|The Blazar Times|
|A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena|
|No. 63 - August 2004||Editor: Travis A. Rector (email@example.com)|
Journal Abstracts 1
Abstract Guidelines 4
2QZJ215454.3-305654: a radio-quiet BL Lac object or lineless QSO? D. Londish1,2, J. Heidt3, B.J. Boyle4,2, S.M. Croom2, L. Kedziora-Chudczer1,4 1 University of Sydney, School of Physics, Sydney NSW 2006, Australia
High signal-to-noise spectroscopy has established a redshift of z=0.494 for the source 2QZJ215454.3-305654, originally selected from the 2dF/6dF QSO Redshift Surveys as one of 45 candidate BL Lac objects displaying a featureless continuum at optical wavelengths. Radio observations using the Australia Telescope Compact Array at 1.4 GHz place a 3 sigma upper limit on the object's radio flux density of approx 0.14mJy. The radio-to-optical flux ratio of this object is thus more than 7 times lower than the lowest such ratio observed in BL Lac objects. While the optical properties of 2QZJ215454.3-305654 are consistent with a BL Lac identification, the lack of radio and/or X-ray emission is not. It is uncertain whether this object is an AGN dominated by optical continuum emission from an accretion disk, or is similar to a BL Lac object with optical nonthermal emission from a relativistic jet. Accepted by MNRAS
For preprints contact: firstname.lastname@example.org For preprints via ftp or WWW: http://www.physics.usyd.edu.au/~dlondish
A sample of low redshift BL Lacs. I. The radio data. M. Giroletti1,2, G. Giovannini1,2, G. B. Taylor3 and R. Falomo4 1 Istituto di Radioastronomia, via Gobetti 101, 40129, Bologna, Italy
We present a new sample of 30 nearby (z < 0.2) BL Lacs, selected to study the nuclear as well as the large scale properties of low power radio sources. In this first paper, we show and discuss new radio data taken with the VLA (19 objects at 1.4 GHz, either in A or C configuration, or both) as well as with the VLBA (15 sources at 5 GHz). On the kiloparsec scale, all objects exhibit a compact core and a variety of radio morphologies (jets, halos, secondary compact components). On the parsec scale, we find weak cores and a few short, one-sided, jets. From the jet/counter-jet ratio, core dominance, and synchrotron self Compton model we estimate the intrinsic orientation and velocity of the jets. The resulting properties of BL Lacs are similar to those of a parent population composed of FR I radio galaxies. Accepted by ApJ
For preprints contact: email@example.com For preprints via WWW: http://arxiv.org/abs/astro-ph/0406255
Near Infrared Intraday Variability of Mrk 421 A. C. Gupta1, D. P. K. Banerjee2, N. M. Ashok2 and U. C. Joshi2 1 Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad - 211 019, India
We report results from our monitoring of the BL Lac object Mrk 421 in the near-IR J band. The observations, aimed at studying the intraday variability (IDV) of the object, were carried out systematically over an extended (and near-continuous) period of eight nights from the 1.2m Mount Abu Infrared Telescope, India. There are limited studies for Mrk 421 in the J band for such an extended period. The observation epoch for this study (25 February - 5 March 2003) was chosen to significantly overlap other concurrent studies of Mrk 421 in the X-ray/g-ray regions being conducted using the Rossi X-ray timing explorer (RXTE) and the solar tower atmospheric Cherenkov effect experiment (STACEE). Hence these results could be useful for a multi-wavelength analysis of the variability behavior of Mrk 421. We find that Mrk 421 was quite active during the observed period and showed significant IDV and short term variability. A maximum variation of 0.89 magnitudes is seen over the entirety of the observed period. Flaring activity, with typical brightness variations of ~ 0.4, are also seen on several occasions. The extent of the variability observed by us is compared with the results of other similar studies of Mrk 421 in the J band. Accepted by A & A
For preprints contact: firstname.lastname@example.org For preprints via ftp or WWW: http://xxx.lanl.gov/abs/astro-ph/0405186
The WEBT campaigns on BL Lacertae
1 Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
The Whole Earth Blazar Telescope (WEBT) collaboration has collected a large amount of optical and radio data on BL Lacertae in the last years, which, when added to literature data, allow to construct well-sampled light curves of the source from 1968 to the end of 2003. These optical and radio data are here analysed with three statistical methods designed for unevenly-sampled data trains in order to search for possible periodicities. While the main radio outbursts repeat every ~ 8 years, with a possible progressive stretching of the period, the evidence of an optical periodicity is much less clear. Radio light curves from 4.8 to 37 GHz are well correlated, with variations at the higher frequencies leading the lower-frequency ones by a few weeks for contiguous bands, up to a few months when considering the largest frequency separations. The radio behaviour reveals the presence of two different components, the softer-spectrum one constituting the bulk of the radio emission. On the other hand, the harder component shows itself as radio events which appear enhanced at the higher frequencies and seem to have optical counterparts. Cross-correlation between the optical light curve and radio hardness ratios indicates a radio time delay of more than 3 months. Thus, our analysis suggests a scenario where flux variations propagate towards less and less opaque regions, giving rise to related optical and hard radio events and, in more extended zones, to soft events apparently uncorrelated with the former ones. Accepted by A&A
For preprints contact: email@example.com For preprints via ftp or WWW: http://www.to.astro.it/blazars/bllac2001b_preprint.zip
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