Long-term multi-wavelength variations of Fermi blazar 3C 279

Long-term optical, X-ray and γ-ray data of blazar 3 C 279 have been compiled from Swift-XRT,RXTE-PCA, Fermi-LAT, SMARTS and literature. The source exhibits strong variability on long timescales.From the 1980 s until now, the optical R band light curve spans more than 32 yr, and a possible 5.6-yr-long quasi-periodic variation component has been found in it. The optical spectral behavior has been investigated. In the optical band, the mean spectral index is –1.71. The source exhibits an obvious special spectral behavior. In the low state, the source manifests a clear bluer-when-brighter behavior in the sense that the optical spectrum turns harder(flatter) when the brightness increases. While in the high state, the optical spectrum is stable, which means the source spectral index does not vary with brightness. The correlation analysis has been performed among optical, X-ray and γ-ray energy bands. The result indicates that the variations of γ-ray and X-ray bands are well correlated without time delay on the timescale of days, and their variations exhibit weak correlations with those of the optical band. The variations, especially outbursts,are simultaneous, but the magnitude of variations is disproportionate. The detailed analysis reveals that the main outbursts exhibit strong correlations in different γ-ray, X-ray and optical bands.     

An Impulsive Heating Model for the Evolution of Coronal Loops

It was suggested by Parker that the solar corona is heated by many small energy release events generally called microflares or nanoflares. More and more observations showed flows and intensity variations in nonflaring loops. Both theories and observations have indicated that the heating of coronal loops should actually be unsteady. Using SOLFTM (Solar Flux Tube Model), we investigate the hydrodynamics of coronal loops undergoing different manners of impulsive heating with the same total energy deposition. The half length of the loops is 110 Mm, a typical length of active region loops. We divide the loops into two categories: loops that experience catastrophic cooling and loops that do not. It is found that when the nanoflare heating sources are in the coronal part, the loops are in non-catastrophic-cooling state and their evolutions are similar. When the heating is localized below the transition region, the loops evolve in quite different ways. It is shown that with increasing number of heating pulses and inter-pulse time, the catastrophic cooling is weakened, delayed, or even disappears altogether.     

Model simulation for periodic double-peaked outbursts in blazar OJ 287: binary black hole plus lighthouse effect

The mechanism of formation for double-peaked optical outbursts observed in blazar OJ 287 is studied. It is shown that they could be explained in terms of a lighthouse effect for superluminal optical knots ejected from the center of the galaxy that move along helical magnetic fields. It is assumed that the orbital motion of the secondary black hole in the supermassive binary black hole system induces the 12-year quasi-periodicity in major optical outbursts by the interaction with the disk around the primary black hole. This interaction between the secondary black hole and the disk of the primary black hole(e.g. tidal effects or magnetic coupling) excites or injects plasmons(or relativistic plasmas plus magnetic field) into the jet which form superluminal knots. These knots are assumed to move along helical magnetic field lines to produce the optical double-peaked outbursts by the lighthouse effect. The four double-peaked outbursts observed in 1972, 1983, 1995 and 2005 are simulated using this model. It is shown that such lighthouse models are quite plausible and feasible for fitting the double-flaring behavior of the outbursts. The main requirement may be that in OJ 287 there exists a rather long(～40–60 pc) highly collimated zone, where the lighthouse effect occurs.     

The Two Mini-lobes of the CSO OQ208—— VLBI Observations at 5 GHz and 8.4 GHz

We present the results of VLBI observations at 5 GHz and 8.4 GHz of the compact symmetric object (CSO) OQ208. Images taken on four epochs at 5GHz and one at 8.4GHz show that the parsec radio structure of the source consists of two mini-lobes, both of them are resolved into two hot-spots. We note that the component D is stronger than the component C in the south-west region at 5 GHz, indicating that component D is less free-free absorbed than C at low frequency. On the basis of the separation of components A and D, a proper motion of 0.032±0.02 mas yr~(-1) between the two mini-lobes is estimated. This value is about half the previous estimates based on the separation of components A and C with 8.4 GHz VLBI data. The reason for the decrease in the expansion velocity is discussed.     

