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Periodicity Search for Possible X-ray Counterparts to Gamma-ray Pulsar Candidates

Periodicity Search for Possible X-ray Counterparts to Gamma-ray Pulsar Candidates. Introduction and Background. Archive data of different instruments and their features. Our way to find possible X-ray pulsation. Compare our results with known Gamma-ray pulsars.

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Periodicity Search for Possible X-ray Counterparts to Gamma-ray Pulsar Candidates

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  1. Periodicity Search for Possible X-ray Counterparts to Gamma-ray Pulsar Candidates Introduction and Background Archive data of different instruments and their features Our way to find possible X-ray pulsation Compare our results with known Gamma-ray pulsars Conclusion and try to find some way to improve my work

  2. Background of my research Solving the mystery of the unidentified EGRET sources. Are they pulsars like Vela or Geminga? According to Lamb and Macomb, 1997; there are around 30 sources in the sky with GeV fluxes above 4x10-8 photons cm-2 s-1. 3-5 of these are blazars, 5-6 are identified pulsars, the rest, which lie almost exclusively along the Galactic plane, are currently unidentified. From Roberts and Romani, they present a catalog of 2-10 keV ASCA GIS images of fields containing bright sources of GeV emission. The images cover ~85% of the 95% confidence position contour for 28 of the 30 sources. Among the unidentified sources of Robert’s catalog, we work on the periodicity search for 13 possible X-ray counterparts to gamma-ray pulsar candidates.

  3. X-ray Satellites: ROSAT(1990-1999) ASCA(1993-2001) RXTE(1995-) BeppoSAX(1996-2002) Chandra(1999-) XMM(1999-) XMM-Newton MOS 0.1-15 keV ; 1.5 ms-2.6s PN 0.1-15 keV ; 7 μs-73.4 ms BeepoSAX LECS 0.1-10 keV ; 16 μs MECS 1.3-10 keV ; 15 μs ROSAT PSPC 0.1-2 keV ; 130 μs HRI 0.1-2.5 keV ; 61 μs ASCA GIS 0.8-12 keV ; 62.5ms/2N; 500ms/2N SIS 0.4-12 keV ; Chandra ACIS 0.2-10 keV ; 2.8 ms HRC 0.1-10 keV ; 16 μs --The archive data that we used--

  4. Our approach Choose the data whose source photons > 100 But in the case of small samples (10 ≤ n ≤ 100): Prob(H>h)~w(h) e-bn∙h De Jager et al., 1989

  5. Upper limit of pulsed fraction for H > 0.3 for H > 0.3 De Jager et al., 1994 If we assume all the photons are contributed from the source: δ=0.3, H=50, N=100; P2σ=0.7599 δ=0.3, H=50, N=400; P2σ=0.3799 δ=0.1, H=50, N=100; P2σ=0.3896 δ=0.3, H=30, N=100; P2σ=0.6425 (H=30, prob.=9.95x10-6 ; H=50, prob.=4x10-8) More exposure time may help us get more source photons…..

  6. Our approach Try to find any stronger signal from any way of timing analysis by blind search. (including epoch folding , Zm2-test, H-test) Example: The ROSAT data of RXJ2020.2+4026 (If there isn’t any significant signal…) 242(35'':0.1-2.5keV) 6.2x106 trials 159(60'':0.1-2keV) 3.2x107 trials

  7. Analysis 1. If there is no evident known pulsar to be the counterpart….. Based on 4-7 independent significant trial periods of each data, we search related periods in other data of the same source by the condition that the characteristic age of the pulsar is larger than 1000 years. Furthermore, in order to let our choice to be more convincible, we only select that the random probability to corresponding H-value of the trial period times searching trials is less than 0.02. Example: The cross-checking results of RXJ2020.2+4026 1996-11-02 Frequency: 0.72059200Hz ; Period: 1.3877478518s 1993-10-23+1993-10-26 1.3867432888559s 26.2 3.49x10-5 0.72111400Hz 2087.018yr 105.3x10-13 total searching trials ~360 --------------------------------------------------------------------------- 1996-11-02 Frequency: 12.15149200Hz ; Period: 0.0822944211s 1993-10-23+1993-10-26 0.0822321867897s 35.9 1.62x10-6 12.16068840Hz 1997.680yr 6.5x10-13 total searching trials ~6100

