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

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
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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-type
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, 281,1033
• 6. Becker, W., el al., ApJ,615, 897
~~~Thank You~~~