Einstein X-ray observations of cataclysmic variables

Observations with the imaging X-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity X-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.     

Einstein X-ray observations of clusters of galaxies

The X-ray imaging capability of the Einstein Observatory has provided new observational material in many branches of astrophysics. In this contribution we will review the implications of the X-ray observations for the classification of clusters, the formation of SO galaxies, and the interaction of the galaxies with the intracluster gas.     

Einstein observatory results on active galactic nuclei

The Einstein Observatory, by virtue of its increased sensitivity and improved angular resolution, has increased substantially the number of known X-ray emitting active galactic nuclei. This has made possible the detailed study of the relation of X-ray flux to both the continuum flux in the optical and radio bands, and to the line emission properties of these objects. In addition, the Einstein imaging instruments have detected morphology in AGN X-ray emission, in particular from jetlike structures in Cen-A, M87, and 3C273.The improved energy resolution and sensitivity of the spectrometers onboard the Observatory has provided detailed information on the geometry and ionization structure of the region responsible for the broad optical emission lines in a few AGN's. Such information, combined with detailed theoretical modeling and IUE and optical observations, have allowed us to construct a moderately detailed picture of the broad line region in these objects.     

Observational evidence for the binary model of X-ray bursters

Most, but not all, theoretical models of X-ray bursters require a binary system consisting of a mass donating star and a neutron star. The observational evidence in support of this model, however, is both indirect and meager. We have detected absorption dips in the X-ray spectrum of the Burster MXB 1916-05 with the IPC and the MPC on the Einstein Observatory which occur with a binary period of 2985 seconds. These dips are shown to be the result of a gas stream emanating from a companion star and hence this data represents the first direct evidence of the binary nature of X-ray bursters. Detailed models of the interaction of the gas stream with the accretion disk are presented. A 22nd mag. optical candidate for the system has been found.     

ROSAT PSPC observations of two starburst galaxies

We present results from ROSAT observations of NGC 1808 and NGC 2903. Exposures of 10 ksec each with the PSPC detector show X-ray sources at the central positions of both galaxies which are classified as nuclear starburst galaxies. Both targets, NGC 1808 and NGC 2903 appear slightly extended in X-ray maps in the energy band 0.1–2.4 keV. The X-ray spectrum of NGC 1808 shows almost complete absorption below 0.5 keV, indicating an extremely high hydrogen column density towards that source (N_H ≈ 8 × 10²¹cm⁻² resulting from model fits on the PSPC spectrum). In case of NGC 2903, the number of counts in the ROSAT band is significantly lower than expected from a previous EINSTEIN investigation of the source.     

ROSAT PSPC spectra of six Seyfert 1 galaxies

We present six ROSAT PSPC observations of Seyfert 1 galaxies chosen to have low Galactic line-of-sight absorption (N_H 10²⁰ cm⁻²). As expected, it is found that all of these sources possess significantly steeper spectra below 1 keV, than that observed at higher X-ray energies. In addition we find evidence for soft X-ray spectral features, which are best parameterized as line emission at 0.63 keV in NGC7469 and 0.75 keV in ESO198-G24. We examine these results in the light of the accuracy of the PSPC spectral calibration.     

Direct evidence for chromospheric evaporation in a well-observed compact flare

We have observed the flare of 1980 May 7 1456 UT with several Solar Maximum Mission instruments, in coordination with the Sacramento Peak Observatory Vacuum Tower Telescope. From the X-ray data we determine the total amount of plasma at T > 2 × 10⁶ K, commonly attributed to chromospheric evaporation. From Hα we have determined the amount of plasma that has been evaporated from the chromosphere. We find that enough material has been evaporated from the chromosphere to account for the X-ray plasma. Taken together, the Hα, soft and hard X-ray images suggest that chromospheric evaporation is driven both by flare accelerated electrons, during the impulsive phase, and conduction, during the thermal phase.     

Exploring the Dynamic X-ray Universe:Scientific Opportunities for the Einstein Probe Mission

Time-domain astrophysics will enter a golden era towards the end of this decade with the advent of major facilities across the electromagnetic spectrum and in the multi-messenger realms of gravitational wave and neutrino. In the soft X-ray regime, the novel micro-pore lobster-eye optics provides a promising technology to realise, for the first time, focusing X-ray optics for wide-angle monitors to achieve a good combination of sensitivity and wide field of view. In this context Einstein Probe, a soft X-ray all-sky monitor mission, was proposed and selected as a candidate mission of priority in the space science programme of the Chinese Academy of Sciences. This paper reviews the most important science developments and key questions in this field towards 2020 and beyond, and how to achieve them technologically. It also introduces the Einstein Probe mission, including its key science goals and mission definition, as well as some of the key technological issues.      

