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1.
We calculate the spectral energy distribution (SED) of electromagnetic radiation and the spectrum of high-energy neutrinos from BL Lac objects in the context of the synchrotron proton blazar model. In this model, the high-energy hump of the SED is due to accelerated protons, while most of the low-energy hump is due to synchrotron radiation by co-accelerated electrons. To accelerate protons to sufficiently high energies to produce the high-energy hump, rather high magnetic fields are required. Assuming reasonable emission region volumes and Doppler factors, we then find that in low-frequency peaked BL Lacs (LBLs), which have higher luminosities than high-frequency peaked BL Lacs (HBLs), there is a significant contribution to the high-frequency hump of the SED from pion photoproduction and subsequent cascading, including synchrotron radiation by muons. In contrast, in HBLs we find that the high-frequency hump of the SED is dominated by proton synchrotron radiation. We are able to model the SED of typical LBLs and HBLs, and to model the famous 1997 flare of Markarian 501. We also calculate the expected neutrino output of typical BL Lac objects, and estimate the diffuse neutrino intensity due to all BL Lacs. Because pion photoproduction is inefficient in HBLs, as protons lose energy predominantly by synchrotron radiation, the contribution of LBLs dominates the diffuse neutrino intensity. We suggest that nearby LBLs may well be observable with future high-sensitivity TeV γ-ray telescopes.  相似文献   

2.
L.S. Mao 《New Astronomy》2011,16(8):503-529
In this paper, we have searched for the Two Micron All Sky Survey (2MASS) counterparts of 1434 BL Lacs. Eight hundred and thirty-three of 1434 BL Lacs (～58%) have spatially coincident 2MASS counterparts. Fermi-detected BL Lacs (FBLs) have a much higher 2MASS detection rate than non-Fermi-detected BL Lacs (non-FBLs) (～95% vs 49%). We compare the near-infrared (NIR) apparent magnitudes, monochromatic luminosities and spectral indices of different subclasses of BL Lacs: (i) FBLs are significantly brighter and more luminous than non-FBLs; (ii) low-energy peaked BL Lacs (LBLs) are significantly more luminous than high-energy peaked BL Lacs (HBLs); (iii) the NIR spectral index, αIR, shows a sequence of decrease from LBLs to intermediate-energy peaked BL Lacs (IBLs) then to HBLs. The KS band luminosity and NIR spectral index are both strongly anti-correlated with the synchrotron peak frequency (νpeak). About 66% of BL Lacs in our sample are located close to the power law line in the J-H–H-KS diagram, which implies predominantly non-thermal radiation in the NIR range. We label 218 BL Lacs whose NIR spectra show convex curvatures probably due to the significant contaminations of host-galaxy starlight. Finally we investigate the correlation between NIR and gamma-ray emission using the 2MASS observational data.  相似文献   

3.
从Fermi 3期源表(3FGL)中选择了一个含935个耀变体(blazar)的样本, 包括415个平谱射电源(Flat Spectrum Radio Quasar, FSRQ), 520个蝎虎天体(BL Lac object, BL Lac), 其中高同步峰BL Lac (HBL) 233个, 中同步峰BL Lac (IBL) 144个, 低同步峰BL Lac (LBL) 143个. 研究了总样本、FSRQ、BL Lac及其子类HBL、LBL的射电1.4GHz 与gamma射线在0.1、0.3、1、3、10GeV处辐射流量密度的关系. 结果显示: 所有样本的射电1.4GHz与5个波段gamma射线的辐射流量都有强相关, 相关系数在0.48--0.81之间, 机会概率均小于$10^{-4; 对于不同的样本相关系数随着gamma射线辐射频率的变化有不同的变化趋势, 所有样本在5个波段的相关系数平均值随gamma射线频率的增加而减小. 该结果暗示, 随着频率的升高, blazar的gamma射线辐射主导机制在发生变化, 在相同频率处, 不同类型天体的辐射主导机制存在差异; HBL的gamma射线辐射主要由同步自康普顿主导, 而LBL的其他成份比HBL的更复杂; FSRQ的gamma射线起源较BL Lac的复杂.  相似文献   