Temporal variations and spectral properties of the Be/X-ray pulsar GRO J1008–57 studied by INTEGRAL

The spin period variations and hard X-ray spectral properties of the Be/Xray pulsar GRO J1008–57 are studied with INTEGRAL observations during two outbursts in 2004 June and 2009 March.The pulsation periods of～93.66 s in 2004and～93.73 s in 2009 are determined.Pulse profiles of GRO J1008–57 during outbursts are strongly energy dependent with a double-peaked profile from 3–7 keV and a single-peaked profile in hard X-rays above 7 keV.Combined with previous measurements,we find that GRO J1008–57 has undergone a spin-down trend from 1993–2009 with a rate of～4.1×10-5s d-1,and could have changed into a spin-up trend after 2009.We find a relatively soft spectrum in the early phase of the 2009 outburst with cutoff energy～13 keV.Above a hard X-ray flux of～10-9erg cm-2s-1,the spectra of GRO J1008–57 during outbursts need an enhanced hydrogen absorption with column density～6×1022cm-2.The observed dip-like pulse profile of GRO J1008–57 in soft X-ray bands could be caused by this intrinsic absorption.Around the outburst peaks,a possible cyclotron resonance scattering feature at～74 keV is detected in the spectra of GRO J1008–57 which is consistent with the feature that was reported in MAXI/GSC observations,making the source a neutron star with the highest known magnetic field(～6.6×1012G)among accreting X-ray pulsars.This marginal feature is supported by the present detections in GRO J1008–57 following the correlation between the fundamental line energies and cutoff energies in accreting X-ray pulsars.Finally we discovered two modulation periods at～124.38 d and～248.78 d using RXTE/ASM light curves of GRO J1008–57.Two flare peaks appearing in the folded light curve had different spectral properties.The normal outburst lasting 0.1 of an orbital phase had a hard spectrum and could not be significantly detected below 3 keV.The second flare lasting ten days showed a very soft spectrum without significant detections above 5 keV.GRO J1008–57 is a good candidate of an accreting system with an equatorial circumstellar disk around the companion star.The neutron star passing the disk of the Be star near periastron and apastron produces two X-ray flares.The soft spectral properties in the secondary flares still need further detailed studies with soft X-ray spectroscopy.     

Observational Characteristics of Radio Emission Related to Multi-polar Magnetic Configuration

We present a, large complex radio burst and its associated fast tune structures observed on 2001 April 10 in the frequency range of 0.65-7.6 GHz. The NoRH radio image observation shows very complex radio source structures which include preexisting, newly emerging, submerging/cancelling polarities and a bipolar, a tripolar (a 'bipolar + remote unipolar'), and a quadrupolar structure. This suggests that the radio burst is generated from a very complicated loop structure. According to the spectral and image observations, we assume that the beginning of this flare was caused by a single bipolar loop configuration with a 'Y-type' re-connection structure. A composite of radio continuum and fast time structures is contained in this flare. The various fast radio emission phenomena include normal and reverse drifting type III bursts, and slowly drifting and no-drift structures. The tripolar configurations may form a double-loop with a 'three-legged' structure, which is an important source of the various types of fast time structures. The two-loop reconnection model can lead simultaneously to electron acceleration and corona heating. We have also analyzed the behaviors of coronal magnetic polarities and the emission processes of different types radio emission qualitatively. Interactions of a bipolar or multi-polar loop are consistent with our observational results. Our observations favor the magnetic reconnection configurations of the 'inverted Y-type' (bipolar) and the 'three-legged' structures (tripolar or quadrupolar).     

