Radio-quiet Isolated Neutron Stars(RQINs)

Jeng-Lwen, ChiuInstitute of Astronomy,

NTHU2004/09/30

Outline

n Neutron starsn AXPs & SGRsn CCOsn XDINs (with RX J1856.5-3754)n Comparisonn Othersn Future work

Neutron stars

Neutron Stars (~1400)

Isolated Neutron Stars In Binary systems

Radio-quiet INS Isolated Radio Pulsars

AXPs (~6)

RQINs without γ-ray

RQINs with γ-ray

SGRs (~5)CCOs (~5)

XDINs (~7)

Others (>7)

Companion?

Radio emission ?

With γ-ray ?

With SNR ?

Introduction

n INS = Isolated (non-binary) Neutron Stars

n RQINs = Radio-Quiet (or radio-silent) Isolated Neutron stars

AXPs

n Anomalous X-ray Pulsarsn apparently young NSs with strong X-ray pulsationn Show a relatively stable period evolution with

dP~(0.05-4)x10-11ss-1 n Not powered by rotationn Tbb~4-7MK ; α~2.5-4 ; Lx~1034-1036erg/s

n τ~3-100 kyr & B~1014-1016G (by magneto-dipole breaking)

SGRs

n Soft Gamma-ray Repeatersn P=5-8s ; dP~10-10ss-1 (from 2 of SGRs)

associated with young (~1-10 kyr) NSs in SNRsn Quiescent spectra can be fit by BB+PL model

(Tbb~5MK,R~1km ; α=1-4) ; Lx~1034-1036erg/sn The energy released during the most powerful

bursts is enormous! (>1044erg for the 1998/08/27 outburst of SGR 1900+14)

SGRs vs. AXPs

n Their period are in a narrow range of 5-12s, substantially exceeding typical periods of radio pulsars

n Both are suggested as “magnetars” – NSs with superstrong magnetic fields

n Strongly different in their gamma-ray activity : no gamma-ray emission has been detected from AXPs ; SGRs emit occasional gamma-ray bursts of enormous energy, up to 1042-1044erg

CCOsn Compact Central Objects Unusual X-ray spectra (BB+PL?) Very high effective temperatures (~MK) High X-ray to optical ratio (?) No evidence for pulsations (except 1 case) No evidence for a wind as seen in young

rotation-powered pulsars No evidence for companion star that could be

powering the X-ray emission via accretion

XDINs (e.g. RX J1856.5-3754)

n X-ray-Dim Isolated Neutron stars No association with SNR (truly isolated!!) No evidence for radio pulsations or accretion Temperature lower than those in SNRs 4 of them have been detected their periods Very soft X-ray spectra described by a blackbody

(50~120eV) with no apparent magnetospheric contribution

High X-ray to optical ratio (~103-105) Low NH derived from X-ray spectrum

Problems of XDINs

n Tbb = 0.6~1.4MK –(typical NS) young cooling PSR with radio emission & P<1s

n Long P –(inside lifetime) need unusually long initial P or unusually strong B-field

n The optical emission is too bright to be the low-energy extrapolation of the X-ray spectrum

n Target name : RX J1856.5-3754n RA1 : 18h 56m 35.35sn DEC1 : -37°54’32” (±1.5”)n Magnitude : V ~ 25.7n kTbb : ~63 eV (7x105 K)n Radius5 : R ~ 6 km ?n Mass5 : M ~ 0.9Mּס ?n Distance : d ~ 117 pc n Proper motion4 : ~185 km/s (332 mas/yr) (α~326.7 mas/yr ; δ:-59.1 mas/yr)

RX J1856.5-3754 (parameters)

n Discovered as a bright X-ray source in 1992 with ROSAT and concluded to be an INS in 1997. (Walter et al, 1996)

n Identified with a very faint (V~25.6) optical counterpart. (Walter & Matthews, 1997)

n Determination of distance by parallax. (~61pc(walter 2001) ~143pc(Kaplan 2002) ~117pc(walter 2002))n Researches of thermal radiation

(1) kTbb ~ 57eV (1bb) (Walter 1996)

(2) kTbb ~ 55.3eV & 20.0eV (2bb) (Pons 2002)

(3) kTbb ~ 63eV & <33eV (2bb) or

kTbb ~ 63eV with X-ray emissivity 0.15 (Burwitz2003)

RX J1856.5-3754 (history)

n Pons 20025 ROSAT 53ks (simulation) 6% (0.1 s - 20 s)n Burwitz 200111 CXO 55ks 8% (25 ms - 103 s) (2.1σ)

n Ransom 20026 CXO 505ks 4.5% (10 ms - 103 s) (99%)

n Drake 20029 CXO 505ks 2.7% (10 ms - 104 s) (99%)

n Burwitz 200312 XMM 57ks ( Z12

,MAX = 33.3 ) 1.3% (20 ms - 103 s) (2σ)

RX J1856.5-3754 (pulsation?)

RX J1856.5-3754 (XDINs)

n No pulsation has been detected (only the upper limit has been set) co-alignment of “magnetic-axis and spin axis“ or “spin axis and line of sight” ?

n The optical emission is too bright to be the low-energy extrapolation of the X-ray spectrum

Comparison (I)

Comparison (II)

Others? (undetermined?)

n RX J0002+6246 (truly-INS?)n PSR J0205+6449 (3C 58)n PSR J0537-6910 (N157B)n PSR J1124-5916 (G292.0+1.8)n AX J1811.5-1926 (G11.2-0.3)n PSR J1846-0258 (Kes75)n AXS J161730-505505 (near RCW103?)

Future Work

n Check what the undetermined sources aren To know the properties of the sources and the

detail mechanismn Arrange the known in formation of RQINs

without γ-ray and check the unsolved problems to obtain a better table

n Discuss : Evolutionary relation between these objects? Indication of different kind of mechanism?

n More…?

Main referencesn The Anomalous X-ray Pulsars (Mereghetti, S., et al. in: We-Heraeus Seminar on Neutrob Stars, Pulsars and Supernova Remants. M

PE-Report, vol. 278, pp, 29-43, 2002)

n The 4.5±0.5 Soft Gamma Repeaters in Review (Hurley, K. in: 5th Huntsville GRB Symposium, AIP Conference Proceedings, vol. 525, p.763, 2000)

n The Puzzling Compact Objects in Supernova Remnants (Pavlov, G.G, et al. astro/ph/0112322)

n AXPs and X-ray-dim isolated neutron stars: recent XMM-Newton and Chandra results

(Haberl, F. 2002, AdSpR, 33, 638H)

n Isolated Neutron Stars (Kaspi, M.K., et al. astro-ph/0402136)

n Pulsars and Isolated Neutron Stars (Becker, W. & Pavlov, G. astro-ph/0208356)

~ Thank You ~