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1.
LS 5039 is a well-known γ-ray binary system which consists of an unknown compact object and a massive companion O star. It shows rather stable emissions at high energies over years and hence serves as an ideal laboratory to investigate the emission mechanism for such peculiar systems which emit prominent γ-rays. To this end, we take the orbital phase resolved energy spectrum as observed by Fermi-LAT over 10 years. We divide the orbit into four orbital phases, each with an orbital phase range of 0.25,centered at 0.00, 0.25, 0.50 and 0.75 respectively, where the phase 0.0 is the periastron and phase 0.5 is the apastron. The phases around 0.25 and 0.75 are symmetric and hence are supposed to have identical local acceleration environment. The spectral analysis shows that the Fermi-LAT spectra are largely different from these two symmetric orbital phases: the emission from orbital phase 0.25 turns out to be significantly stronger than that from 0.75. This result does not fit a scenario that γ-rays are Doppler boosted emission from bow shock tails if LS 5039 has a shock configuration similar to PSR B1259-63, and indicates that the inverse Compton scatterings between the shock accelerated plasma and the stellar particle environment is the underline procedure. We also find that the previous report for a disappearance of the orbital modulation at 3–20 GeV is due to the similar spectral turn-over energies of the different orbital phases. The spectral properties of periastron and apastron regions are addressed in the context of the measurements in phase regions around 0.25 and 0.75.  相似文献   

2.
The ejection of energetic electrons and protons,and γ-ray burst are revealed by solar space observations,which have confirmed some related theories of solar radio emission and uncovered the nuclear reaction in flares.The difference and relationship between CME and plasma cloud in flares are shown by space observations.The hot and cold regions of flares are known.The theory of nonlinear magnetohydrodynamics is developed by solar and heliospheric magnetic field observations.  相似文献   

3.
We conducted photometric and spectroscopic observations of Ross 15 in order to further study the flare properties of this less observed flare star.A total of 28 B-band flares are detected in 128 hr of photometric observations,leading to a total flare rate of 0.22-0.040.04 h-1,more accurate than that provided by previous work.We give the energy range of the B-band flare(1029.5-1031.5 erg) and the flare frequency distribution(FFD) for the star.Within the same energy range,the FFD is lower than that of GJ 1243(M4)and YZ CMi(M4.5),roughly in the middle of those of three M5-type stars and higher than the average FFDs of spectral types> M6.We performed,for the first time for Ross 15,simultaneous high-cadence spectroscopic and photometric observations,resulting in detection of the most energetic flare in our sample.The intensity enhancements of the continuum and Balmer lines with significant correlations between them are detected during the flare,which is the same as those of other deeply studied flare stars with similar spectral type.  相似文献   

4.
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.  相似文献   

5.
We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa(P_(orb) ≈0.48 d). In two Chandra ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly( 0.125 P_(orb)) after a primary eclipse, and the other two happening shortly( 0.05 P_(orb)) before a primary eclipse. Two flares occurred within roughly one orbital period(?φ≈1.024 P_(orb)) of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales during both quiescence and flares, as well as the timing of the flares. We explore the possibility that the flares are orbit-induced by introducing a small orbital eccentricity, which is quite challenging for this close binary.  相似文献   

6.
Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The majority of identified extragalactic sources in γ-ray catalogs of EGRET and Fermi are blazars. Observationally,blazars can be divided into two classes: flat spectrum radio quasars(FSRQs) and BL Lacs. BL Lacs usually exhibit lower γ-ray luminosity and harder power law spectra at γ-ray energies than FSRQs. We attempt to explain the high energy properties of FSRQs and BL Lacs from Fermi γ-ray space telescope observations. It was argued previously that the difference in accretion rates is mainly responsible for the large mismatch in observed luminosity in γ-ray. However, when intrinsic luminosities are derived by correcting for beaming effects, this difference in γ-ray luminosity between the two classes is significantly reduced. In order to explain this difference in intrinsic luminosities, we propose that spin plays an important role in the luminosity distribution dichotomy of BL Lacs and FSRQs. As the outflow power of a blazar increases with increasing spin of a central black hole, we suggest that the spin plays a crucial role in making BL Lac sources low luminous and slow rotators compared to FSRQ sources.  相似文献   

