BL Lacertae： Hard Optical Spectrum and GeV γ-ray Emission

The spectral energy distribution (SED) of the γ-ray flare observed in July 1997 in BL Lacertae is re-considered. It is pointed out that the optical observations made by Webb et al. showed the associated optical flare has a hard spectrum (the average spectral index αopt～0.48, Fν∝ν^-α), and the ASCA observations made by Tanihata et al. showed very steep spectra in the soft X-ray band (0.7-1.5 keV) (αx～3-4). We find that the flux densities and spectral indices in both the optical and soft X-ray bands are closely consistent with a ‘canonical‘ synchrotron spectrum emitted by relativistic electrons of a power-law energy distribution with a high energy cutoff, and thus the peak of the SED of the synchrotron radiation (in representation of νFν) is located in the EUV - soft X-ray bands. Therefore, the GeV γ-ray emission observed in the July 1997 outburst may be mainly due to the synchrotron self-Compton (SSC) process, contrasting with the current explanations in terms of external radiation Compton (ERC) process, in which the seed photons are mostly taken to be the UV emission from the clouds of the broad emission line region. We argue that the hard optical spectra observed during the γ-ray outburst may be an important signature for the acceleration of high energy electrons (γe-10^4) in the γ-ray emitting region.     

Fermi/LAT observations of lobe-dominant radio galaxy 3C 207 and possible radiation region of γ-rays

3 C 207 is a lobe-dominant radio galaxy with a one sided jet and bright knots, spanning a kpcMpc scale, which have been resolved in the radio, optical and X-ray bands. This target was confirmed as a γ-ray emitter with Fermi/LAT, but it is uncertain whether the γ-ray emission region is the core or knots due to the low spatial resolution of Fermi/LAT. We present an analysis of its Fermi/LAT data acquired during the past 9 years. Different from the radio and optical emission from the core, it is found that theγ-ray emission is steady without detection of flux variation at over a 2σ confidence level. This likely implies that the γ-ray emission is from its knots. We collect the radio, optical and X-ray data of knot-A,the closest knot from the core at 1.4′′, and compile its spectral energy distribution(SED). Although the single-zone synchrotron+SSC+IC/CMB model that assumes knot-A is at rest can reproduce the SED in the radio-optical-X-ray band, the predicted γ-ray flux is lower than the LAT observations and the derived magnetic field strength deviates from the equipartition condition by 3 orders of magnitude. Assuming that knot-A is moving relativistically, its SED from radio to γ-ray bands would be represented well with the single-zone synchrotron+SSC+IC/CMB model under the equipartition condition. These results likely suggest that the γ-ray emission may be from knot-A via the IC/CMB process and the knot should have relativistical motion. The jet power derived from our model parameters is also roughly consistent with the kinetic power estimated with radio data.     

The nature of the γ-ray flare associated with blazar 3C 454.3

We have studied the simultaneous spectral energy distributions(SEDs) of the 2009 December flare and those of the quiescent state of blazar 3C 454.3 by constructing a multi-component model. We find that all six SEDs can be explained by a one-zone leptonic model involving synchrotron self-Compton(SSC) plus external Compton emission from an accretion disk(ECD) and that from a broad-line region(ECC). X-ray emission is dominated by the SSC mechanism, and the γ-ray spectrum is well represented by a combination of ECD and ECC processes. Our results indicate that the energy density of the magnetic field and electrons decrease with distance from the central engine, and the Doppler factor increases with the blob moving outward in the development of the 2009 December flare. The increase in the observed flux density is possibly due to the increase in the Doppler factor of the blob. The relation between the Doppler factor δb and the distance from the central black hole suggests the magnetically driven jets span a sub-pc scale, and the relation between the magnetic field B′ and the dimension of the emission region R′b is in good agreement with what is required by conservation of magnetic flux. The weak "harder-when-brighter" behavior of the γ-ray spectrum could be a result of the increase in Doppler factor during the outward motion of the blob. The parameters during the quiescent state obviously deviate from those during the flare state. We propose that the flare was likely caused by the ejection of a new blob. The gamma-ray emissions in different states are associated with the evolution of the blob.     

