Radio-quiet Isolated Neutron Stars

Jeng-Lwen, ChiuInstitute 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• 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 ~ 0.9Mּס

• Tbb7 : ~60 eV (7x105 K)• Proper motion4 : ~108 km/s (332 mas/yr) (α~326.7 mas/yr ; δ:-59.1 mas/yr)

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)

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.

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 200

0/03 for 55ks by LETG and HRC-S data.

Radio-quiet Isolated Neutron Stars

• Neutron stars Only ~103 NSs are directly observed as pulsars or as sources in X- r

ay 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 lumino

sity could be detected in soft X-ray

• Radio-quiet Old NSs Hot NSs (Radio pulsars) cool down thermal radiation accretion fr

om ISM X-ray source

7 candidates

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 ~~~ ?

Thanks a lot ~~~

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?

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 ?!!!