7.
The curvature of the γ-ray spectrum in blazars may reflect the intrinsic distribution of emitting electrons, which will further give some information on the possible acceleration and cooling processes in the emitting region. The γ-ray spectra of Fermi blazars are normally fitted either by a single power-law(PL) or a log-normal(call Logarithmic Parabola, LP) form. The possible reason for this difference is not clear. We statistically explore this issue based on the different observational properties of 1419 Fermi blazars in the 3 LAC Clean Sample. We find that the γ-ray flux(100 Me V–100 Ge V) and variability index follow bimodal distributions for PL and LP blazars, where the γ-ray flux and variability index show a positive correlation. However, the distributions of γ-ray luminosity and redshift follow a unimodal distribution. Our results suggest that the bimodal distribution of γ-ray fluxes for LP and PL blazars may not be intrinsic and all blazars may have an intrinsically curved γ-ray spectrum, and the PL spectrum is just caused by the fitting effect due to less photons.  相似文献   

8.
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.  相似文献   

9.
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.  相似文献   

10.
Stellar flare is one of the most challenging problems in Astrophysics. Up to now, most of the detected flare stars are of the late spectral type (e.g. UV Ceti type stars etc.). The non-classical flare stars with early spectral type are very rare, In 1975, Kunkel collected a few possible early type flare stars in his review paper, all of which had emission line spectra (W.E.Kunkal, 1975). They are many orders of magnitude more powerful than dMe flares. The nature of this kind of flare stars are unknown.Recently, a later A-type flare star BD 47 819, near the open cluster a Persei, was discovered by Jun-jie Wang. The V magnitude of the star was 9.25, ans B-V = 0.413(Prosser, 1992). Its spectral type was A7 in CSI catalog of Strasbourg (1979), and A5 in Fehrenbach's list(Fehrenbach, 1987).BD 47 819 will be taken a special interest to be recgnized, not only for lack of knowledge on the nature of all the early type flare stars, but also as it is a peculiar A-5 type variable with flare activity. From its spect  相似文献   

11.
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.  相似文献   

12.
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  相似文献   

13.
We collect 119 v-ray-loud blazars (97 flat spectrum radio quasars (FSRQs) and 22 BL Lacertae objects (BL Lacs)), and investigate possible correlations between their γ-ray emission (maximum, minimum and average values) at 1 GeV and the radio emission at 8.4 GHz. Our main results are as follows. For the lower state γ-ray data, there is no correlation between the γ-ray and radio flux density; For the high state γ-ray data, there are good correlations for the whole 119 blazars and 97 FSRQs, and a weak correlation for the 22 BL Lac objects; For the average γ-ray data, there are good correlations. According to our analysis, we propose that the γ-rays are associated with the radio emission from the jet, and that the γ-ray emission is likely from the SSC process in this case.  相似文献   

14.
We suggest a short-lived supermassive magnetar model to account for the X-ray flares following shortγ-ray bursts. In this model the central engine of the shortγ-ray bursts is a supermassive millisecond magnetar, formed in coalescence of double neutron stars. The X-ray flares are powered by the dipole radiation of the magnetar. When the magnetar has lost a significant part of its angular momentum, it collapses to a black hole and the X-ray flares cease abruptly.  相似文献   

15.
The DArk Matter Particle Explorer(DAMPE),also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at～10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.  相似文献   

16.
The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk.The first major flare(of class X2.2) of the current solar cycle occurred in this active region on 2011 February 15 around 01:50 UT.We have analyzed the Dopplergrams and magnetograms obtained by the Helioseismic and Magnetic Imager(HMI) instrument onboard Solar Dynamics Observatory to examine the photospheric velocity and magnetic field changes associated with this flare.The HMI instrument provides high-quality Doppler and magnetic maps of the solar disk with 0.5 spatial scale at a cadence of 45 s along with imaging spectroscopy.We have identified five locations of velocity transients in the active region during the flare.These transient velocity signals are located in and around the flare ribbons as observed by Hinode in the Ca II H wavelength and the footpoints of hard X-ray enhancement are in the energy range 12–25 keV from RHESSI.The changes in shape and width of two circular polarization states have been observed at the time of transients in three out of five locations.Forward modeling of the line profiles shows that the change in atmospheric parameters such as magnetic field strength,Doppler velocity and source function could explain the observed changes in the line profiles with respect to the pre-flare condition.  相似文献   