Similarity of jet radiation between flat spectrum radio quasars and GeV narrow-line Seyfert 1 galaxies: a universal δ-L_c correlation

By modeling the broadband spectral energy distributions(SEDs) of a typical flat spectrum radio quasar(FSRQ, 3C 279) and two GeV narrow-line Seyfert 1 galaxies(NLS1s, PMN J0948+0022 and 1H0323+342) in different flux stages with one-zone leptonic models, we find a universal correlation between their Doppler factors(δ) and peak luminosities(L_c) of external Compton scattering bumps. Compiling a combined sample of FSRQs and GeV NLS1s, it is found that both FSRQs and GeV NLS1s in different stages and in different sources follow the same δ-L_c correlation well. This indicates that the variations of observed luminosities may be essentially due to the Doppler boosting effect. The universal δ-L_c relation between FSRQs and GeV NLS1s in different stages may be further evidence that the particle acceleration and radiation mechanisms for the two kinds of sources are similar. In addition, by replacing L_c with the observed luminosity in the Fermi/LAT band(L_(LAT)), this correlation holds and it may serve as an empirical indicator of δ. We estimate the δ values with L_(LAT) for 484 FSRQs in the Fermi/LAT Catalog and they range from 3 to 41, with a median of 16, which are statistically consistent with the values derived by other methods.     

Flux and spectral variation characteristics of 3C 454.3 at the GeV band

We analyze the long-term lightcurve of 3C 454.3 observed with Fermi/LAT and investigate its relation to flux in the radio,optical and X-ray bands.By fitting the 1-day binned Ge V lightcurve with multiple Gaussian functions(MGF),we propose that the typical variability timescale in the Ge V band is 1–10 d.The Ge V flux variation is accompanied by the spectral variation characterized as fluxtracking,i.e.,"harder when brighter."The Ge V flux is correlated with the optical and X-ray fluxes,and a weak correlation betweenγ-ray flux and radio flux is also observed.Theγ-ray flux is not correlated with the optical linear polarization degree for the global lightcurves,but they show a correlation for the lightcurves before MJD 56000.The power density spectrum of the global lightcurve shows an obvious turnover at~7.7 d,which may indicate a typical variability timescale of 3C 454.3 in theγ-ray band.This is also consistent with the derived timescales by fitting the global lightcurve with MGF.The spectral evolution and an increase in the optical linear polarization degree along with the increase inγ-ray flux may indicate that the radiation particles are accelerated and the magnetic field is ordered by the shock processes during the outbursts.In addition,the nature of 3C 454.3 may be consistent with a self-organized criticality system,similar to Sagittariusand thus the outbursts could be from plasmoid ejections driven by magnetic reconnection.This may further support the idea that the jet radiation regions are magnetized.     

Highly variable γ-ray emission of CTD 135 and implications for its compact symmetric structure

The γ-ray emission properties of CTD 135,a typical compact symmetric object(CSO),are investigated with ～11-year Fermi/LAT observations.We show that it has bright and significantly variable GeV emission,with the γ-ray luminosity of L_γ～ 10~(47) erg s~(-1) and a variation index of TS_(var)=1002.A quasi-periodic oscillation(QPO) with a periodicity of ～460 days is detected in the global 95% false-alarm level.These γ-ray emission features are similar to that of blazars.Its broadband spectral energy distribution(SED) can be attributed to the radiations of the relativistic electrons accelerated in the core region and the extended region.The SED modeling shows that the γ-rays are from the core region,which has a Doppler boosting factor of δ～10.8 and relativistically moves with a small viewing angle,being similar to blazar jets.On the base of the analysis results,we propose that the episodic activity of the central engine in CTD135 results in a blazar-like jet and the bubble-like lobes as the Fermi bubbles in the Galaxy.The strong 7-ray emission with obvious variability is from the jet radiations and the symmetric radio structure is attributed to the bubbles.The jet radiation power and disk luminosity in units of Eddington luminosity of CTD 135 follow the same relation as other young radio sources,indicating that its jet radiation may also be driven by the Eddington ratio.     

