用位相相关方法测量Geminga脉冲星的守时参数

利用γ射线脉冲星Ｇｅｍｉｎｇａ自旋及频率变化的稳定性，采用位相相关的方法分析了ＥＧＲＥＴ对脉冲星Ｇｅｍｉｎｇａ四次观测间隔较长的数据，得到较为准确的守时参数ｆ，位相相关的结果与更长数据段折叠搜索的结果较为接近，对于自旋和频率变化都较为稳定的γ射线脉冲星，位相相关分析方法可以作为提高脉冲星参数精度的有效方法。     

用位相相关方法测量Geminga脉冲星的守时参数

利用γ射线脉冲星Ｇｅｍｉｎｇａ自旋及频率变化的稳定性，采用位相相关的方法分析了ＥＧＲＥＴ对脉冲星Ｇｅｍｉｎｇａ四次观测间隔较长的数据，得到较为准确的守时参数ｆ．位相相关的结果与更长数据段折叠搜索的结果较为接近，表明对于自旋和频率变化都较为稳定的γ射线脉冲星，位相相关分析方法可以作为提高脉冲星参数精度的有效方法．     

利用γ射线数据测量Geminga脉冲星的自行

通过比较不同观测中Ｇｅｍｉｎｇａ脉冲星的γ射线绝对位相，测量出了不同时间Ｇｅｍｉｎｇａ的位置。这些位置表明Ｇｅｍｉｎｇａ自行的赤经分量为０．２２６±０．０３弧秒／年，与它的一个最可能的光学对应体Ｇ″的自行相一致，从而独立地确定了Ｇ″与Ｇｅｍｉｎｇａ之间的对应关系。     

利用γ射线数据测量Geminga脉冲星的自行

通过比较不同观测中Ｇｅｍｉｎｇａ脉冲星的γ射线绝对位相，测量出了不同时间Ｇｅｍｉｎｇａ的位置。这些位置表明Ｇｅｍｉｎｇａ自行的赤经分量为０．２２６±０．０３弧秒／年，与它的一个最可能的光学对应体Ｇ″的自行相一致，从而独立地确定了Ｇ″与Ｇｅｍｉｎｇａ之间的对应关系。     

脉冲星Geminga MeV脉冲辐射证据

利用直接解调方法分析ＣＯＭＰＴＥＬ ＶＰ１数据,得到了脉冲星Ｇｅｍｉｎｇａ １０－３０ＭｅＶ脉冲辐射存在的证据;全位相及分位相成像均得到了Ｇｅｍｉｎｇａ。分位相成像结果显示,江变曲线的峰值位于ｐｕｌｓｅ１附近,而闰相区域只能给出上限。由于成 像分析不存在的选择效应,该成像结果表明,Ｇｅｍｉｎｇａ在ＭｅＶ能区仍存在脉冲辐射,虽然Ｇｅｍｉｎｇａ的弱ＭｅＶ辐射使得很难就ＶＰ１数据作时间分析,但仍得到了一     

Compton γ射线望远镜的直接解调成像

Ｃｏｍｐｔｏｎγ射线望远镜ＣＯＭＰＴＥＬ／ＣＧＲＯ工作于０．７５－３０ＭｅＶ能区，本文应用直接解调方法分析ＣＧＲＯ＃１观测的ＣＯＭＰＴＥＬ数据，准确定出Ｃｒａｂγ射线源的位置，在１０－３０ＭｅＶ能区，分辨开最大似然法所不能完全分辨的Ｃｒａｂγ射线源和类星体ＰＫＳ０５２８＋１３４，得出优于传统成像方法所得的成像结果．应用直接成像方法处理γ射线脉冲星Ｇｅｍｉｎｇａ分位相数据，发现Ｇｅｍｉｎｇａ在１０－３０ＭｅＶ能区仍存在辐射，辐射集中在Ｇｅｍｉｎｇａ第一个峰的位相区域．结果表明，应用直接解调方法对Ｃｏｍｐｔｏｎ望远镜数据作成像分析是完全可行的     

