. 1998)

Isolated accreting BHs (Fujita et al. astro-ph/ ) ADAF 10 solar masses The objects mostly emit in X-rays or IR.

The galactic population of accreting isolated BHs (astro-ph/ ) The luminosity distribution is mostly determined by the ISM distribution, then – by the galactic potential. It is important that maxima of the ISM distribution and distribution of compact objects roughly coincide. This results in relatively sharp maximum in the luminosity distribution.

Searching in deep surveys Agol, Kamionkowski (astro-ph/ ) demonstrated that satellites like XMM or Chandra can discover about few dozens of such sources. However, it is very difficult to identify isolated accreting BHs. (astro-ph/ )

Microlensing and isolated BHs Mao et al. astro-ph/ Event OGLE-1999-BUL-32 A very long event: 641 days. Mass estimate for the lense >4 М 0

Microlensing – the MACHO project (Bennet et al. astro-ph/ ) MACHO-96-BLG solar masses.

Again MACHO! MACHO-98-BLG solar masses. (Bennet et al. astro-ph/ )

Digging in the SDSS (Chisholm et al. astro-ph/ ) The idea is that the synchrotron emission can appear in the optical range and in X-rays. Cross-correlation between SDSS and ROSAT data resulted in 57 candidates. ADAF IP CDAF

Radio emission from isolated BHs (Maccarone astro-ph/ ) L R ~ L X 0.7 The task for LOFAR?

Black holes around us Black holes are formed from very massive stars It is very difficult to see an isolated black hole:  Microlensing  Accretion  …….? It is very improtant to have even a very approximate idea where to serach. Let us look at our neighbouhood.... There should be about several tens of million isolated BHs in the Galaxy

The Solar proximity The solar vicinity is not just an average “standard” region The Gould Belt R= pc Age: mill. years SN in a Myr (Grenier 2000) The Local Bubble Up 6 SN in several Myrs

The Gould Belt Poppel (1997) R=300 – 500 pc The age is about million years A disc-like structure with a center pc from the Sun Inclined respect to the galactic plane by ~20 o 2/3 of massive stars in 600 pc from the Sun belong to the Belt

Close-by BHs and runaway stars 56 runaway stars inside 750 pc (Hoogerwerf et al. 2001) Four of them have M > 30 M solar Prokhorov, Popov (2002) [astro-ph/ ] StarMassVelocit y km/s Age, Myr ξ Per33651 HD ς Pup67622 λ Cep

SN explosion in a binary Normal stars Pre-supernova Envelope Center of mass of the system Black Hole Optical star Black hole Opt. star

ς Pup Distance: pc Velocity: km/s Error box: 12 o x 12 o N EGRET : 1

ξ Per Distance: pc Velocity: km/s Error box: 7 o x 7 o N EGRET : 1

Gamma-ray emission from isolated BHs astro-ph/ , – application to EGRET sources Kerr-Newman isolated BH. Magnitosphere. B ~ Gs Jets. See details about this theory in Punsly 1998, 1999.

Runaway BHs Approximate positions of young close-by BHs can be estimated basing on data on massive runaway stars For two cases we obtained relatively small error boxes For HD and for λ Cep we obtained very large error boxes (40-50 o ) Several EGRET sources inside

Resume for Part 2. 1.Accreting stellar mass isolated BHs They should be! And the number is huge! But sources are very weak. Problems with identification, if there are no data in several wavelengths 2. Microlensing on isolated stellar mass BHs There are several good candidates But it is necessary to find the black hole ITSELF! 3. Runaway stars A rare case to make even rough estimates of parameters Error-boxes too large for any band except gamma-rays All hope on the exotic mechanisms (Torres et al. astro-ph/ )

Part. 3 Accreting isolated neutron stars Why are they so important? Can show us how old NSs look like 1. Magnetic field decay 2. Spin evolution Physics of accretion at low rates NS velocity distribution New probe of NS surface and interiors ISM probe

