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1.
We have collected a sample of 70 BL Lacs (33 radio-selected BL Lacs and 37 X-ray selected BL Lacs) with multi-waveband data for investigating the classifying criteria of BL Lacertae Objects. For each source, we estimate its luminosities in radio, optical and X-ray, the broad-band spectral index from radio to X-ray and the peak frequency of the syn- chrotron emission, and make a statistical analysis of the data obtained. Our main results are as follows: (1) The broad-band spectral index and the peak frequency have no correlation with the redshift, while they are inversely correlated with each other and they could be regarded as equivalent classifying criteria of BL Lac objects. (2) There are significant effects of the luminosity/redshift relation on the observed luminosity distribution in our sample, hence, if the radio luminosity is to be used as a classifying criterion of BL Lac objects, it should not be regarded as equivalent to the broad-band spectral index or the peak frequency. (3) Our re- sults supply a specific piece of evidence for the suggestion that the use of luminosities always introduces a redshift bias to the data and show that the location of the peak frequency is not always linked to the luminosity of any wave band.  相似文献   

2.
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   

3.
A tight correlation between γ-ray and radio emission is found for a sample of BL Lacertae(BL Lac) objects detected by the Fermi Gamma-ray Space Telescope(Fermi) and the Energetic Gamma-Ray Experiment Telescope(EGRET) . The γ-ray emission of BL Lac objects exhibits strong variability,and the detection rate of γ-ray BL Lac objects is low,which may be related to the γ-ray duty cycle of BL Lac objects. We estimate the γ-ray duty cycle,δγ 0.11,for BL Lac objects detected by EGRET and Fermi. Using the empirical r...  相似文献   

4.
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.  相似文献   

5.
Quasars with redshifts greater than 4 are rare, and can be used to probe the structure and evolution of the early universe. Here we report the discovery of six new quasars with i-band magnitudes brighter than 19.5 and redshifts between 2.4 and 4.6 from spectroscopy with the Yunnan Faint Object Spectrograph and Camera (YFOSC) at the Lijiang 2.4 m telescope in February, 2012. These quasars are in the list of z > 3.6 quasar candidates selected by using our proposed J K/i Y criterion and the photometric redshift estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine candidates were observed by YFOSC, and five among six new quasars were identified as z > 3.6 quasars. One of the other three objects was identified as a star and the other two were unidentified due to the lower signal-to-noise ratio of their spectra. This is the first time that z > 4 quasars have been discovered using a telescope in China. Thanks to the Chinese Telescope Access Program (TAP), the redshift of 4.6 for one of these quasars was confirmed by the Multiple Mirror Telescope (MMT) Red Channel spectroscopy. The continuum and emission line properties of these six quasars, as well as their central black hole masses and Eddington ratios, were obtained.  相似文献   

6.
The external Compton(EC) model is used to study the high energy emission of some blazars,in which the external photon field is considered to dominate inverse Compton radiation. We explore the properties of the external photon field through analyzing the FERMI LAT bright AGN sample within three months of the start of operations in sky-survey mode. In the sample,assuming the high energy radiation of low synchrotron peaked blazars is from the EC process,we find that the external photon parameter Uext/νext may ...  相似文献   

7.
In the fourth Fermi Large Area Telescope source catalog(4 FGL),5064γ-ray sources are reported,including 3207 active galactic nuclei(AGNs),239 pulsars,1336 unassociated sources,92 sources with weak association with blazars at low Galactic latitudes and 190 other sources.We employ two different supervised machine learning classifiers,combined with the direct observation parameters given by the 4 FGL fits table,to search for sources potentially classified as AGNs and pulsars in the 1336 unassociated sources.In order to reduce the error caused by the large difference in the sizes of samples,we divide the classification process into two separate steps in order to identify the AGNs and the pulsars.First,we select the identified AGNs from all of the samples,and then select the identified pulsars from the remaining cases.Using the 4 FGL sources associated or identified as AGNs,pulsars and other sources with the features selected through the K-S test and the random forest(RF)feature importance measurement,we trained,optimized and tested our classifier models.Then,the models are applied to classify the 1336 unassociated sources.According to the calculation results of the two classifiers,we report the sensitivity,specificity,accuracy in each step and the class of unassociated sources given by each classifier.The accuracy obtained in the first step is approximately 9595%;in the second step,the obtained overall accuracy is approximately 80%.Combining the results of the two classifiers,we predict that there are 583 AGN-type candidates,115 pulsar-type candidates,154 other types ofγ-ray candidates and 484 of uncertain types.  相似文献   