Geminga缺射电脉冲的一种可能机制

应用Ｕｓｏｖ和Ｍｅｌｒｏｓｅγ射线脉冲星的修正的极冠区内间隙模型,得到了γ射线脉冲星Ｇｅｍｉｎｇａ为什么没射电脉冲辐射或射电脉冲辐射很弱的一种可能解释,同时,也可看出,中子星表面的多极场有着重要的作用。     

Geminga缺射电脉冲的一种可能机制

应用Ｕｓｏｖ和Ｍｅｌｒｏｓｅγ射线脉冲星的修正的极冠区内间隙模型,得出了γ射线脉冲星Ｇｅｍｉｎｇａ为什么没有射电脉冲辐射或射电脉冲辐射很弱的一种可能解释．同时,也可看出,中子星表面的多极场有着重要的作用．     

Geminga 多波段研究的新进展

简要介绍了特殊天体Ｇｅｍｉｎｇａ的发现、证认、定位和距离测量等工作,详细综 了近年来有关Ｇｅｍｉｎｇａ低频射电辐射和高能辐射的观测进展以及人们对这些结果的理论解释。Ｇｅｍｉｎｇａ是否代表一类没有射电辐射的射电脉冲星（辐射能由转动能量而来的非吸积型脉冲星）,理论上具有重要意义,以前人们在高于１０３ＭＨｚ的射电波段对Ｇｅｍｉｎｇａ做过多次高灵敏度观测,都没有测到有意义。以前人们在高于１０３ＭＨｚ的射电     

Geminga脉冲星的COS-B和HEAO-B卫星资料分析

本文利用COS-B和HEAO-B卫星资料对Geminga脉冲星进行了守时性分析和谱分析,结果进一步证实了Geminga脉冲星是一颗具有强γ辐射,弱X辐射的γ射线脉冲星.     

脉冲星Geminga MeV 脉冲辐射证据

利用直接解调方法分析COMPTELVPI数据,得到了脉冲星Geminga10-30MeV脉冲辐射存在的证据：全位相及分位相成像均得到了Geminga．分位相成像结果显示,光变曲线的峰值位于pulse1附近,而其它位相区域只能给出上限．由于成像分析不存在选择效应,该成像结果表明,Geminga在MeV能区仍存在脉冲辐射．虽然Geminga的弱MeV辐射使得很难就VP1数据作时间分析,但仍得到了一些周期信号的迹象,并且与成像结果不相矛盾．进一步考察EGRET观测Geminga在30MeV以上的强度比Pulse2／Pulse1,发现在VP1观测的较低能区,Pulse1有渐强于Pulse2的趋势,这和我们在MeV能区的成像及时间分析结果相一致．成像得到的流强表明,Geminga的能谱至少在10MeV以上不应出现偏折．     

Measuring the proper motion of the pulsar Geminga using γ-ray data

We have measured the right ascension of Geminga at different epochs by comparing the absolute phases between the different γ-ray observations. These values show that the right-ascension component of the proper motion of Geminga is 0.226±0.03 arcsec per year, which is consistent with that of G″, the most probable optical counterpart, thus independently confirming the correspondence between G″ and Geminga.     

Gamma-ray pulsars: the pulse profiles and phase-resolved spectra of Geminga

We present a calculation of a three-dimensional pulsar magnetosphere model to explain high-energy emission from the Geminga pulsar with a thick outer gap. High-energy γ -rays are produced by primary accelerated particles with a power-law energy distribution through curvature radiation inside the outer gap. We also calculate the emission pattern, pulse profile and phase-resolved spectra of high-energy γ -rays of the Geminga pulsar, and find that its pulse profile is consistent with the observed one if the magnetic inclination and viewing angle are ∼50° and ∼86° respectively. We describe the relative phases among soft (thermal) X-rays, hard (non-thermal) X-rays, and γ -rays. Our results indicate that X-ray and γ -ray emission from the Geminga pulsar may be explained by the single thick outer gap model. Finally, we discuss the implications of the radio and optical emission of the Geminga pulsar.     