4.
Blazar 的X射线谱性质   总被引：1，自引：0，他引：1  
从Donato文献中选择了一个含有69个Blazar的样本，样本中每个源有多个X射线辐射流量数据，用该样本研究了流量密度和谱指数之间的关系，以及研究了三类源（HBL，LBL，FSRQ）的红移和谱指数的分布。结果表明：对于HBLs，谱指数和流量密度之间有一个较好的反相关关系存在，而对于LBLs和FSRQs却没有相关。因此认为HBL的X射线是同步辐射所致，而LBL和FSRQ的X射线辐射较为复杂可能是同步自康普顿过程导致。HBL显示软X射线谱，而FSRQ显示硬X射线谱，LBL居中。在谱图中HBL位于近端，rSRQ位于远端，LBL居中。  相似文献   

5.
Many quasi-simultaneous optical observations of nine BL Lac objects are obtained from literature. We study the relationship between the optical spectral index and the luminosity of BL Lac objects, and are tempted to exploit spectral evolution in the optical frequency ranges. Our results show that: (i) The optical spectra index of the low-frequency peaked BL Lac objects (LBLs) is steeper than the high-frequency peaked BL Lac objects (HBLs); (ii) The spectra tend to be softer when the source becomes brighter for LBLs and the intermediate BL Lac objects (IBLs) (i.e., bluer-when-brighter), and the spectra of HBLs does not vary when the brightness of HBLs changes. Possible explanations are briefly discussed for this phenomenon.  相似文献   

6.
Making use of the 2MASS Data Release, we have searched for near-infrared (JHK) counterparts to 268 blazars from Donato et al. and obtained 238 counterparts within 5" in the area covered by 2MASS. It provides us a sample with infrared data several times larger than the previous one of the same kind. Based on our sample and the sample by Donato et al., we have compared in detail the properties of HBLs, LBLs and FSRQs from five aspects and found that HBLs are significantly different from LBLs and FSRQs while LBLs are not obviously different from FSRQs. Our results strongly support the division of BL Lac objects into the high-frequency peaked (HBL) and low-frequency peaked (LBL) objects introduced by Padovani & Giommi and show that HBLs and LBLs are two kinds of blazar having different physical properties.  相似文献   

7.
1 INTRODUCTIONBlazars, including BL Lacertae objects and Optical Violently Variable (OVV) quasars,belong to a class of active ga1actic nuclei (AGNs), the spectrum of which is dominated bynontherma1 radiation from re1ativistic electrons in jets pointing at us (e.g. BlandfOrd & Rees1978; Urry & Padovani 1995). The entire electromagnetic spectraI energy distributions (SEDs)usually reveal two broad components, the low energy part, peaking in the IR to soft X-rayrange, and the high en…  相似文献   

8.
We present the Wide-field Infrared Survey Explorer (WISE) photometric data of 158 Fermi-detected BL Lacs and investigate the nature of their mid-infrared (MIR) continuum emission. In the [3.4]-[4.6]-[12] μm color–color diagram, nearly all their colors lie within the WISE Blazar strip (WBS), which is an effective diagnostic tool to separate sources dominated by non-thermal radiation from those dominated by thermal radiation. This feature indicates that their MIR emission is predominantly non-thermal. This argument is further supported by the strong radio-MIR flux correlation. We derive their MIR spectral indices and compare them with the near-infrared (NIR) spectral indices. We find that there is a prevalent steepening from MIR spectrum to NIR spectrum. The low-frequency-peaked BL Lacs (LBLs) have on average a larger MIR spectral index and a higher MIR luminosity than the high-frequency-peaked BL Lacs (HBLs), and the intermediate-frequency-peaked BL Lacs (IBLs) appear to bridge them. The MIR-γ-ray flux correlation is highly significant. A strong positive correlation is also found between the MIR and γ-ray spectral indices. The γ-ray-MIR loudness is significantly correlated with the synchrotron peak frequency. Finally we propose that the γ-rays are highly associated with the MIR emission from the jet, and the γ-ray emission is likely from the synchrotron self-Compton process for the Fermi-detected BL Lacs in our sample.  相似文献   

9.
We present new BeppoSAX observations of seven BL Lacertae objects selected from the 1-Jy sample plus one additional source. The collected data cover the energy range     (observer's frame), reaching ∼50 keV for one source (BL Lac). All sources characterized by a peak in their multifrequency spectra at infrared/optical energies (i.e., of the low-energy peaked BL Lac type, LBL) display a relatively flat     X-ray spectrum, which we interpret as inverse Compton emission. Four objects (two-thirds of the LBLs) show some evidence for a low-energy steepening, which is probably due to the synchrotron tail merging into the inverse Compton component around ∼     . If this were generally the case with LBLs, it would explain why the     ROSAT spectra of our sources are systematically steeper than the BeppoSAX ones     . The broad-band spectral energy distributions fully confirm this picture, and a synchrotron inverse Compton model allows us to derive the physical parameters (intrinsic power, magnetic field, etc.) of our sources. Combining our results with those obtained by BeppoSAX on BL Lacs covering a wide range of synchrotron peak frequency, ν peak, we confirm and clarify the dependence of the X-ray spectral index on ν peak originally found in ROSAT data.  相似文献   

10.
We present a large sample which includes 82 BL Lac objects with redshifts below 0.2 from recent literature. We find strong correlations in both flux and luminosity between the radio (5 GHz) and optical bands (5500 A). The correlations in other bands are very weak. Five TeV BL Lacs and two suspect sources are found to have similar properties as high-frequency-peaked BL Lacs (HBLs). Our results suggest that both the radio and optical emissions are from the same radiation mech anism in the SSC model. The TeV BL Lac candidates should be HBLs or HBL-like objects with small redshifts.  相似文献   

11.
Observations at millimetre wavelengths are presented for a representative sample of 22 X-ray-selected BL Lac objects (XBLs). This sample comprises 19 high-energy cut-off BL Lac objects (HBLs), 1 low-energy cut-off BL Lac object (LBL) and 2 'intermediate' sources. Data for LBLs, which are mostly radio-selected BL Lac objects (RBLs), are taken from the literature. It is shown that the radio–millimetre spectral indices of HBLs     are slightly steeper than those of the LBLs     . A correlation exists between α 5–230 and 230 GHz luminosity. While this correlation could be an artefact of comparing two populations of BL Lac objects with intrinsically different radio properties, it is also consistent with the predictions of existing unified schemes that relate BL Lac objects to Fanaroff–Riley class I radio galaxies.
The HBLs have significantly flatter submillimetre–X-ray spectral indices     than the LBLs     although the two intermediate sources also have intermediate values of α 230–X∼−0.9. It is argued that this difference cannot be explained entirely by the viewing-angle hypothesis and requires a difference in physical-source parameters. The α 230–X values for the HBLs are close to the canonical value found for large samples of radio sources and thus suggest that synchrotron radiation is the mechanism that produces the X-ray emission. As suggested by Padovani & Giommi, the inverse-Compton mechanism is likely to dominate in the LBLs requiring the synchrotron spectra of these sources to steepen or cut off at lower frequencies than those of the HBLs.  相似文献   

12.
Many quasi-simultaneous optical observations of 17 blazars are obtained from previous papers published over the last 19 years in order to investigate the spectral slope variability and understand the radiation mechanism of blazars. The long-period dereddened optical spectral slopes are calculated. We analyse the average spectral slope distribution, which suggests that the spectra of flat spectrum radio quasars (FSRQs) and high energy peaked BL Lac objects (HBLs) are probably deformed by other emission components. The average spectral slopes of low energy peaked BL Lac objects(LBLs), which scatter around 1.5, show a good accordance with the synchrotron self-Compton (SSC) loss-dominated model. We present and discuss the variability between the spectral slope and optical luminosity. The spectra of all HBLs and LBLs get flatter when they turn brighter, while for FSRQs this trend does not exist or may even be reversed. This phenomenon may imply that there is a thermal contribution to the optical spectrum for FSRQs. For the FSRQ 1156+295, there is a hint that the slope gets flatter at both the brightest and faintest states. Our result shows that three subclasses locate in different regions in the pattern of slope variability indicator versus average spectral slope. The relativistic jet mechanism is supported by the significant correlation between the optical Doppler factor and the average spectral slope.  相似文献   

13.
Using γ-ray data (α γ , F γ ) detected by Fermi Large Area Telescope (LAT) and black hole mass which has been compiled from literatures for 116 Fermi blazars, we calculated intrinsic γ-ray luminosity, intrinsic bolometric luminosity, intrinsic Eddington ratio and studied the relationships between all above parameters and redshift, between α γ and L γ . Furthermore, we obtained the histograms of key parameters. Our results are the following: (1) The main reason for the evolutionary sequence of three subclasses (HBLs, LBLs, FSRQs) may be Eddington ratio rather than black hole mass; (2) FSRQs occupy in the earlier, high-luminosity, high Eddington ratio, violent phase of the galactic evolution sequence, while BL Lac objects occur in the low luminosity, low Eddington ratio, late phase of the galactic evolution sequence; (3) These results imply that the evolutionary track of Fermi blazars is FSRQs ? LBLs ? HBLs.  相似文献   

14.
We studied mid-infrared (MIR) variability of a large sample of blazars detected by LAT/Fermi (called Fermi-detected blazars) and those not detected by LAT/Fermi (called non-Fermi-detected blazars) in order to investigate any difference in the variability characteristics between them as well as between FSRQs and BL Lacs. Making use of NEOWISE archival data from October 2013 to December 2017, we constructed the long-term 3.4 μm and 4.6 μm light curves of 2,573 blazars and computed their intrinsic variability amplitudes, \(\varPsi \). As a result, we found that (1) Fermi-detected blazars show higher \(\varPsi \) than non-Fermi-detected blazars; (2) Fermi-detected FSRQs show higher \(\varPsi \) than non-Fermi-detected FSRQs; (3) Fermi-detected BL Lacs show higher \(\varPsi \) than non-Fermi-detected BL Lacs; (4) FSRQs show higher \(\varPsi \) than BL Lacs. By comparing their distributions of “\(\mathit{var}\_\mathit{flg}\)” in the ALLWISE database, we also found that Fermi-detected blazars/FSRQs/BL Lacs tend to be more variable than non-Fermi-detected blazars/FSRQs/BL Lacs. For the Fermi-detected blazars, there are highly significant correlations between the flux densities and spectral indices in the MIR and gamma-ray bands. These results imply that the activity in the two bands is connected. Our results are consistent with several earlier results on the differences between Fermi-detected blazars and non-Fermi-detected blazars. We also give some possible explanations about the statistical results.  相似文献   

15.
The X-ray emissions of blazars are located at the end of synchrotron radiation and the beginning of inverse Compton radiation. Therefore, the origin of the X-ray emissions is rather complex. The spectral energy distributions (SEDs) of blazars from radio to X-ray bands can be fitted approximatively by a parabolic function. If we consider approximately the fitting curves as the physical spectra of blazars to analyze the X-ray emissions of Fermi blazars, the results show that: (1) The X-ray emissions of blazars contain two components, i.e. the synchrotron radiation and inverse Compton radiation, which can be simply separated by these fitting curves; (2) the higher the synchrotron peak frequency of the source, the greater the synchrotron radiation component, and the less the inverse Compton radiation component; (3) at 1 keV of the X-ray waveband, the synchrotron radiation component accounts for 17%, 27%, and 73% of the total X-ray emission, for FSRQs (Flat Spectrum Radio Quasars), LBLs (Low synchrotron peak frequency BL Lac objects), and HBLs (High synchrotron peak frequency BL Lac objects), respectively; (4) there is a strong positive correlation between the synchrotron peak frequency and the synchrotron radiation flux density at 1 keV, while no correlation exists between the synchrotron peak frequency and the inverse Compton radiation flux density; (5) the radiation mechanism of LBLs may be similar to that of FSRQs in the X-ray waveband.  相似文献   

