Jeng-Lwen, Chiu

Institute of Astronomy, NTHU

2005/05/05

Periodicity Search from the compact central object CXOU J085201.4-461753

Outline

• Introduction (to the object)

• History of RX J0852-4622

• Data reduction & selection

• Periodicity Search

• Results of complete search

• Results of cross-checking

• Conclusion

• (L) Vela Junior ; (C) Vela SNR ; (R) Pup A• Vela Junior = SNR G266.2-1.2 = RX J0852-4622• Compact Central Object : CXOU J085201.4-461753

Introduction

Compact Central Objects (CCOs)

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 pulsarsNo evidence for companion star that could be powering

the X-ray emission via accretion

Neutron stars

Neutron Stars (>1500)

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 ?

• INS = Isolated (non-binary) Neutron Stars• RQINs = Radio-Quiet (or radio-silent) Isolated Neutron stars

• RX J0852-4622 was discovered at the southwest corner of the Vela SNR by Aschenbach (1998) in the RASS.

• 1.156 MeV γ-ray line of 44Ti (τ~90 yr) was detected with CGRO (Iyudin et al. 1998)

age ~ 680 yr ; distance ~ 200 pc

• Observations with ASCA : non-thermal X-ray spectrum & higher hydrogen column density (by fitting with a PL) (Tsunemi et al. 2000 & Slane et al. 2001)

distance ~ 1-2 kpc ; age ~ a few thousand yrs

History

History• 3-ks Chandra ACIS observation (2

000) :

to detect the point source and measure its position with high accuracy.

• Optical counterpart? HD 76060 (mv=7.88, mB=7.79)

Wray 16-30 (V=13.8)

• 30-ks Chandra ACIS observation (2001) :

PL (in RX J0852-4622) + BB (central?)

Periodicity search by Kargaltsev et al. (2002) (next page…)

Periodicity search from CXO

• The two most significant peaks we found are at f = 3.324231 Hz ± 3μHz (P ~ 301 ms) and f = 30.369484 Hz ± 2μHz (P ~ 33 ms).

• The most significant Zm, max values, Z4, max = 52.9 for the 301 ms period and Z1, max = 36.7 for the 33 ms period, correspond to 96.7% and 96.8% significance levels, respectively, for the number of independent trials N = fmaxTspan ~ 3 × 106 .

• The pulsed fractions obtained from the pulse profiles are 13% ± 3% and 9.1% ± 2.5% for the 301 and 33 ms period candidates, respectively. Because of the low significance, we consider 13% as an upper limit for the pulsed fraction.

Recent Archive DataChandra• 1032 2000-10-26 14:21:28 ACIS-INONE 3.04ks GTO Garmire 3.500

• 1034 2001-09-17 03:14:46 ACIS-SNONE  31.49ks GTO Garmire 0.921

XMM-Newton• 0112870601 2001-04-27 12:34:42 21740s Aschenbach Bernd 2.459

• 0147750101 2003-05-21 09:10:51 56053s Becker Werner 1.041

• 0147750201 2003-06-25 23:09:39 16918s Becker Werner 1.049

Data Reduction & Selection

• The XMM data of CXOU J085201.4-461753 that we used in the analysis are those from the 43 ks observation on 2003 May 21 (hereafter '101') and the 17 ks observation on 2003 June 25 (hereafter '201').

• The time resolution of the pn detector, with which we conduct the periodicity search, is about 6 ms.

• Using the XMM Science Analysis System (SAS) package, we picked events within a 15"-radius circle centered at the source position for the two data sets.

• These events were further restricted in the energy range of 0.2 keV - 12 keV.

• The resultant total number of photons are 14409 for '101' and 6111 for '201', respectively.

• The solar system barycentric time correction was performed to yield an event time list for analysis.