Critical periods for isolated NSs Transition from Ejector to Propeller (supersonic)Duration of the ejector stage Transition from supersonic Propeller to subsonic Propeller or Accretor A kind of equilibrium period for the case of accretion from turbulent medium Condition for the Georotator formation (instead of Propeller or Accretor) (see, for example, astro-ph/ )

Expected properties 1. Accretion rate An upper limit can be given by the Bondi formula: Mdot = π R G 2 ρ v, R G ~ v -2 Mdot = g/s (v/10 km/s) -3 n L=0.1 Mdot c 2 ~ erg/s However, accretion can be smaller due to the influence of a magnetosphere of a NS (see numerical studies by Toropina et al.). 2.Periods Periods of old accreting NSs are uncertain, because we do not know evolution well enough. R A =R co

Subsonic propeller Even after R co >R A accretion can be inhibited. This have been noted already in the pioneer papers by Davies et al. Due to rapid (however, subsonic) rotation a hot envelope is formed around the magnetosphere. So, a new critical period appear. (Ikhsanov astro-ph/ ) If this stage is realized (inefficient cooling) then accretion starts later accretors have longer periods

Equilibrium period A kind of equilibrium period for the case of accretion from turbulent medium Interstellar medium is turbulized. If we put a non-rotating NS in the ISM, then because of accretions of turbulized matter it’ll start to rotate. This clearly illustrates, that a spinning-down accreting isolated NS in a realistic ISM should reach some equilibrium period. RGRG [A&A 381, 1000 (2002)] n=1 cm -3 n=0.1 cm -3 v<60 v<15 km s -1 v<35

Expected properties-2 3. Temperatures Depend on the magnetic field. The size of polar caps depends on the field and accretion rate: ~ R (R/R A ) 1/2 4. Magnetic fields Very uncertain, as models of the field decay cannot give any solid predictions for very long time scales (billions of years). 5. Flux variiability. Due to fluctuations of matter density and turbulent velocity in the ISM it is expected that isolated accretors are variable on a time scale ~ R G /v ~ days - months Still, isolated accretors are expected to be numerous at low fluxes (their total number in the Galaxy is large than the number of coolers of comparable luminosity). They should be hotter than coolers, and have much longer spin periods.

Properties of accretors (astro-ph/ ) In the framework of a simplified model (no subsonic propeller, no field decay, no accretion inhibition, etc.) one can estimate properties of isolated accretors. Slow, hot, dim, numerous at low fluxes (< erg/cm 2 /s) Reality is more uncertain.

Accreting isolated NSs At small fluxes < erg/s/cm 2 accretors can become more abundant than coolers. Accretors are expected to be slightly harder: eV vs eV. Good targets for eROSITA! From several hundreds up to several thousands objects at fluxes about few ∙10 -14, but difficult to identify. Monitoring is important. Also isolated accretors can be found in the Galactic center (Zane et al. 1996, Deegan, Nayakshin 2006). astro-ph/

Where and how to look for As sources are dim even in X-rays, and probably are extremely dim in other bands it is very difficult to find them. In an optimistic scenario they outnumber cooling NSs at low fluxes. Probably, for ROSAT they are to dim. We hope that eROSITA will be able to identify accreting INSs. Their spatial density at fluxes ~ erg/cm 2 /s is expected to be ~few per sq.degree in directions close to the galactic plane. It is necessary to have an X-ray survey at ~ eV with good resolution. In a recent paper by Muno et al.the authors put interesting limits on the number of nidentified magnetars. The same results can be rescaled to give limits on the M7-like sources.

Some reviews on isolated neutron stars NS basics: physics/ physics/ astro-ph/ SGRs & AXPs: astro-ph/ arXiv: arXiv: CCOs: astro-ph/ arxiv: arxiv: Quark stars: arxiv: arxiv: The Magnificent Seven: astro-ph/ arxiv: RRATs: arXiv: arXiv: Cooling of NSs: astro-ph/ astro-ph/ astro-ph/ NS structure arXiv: EoS astro-ph/ NS atmospheres astro-ph/ NS magnetic fields arxiv: arxiv: arxiv: arxiv: