共查询到20条相似文献，搜索用时 15 毫秒
1.
Shao Ming Hu J. H. Wu G. Zhao X. Zhou 《Monthly notices of the Royal Astronomical Society》2006,373(1):209-216
The aim of our observations is to investigate the intranight variability properties and the spectral variability of BL Lacertae. 799 optical multiband observations were intensively made with the Beijing–Arizona–Taiwan–Connecticut (BATC) 60/90 cm Schmidt telescope during the outburst composed of two subsequent flares in 2005. The second flare, whose rising phase lasted at least 44 d, was observed with amplitudes of more than 1.1 mag in three BATC optical bands. In general, on intranight time-scale the amplitude of variability and the variation rate are larger at the shorter wavelength, and the variation rate is comparable in the rising and decaying phases within each band. A possible time-lag between the light curves in bands e and m , around 11.6 min, was obtained. Based on the analysis of the colour index variation with the source brightness, the variability of BL Lacertae can be interpreted as having two components: a 'strongly chromatic' intranight component and a 'mildly chromatic' internight component, which may be the results of both intrinsic physical mechanism and geometric effects. 相似文献
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E. Massaro R. Nesci M. Maesano F. Montagni & F. D'Alessio 《Monthly notices of the Royal Astronomical Society》1998,299(1):47-50
We present the results of photometric observations of BL Lacertae at 1 μm performed during the strong outburst that occurred in the summer of 1997. Measurements were carried out using the F99 filter of the Arizona system. Simultaneous observations in the B V bands were made with other telescopes. Large and fast variations were observed on the night of August 2 when the brightness of BL Lacertae changed by ∼ 0.5 mag in about 2 h: the variation amplitude is greater at higher frequency. Some implications of these results for the origin of the fast variations are discussed. We also report the first F99 calibration for three reference stars in the BL Lac field. 相似文献
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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
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B. Z. Dai X. H. Li Z. M. Liu B. K. Zhang W. W. Na Y. F. Wu J. M. Hao Y. Xiang Z. J. Jiang L. Zhang 《Monthly notices of the Royal Astronomical Society》2009,392(3):1181-1192
The long baseline simultaneous multiband ( BVRI ) observations of blazar 3C 273 are presented. We have made 758 optical multiband observations with the Yunnan Astronomical Observatory (YAO) 103 cm and Shanghai Astronomical Observatory (SHAO) 156 cm from 2003 January to 2005 April. In our observational campaign, the average colour indices are B − V = 0.21, V − R = 0.26 and R − I = 0.31 . The mean magnitudes in B, V, R and I are 12.895, 12.698, 12.441 and 12.139, respectively. The source is in a steady state over observational campaign. The correlations between colour index and brightness are discussed. We find that the correlations of B − V versus B , V − R versus V and R − I versus R have significant negative correlation, while B − V versus V , V − R versus R and R − I versus I have positive correlation. These strong correlations imply that the spectrum becomes bluer (flatter) when the source becomes brighter, and redden (softer) when the source fades both in intraday and long-term variability. The spectral evolution trends of 3C 273 are consistent with those of BL Lac objects. 相似文献
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C. Reynolds T.V. Cawthorne D.C. Gabuzda 《Monthly notices of the Royal Astronomical Society》2001,327(4):1071-1080
External Faraday rotation has been detected in both the core and the parsec-scale jet of BL Lac in a four-frequency very long baseline interferometry (VLBI) experiment. This unexpected result indicates the presence of significant amounts of thermal gas close to the nucleus of this object. The rotation measure (RM) in the jet components is constant, and differs from the currently accepted Galactic RM, indicating that this value (−205 rad m−2 ) is not applicable to the components in the parsec-scale jet. The similarity of the RM in these jet components leads us to suspect that the jet RM is caused by a foreground screen in our Galaxy, although we cannot rule out a combination of Galactic RM and RM local to the jet. If the jet RM is due solely to the Galaxy, this would mean that the currently accepted value of the foreground RM (−205 rad m−2 ) is not correct, either because the value changed between 1982 and 1997, or because the assumption of no intrinsic source rotation was incorrect, as it was at our later epoch of observation. Our observations suggest a value of .