X-ray activity from different types of stars

X-ray emission is an important indicator of stellar activity. In this paper, we study stellar Xray activity using the XMM-Newton and LAMOST data for different types of stars. We provide a sample including 1259 X-ray-emitting stars, of which 1090 have accurate stellar parameter estimations. Our sample size is much larger than those used in previous works. We find a bimodal distribution of the X-ray to optical flux ratio(log(fX/fV)) for G and K stars. We interpret that this bimodality is due to two subpopulations with different coronal heating rates. Furthermore, using the full widths at half maxima calculated from Hα and Hβ lines, we show that these stars in the inactive peaks have smaller rotational velocities. This is consistent with the magnetic dynamo theory that presumes stars with low rotational velocities have low levels of stellar activity. We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the Hα line, and find a tight relation between the coronal and chromospheric activity indicators.     

Linear Correlations between Peak Frequency of Gyrosynchrotron Spectrum and Photosphere Magnetic Fields

The gyrosynchrotron spectra are computed in a nonuniform magnetic field case, taking into account the self-and gyroresonanceabsorption. It is found that the peak frequency νp of the gyrosynchrotron spectrum systematically increases with the increasing photosphere magnetic field strength B0 and increasing viewing angle θ. It is also found for the first time that there are good positive linear correlations between νp and B0, and between log νp and log θ, with linear correlation coefficient 0.99 between νp and B0 and 0.95 between log νp and log θ. We apply the correlations to analyze two burst events observed with OVSA and find that the evolution tendencies of the photosphere magnetic field strength B0 estimated from the above expression are comparable with the observational results of SOHO/MDI. We also give a comparison of the diagnostic results of coronal magnetic field strength in both uniform and nonuniform source models.     

Prediction verification of solar cycles 18–24 and a preliminary prediction of the maximum amplitude of solar cycle 25 based on the Precursor Method

Predictions of the strength of solar cycles are important and are necessary for planning long-term missions.A new solar cycle 25 is coming soon,and the amplitude is needed for space weather operators.Some predictions have been made using different methods and the values are drastically different.However,since 2015 July 1,the original sunspot number data have been entirely replaced by the Version 2.0 data series,and the sunspot number values have changed greatly.In this paper,using Version 2 smoothed sunspot numbers and aa indices,we verify the predictions for cycles 18–24 based on Ohl’s Precursor Method.Then a similar-cycles method is used to evaluate the aa minimum of 9.7(±1.1)near the start of cycle 25 and based on the linear regression relationship between sunspot maxima and aa minima,our predicted Version 2maximum sunspot number for cycle 25 is 121.5(±32.9).     

Long-term photometric behavior of the eclipsing Z Cam-type dwarf nova AY Psc

New eclipse timings of the Z Cam-type dwarf nova AY Psc were measured and the orbital ephemeris was revised.In addition,based on long-term AAVSO data,the outburst behaviors were also explored.Our analysis suggests that normal outbursts are quasi-periodic,with an amplitude of~2.5(±0.1) mag and a period of ~ 18.3(±0.7) d.The amplitude vs.recurrence-time relation of AY Psc is discussed,and we conclude that this relation may represent general properties of dwarf nova outbursts.The observed standstill ends with an outburst,which is inconsistent with the general picture of Z Camtype stars.This unusual behavior was considered to be related to mass-transfer outbursts.Moreover,the average luminosity is brighter during standstills than during outburst cycles.The changes in brightness mark variations in M_2 due to the fact that the disk of AY Psc is nearly steady state.M_2 value was limited to the range from 6.35×10~(-9) to 1.18×10~(-8) M1⊙yr~(-1).More detailed examination shows that there are a few small outbursts present during standstills.These events with amplitudes of~0.5-0.9 mag are very similar to the stunted outbursts reported in some nova-like cataclysmic variables.We discussed several possible mechanisms and suggested that the most reasonable mechanism for these stunted outbursts is a changing mass-transfer rate.     