16.
同步+同步自康普顿(Synchrotron+Synchrotron Self Compton (SSC))模型用于拟合蝎虎天体(BL Lac object, BL Lac)准同时性多波段观测数据,可以获得相关的喷流物理参数,从而能对BL Lac天体喷流的物理性质进行解释.在同步自康普顿模型中,较多的自由参数给计算结果带来很大的不确定性,同时,由于这些模型参数范围太大降低了能谱拟合效率.利用多波段观测数据获得的物理量值,对双幂律电子分布情况下的单区、均匀SSC模型中涉及到的8个模型参数进行限定.另外,还利用模型计算两个典型的BL Lac天体多波段能谱对参数限定的结果进行检验.结果表明:在8个模型参数限定的范围内,选取的模型参数值计算出的理论光子谱与两个BL Lac天体的多波段准同时性观测数据符合较好.  相似文献   

17.
The long-term optical and infrared color variability of blazars has been investigated with monitoring data from the Small and Moderate Aperture Research Telescope System(SMARTS). The sample in this study consists of 49 flat spectrum radio quasars(FSRQs) and 22 BL Lacertae objects(BL Lacs). The fractional variability amplitudes of each source have been calculated in both optical R band and infrared J band. Overall, the variability amplitudes of FSRQs are larger than those of BL Lacs. The results also suggest that the variability amplitude of most FSRQs is larger at a lower energy band(J band) than at a higher one(R band), but the variability amplitude of BL Lacs is larger at the higher energy band. Both types of blazars display color variation along with variability in brightness. However, they show different variation behaviors in general. In the whole data set, 35 FSRQs exhibit redder-whenbrighter trends, and 11 FSRQs exhibit opposite trends; 11 BL Lacs follow bluer-whenbrighter trends, and seven BL Lacs follow opposite trends. A detailed examination indicates that there are 10 blazars showing redder-when-brighter trends in their low state, and bluer-when-brighter or stable-when-brighter trends in their high state. Some more complicated color behaviors have also been detected in several blazars. The nonthermal jet emission and the thermal emission from the accretion disk are employed to explain the observed color behaviors.  相似文献   

18.
It is generally believed that the high energy end of synchrotron emission, generated by the most energetic tail of relativistic electrons in the jets, account for the X‐ray emission of high‐energy peaked BL Lac objects (HBLs) and the optical emission of intermediate‐energy peaked BL Lac objects (IBLs). It is thus expected that both should show similar variability characteristics. One of the important variability parameters is the inter‐band time lag which probes the acceleration and cooling of relativistic particles responsible for the emission. The switches between soft and hard lags have been detected in the intra‐day X‐ray variability of a few HBLs, which is not the case for the intra‐day optical variability of IBLs yet. We present the results of our intra‐night optical observations for BL Lacertae, aiming at searching for hard lags of its optical variations, performed with the 80 cm telescope in fourteen nights of 2010 September‐November. Intra‐night changes of ∼0.2 mag were detected in most of nights. The intra‐night variability amplitude tends to become larger from red to blue wavelength, and the optical spectrum hardens with increasing brightness. The intra‐night variations correlate between different wavebands, but we did not find significant time lags, either soft or hard. Nevertheless, on November 2, the B band variations showed a sign of lagging the R band ones by 317±214 s. The claim of this hard lag is strongly limited by the photometric precision and time resolution. Therefore, the switches between soft and hard lags of IBLs in the optical bands needs further demonstration with more higher quality observations. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
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20.
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   

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