8.
This paper presents a hadronic dominated jet model to investigate multiwavelength emission from the microquasar LS I + 61 303.In this scenario,we take into account evolutions of the primary particles and secondary e± pairs;these pairs are produced by the collisional interactions of the accelerated protons with the cold jet protons and the stellar wind ions.In this model,the non-thermal photons are produced by π0 decay emission,synchrotron and inverse Compton scattering processes from the primary electrons a...  相似文献   

9.
We present a study of the dwarf elliptical galaxy NGC 855 using the narrow-band Hα and Spitzer data. Both the Hα and Spitzer IRAC images confirm star-forming activity in the center of NGC 855. We obtained a star formation rate (SFR) of 0.022 and 0.025M◎yr-1,respectively,from the Spitzer IRAC 8.0μm and MIPS 24μm emission data. The HI observa-tion suggests that the star-forming activity might be triggered by a minor merger. We also find that there is a distinct IR emission region in 5.8 and 8.0μm bands,located at about 10 away from the nucleus of NGC 855. Given the strong 8.0μm but faint Hα emission,we expect that it is a heavily obscured star-forming region,which needs to be confirmed by further optical spectroscopic observations.  相似文献   

10.
1FGL J1018.6–5856 is a high mass gamma-ray binary containing a compact object orbiting around a massive star with a period of 16.544 d. If the compact object is a pulsar, non-thermal emissions are likely produced by electrons accelerated at the termination shock, and may also originate from the magnetosphere and the un-shocked wind of the pulsar. In this paper, we investigate the non-thermal emissions from the wind and the shock with different viewing geometries and study the multi-wavelength emissions from 1FGL J1018.6–5856. We present the analysis results of the Fermi/LAT using nearly 10 years of data. The phase-resolved spectra indicate that the Ge V emissions comprise a rather steady component that does not vary with orbital motion and a modulated component that shows flux maximum around inferior conjunction. The ke V/Te V light curves of 1FGL J1018.6–5856 also exhibit a sharp peak around inferior conjunction, which are attributed to the boosted emission from the shock, while the broad sinusoidal modulations could be originating from the deflected shock tail at a larger distance. The modulations of Ge V flux are likely caused by the boosted synchrotron emission from the shock and the IC emission from the unshocked pulsar wind, while the steady component comes from the outer gap of the pulsar magnetosphere.Finally, we discuss the similarities and differences of 1FGL J1018.6–5856 with other binaries, like LS 5039.  相似文献   

11.
PMN J0218-2307(4 FGL J0218.9-2305) is classified as a blazar candidate with unknown type(BCU) in the fourth source catalog from the Fermi Large Area Telescope(Fermi-LAT).With the updated Fermi-LAT Pass 8 data,the γ-ray flaring activity toward PMN J0218-2307 is detected.The test statistic(TS) value of PMN J0218-2307 in energy band of 100 MeV-500 GeV is 133.893 with a significance level of 10.96σ.The maximum-likelihood photon flux is(8.131 ± 1.359) × 10~(-9) ph cm~(-2) s~(-1).A significantγ-ray flare in the period from 2008 August 4 to 2019 August 25 is found from the source.The spectral characteristics of GeV energy band of PMN J0218-2307 is similar to that of flat-spectrum radio quasars(FSRQs) in the local Universe.  相似文献   

12.
This paper reports on the statistical behavior of the optical Intraday Variability of BL Lac S5 0716+714. Available Intraday Variability data in the optical are tested to see whether or not the magnitude is lognormally distributed. Our results consistently indicate that this is not the case. This is in agreement with a previous discussion about data for the same object but in a different observational period.Simultaneously, the spectral slope of the light curves is calculated. The implications of these findings on models that describe both the location and source of Intraday Variability are presented.  相似文献   

13.
We present multi-wavelength imagery of the merger remnant galaxy NGC 1316 with an objective to study the dust content and its association with the other phases of the interstellar medium. Color-index maps as well as extinction maps derived for this galaxy reveal an intricate and complex dust morphology in NGC 1316, i.e. there is a prominent lane in the inner part, while at about 6-7 kpc it apparently takes the form of an arc-like pattern extending along the northeast direction. In addition to this, several other dust clumps and knots are also evident in this galaxy. The dust emission mapped using Spitzer data at 8 μm indicates even more complex morphological structures of the dust in NGC 1316. The extinction curve derived over the optical to near-IR bands closely follows the standard Galactic curve, suggesting similar properties of the dust grains. The dust content of NGC 1316, estimated from optical extinction, is ～ 2.13 105M⊙ . This is a lower limit compared to that estimated using the IRAS flux densities of ～5.17×106M⊙ and the flux densities at 24, 70 and 160 μm from MIPS ～3.2×107M⊙ . High resolution Chandra observations of this merger remnant system have provided an unprecedented view of the complex nature exhibited by the distribution of hot gas in NGC 1316, which closely matches the morphology of ionized gas and to some extent also the dust. X-ray color-color plots for the resolved sources within the optical D 25 extent of NGC 1316 have enabled us to separate them into different classes.  相似文献   

