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Radio-quiet Isolated Neutron Stars

Radio-quiet Isolated Neutron Stars. Jeng-Lwen, Chiu Institute of Astronomy, NTHU 2003/10/30. Outline. RX J1856.5-3754 Introductions Background Pictures Isolated Neutron star (INS) Introduction Candidates Future work. Introduction. Target name : RX J1856.5-3754

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Radio-quiet Isolated Neutron Stars

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  1. Radio-quiet Isolated Neutron Stars Jeng-Lwen, Chiu Institute of Astronomy, NTHU 2003/10/30

  2. Outline • RX J1856.5-3754 Introductions Background Pictures • Isolated Neutron star (INS) Introduction Candidates • Future work

  3. Introduction • Target name : RX J1856.5-3754 • RA1 : 18h 56m 35.35s • DEC1 : -37°54’32” (±1.5”) • Magnitude : V ~ 25.6 • Distance4 : d ~ 61 pc • Radius5 : R ~ 6 km • Mass5 : M ~ 0.9Mסּ • Tbb7 : ~60 eV (7x105 K) • Proper motion4 : ~108 km/s (332 mas/yr) (α~326.7 mas/yr ; δ:-59.1 mas/yr)

  4. References of RX J1856.5-3754 • Discovery of a nearby isolated neutron star 1 (Walter,F.M., Wolk,S.J., & Neuhäuser,R. 1996, Nature, 379, 233) • On the X-ray position and deep optical imaging of the neutron star candidate RXJ1856.5-3754 2 (Neuhäuser, R., Thomas, H., Danner, R., Peschke, S., & Walter, F.M. 1997, A&A, 318, L43) • Isolated Neutron stars : Accretors and Coolers 3 (Treves, A., Turolla, R., Zane, S., & Colpi, M. 2000, PASP, 112, 297) • THE PROPER MOTION, PARALLAX, AND ORIGIN OF THE ISOLATED NEUTRON STAR RX J1856.5-37544 (Walter, F.M. 2001, ApJ, 549, 433 ) • TOWARD A MASS AND RADIUS DETERNMINATION OF THE NEARBY ISOLATED NEUTRON STARS RX J185635-3754 5 (Pons, J.A., Walter, F.M., Lattimer, J.M., Prakash, M., Neuhäuser, R., & An, P. 2002, APJ, 564, 981) • A DEEP SEARCH FOR PULSATIONS FROM THE NEARBY ISOLATED NEUTRON STAR RX J1856.5-3754 6 (Ransom, S.M., Gaensler, B.M., & Slane, P.O. 2002, APJ, 570, L75) • IS RXJ1856.5-3754 A QUARK STAR ?7 (Drake, J.J., Marshall, H.L., Dreizler, S., Freeman, P.E., Fruscione, A., Juda, M., Kashyap, V., Nicastro, F., Pease, D.O., Wargelin, B.J., & Werner, K. 2002, APJ, 572, 996)

  5. History • Discovered as a bright X-ray source in 1992 with the ROSAT X-ray satellite observatory. (Walter et al, 1996) • Identified with a very faint (V~25.6) optical counterpart. (Walter & Matthews, 1997) • Sco OB association  R CrA Originated from Upper Scropius Association  RX J1856.5-3754 + Zeta Ophiuchus + PSR B1929+10 • Determination of distance.

  6. First Observations of RX J1856.5-3754 • ROSAT • Detected in the RASS between 1990/09/14~1990/10/02. • Identified with the 1992/10/16 PSPC data. • No variability at levels greater than ~1% in 1hr, or <30% on timescale up to 15 years. • HST  Calculate out its proper motion and distance with 1996/10/06, 1999/03/30, and 1999/09/16 WFPC data. • CHANDRA  Obtain an upper limit of 2.7% on the unaccelerated pulse fraction in 2000/03 for 55ks by LETG and HRC-S data.

  7. Radio-quiet Isolated Neutron Stars • Neutron stars Only ~103 NSs are directly observed as pulsars or as sources in X- ray binaries in 109 NSs (estimated). • No companion  Isolated • X-ray source  Accreting NS In priciple, the accretion of the ISM may make INS shine, and their luminosity could be detected in soft X-ray • Radio-quiet  Old NSs Hot NSs (Radio pulsars)  cool down  thermal radiation  accretion from ISM  X-ray source

  8. 7 candidates

  9. Future Work • To know more about the pulsation (variability) of RX J1856.5-3754 • What skills have been used before ? • The upper limit of pulse fraction ? • What satellite & what software ? • And ~~~ ?

  10. Thanks a lot ~~~

  11. Note • History, Observations, • Background location & origin SNR (bow nebula) ? Tbb, mag, distance, radius, ...etc... • Mechanism & Theory Blackbody spectrum? Quark star? • INS (ONS) Radio quiet X-ray spectrum "accreting disk" or "cooler" ? • Why no gamma ray? radio emission?

  12. Q • Why moving from Sco-Cen OB to R Cra ? • How to deternmine mass ? • Ra & Dec ? • bow nebula ? • Tbb ? • detail proper motion ? • "Radio quiet" vs "Isolated" ?!!! • "INS" vs "ONS" ?!!! • A quark star ?!!!

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