An explanation for 13 consecutive day activities of Mrk 421

It is surprising to find an instance of migration in the peak positions of synchrotron spectral energy distribution components during the activity epochs of Markarian 421(Mrk 421),accompanying an orphan flare at the X-ray and GeV-TeVγ-ray bands.A geometric interpretation and standard shock or stochastic acceleration models of blazar emission have difficulty reproducing these observed behaviors.The present paper introduces a linear acceleration by integrating the reconnection electric field into the particle transport model for the observed behaviors of Mrk 421.We note that strong evidence for evolution in characteristic of multi-wavelength spectral energy distribution including shifting the peak frequency,accompanying an orphan flare at the X-ray and GeV-TeVγ-ray bands provides an important electrostatic acceleration diagnostic in a blazar jet.Assuming suitable model parameters,we apply the results of the simulation to the 13-day flaring event in March 2010 of Mrk 421,concentrating on the evolution of multiwavelength spectral energy distribution characteristic by shifting the peak frequency.It is clear that the ratio of the electric field and magnetic field strength plays an important role in temporal evolution of the peak frequency of synchrotron spectral energy distribution component.We suggest it is reasonable that the electrostatic acceleration is responsible for the evolution of multi-wavelength spectral energy distribution characteristic by shifting the peak frequency.Based on the model results,we assert that the peak frequency of the synchrotron spectral energy distribution component may signify a temporary characteristic of blazars,rather than a permanent one.     

Study of temporal and spectral characteristics of the X-ray emission from solar flares

Temporal and spectral characteristics of X-ray emission from 60 flares of intensity ≥C class observed by the Solar X-ray Spectrometer(SOXS) during 2003–2011 are presented. We analyze the X-ray emission observed in four and three energy bands by the Si and Cadmium-Zinc-Telluride(CZT)detectors, respectively. The number of peaks in the intensity profile of the flares varies between 1 and 3. We find moderate correlation(R ≈0.2) between the rise time and the peak flux of the first peak of the flare irrespective of energy band, which is indicative of its energy-independent nature. Moreover, the magnetic field complexity of the flaring region is found to be highly anti-correlated(R = 0.61) with the rise time of the flares while positively correlated(R = 0.28) with the peak flux of the flare. The time delay between the peak of the X-ray emission in a given energy band and that in 25–30 keV decreases with increasing energy, suggesting conduction cooling is dominant in the lower energies. Analysis of 340 spectra from 14 flares reveals that the peak of differential emission measure(DEM) evolution is delayed by 60–360 s relative to that of the temperature, and this time delay is inversely proportional to the peak flux of the flare. We conclude that temporal and intensity characteristics of flares are dependent on energy as well as the magnetic field configuration of the active region.     

Possible distance indicators in gamma-ray pulsars

Distance measurement of gamma-ray pulsars is a current challenge in pulsar studies.The Large Area Telescope(LAT) aboard the Fermi gamma-ray observatory discovered more than 70 gamma-ray pulsars including 24 new gamma-selected pulsars with almost no distance information.We study the relation between gammaray emission efficiency(η=Lγ/E˙) and pulsar parameters for young radio-selected gamma-ray pulsars with known distance information in the first gamma-ray pulsar catalog reported by Fermi/LAT.We have introduce...     

The circumstellar matter of type Ⅱ intermediate luminosity optical transients(ILOTs)

I find that a ■ outflowing equatorial dusty disk (torus) that the binary system progenitor of an intermediate luminosity optical transient (ILOT) ejects several years to several months before and during the outburst can reduce the total emission to an equatorial observer by two orders of magnitude and shifts the emission to wavelengths of mainly λ■10μm.This is termed a type Ⅱ ILOT(ILOT Ⅱ).To reach this conclusion,I use calculations of type Ⅱ active galactic nuclei and apply them to the equatorial ejecta (disk/torus) of ILOTs Ⅱ.This reduction in emission can last for tens of years after outburst.Most of the radiation escapes along the polar directions.The attenuation of the emission for wavelengths ofλ5μm can be more than three orders of magnitude,and the emission at λ■2μm is negligible.Jets that the binary system launches during the outburst can collide with polar CSM and emit radiation above the equatorial plane and dust in the polar outflow can reflect emission from the central source.Therefore,during the event itself the equatorial observer might detect an ILOT.I strengthen the previously suggested ILOT Ⅱ scenario to the event N6946-BH1,where a red giant star disappeared in the visible.     