Measurements of X-ray scattering from interstellar dust

We have examined the surface brightness profiles of four of the brightest compact galactic X-ray sources observed with the Imaging Proportional Counter (IPC) aboard the Einstein Observatory for the existence of halos produced by the scattering of X-rays from interstellar dust. The sources are CYG X-3, 4U1658-48, GX13+1, and 4U1254-69. The halos are apparent when a comparison is made between each source's measured surface brightness profile and a model profile based upon a point response function (PRF) for each source. These model profiles depend upon knowledge of the source's spectrum, which is derived from the IPC itself and corroborated by the Einstein Monitor Proportional Counter and/or previous measurements.As conclusions rest entirely on a knowledge of the system (IPC and Mirror) PRF, we began this study with a comprehensive examination of the calibration data taken for the Observatory prior to launch. Point-source images for both the IPC and the HRI have been analyzed at various energies in order to gain a quantitative understanding of scattering by the mirror surface elements and the IPC's spatial resolution.All four sources show a significant excess above the response from a point-source. The attribution of the excess to X-rays scattered from interstellar dust is strengthened by the positive correlation of the magnitude of this excess with the observed column density of material along the line of sight. Furthermore, we have examined the surface brightness profiles of LMC X-1 and 3C273 and found them to have a greatly reduced excess above their model profiles. Because of their high galactic latitude and because only dust within our own galaxy will lead to the formation of a halo that extends beyond a few arcminutes, only a small effect is expected for these sources.     

COMPTEL observations of AGNs

During the first part of the COMPTON Gamma Ray Observatory sky survey, COMPTEL has detected the quasars 3C273 and 3C279 and the radio galaxy Centaurus A. This paper summarizes the preliminary findings and gives an upper limit on the MeV flux of the Seyfert galaxy NGC4151.     

Nature of gamma-ray burst sources

Observational evidence suggests that gamma ray bursts have a local galactic origin involving neutron stars. In this light we make a critical review of physics of the thermonuclear runaway model placing emphasis on self-consistency. We further show that some of the proposed models can be observationally excluded in the light of existing data from the Einstein Observatory. The possibility of gamma bursts arising in low mass binaries is finally discussed in the light of evolutionary scenarios leading to low luminosity systems.     

类星体的X射线辐射研究

由爱因斯坦天文台最近观测到的273个类星体、Ⅰ型Seyfeft星系的软X射线光度(L_x为0.5—4.5keV)资料,与它们的红移z值构成一个连续序列(图1)。利用球对称吸积模型计算得到:高红移的类星体,由于其较大的吸积率,在这个序列上停留的时间较短(～106年);而低红移类星体及Ⅰ型Seyfert星系停留的时间较长(～108年)。利用现有的107个类星体的射电单色光度l_r,光学单色光度l_o以及X射线单色光度l_x的资料,讨论了类星体大尺度谱的硬度,发现类星体的光学光度有两个不同的演化阶段;文中还定性地讨论了类星体射电辐射机制不同于光学和射电辐射的机制之处。      

The role of stars in the energetics of LINERs

Imaging studies have shown that ∼ 25% of LINER galaxies display a compact nuclear UV source. I compare the HST ultraviolet (1150–3200 Å) spectra that are now available for seven such “UV-bright” LINERs. The spectra of NGC 404, NGC 4569, and NGC 5055 show clear absorption-line signatures of massive stars, indicating a stellar origin for the UV continuum. Similar features are probably present in NGC 6500. The same stellar signatures may be present but undetectable in NGC 4594, due to the low signal-to-noise ratio of the spectrum, and in M81 and NGC 4579, due to superposed strong, broad emission lines. The compact central UV continuum source that is observed in these galaxies is a nuclear star cluster rather than a low-luminosity active galactic nucleus (AGN), at least in some cases. At least four of the LINERs suffer from an ionizing photon deficit, in the sense that the ionizing photon flux inferred from the observed far-UV continuum is insufficient to drive the optical H I recombination lines. Examination of the nuclear X-ray flux of each galaxy shows a high X-ray UV ratio in the four “UV-photon starved” LINERs. In these four objects, a separate component, emitting predominantly in the extreme-UV, is the likely ionizing agent, and is perhaps unrelated to the observed nuclear UV emission. Future observations can determine whether the UV continuum in LINERs is always dominated by a starburst or, alternatively, that there are two types of UV-bright LINERs: starburst-dominated and AGN-dominated. Interestingly, recent results show that starbursts dominate the nuclear energetics in many Seyfert 2s as well.     

