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 RA 1 : 18h 56m 35.35s DEC 1 : -37°54’32” (±1.5”) Magnitude : V ~ 25.6 Distance 4 : d ~ 61 pc Radius 5 : R ~ 6 km Mass 5 : M ~ 0.9Mסּ T bb 7 : ~60 eV (7x10 5 K) Proper motion 4 : ~108 km/s (332 mas/yr) (α~326.7 mas/yr ; δ:-59.1 mas/yr)

5. 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 J1856.5-3754 4 (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)

6. 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.

12. 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.

13. Radio-quiet Isolated Neutron Stars Neutron stars Only ~10 3 NSs are directly observed as pulsars or as sources in X- ray binaries in 10 9 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

14. 7 candidates

15. 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 ~~~ ?

16. Thanks a lot ~~~

17. 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?

18. 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 ?!!!