17.
We report multi-wavelength observations of four solar flares on 2014 July 07.We firstly select these flares according to the soft X-ray(SXR)and extreme ultraviolet(EUV)emissions recorded by the Extreme Ultraviolet Variability Experiment and Geostationary Orbiting Environmental S atellites.Then their locations and geometries are identified from the full-disk images measured by the Atmospheric Imaging Assembly(AIA),and the time delays among the light curves in different channels are identified.The electron number densities are estimated using the differential emission measure method.We find that three of four flares show strong emissions in SXR channels and high temperature(>6 MK)EUV wavelengths during the impulsive phase,i.e.,AIA 131 A and 94 A,and then they emit peak radiation subsequently in the middle temperature(~0.6-3 MK)EUV channels.Moreover,they last for a long time and have smaller electron densities,which are probably driven by the interaction of hot diffuse flare loops.Only one flare emits radiation at almost the same time in all the observed wavelengths,lasts for a relatively short time,and has a larger electron density.It is also accompanied by a typeⅢradio burst.The bright emission at the EUV channel could be corresponding to the associated erupting filament.  相似文献   

18.
Flare-induced signals in polarization measurements which were manifested as apparent polarity reversal in magnetograms have been reported since 1981. We are motivated to further quantify the phenomenon by asking two questions： can we distinguish the flare-induced signals from real magnetic changes during flares, and what we can learn about flare energy release from the flare-induced signals？ We select the X2.6 flare that occurred on 2005 January 15, for further study. The flare took place in NOAA active region （AR） 10720 at approximately the central meridian, which makes the interpretation of the vector magnetograms less ambiguous. We have identified that flare-induced signals during this flare appeared in six zones. The zones are located within an average distance of 5 Mm from their weight center to the main magnetic neutral line, have an average size of （0.6±0.4） ×10^17 cm^2, duration of 13±4 min, and flux density change of 181±125 G in the area of reversed polarity. The following new facts have been revealed by this study： （1） the flare-induced signal is also seen in the transverse magnetograms but with smaller magnitude, e.g., about 50 G; （2） the flare-induced signal mainly manifests itself as apparent polarity reversal, but the signal starts and ends as a weakening of flux density; （3） The flare-induced signals appear in phase with the peaks of hard X-ray emission as observed by the Ramaty High Energy Solar Spectroscopic Imager （RHESSI）, and mostly trace the position of RHESSI hard X-ray footpoint sources. （4） in four zones, it takes place cotemporally with real magnetic changes which persist after the flare. Only for the other two zones does the flux density recover to the pre-flare level immediately after the flare. The physical implications of the flare-induced signal are discussed in view of its relevance to the non-thermal electron precipitation and primary energy release in the flare.  相似文献   

19.
On 2002 July23,a 2B/X4.8 flare was observed in the Hα line spec-tropolarimetrically by the Large Solar Vacuum Telescope of Baikal Astrophysical Observatory.Linear polarization of 3%-10% was detected in the Hα line,particu-larly where the line showed central reversal.The linear polarization is mainly radial on the solar disk and appears at the impulsive phase of the hard X-ray and γ-ray bursts.It is limited to some relatively small regions of the flare.The polarization in a limited small region(～4″-5″）changed its direction within a short period of time(～10s).  相似文献   

20.
Efforts are made to understand the timing behaviors (e.g., the jumps in the projected pulsar semimajor axis at the periastron passages) observed in the 13-year monitoring of PSR B1259-63. Planet-like objects are suggested to orbit around the Be star, which may gravitationally perturb the (probably low mass) pulsar when it passes through periastron. An accretion disk should exist outside the pulsar's light cylinder, which creates a spindown torque on the pulsar due to the propeller effect. The observed negative braking index and the discrepant timing residuals close to periastron could be related to the existence of a disk with a varying accretion rate. A speculation is presented that the accretion rate may increase on a long timescale in order to explain the negative braking index.  相似文献   

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