1. The Nature of γ-ray Source 3EG J2020+4017 陳致維 Chen Chih-Wei

2. Outline 1. Gamma-ray telescope 2. Geminga 3. 3EG J2020+4017(2CG078+2, 2EG J2020+4026) 4. RX J2020.2+4026 5. S312 6. Summary

3. Gamma-ray telescope 1.position error is large 2.count rate is very slow 3.EGRET on the CGRO 4.GLAST: GLAST has a detector area of about one square metre and will detect and locate burst with energies 20-300 MeV within a field of view of 2 steradians.(ref.1)

4. Geminga 1.meaning: a. Gamma-ray source in Gemini b. It is not there(ref.1) 2.period : 273ms(ref.2) 3.radio quiet (ref.1) : a. radio beam is not intersecting our line of sign: radio beam misaligned with gamma ray beam. b. no radio beam: the properties of the magnetosphere.

5. 3EG J2020+4017 1. gamma ray pulsar properties:(ref.3) a. constant sources on long time scale. b. hard spectra in 100Mev~1Gev. c. energy output is concentrated in gamma-ray band. d. high energy cut-offs at a few GeV

6. 2EG J2020+4026 Spectrum( ref.4): ~~gamma ray data

7. 2. Brazier used “evolutionary” method to try to find pulsation in gamma ray data in the range 13.3 ≧ f ≧ 2, f’ ≦ 10^(-11) => no pulsation => they thought the proximity of sever other EGRET source weakened it. (2EG J2026+3610,2EG J2019+3719, and 2EG J2033+4112.) (ref.5)

8. RX J2020.2+4026(ref.5) 1.ROSAT Data:

9. 2. single point –like X-ray source within the EGRET 95 per cent confidence box. 3. With total about 140 source counts and a high, complex background, it was not possible to calculate the shape of the source spectrum from existing data.

11. 4.optical counterparts to RX J2020.2+4023 a. optical spectrum is K0V star b. F γ /Fx is consistent with the late-type stars c. the association between star “A” and RX J2020.2+4023

13. Pulsar or other options? 1. pulsar: did not find pulsation. 2. diffuse source: hard to explain high energy break. 3. Brazier suggested => a young pulsar.(ref.5)

14. S312(ref.6)

18. 1. Chandra data ( observation ID 3856) 2. counterparts a.USNO-B1.0 position (optical)=> match the optical K0V star b. 2MASS position( infrared) => match K0V star 3. spectral analysis: ( energy range from 0.5 to 8.0 keV) a. absorbed power law => spectral index= 8.2 ﹗ b. blackbody c. MEKAL spectrum =>S312 is a K0V star

21. 4. radio observation: a. GBT( Green Bank Telescope) b. no convincing pulsar –like signal were found. c. 3EG J2020+4017 is radio quiet

23. Summary(ref.6) 1. 3EG J2020+4017 is radio quiet 2. Becker suggested that : X-ray emission may not be due to the main-sequence star but could arise from an accreting compact companion. 3. 3EG J2020+4017 is a neutron star with an X-ray luminosity similar to that observed from Vela-like to middle-age pulsars 4. pulsation and further observation=> GLAST

24. Reference: 1. Pulsar Astronomy, A.G. Lyne and Francis Graham-Smith 2. Halpern J.P., Holt S.,1992,Nat,357,222 3. Thompson D. J. et al.,1994, ApJ,436,229 4. Merck M. et al., A&AS,120,465 5. Brazier K. T. S., et al, 1996,MNRAS, 281,1033 6. Becker, W., el al., ApJ,615, 897

25. ~~~Thank You ~~~