Periodicity Search

• Complete search We applied the H-test (de Jager et al. 1989) to a complete search

on both XMM data '101' and '201' in the range of 0.001 Hz to 100 Hz with equal steps of 1x10-6 Hz. (by H.K., regina, and CJL)

• Cross-checking To confirm the reality of a feature in such a complete search with a

huge number of independent trials (108 in the current case), cross-checking in other data sets is necessary.

Result (1)

• There are no significant peaks around

f = 3.324231 Hz

(P ~ 301 msec)

and

f = 30.369484 Hz

(P ~ 33 msec)

, which were reported by Kargaltsev (2002) based on Chandra data.

Something happened ?!

Some spiky features with very high H-values

101 201

Harmonics from time resolution ( ~176 Hz (~5.67 ms) )

Something happened ?!

Then, exclude these frequency bands…

Highest H-value frequencies

101 (>40) Frequency H-value• 16.524261 47.0429 • 35.214185 46.9654 • 38.979807 41.7614 • 46.106899 43.5353 • 46.399962 42.0609 • 49.950212 41.3795 • 54.943753 46.4846 • 96.174079 41.7649

201 (>37) Frequency H-value• 2.356172 37.8794• 30.373753 38.7681• 32.883769 38.1654• 45.075516 39.3236• 60.747506 37.8369• 72.390650 39.1577• 90.660023 38.2217 • 95.880736 37.0235

f = 16.524261 Hz, H = 47.0429

Highest H-value feature in this study

However…

Upper limit of pulsed fraction

• Upper limit

• loading “duty cycle (δ)” & “H-value (H)” x2σ(with number of events (N)) pulsed fraction (p)

20.24 0.13

2 101.3 8.7 0.174 exp 0.03 0.13 log 0.174x H H

20.17 0.14

3 101.5 10.7 0.174 exp 0.08 0.15 log 0.174x H H

for H > 0.3

for H > 0.3

t t t bx p N p x N p p N N N

The Upper Limits

• 101 f = 16.524261 Hz, H = 47.0429, m =15, random probability = 8.05589x10^-8

Photon events = 14409, bkg. avg = 1358 δ= 0.5 ： Pt2 = 0.0967396203 => p2=10.68% ； Pt3 = 0.1075527730 => p3=11.87%

δ= 0.3 ： Pt2 = 0.0620269310 => p2= 6.85% ； Pt3 = 0.0680025614 => p3= 7.51%

δ= 0.1 ： Pt2 = 0.0318941384 => p2= 3.52% ； Pt3 = 0.0341201405 => p3= 3.77%

• 201 f = 45.075516 Hz, H = 39.3236, m =08, random probability = 6.05168x10^-7

Photon events = 6111, bkg. avg = 607 δ= 0.5 ： Pt2 = 0.1388382470 => p2=15.41% ； Pt3 = 0.1548959110 => p3=17.20%

δ= 0.3 ： Pt2 = 0.0897522864 => p2= 9.97% ； Pt3 = 0.0988316811 => p3=10.97%

δ= 0.1 ： Pt2 = 0.0465303787 => p2= 5.17% ； Pt3 = 0.0500419578 => p3= 5.56%

Result (2)• In all the search, the highest feature found was a

n H-value of 47.0429 (corresponding to a random probability of 8.06×10-8 for a single trial) at f = 16.524261 Hz in the ‘101’ data. Unfortunately, this feature at about 16.5 Hz was not found in the ‘201’ data set.

• By cross-checking the highest H-value features shown in the list, there were no corresponding features inside the list.

• the upper limits of the pulsed fraction based on the H-test (de Jager 1994) was estimated to be about 10.7% at the 2-σ level.

Highest H-value frequencies101 (>40) Frequency H-value• 16.524261 47.0429 • 35.214185 46.9654 • 38.979807 41.7614 • 46.106899 43.5353 • 46.399962 42.0609 !• 49.950212 41.3795 • 54.943753 46.4846 • 96.174079 41.7649 !

