Transcript 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
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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)
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 2000/03 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- 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
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
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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 ?!!!