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Home -> Astronomy News -> Cosmology News -> BL Lacertae
Post Info TOPIC: BL Lacertae
Blobrana


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2MASS J22024329+4216400
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ATel 9600: Optical Observations of Correlated Outburst Activity in BL Lacertae



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Blobrana


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RE: BL Lacertae
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Distant Black Hole Wave Twists Like Giant Whip

Fast-moving magnetic waves emanating from a distant supermassive black hole undulate like a whip whose handle is being shaken by a giant hand, according to a new study using data from the National Radio Astronomy Observatory's Very Long Baseline Array. Scientists used this instrument to explore the galaxy/black hole system known as BL Lacertae (BL Lac) in high resolution.
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Title: Rapid TeV Gamma-Ray Flaring of BL Lacertae
Authors: T. Arlen, T. Aune, M. Beilicke, W. Benbow, A. Bouvier, J. H. Buckley, V. Bugaev, A. Cesarini, L. Ciupik, M. P. Connolly, W. Cui, R. Dickherber, J. Dumm, M. Errando, A. Falcone, S. Federici, Q. Feng, J. P. Finley, G. Finnegan, L. Fortson, A. Furniss, N. Galante, D. Gall, S. Griffin, J. Grube, G. Gyuk, D. Hanna, J. Holder, T. B. Humensky, P. Kaaret, N. Karlsson, M. Kertzman, Y. Khassen, D. Kieda, H. Krawczynski, F. Krennrich, G. Maier, P. Moriarty, R. Mukherjee, T. Nelson, A. O'Faolain de Bhroithe, R. A. Ong, M. Orr, N. Park, J. S. Perkins, A. Pichel, M. Pohl, H. Prokoph, J. Quinn, K. Ragan, L. C. Reyes, P. T. Reynolds, E. Roache, D. B. Saxon, M. Schroedter, G. H. Sembroski, D. Staszak, I. Telezhinsky, G. Tesic, M. Theiling, K. Tsurusaki, A. Varlotta, S. Vincent, S. P. Wakely, T. C. Weekes, et al. (21 additional authors not shown)

We report on the detection of a very rapid TeV gamma-ray flare from BL Lacertae on 2011 June 28 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The flaring activity was observed during a 34.6-minute exposure, when the integral flux above 200 GeV reached (3.4±0.6) x 10^{-6} \;{photons}\;{m}^{-2}{s}^{-1}, roughly 125% of the Crab Nebula flux measured by VERITAS. The light curve indicates that the observations missed the rising phase of the flare but covered a significant portion of the decaying phase. The exponential decay time was determined to be 13±4 minutes, making it one of the most rapid gamma-ray flares seen from a TeV blazar. The gamma-ray spectrum of BL Lacertae during the flare was soft, with a photon index of 3.6±0.4, which is in agreement with the measurement made previously by MAGIC in a lower flaring state. Contemporaneous radio observations of the source with the Very Long Baseline Array (VLBA) revealed the emergence of a new, superluminal component from the core around the time of the TeV gamma-ray flare, accompanied by changes in the optical polarization angle. Changes in flux also appear to have occurred at optical, UV, and GeV gamma-ray wavelengths at the time of the flare, although they are difficult to quantify precisely due to sparse coverage. A strong flare was seen at radio wavelengths roughly four months later, which might be related to the gamma-ray flaring activities. We discuss the implications of these multiwavelength results.

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Title: Parsec-scale jet precession in BL Lacertae (2200+420)
Authors: Anderson Caproni (NAT-Universidade Cruzeiro do Sul), Zulema Abraham (IAG/USP), Hektor Monteiro (UNIFEI)

BL Lacertae is the prototype of the BL Lac class of active galactic nuclei, exhibiting intensive activity on parsec (pc) scales, such as intense core variability and multiple ejections of jet components. In particular, in previous works the existence of precession motions in the pc-scale jet of BL Lacertae has been suggested. In this work we revisit this issue, investigating temporal changes of the observed right ascension and declination offsets of the jet knots in terms of our relativistic jet-precession model. The seven free parameters of our precession model were optimised via a heuristic cross-entropy method, comparing the projected precession helix with the positions of the jet components on the plane of the sky and imposing constraints on their maximum and minimum superluminal velocities. Our optimised best model is compatible with a jet having a bulk velocity of 0.9824c, which is precessing with a period of about 12.1 yr in the observer's reference frame and changing its orientation in relation to the line of sight between 4 and 5 degrees, approximately. Assuming that the jet precession has its origin in a supermassive binary black hole system, we show that the 2.3-yr periodic variation in the structural position angle of the very-long-baseline interferometry (VLBI) core of BL Lacertae reported by Stirling et al. is compatible with a nutation phenomenon if the secondary black hole has a mass higher than about six times that of the primary black hole.

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The variable object BL Lacertae has increased in brightness to R = 12.60 (22nd July 2012), visual magnitude 13.2 (23rd July, Gary Poyner - Birmingham, England).



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BL Lacertae or BL Lac is a highly variable, extragalactic AGN (active galactic nucleus or active galaxy). It was first discovered by Cuno Hoffmeister in 1929, but was originally thought to be an irregular variable star in the Milky Way galaxy and so was given a variable star designation.
BL Lacertae changes in apparent magnitude over fairly small time periods between values of 14 and 17.
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Google earth file: BL Lacertae.kmz (1kb, kmz)

Position(2000): RA 22 02 43.29137, Dec +42 16 39.9799



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