日面耀斑环中物质的运动

利用云南天文台1980年7月14日3B级双带耀斑的光学观测资料,以及SMM卫星对同一耀斑的X射线观测结果,讨论日面耀斑环中物质的运动规律。先比较耀斑Hα象和X射线象的日面位置,根据投影效应确定耀斑环的高度;然后从理论上估算由于耀斑环中物质下落,所形成的耀斑活动区视向速度的分布。所得结果与观测资料基本相符。      

Some recent results on extragalactic X-ray sources from the Einstein observatory

Extragalactic research studies by the Harvard/Smithsonian group with the Einstein Observatory have emphasized quasars and clusters of galaxies. More than 100 QSO's have been detected, including 20 serendipitous discoveries. The ratio of L_x/L_o for radio loud quasars is on the average 3 times that of radio quiet ones. QSO's with a large intrinsic optical luminosity have a smaller ratio of L_x/L_o. X-ray images of clusters of galaxies reveal a variety of morphological types which may correspond to different stages in their evolution. Several examples of bi-modal clusters have been discovered. An X-ray plume associated with M86 is apparently gas being stripped. From X-ray studies, a mass between 1.7 × 10¹³M_θ and 4.0 × 10¹³ M_θ has been derived for M87.     

类星体X射线辐射的性质

本文对247个类星体的X射线性质进行了统计分析,这些X射线资料是由爱因斯坦卫星在0.5—4.5keV的能带内观测到的。主要结果是:在各种视亮度和红移(或距离)的已知1619个类星体中,都有百分比相近的部分为X射线源。Ⅰ型Seyferc星系的发射线H_β与[OⅢ]的等值宽度比R_EW同X射线光度L_x强相关,这可作为Ⅰ型Seyfert星系的X射线光度的一个新指标。光学辐射以及2.5GHz以上的高频射电辐射都同X射线辐射相关,说明这三种辐射的区域依次相邻而且机制也相似。色指数U-B和B-V都同X射线辐射不相关,但U-B同B-V弱相关。      

Observations of compact X-ray binaries with the Chandra X-ray Observatory

The Chandra X-ray Observatory was launched on July 23, 1999. The first X-ray photons were detected on August 12 of that same year. Subsequently observations with the Observatory, which features sub-arcsecond angular resolution, have revolutionized our understanding of the X-ray emitting sky providing hosts of spectacular energy-resolved images and high-resolution spectra. Here we present a brief overview of Chandra X-ray Observatory observations of compact X-ray binaries.     

Optical and X-ray observations of 4U2129+47/V1727 CYG in a quiescent state

We observed the 5.2 h X-ray binary 4U2129+47 for more than one orbital cycle on 29 September and 4 October 1983 using the LE, ME and GSPC detectors of the ESA X-ray satellite EXOSAT. In neither detector an X-ray flux from the source could be detected. Quasi-simultaneous UBV observations using the 2.2 m telescop at the German-Spanish Astronomical Center, Calar Alto, failed to detect the large amplitude light curve reported in earlier observations but show the optical companion in a low intensity state. The large amplitude light curve has been interpreted as due to X-ray heating of the optical star by the X-ray source similar to the system Her X-1/HZ Her. Our optical observations indicate that the heating X-ray source has been shut off and nicely explain that EXOSAT failed to detect the source. 4U2129+47 seems to behave similar to Her X-1 in the optical quiescent state, seen for instance from 1949 to 1956.     

Progress and Prospects of the Strategic Priority Program on Space Science

In May 2018, the second phase of the Strategic Priority Program on Space Science (SPP II) was officially approved by the Chinese Academy of Sciences, in view of the significant scientific achievements of the first phase of the Strategic Priority Program on Space Science (SPP I) which includes 4 space science missions:the Dark Matter Particle Explorer (DAMPE), ShiJian-10 (SJ-10), Quantum Experiments at Space Scale (QUESS) and Hard X-ray Modulation Telescope (HXMT). Aiming to address fundamental scientific questions, SPP II focuses on two major themes:How the universe and life originate and evolve and What is the relationship between the solar system and human beings. In areas that Chinese scientists have advantages, new space science missions including Graviational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM), the Advanced space-based Solar Observatory (ASO-S), the Einstein Probe (EP), and Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) have been approved in the framework of SPP II. This paper presents the research highlights of the SPP I, introduces the recent progress of SPP II, and puts forward the prospects for future development.      

Observations of extragalactic objects with telescope ART-P onboard Granat

During 1990–1991 more than two dozens of extragalactic objects were observed by X-ray instruments aboard the Granat satellite. Among them there were AGNs and Seyfert galaxies (NGC4151, NGC5548, MCG-30-15, IC4329 etc.), quasars (3C273, 3C390.3 etc.), radio galaxies (Cen A, M87 etc.) and clusters of galaxies (Virgo, Perseus, Coma etc.). We will discuss below the preliminary results obtained with the ART-P telescope during the observations of five sources: NGC4151, 3C273, Cen A and the galaxies M87 and NGC4388 on the Virgo cluster.