14.
We analyze the optical spectrum of type 1 QSO SDSS J1425+3231.This object is interesting since its narrow emission lines,such as O IIIλλ4959,5007,are double-peaked,and the line structure can be modeled well by three Gaussian components:two components for the two peaks (we refer to the peaks at low/high redshift as the blue/red component) and another one for the line wing which has the same line center as that of the blue component,but is ～ 3 times broader.The separation between the blue and red components i...  相似文献   

15.
We select 947 star-forming galaxies from SDSS-DR7 with [O III]λ4363emission lines detected at a signal-to-noise ratio larger than 5σ. Their electron temperatures and direct oxygen abundances are then determined. We compare the results from different methods. t2, the electron temperature in the low ionization region, estimated from t3, that in the high ionization region, is compared using three analysis relations between t2- t3. These show obvious differences, which result in some different ionic oxygen abundances. The results of t3, t2, O++/H+and O+/H+derived by using methods from IRAF and literature are also compared. The ionic abundances O++/H+are higher than O+/H+for most cases. The different oxygen abundances derived from Teand the strong-line ratios show a clear discrepancy, which is more obvious following increasing stellar mass and strong-line ratio R23. The sample of galaxies from SDSS with detected [O III]λ4363 have lower metallicites and higher star formation rates, so they may not be typical representatives of the whole population of galaxies. Adopting data objects from Andrews Martini, Liang et al. and Lee et al. data, we derive new relations of stellar mass and metallicity for star-forming galaxies in a much wider stellar mass range: from 106 M to 1011 M.  相似文献   

16.
The physics behind the spectral energy distribution (SED) of blazars remains open. We assembled 36 blazars to tackle the factors that control their SED. Now, many blazar spec- tra have the "double hump" feature in the radio and far-IR frequencies. For these a parameter, , is created to characterize the behavior of the SED. We found a significant correlation be- tween the broad-line luminosity (LBLR) and . Because LBLR is an indicator of the accreting power of the source in blazars, we derived a linear correlation, ∝ M˙1/3.18, which suggests that the SED of blazars may depend on the accretion rate, like that of BL Lac objects. We also found a significant correlation between ■ and for a sample of 11 blazars (out of one of 36) with available black hole masses. This implies the Eddington accretion ratio may influence the shape of the SED of blazars.  相似文献   

17.
PSR J0742-2822 is known for its quasi-periodic changes in the observed pulse profile and spindown rate.In this paper,we analyzed 13 years of timing data obtained with the Nanshan 25-m radio telescope and the Parkes 64-m radio telescope.We found that the average values of the spin-down rate((v))of this pulsar changed in four different states.We investigated the correlation between v and W50,and ascertained that the correlation changed in different states.Moreover,not all the changes in states and correlation can be associated with glitch activities.We examined the long term evolution ofγ-ray flux(0.1-300 GeV)and the pulse profiles corresponding to the four different states using Fermi-LAT Pass8(P8 R3)data from 2008 August 5 to 2019 October 1.We did not detect a significant change inγ-ray flux or the pulse profile.Our results suggest that the connection between pulsar rotation and emission is more complex than previously reported for this pulsar.  相似文献   

18.
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   

19.
We report our detailed data analysis of 39 γ-ray sources selected from the 992 unassociated sources in the third Fermi Large Area Telescope Third Source Catalog.The selection criteria,which were set for finding candidate millisecond pulsars(MSPs),are non-variables with curved spectra and 5?Galactic latitudes.From our analysis,24 sources were found to be point-like sources not contaminated by background or nearby unknown sources.Three of them,J1544.6-1125,J1625.1-0021 and J1653.6-0158,have been previously studied,indicating that they are likely MSPs.The spectra of J0318.1+0252 and J2053.9+2922 do not have properties similar to known γ-ray MSPs,and we thus suggest that they are not MSPs.Analysis of archival X-ray data for most of the 24 sources was also conducted.Four sources were found with X-ray objects in their error circles,and 16 with no detection.The ratios between the γ-ray fluxes and X-ray fluxes or flux upper limits are generally lower than those of known γ-ray MSPs,suggesting that if the γ-ray sources are MSPs,none of the X-ray objects are their counterparts.Deep X-ray or radio observations of these sources are needed in order to identify their MSP nature.  相似文献   

20.
We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered proto- globular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.  相似文献   

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