Jeng-Lwen, Chiu Institute of Astronomy, NTHU 2005/05/05 Periodicity Search from the compact central object CXOU J

Outline Introduction (to the object) History of RX J 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 G = RX J Compact Central Object : CXOU J 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 pulsars No evidence for companion star that could be powering the X-ray emission via accretion

Neutron stars Neutron Stars (>1500) Isolated Neutron Stars Radio-quiet INS AXPs (~6) SGRs (~5) RQINs with γ-ray RQINs without γ-ray CCOs (~5) XDINs (~7) Others (>7) With SNR ? With γ-ray ? Isolated Radio Pulsars Radio emission ? In Binary systems Companion? INS = Isolated (non-binary) Neutron Stars RQINs = Radio-Quiet (or radio-silent) Isolated Neutron stars

RX J was discovered at the southwest corner of the Vela SNR by Aschenbach (1998) in the RASS 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 & Slane et al. 2001)  distance ~ 1-2 kpc ; age ~ a few thousand yrs History

3-ks Chandra ACIS observation (2000) : to detect the point source and measure its position with high accuracy. Optical counterpart? HD (m v =7.88, m B =7.79) Wray (V=13.8) 30-ks Chandra ACIS observation (2001) : PL (in RX J ) + 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 = Hz ± 3μHz (P ~ 301 ms) and f = Hz ± 2μHz (P ~ 33 ms). The most significant Z m, max values, Z 4, max = 52.9 for the 301 ms period and Z 1, 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 = f max T span ~ 3 × 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 Data Chandra :21:28 ACIS-INONE 3.04ks GTO Garmire :14:46 ACIS-SNONE 31.49ks GTO Garmire XMM-Newton :34: s Aschenbach Bernd :10: s Becker Werner :09: s Becker Werner 1.049

Data Reduction & Selection The XMM data of CXOU J 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 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 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 (10 8 in the current case), cross- checking in other data sets is necessary.

Result (1) There are no significant peaks around f = Hz (P ~ 301 msec) and f = Hz (P ~ 33 msec), which were reported by Kargaltsev (2002) based on Chandra data.

Something happened ?! Some spiky features with very high H-values

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 (>37) Frequency H-value

f = Hz, H = Highest H-value feature in this study However…

Upper limit of pulsed fraction Upper limit loading “duty cycle (δ)” & “H-value (H)”  x 2σ (with number of events (N))  pulsed fraction (p) for H > 0.3

The Upper Limits 101 f = Hz, H = , m =15, random probability = x10^-8 Photon events = 14409, bkg. avg = 1358 δ= 0.5 ： Pt2 = => p2=10.68% ； Pt3 = => p3=11.87% δ= 0.3 ： Pt2 = => p2= 6.85% ； Pt3 = => p3= 7.51% δ= 0.1 ： Pt2 = => p2= 3.52% ； Pt3 = => p3= 3.77% 201 f = Hz, H = , m =08, random probability = x10^-7 Photon events = 6111, bkg. avg = 607 δ= 0.5 ： Pt2 = => p2=15.41% ； Pt3 = => p3=17.20% δ= 0.3 ： Pt2 = => p2= 9.97% ； Pt3 = => p3=10.97% δ= 0.1 ： Pt2 = => p2= 5.17% ； Pt3 = => p3= 5.56%

Result (2) In all the search, the highest feature found was an H-value of (corresponding to a random probability of 8.06×10 -8 for a single trial) at f = 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 frequencies 101 (>40) Frequency H-value ! ! 201 (>37) Frequency H-value ∆T~ 36d 09h 33m 41s = s Further cross-checking with age>500 & h>30 ( characteristic age ~ P / (2 dP) )

(101) Hz ( ms) (201) Hz ( 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 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 n H )(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/ (CCO)

Thank You

Functions H-test Upper limit for H > 0.3 ψ≡ fractional part of

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

201

XDINs (e.g. RX J )RX J X-ray-Dim Isolated Neutron stars No association with SNR (truly isolated!!) No evidence for radio pulsations or accretion Temperature lower than those in SNRs 4 of them have been detected their periods 4 Very soft X-ray spectra described by a blackbody (50~120eV) with no apparent magnetospheric contribution High X-ray to optical ratio (~ ) Low N H derived from X-ray spectrum

Problems of XDINs T bb = 0.6~1.4MK –(typical NS)  young cooling PSR with radio emission & P<1sNS 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 J (truly-INS?) PSR J (3C 58) PSR J (N157B) PSR J (G ) AX J (G ) PSR J (Kes75) AXS J (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…?

CCOs