  8. Analysis 2. If there is evident known pulsar to be the counterpart….. Example: Chandra data of AX J2021.1+3651 Epoch(MJD)=52682.60172 From the right panel, we can estimate the pulse frequency of Chandra data = 9.640923869(13) s-1 (Roberts et al., 2004) ~250 trials (Telapse=20.8ks)`

  9. Roberts et al., 2004

  10. Unidentified GeV sources near pulsars (L. Zhang & K.S. Cheng, 1998; Roberts et. al, 2001 & 2002; Cordes & Lazio, 2002)

  11. Our results of Periodicity Search We have 13 GeV pulsar candidates to search for X-ray counterparts. But we can’t resolve the point source in any X-ray archive data corresponding to the position error box of GeV J1800-2328 and GeV J1856+0115. (Although there is a radio pulsar in the error box of each γ-ray source……..) Because we can’t find any significant pulse period in X-ray archival data of these samples, we must have at least two useable data sets to work on cross-checking. On the purpose of periodicity search, AX J1907.1+0549 & AX J2035.4+4222 which are the X-ray counterparts of GeV J1907+0557 & GeV J2035+4214 only have one ASCA data to be analyzed. Let’s see the recommended pulse periods of the left 9 GeV sources by periodicity search for possible X-ray counterparts .

  12. Results of Cross-checking GeV J0008+7304(3EG J0010+7309) ↔ RX J0007.0+7302(CTA 1) The R. P. (random prob.) in the Table of each feature has taken into account total number of trials, but excluding the number of periods which are picked out on discussion in our method. (Lupin & Chang, 2004)

  13. Results of Cross-checking GeV J1025-5809(3EG J1027-5817) ↔ AX J1025.9-5749 ↔1E 1024.0-5732 GeV J1417-6100(3EG J1420-6048) ↔ AX J1418.2-6047 GeV J1417-6100(3EG J1420-6048) ↔ AX J1418.6-6045

  14. Results of Cross-checking GeV J1417-6100(3EG J1420-6048) ↔ AX J1420.1-6049 ↔ PSR J1420-6048

  15. Results of Cross-checking GeV J1809-2327(3EG J1809-2328) ↔ AX J1809.8-2332 GeV J1825-1310(3EG J1826-1302) ↔ PSR B1823-13

  16. Results of Cross-checking GeV J1835+5921(3EG J1835+5918) ↔ AX J1836.2+5928, RX J1836.2+5925 GeV J1837-0610(3EG J1837-0606) ↔ AX J1837.5-0610 This work is done by Wohemos, and the results will be reported in PSROC 2007. GeV J2020+3658(3EG J2021+3716) ↔ AX J2021.1+3651 ↔PSR J2021+3651

  17. Results of Cross-checking GeV J2020+4023(3EG J2020+4017) ↔ RX J2020.2+4026(γCygni, 2CG078+2) After the work of cross-checking related data sets, did we find any tentative pulse period consistent with the pulsation of radio pulsar near these X-ray sources? NO!! What does it mean? 1. Our way is not good enough to reduce the effect of background photons. 2. These X-ray sources has no relation with those pulsars. Is there any significant feature in each data from the periods of those known pulsars? I have not finished the check of all the data. But for those obvious features that can be detected had already been reported in some articles.

  18. Compare with known γ-ray pulsars (Thompson et al., 1999)

  19. The way to improve our work Obviously, the easiest way is to apply for a better data. Based on the pulsed fraction of one selected pulse period, to estimate the related one can be detected or not in another instrument by it’s upper limit of the pulsed fraction. Compare with the similarity of the pulsed profile in the selected cross-checking results. -- Fisher exact test? Kolmogorov-Smirnov test? Numerical Recipes -- William H. Press er al Practical Statistics for Astronomers – J. V. Wall & C. R. Jenkins Astrostatistics – G. J. Babu and E. D. Feigelson Is our way really useful to detect the pulse period of the weak pulsar candidates? We can examine some dim neutron stars with weak pulse.

  20. XDINS (Pavlov, Sanwal & Garmire; 2001) CCO (Haberl ; 2004)

  21. Future Work There still remain some candidates of radio-quiet neutron stars. (Brazier & Johnson; 1999)

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