The Nature of γ-ray Source 3EG J2020+4017

陳致維Chen Chih-Wei

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

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)

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.

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

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

• 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)

RX J2020.2+4026(ref.5)

• 1.ROSAT Data:

• 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.

• 4.optical counterparts to RX J2020.2+4023 a. optical spectrum is K0V star b. Fγ/Fx is consistent with the late-t

ype stars c. the association between star “A

” and RX J2020.2+4023

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)

S312(ref.6)

S312(ref.6)• 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

• 4. radio observation: a. GBT( Green Bank Telescope) b. no convincing pulsar –like

signal were found. c. 3EG J2020+4017 is radio

quiet

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

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, 281,103

3 • 6. Becker, W., el al., ApJ,615, 897

~~~Thank You~~~