After correcting for the foreground RM, the core value is −427 rad m−2 , which is unexpected since, owing to the weakness of their line emission, BL Lac objects are often assumed to be depleted in gas. The core RM appears to be variable, probably because of the presence of at least two polarized components close to the core the relative contributions of which vary with time. 相似文献
After correcting for the foreground RM, the core value is −427 rad m
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Jun-Hui Fan Yong Huang Yu-Hai Yuan Jiang-He Yang Yi Liu Jun Tao Ying Gao Tong-Xu Hua Rui-Guang Lin Jiang-Shui Zhang Jing-Yi Zhang Yi-Ping Qin 《中国天文和天体物理学报》2009,9(7)
Using the database of the University of Michigan Radio Astronomy Observatory (UMRAO) at three radio frequencies (4.8, 8 and 14.5 GHz), we determined the short-term variability timescales for 166 radio sources. The timescales are 0.15d (2007+777) to 176.17d (0528-250) with an average timescale of △tobs=17.1±16.5d for the whole sample. The timescales are used to calculate the brightness temperatures, TB. The value of log TB is in the range of log TB = 10.47 to 19.06 K. In addition, we also estimated the boosting factor for the sources. The correlation between the polarization and the Doppler factor is also discussed. 相似文献
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《New Astronomy》2015
Well-sampled optical and radio light curves of BL Lacertae in bands and 4.8, 8.0, 14.5 GHz from 1968 to 2014 were presented in this paper. A possible yr period in optical bands and a yr period in radio bands were detected based on discrete correlation function, structure function as well as Jurkevich method. Correlations among different bands were also analyzed and no reliable time delay was found between optical bands. Very weak correlations were detected between V band and radio bands. However, in radio bands the variation at low frequency lagged that at high frequency obviously. The spectrum of BL Lacertae turned mildly bluer when the object turned brighter, and stronger bluer-when-brighter trends were found for short flares. A scenario including a precessing helical jet and periodic shocks was put forward to interpret the variation characteristics of BL Lacertae. 相似文献
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Arti Goyal Gopal-Krishna G. C. Anupama D. K. Sahu R. Sagar S. Britzen M. Karouzos † M. F. Aller H. D. Aller 《Monthly notices of the Royal Astronomical Society》2009,399(3):1622-1632
We present the result of our extensive intranight optical monitoring of the well-known low-energy peaked BL Lac (LBL) object PKS 0735+178. This long-term follow-up consists of R -band monitoring for a minimum duration of ∼4 hours, on 17 nights spanning 11 years (1998–2008). Using the CCD as an N-star photometer, a detection limit of around 1 per cent was attained for the intranight optical variability (INOV). Remarkably, an INOV amplitude of ≥3 per cent on hour-like time-scale was not observed on any of the 17 nights, even though the likelihood of a typical LBL showing such INOV levels in a single session of ≳4 hours duration is known to be high (∼50 per cent) . Our observations have thus established a peculiar long-term INOV quiescence of this radio-selected BL Lac object. Moreover, the access to unpublished optical monitoring data of similarly high sensitivity, acquired in another programme, has allowed us to confirm the same anomalous INOV quiescence of this LBL all the way back to 1989, the epoch of its historically largest radio outburst. Here, we present observational evidence revealing the very unusual INOV behaviour of this classical BL Lac object and discuss this briefly in the context of its other known exceptional properties. 相似文献
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Jun-Hui Fan Jun Tao Bo-Chen Qian Yi Liu Jiang-He Yang Fei-Peng Pi Wei Xu Center for Astrophysics Guangzhou University Guangzhou China Astronomy Science Technology Research Laboratory of 《中国天文和天体物理学报》2011,(11)
S5 0716+714 is one of the targets in our long term blazar monitoring program carried out with the 1.56-m telescope at Sheshan Station of Shanghai Astronomical Observatory,China.We report a very rapid variability of ΔI = 0.611 ± 0.102 mag over 3.6 min detected in our monitoring program during the period from December 2000 to March 2007.The rapid variability suggests that the mass for the central black hole is log(M/M) = 7.68 8.38. 相似文献
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Invisible plasma content in blazar jets such as protons and/or thermal electron–positron ( e ± ) pairs is explored through combined arguments of dynamical and radiative processes. By comparing physical quantities required by the internal shock model with those obtained through the observed broad-band spectra for Mrk 421, we obtain that the ratio of the Lorentz factors of a pair of cold shells resides in about 2 ∼ 20, which implies that the shocks are at most mildly relativistic. Using the obtained Lorentz factors, the total mass density ρ in the shocked shells is investigated. The upper limit of ρ is obtained from the condition that thermal bremsstrahlung emission should not exceed the observed γ-ray luminosity, whilst the lower limit is constrained from the condition that the energy density of non-thermal electrons is smaller than that of the total plasma. Then, we find ρ is 102 –103 times heavier than that of non-thermal electrons for pure e ± pairs, while 102 –106 times heavier for pure electron–proton ( e / p ) content, implying the existence of a large amount of invisible plasma. The origin of the continuous blazar sequence is briefly discussed and we speculate that the total mass density and/or the blending ratio of e ± pairs and e / p plasma could be new key quantities for the origin of the sequence. 相似文献
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E. A. Corbett A. Robinson D. J. Axon J. H. Hough 《Monthly notices of the Royal Astronomical Society》2000,311(3):485-492
We present a series of new spectroscopic observations of BL Lacertae. The observations were obtained over a period of 30 months and sample the violent continuum flare of 1997 June–August. The equivalent width of the recently discovered broad H α line varies approximately inversely with the optical continuum flux, implying that the broad-line-emitting gas does not respond significantly to large variations in the beamed synchrotron continuum which dominates the spectrum at optical wavelengths. The simplest and most plausible interpretation of this result is that the broad-line region in BL Lacertae is 'unaware' of the synchrotron beam and is photoionized by another source, a likely candidate being a hot accretion disc. Alternatively, similar behaviour would be observed if the broad-line region is indeed photoionized by the synchrotron beam but is predominantly matter-bounded so that it absorbs only a small fraction of the incident ionizing photon flux. 相似文献
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Guang-Zhong Xie Ben-Zhong Dai En-Wei Liang Zhao-Hua Xie Yunnan Astronomical Observatory Chinese Academy of Science Kunming National Astronomical Observatories Chinese Academy of Sciences Beijing Yunnan Astrophysics Center Yu 《中国天文和天体物理学报》2001,1(6):494-500
1 INTaoDUCTIONMany blazar-boe active galedes have recelltly been detected in MeVGeV 7-ray energyrange by detectors on board the Compton Ganuna-Ray Obsewtory (Von Mootigny et al. 1995;Hartman et al. 1999). More recently, TeV ends8ion is obsemd in some object8, such as Mrk421 (z = 0.031, Punch et al. l992), Mrk 501 (z = 0.034, Qbo et al. 1996), 1ES 2344 514(z == 0.044, Catanese et al. 1998), PKS 2155304 (z = 0.117, Chadwick et al. 1999), and1ES 1959 650 (z = 0.048, NisWa 1999). Th… 相似文献