201 (>37) Frequency H-value• 2.356172 37.8794• 30.373753 38.7681• 32.883769 38.1654• 45.075516 39.3236• 60.747506 37.8369• 72.390650 39.1577• 90.660023 38.2217 • 95.880736 37.0235

∆T~ 36d 09h 33m 41s = 3144821 s

Further cross-checking with age>500 & h>30

( characteristic age ~ P / (2 dP) )

(101) 90.663639 Hz

(11.02978 ms)

(201)90.660023 Hz (11.03022 ms)

Conclusion• No significant detection for periodicity of the source was

found in this search.• We estimate the upper limits of the pulsed fraction based

on the H-test (de Jager 1994) to be about 10.7% at the 2-σ level.

• By further cross-checking between the two data, the frequency about 90.66 Hz (~11.03 ms) is the most probable one , which leads to a characteristic age of about 1200 years.

• The compact source at the center of Vela Junior is apparently a neutron star with very weak modulation in its surface thermal emission. Further observations and theoretical work will help to understand the physical ground of such a phenomenon.

Reference

1) Aschenbach, B. 1998, Nature, 396, 141 (discovery of RX J0852)

2) de Jager, O. C. 1994, ApJ, 436, 239 (Upper limit on H-test)

3) de Jager, O. C., Swanepoel, J. W. H., & Raubenheimer, B. C. 1989, A&A, 221, 180 (H-test)

4) Iyudin, A. F., et al. 1998, Nature, 396, 142 (1.156 MeV γ-ray line of 44Ti)

5) Kargaltsev, O., Pavlov, G. G., Sanwal, D., & Garmire G. P. 2002, ApJ, 580, 1060 (301 & 30 ms “candidate” periods from CXO)

6) Pavlov, G. G., Sanwal, D., Kiziltan, B., & Garmire, G. P. 2001, ApJ, 559, L131 (CXOU J0852 confirmed)

7) Slane, P., Hughes, J. P., Edgar, R. J., Plucinsky, P. P., Miyata, E., Tsunemi, H., & Aschenbach, B. 2001, ApJ, 548, 814 (higher nH )(ASCA)

8) Iyudin, A. F.; Aschenbach, B.; Becker, W.; Dennerl, K.; Haberl, F. 2005, A&A, 429, 225 (XMM observation)

9) Pavlov, G.G, et al. astro/ph/0112322 (CCO)

Thank You

Functions• H-test

• Upper limit

2 2

1 20

2 2

2

1 1 1

4 4 4 4

2cos 2 sin 2

max m Mm

m N N

m i ik i i

H Z m Z M

Z k kN

2 3

0 0 0 0 0 0

1 1

2 6t t t t t t

20.24 0.13

2 101.3 8.7 0.174 exp 0.03 0.13 log 0.174x H H

20.17 0.14

3 101.5 10.7 0.174 exp 0.08 0.15 log 0.174x H H

for H > 0.3

for H > 0.3

ψ≡ fractional part of

x p N p x N

Fig.1 Rosat all-sky survey image of the Vela SNR and its surroundings with photon energies larger than 1.3 keV. RX J0852.0 -4622 shows up in the lower left. (figure taken from Aschenbach 1998)

201

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

• X-ray-Dim Isolated Neutron starsNo association with SNR (truly isolated!!)No evidence for radio pulsations or accretionTemperature lower than those in SNRs4 of them have been detected their periodsVery 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

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

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

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

Comparison (I)

Comparison (II)

Others? (undetermined?)

• RX J0002+6246 (truly-INS?)

• PSR J0205+6449 (3C 58)

• PSR J0537-6910 (N157B)

• PSR J1124-5916 (G292.0+1.8)

• AX J1811.5-1926 (G11.2-0.3)

• PSR J1846-0258 (Kes75)

• AXS J161730-505505 (near RCW103?)

Future Work

• Check what the undetermined sources are• To know the properties of the sources and the

detail mechanism• Arrange the known in formation of RQINs

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

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

• More…?

0208356

0112322CCOs