Upper Limits on the Continuum Emission from Geminga at 74 and 326 MHz

We report a search for radio continuum emission from the gamma-ray pulsar Geminga. We have used the VLA to image the location of the optical counterpart of Geminga at 74 and 326 MHz. We detect no radio counterpart. We derive upper limits to the pulse-averaged flux density of Geminga, taking diffractive scintillation into account. We find that diffractive scintillation is probably quenched at 74 MHz and does not influence our upper limit, S<56 mJy (2 sigma), but that a 95% confidence level at 326 MHz is S<5 mJy. Owing to uncertainties on the other low-frequency detections and the possibility of intrinsic variability or extrinsic variability (refractive interstellar scintillation) or both, our nondetections are nominally consistent with these previous detections.     

Open cluster ASCC21 as a probable birthplace of the neutron star Geminga

We analyze the encounters of the neutron star (pulsar) Geminga with open star clusters in the OB association Ori OB1a through the integration of epicyclic orbits into the past by taking into account the errors in the data. The open cluster ASCC21 is shown to be the most probable birthplace of either a single progenitor star for the Geminga pulsar or a binary progenitor system that subsequently broke up. Monte Carlo simulations of Geminga-ASCC21 encounters with the pulsar radial velocity V _r = ?100±50 km s^?1 have shown that close encounters could occur between them within ≤10 pc at about t = ?0.52 Myr. In addition, the trajectory of the neutron star Geminga passes at a distance of ≈25 pc from the center of the compact OB association λ Ori at about t = ?0.39 Myr, which is close to the age of the pulsar estimated from its timing.     

Ultraviolet emission from young and middle-aged pulsars

We present the UV spectroscopy and timing of three nearby pulsars (Vela, B0656+14 and Geminga) recently observed with the Space Telescope Imaging Spectrograph. We also review the optical and X-ray properties of these pulsars and establish their connection with the UV properties. We show that the multiwavelengths properties of neutron stars (NSs) vary significantly within the sample of middle-aged pulsars. Even larger differences are found between the thermal components of Geminga and B0656+14 as compared to those of radio-quiet isolated NSs. These differences could be attributed to different properties of the NS surface layers. This work was supported by STScI grants GO-9182 and GO-9797 and NASA grant NAG5-10865.     

On the radio-frequency emission from the Geminga pulsar

The famous neutron star Geminga was until quite lately the only pulsar undetected in the radio regime, though observed as a strong pulsating γ- and X-ray source. Three independent groups from the Pushchino Radio Astronomy Observatory (Russia) reported recently the detection of pulsed radio emission from Geminga at 102.5 MHz, i.e., the first detection of the radio pulsar PSR J0633 + 1746 by Kuz'min &38; Losovskii, Malofeev &38; Malov and Shitov &38; Pugachev. This pulsar exhibits the weakest radio luminosity known. Its average pulse profile appears to be very wide, filling an entire 360° pulse window according to Kuz'min &38; Losovskii.   We present a model explaining the peculiarities of the Geminga radio pulsar, based on the assumption that it is an almost aligned rotator. The electromagnetic waves generated in the inner magnetosphere reach the region within the light cylinder with a weak magnetic field (at distances of a few light cylinder radii), where they are strongly damped due to the cyclotron resonance with particles of magnetospheric electron–positron plasma. The lowest frequencies that can escape are determined by the value of the magnetic field in the region where the line of sight passes through the light cylinder. The specific viewing geometry of an almost aligned rotator implies that the observer's line of sight probes the emission region near the bundle of the last open field lines. This explains the unusually weak emission from Geminga's low-frequency radio pulsar.     

The trigonometric parallax of the neutron star Geminga

We obtained a series of four observations of the isolated neutron star Geminga over an 18 month period using the Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) on the Hubble Space Telescope in order to determine its trigonometric parallax. We find the parallax π=4.0±1.3 mas, corresponding to a distance to Geminga of 250 _?62 ⁺¹²⁰  pc, a result 60% larger than the previously published value. The proper motion is 178.2±1.8 mas/year. In this paper, we describe the analysis techniques in detail since the amplitude of the parallactic shift is smaller than the camera’s pixel size. We fit each star in the images with an appropriate effective PSF and applied a distortion correction to generate stellar positions accurate to 0.01 pixels (～0.5 mas). The 134 stars common to all images serve to establish a reference frame for alignment of the image series. Our observations were made around the times of maximum parallactic shift. We discuss the implications of this new distance measurement for the inferred radius of Geminga, and the neutron star equation of state.