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.     

Long term optical variability of bright X-ray point sources in elliptical galaxies

We present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with the Chandra Advanced CCD Imaging Spectrometer array(ACIS-S) and observations from the Hubble Space Telescope(HST) Advanced Camera for Surveys.Out of the 46 bright(X-ray counts 60)sources that are in the common field of view of the Chandra and HST observations,34 of them have potential optical counterparts,while the rest of them are optically dark.After taking into account systematic errors,estimated using optical sources in the field as a reference,we find that four of the X-ray sources(three in NGC 1399 and one in NGC 1427) have variable optical counterparts at a high level of significance.The X-ray luminosities of these sources are ~ 10~(38) erg s~(-1) and are also variable on similar time scales.The optical variability implies that the optical emission is associated with the X-ray source itself rather than being the integrated light from a host globular cluster.For one source,the change in optical magnitude is 0.3,which is one of the highest reported for this class of X-ray sources and this suggests that the optical variability is induced by the X-ray activity.However,the optically variable sources in NGC 1399 have been reported to have blue colors(g- z 1).All four sources have been detected in the infrared(IR) by Spitzer as point sources,and their ratios of 5.8 to 3.6 μm flux are 0.63,indicating that their IR spectra are like those of Active Galactic Nuclei(AGNs).While spectroscopic confirmation is required,it is likely that all four sources are background AGNs.We find none of the X-ray sources having optical/IR colors different from AGNs to be optically variable.     

Prompt optical emission from gamma-ray bursts with multiple timescale variability of central engine activities

Complete high-resolution light curves of GRB 080319B observed by Swift present an opportunity for detailed temporal analysis of prompt optical emission. With a two-component distribution of initial Lorentz factors, we simulate the dynamical process of shells being ejected from the central engine in the framework of the in- ternal shock model. The emitted radiations are decomposed into different frequency ranges for a temporal correlation analysis between the light curves in different energy bands. The resulting prompt optical and gamma-ray emissions show similar tempo- ral profiles, with both showing a superposition of a component with slow variability and a component with fast variability, except that the gamma-ray light curve is much more variable than its optical counterpart. The variability in the simulated light curves and the strong correlation with a time lag between the optical and gamma-ray emis- sions are in good agreement with observations of GRB 080319B. Our simulations suggest that the variations seen in the light curves stem from the temporal structure of the shells injected from the central engine of gamma-ray bursts. Future observations with high temporal resolution of prompt optical emission from GRBs, e.g., by UFFO- Pathfinder and SVOM-GWAC, will provide a useful tool for investigating the central engine activity.     

Multi-wavelength Study of HESS J1303-631 with 14 yr of Fermi-LAT Data

HESS J1303-631 is an extended TeV pulsar wind nebula powered by the pulsar PSR J1301-6305 detected with the High Energy Stereoscopic System. We present an analysis of the GeV γ-ray region of HESS J1303-631 with about14 yr of Fermi Large Area Telescope data. The GeV γ-ray emission, coincident with the very-high-energy source,has a photon index of 1.69 ± 0.09 in 10–500 GeV band, and the GeV morphology has an extension to the same direction as indicated in the TeV band. Moreover, the observed multi...     

The physical origin of optical flares following GRB 110205A and the nature of the outflow

The optical emission of GRB 110205A is distinguished by two flares.We examine two possible scenarios for the optical afterglow emission.In the first scenario,the first optical flare is the reverse shock emission of the main outflow and the second one is powered by the prolonged activity of the central engine.However,we find that it is rather hard to reasonably interpret the late(t > 0.1 d) afterglow data unless the GRB efficiency is very high(～ 0.95).In the second scenario,the first optical flare is the low...     