Effect of Conversion Efficiency on Gamma-Ray Burst Energy

Beaming effect makes it possible that gamma-ray bursts have a standard energy, but the gamma-ray energy release is sensitive to some parameters. Our attention is focused on the effect of the gamma ray conversion efficiency (ηγ), which may range between 0.01 and 0.9, and which probably has a random value for different GRBs under certain conditions. Making use of the afterglow data from the literature, we carried out a complete correction to the conical opening angle formula. Within the framework of the conical jet model, we ran a simple Monte Carlo simulation for random values of ηγ, and found that the gamma-ray energy release is narrowly clustered, whether we use a constant value of ηγ or random values for different gamma-ray bursts.     

Radiative hydrodynamic simulations of the spectral characteristics of solar white-light flares

As one of the most violent activities in the solar atmosphere,white-light flares(WLFs)are generally known for their enhanced white-light(or continuum)emission,which primarily originates in the solar lower atmosphere.However,we know little about how white-light emission is produced.In this study,we aim to investigate the response of the continua at 3600?and 4250?and also the Hαand Lyαlines during WLFs modeled using radiative hydrodynamic simulations.We take non-thermal electron beams as the energy source for the WLFs in two different initial atmospheres and vary their parameters.Our results show that the model with non-thermal electron beam heating clearly shows enhancements in the continua at 3600?and 4250?as well as in the Hαand Lyαlines.A larger electron beam flux,a smaller spectral index,or an initial penumbral atmosphere leads to a stronger emission increase at 3600?,4250?and in the Hαline.The Lyαline,however,is more obviously enhanced in a quiet-Sun initial atmosphere with a larger electron beam spectral index.It is also notable that the continua at 3600?and 4250?and the Hαline exhibit a dimming at the start of heating and reach their peak emissions after the peak time of the heating function,while the Lyαline does not show such behaviors.These results can serve as a reference for the analysis of future WLF observations.     

A Performance Study of the CCD Cameras of the Joint Laboratory of Optical Astronomy

A performance study of several CCD cameras of the Chinese Joint Laboratory of Optical Astronomy (CJLOA) is presented. The main results are: 1) We propose a modified classical method to analyse the linearity of CCD cameras. This method is more sensitive and accurate as well as more intuitive, especially in measuring around the 0.1%-0.2% range of nonlinearity. 2) To illustrate the advantage of the method, the linearity performance of the CCD cameras at CJLOA has been measured and analysed. 3) For the CCD systems tested, there is no unique formula to represent the correlation over the entire CCD frame between the deviation from linearity and the pixel value, i.e., different pixel has different correction even though their pixel values are the same. 4) For the BFOSC (BAO Faint Object Spectrograph Camera) Loral CCD camera and the Tek CCD camera at the 1.56-m reflector, blooming (bleeding) happens long before saturation, and we suspect whether it could have resulted from the charge transfer efficiency (CTE) n     

AstroSat observation of GX 5–1: spectral and timing evolution

We report on the first analysis of an AstroSat observation of the Z-source GX 5–1 on 2017 February 26-27. The hardness-intensity plot reveals that the source traced out the horizontal and normal branches. The 0.8-20 keV spectra from simultaneous SXT and LAXPC data at different locations of the hardness-intensity plot can be described well by disk emission and a thermal Comptonized component. The ratio of the disk flux to the total flux, i.e., the disk flux ratio, increases monotonically along the horizontal branch to the normal one. Thus, the difference between the normal and horizontal branches is that in the normal branch, the disk dominates the flux while in the horizontal one it is the Comptonized component which dominates. The disk flux scales with the inner disk temperature as T_(in)~(5.5 ) and not as T_(in)~4 , suggesting that either the inner radius changes dramatically or that the disk is irradiated by the thermal component changing its hardness factor. The power spectra reveal a quasi-periodic oscillation(QPO) whose frequency changes from ~30 Hz to 50 Hz. The frequency is found to correlate well with the disk flux ratio. In the 3-20 keV LAXPC band, the r.m.s. of the QPO increases with energy(r.m.s. ∝ E~(0.8)), while the harder X-rays seem to lag the soft ones with a time-delay of milliseconds. The results suggest that the spectral properties of the source are characterized by the disk flux ratio and that the QPO has its origin in the corona producing the thermal Comptonized component.     

