Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-02-03
Astrophys.J. 625 (2005) 307-323
Astronomy and Astrophysics
Astrophysics
17 pages including 14 figures, ApJ, 625 in press
Scientific paper
10.1086/429368
We observed the gamma-ray pulsar Geminga with the HST STIS/MAMA detectors to measure the Geminga's UV spectrum and pulsations. The slope of the far-UV (FUV) spectrum is close to that of a Rayleigh-Jeans spectrum, suggesting that the FUV radiation is dominated by thermal emission from the neutron star (NS) surface. The measured FUV flux, F_FUV=(3.7+/-0.2)x10^-15 ergs cm^-2 s^-1 in 1155-1702 A band, corresponds to a brightness temperature T_RJ=(0.3-0.4)(d_200/R_13)^2 MK. The soft thermal component of the Geminga's X-ray spectrum measured with the XMM-Newton observatory corresponds to a temperature T_s=0.49+/-0.01 MK and radius R_s = (12.9+/-1.0)d_200 km. Unlike other NSs detected in the UV-optical, the FUV spectrum of Geminga lies below the extrapolation of the soft thermal component, which might be associated with the Geminga's very low temperature. Surprisingly, the thermal FUV radiation is strongly pulsed, showing a narrow dip at a phase close to that of a broader minimum of the soft X-ray light curve. The strong pulsations might be attributed to partial occultations of the thermal UV radiation by regions of the magnetosphere filled with electron/positron plasma. In contrast with the FUV spectrum, the near-IR (NIR) through near-UV (NUV) spectrum of Geminga is clearly nonthermal. It can be described by a power-law model, F_nu \propto nu^{-alpha} with a slope alpha = 0.43+/-0.15, close to alpha = 0.56+/-0.24 of the hard X-ray (E>2.5 keV) magnetospheric component. The observed NIR-optical-NUV spectrum is marginally consistent with the extrapolation of the X-ray magnetospheric spectrum. The NUV pulsations, however, do not show a clear correlation with the hard X-ray pulsations.
Kargaltsev O. Y.
Pavlov George G.
Romani Roger W.
Zavlin Vyacheslav E.
No associations
LandOfFree
Ultraviolet, X-ray, and Optical Radiation from the Geminga Pulsar does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Ultraviolet, X-ray, and Optical Radiation from the Geminga Pulsar, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ultraviolet, X-ray, and Optical Radiation from the Geminga Pulsar will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-176836