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.     

dMe耀星的X射线的辐射

From Einstein Observatory, we know most nearby dM flare stars have X-ray emissions. X-ray flare energy of dM stars is far larger than that of large flares of sun. The corona temperature of dM stars is higher than that of sun. The X-ray flare time scales are several minutes to hours. Star corona heating model for X-ray flares is loop model, which provide a mechanism to convert magnetic energy to heat energy in star corona.Within identification of ROSAT X-ray sources, we found that X-ray source: RX1102.0 4347 corresponds to WX UMa, a dM5e flare star, which is in a nearby visual binary: Gliese 412A B. The binary is very near to earth, 5.38pc, and has high proper motion, 4".54/ year. The binary is also an Einstein X-ray source: 1 E1103.0 4346.In March 27, 1993, we observed WX UMa by CCD BVRI photometry at BAO 2.16m telescope. Magnitudes of the star are: V = 14.56, B-V = 1.95, V-R = 0.97, R-I = 2.06, which are similar to previous observations.From the ROSAT X-ray survey data in November 7-17, 1990, average X     

X-ray Emission Lines in GRB Afterglows： Evidence for a Two-component Jet Model

X-ray emission lines have been observed in X-ray afterglows of several γ-ray bursts (GRBs). It is a major breakthrough for understanding the nature of the progenitors. It has been proposed that the X-ray emission lines can be well explained by the Geometry-Dominated models, but in these models the illuminating angle is much larger than that of the collimated jet of the GRB. For GRB 011211, we have obtained an illuminating angle of about θ- 45°, while the angle of the GRB jet is only 3.6°. So we propose that the outflow of GRBs with emission lines should have two distinct components: a wide component that illuminates the reprocessing material and produces the emission lines and a narrow one that produces the GRB. Observations show the energy for producing the emission lines is higher than that of the GRB. In this case, when the wide component dominates the afterglows, a bump should appear in the GRB afterglow. For GRB 011211, the bump should occur within 0.05 days of the GRB, which is obviously too early for the observation to catch it. Alongside the X-ray emission lines there should also be a bright emission component between the UV and the soft X-rays. These features can be tested by the Swift satellite in the near future.     

The Multi-Wavelength Quasar Survey Ⅳ. Quasars in the Leo Cluster

We aim to provide a quasar sample that is more complete than any previous surveys by using a combined selection technique to reduce the selection effects. Here we present the observational results for the X-ray candidates in the field of the Leo Cluster. We found 33 X-ray AGNs in this field of which 10 are new discoveries. The X-ray data and optical spectra of these AGNs are given. We also study the near-IR properties of the X-ray-selected AGNs by using the data from 2MASS. Most of the AGNs in our sample span the color range 0.0〈B-J〈2.5,1.0〈 J-Ks 〈2.0 and 0.5〈H-Ks〈1.2.     

Solar flares： radio and X-ray signatures of magnetic reconnection processes

This review summarizes new trends in studies of magnetic reconnection in solar flares. It is shown that plasmoids play a very important role in this primary flare process. Using the results of magnetohydrodynamic and particle-in-cell simulations, we describe how the plasmoids are formed, how they move and interact, and how a flare current sheet is fragmented into a cascade of plasmoids. Furthermore, it is shown that during the interactions of these plasmoids electrons are not only very efficiently accelerated and heated, but electromagnetic（radio） emission is also produced.We also describe possible mechanisms for the triggering of magnetic reconnection.The relevant X-ray and radio signatures of these processes（such as radio drifting pulsation structures, narrowband dm-spikes, and the loop-top and above-the-loop-top X-ray sources） are then described. It is shown that plasmoids can also be formed in kinked magnetic ropes. A mapping of X-points of the magnetic reconnection on the chromosphere（as e.g. a splitting of flare ribbons） is mentioned. Supporting EUV and white-light observations of plasmoids are added. The significance of all these processes for the fast magnetic reconnection and electron acceleration is outlined. Their role in fusion experiments is briefly mentioned.