The Variability of Hardness Ratio 1 observed by ROSAT： Narrow—Line Seyfert 1 Galaxies versus Broad—Line Seyfert 1 Galaxies

We examined the correlation between the ROSAT Hardness Ratio 1 and Count Rates eight Narrow-line Seyfert 1 Galaxies (NLS1s) and 14 Broad-line Seyfert 1 Galaxies (BLS1s). We found that six of the NLS1s show a positive HR1-CTs correlation, and seven of the BLS1s, a negative correlation. The other two NLS1s and seven BLS1s do not show any clear HR1-CTs correlation. Thus, the spectral behavior is statistically different for the NLS1s and BLS1s. The different behaviors can possibly be interpreted in terms of a stable ‘soft excess’ that is strong in NLS1s and weak in BLS1s, plus a power law component, common to both, which softens with increasing flux.     

Re-Identification of the ''''Enigmatic'''' X-ray Source 1RXS J114003.0+124112

The ROSAT X-ray source 1RXS J114003.0 124112 was identified as a starburst galaxy at redshift 0.177 by He et al. The authors also noted that the source is almost two orders of magnitude brighter in X-ray than the X-ray-brightest starburst galaxy and it seems to be in a merging system, making this source an enigmatic system demanding further observations. Here we report a re-identification of 1RXS J114003.0 124112 using observations on the 2.6m telescope at Byurakan Astrophysical Observatory, Armenia and the SDSS data. The results indicate that the starburst activity is associated with the brighter object of the system, while the fainter object is a typical Seyfert 1 galaxy at a different redshift (0.282). Therefore, the two objects are not in a merging system, and the Seyfert 1 galaxy naturally accounts for the high X-ray flux. Three more objects reside in the vicinity, but they are all too faint to be responsible for the high X-ray flux.     

Resonant Heating of Ions by Parallel Propagating Alfvén Waves in Solar Coronal Holes

Resonant heating of H, O+5, and Mg+9 by parallel propagating ion cyclotron Alfven waves in solar coronal holes at a heliocentric distance is studied using the heating rate derived from the quasilinear theory. It is shown that the particle-AlfVen-wave interaction is a significant microscopic process. The temperatures of the ions are rapidly increased up to the observed order in only microseconds, which implies that simply inserting the quasilinear heating rate into the fluid/MHD energy equation to calculate the radial dependence of ion temperatures may cause errors as the time scales do not match. Different species ions are heated by Alfven waves with a power law spectrum in approximately a mass order. To heat O+5 over Mg+9 as measured by the Ultraviolet Coronagraph Spectrometer (UVCS) in the solar coronal hole at a region ≥1.9.R, the energy density of Alfven waves with a frequency close to the O+5-cyclotron frequency must be at least double of that at the Mg+9-cyclotron frequency. With an appropriate wa     

Coherent structures and spectral shapes of kinetic Alfvén wave turbulence in solar wind at 1 AU

This paper presents the generation of kinetic Alfv én wave(KAW) coherent structures of magnetic filaments applicable to solar wind at 1 AU, when the background plasma density is modified by parallel ponderomotive force and Joule heating. The inhomogeneity in the magnetic field, which was included as a perturbation in the transverse direction of the magnetic field, takes energy from the main pump KAWs and generates the filamentary structures. When the intensity is high enough, the filaments are broken down and the energy initially confined to low wavenumbers is redistributed to higher wavenumbers, leading to cascades of energy at small scales less than the ion acoustic gyroradius or comparable to electron gyroradius.The magnetic field spectral profile is generated from the numerical simulation results, and its dependence on different directions of the wavevector and initial conditions of the simulation representing the transverse magnetic field inhomogeneity is studied. The relevance of these results with other spacecraft observations and measurements is also pointed out.     

The temperature of IGM at high redshifts:shock heating and high mach problem

The thermal history of cosmic gas in the dark ages remains largely unknown.It is important to quantify the impact of relevant physics on the IGM temperature between z=10 and z～30,in order to interpret recent and oncoming observations,including results reported by EDGES.We revisit the gas heating due to structure formation shocks in this era,using a set of fixed grid cosmological hydrodynamical simulations performed by three different codes.In all our simulations,the cosmic gas is predicted to be in multiphase state since z 30.The gas surrounding high density peaks gradually develops a relation more sharp than T ∝ρ~(2/3),approximately T ∝ρ~2,from z=30 to z=11,might be due to shock heating.Meanwhile,the gas in void region tends to have a large local Mach number,and their thermal state varies significantly from code to code.In the redshift range 11-20,the mass fraction of gas shock heated above the CMB temperature in our simulations is larger than previous semi-analytical results by a factor of 2 to 8.At z=15,the fraction varies from～19% to 52% among different codes.Between z=11 and z=20,the gas temperature 1/T_K_M~(-1) is predicted to be～10-20 K by two codes,much higher than the adiabatic cooling model and some previous works.However,in our simulations performed by RAMSES,1/T_K_M~(-1)is predicted to be even below the temperature required to explain result of the EDGES.Given the fact that different codes give different predictions,currently,it seems a challenge to make solid prediction on the temperature of gas at z～17 in simulations.     

Infrared variability of the nucleus of the Seyfert galaxy NGC 1068 in 1998–2004

Our 8-year-long JHKLM photometry of the Seyfert galaxy NGC 1068 has confirmed its IR variability. The amplitudes of the brightness variations in the J (1.25 μm) and K (2.2 μm) bands are within 0 _. ^m 15 and 0 _. ^m 3, respectively, and exceed the observational errors by more than a factor of 5. The nucleus of NGC 1068 is a variable source and can be at different phases of activity. The brightness of the galaxy in all bands except J decreased from 1998 until 2004. In this period, there was a tendency for the J brightness to increase. The variable source in NGC 1068 is a complex structured object. At least two sources radiate in the wavelength range 1.25–5 μm: a hot source whose radiation shows up in the range 1.25–1.65 μm and a cold source radiating at long wavelengths (2.2–5 μm). The color temperature of the hot source increased from 2300 K (the beginning of our observations) to ∼2700 K (the end of our observations). In contrast, the temperature of the cold source decreased by several tens of degrees (in the temperature range 800–900 K). The IR brightness and color variations observed in 1998–2004 are attributable to the dispersal of the dust envelope that formed around the galactic nucleus some 30 years ago and reached its maximum density in 1994–1995. Our analysis of the spectral energy distributions for the galaxy has shown that the observed radiation in the range 1.25–5 μm can be represented as the sum of radiations from two blackbody sources. For the first period of our observations (JD 2451400), the temperatures of the hot and cold sources are ∼3100 and 760 K, respectively. For the second period (JD 2453230), they are ∼3200 and 720 K, respectively. The hot source is relatively compact; it is smaller in size than the cold source by several tens of times. The mean sizes of the hot and cold sources are ∼2.35 × 10¹⁶ and ∼7.8 × 10¹⁷ cm, respectively. The total mean luminosity of the two sources did not change between the beginning and the end of our observations. The optical depth of the dust envelope averaged over the spectrum of the hot source is τ ∼ 1.5. In 2004, the state of the dust envelope almost returned to its 1974 level, i.e., the dust envelope formation and dispersal cycle was ∼11 000 days (∼30 yr). Original Russian Text ? O.G. Taranova, V.I. Shenavrin, 2006, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2006, Vol. 32, No. 7, pp. 489–496.