Blazar Times - No. 40 - February 2002
The Blazar Times
A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena
No. 40 - February 2002 Editor: Travis A. Rector (


Editorial 1

Journal Abstracts 1

Abstract Guidelines 5


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Journal Abstracts

BeppoSAX   Spectral Survey of BL Lacs - New Spectra and Results

V. Beckmann1,2, A. Wolter3, A. Celotti4, L. Costamante3, G. Ghisellini3, T. Maccacaro3, and G. Tagliaferri3

1 INTEGRAL Science Data Centre, Chemin d' Ecogia 16, CH-1290 Versoix, Switzerland
2 Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
3 Osservatorio Astronomico di Brera, Via Brera 28, I-20121 Milano, Italy
4 SISSA/ISAS, Via Beirut 2-4, I-34014 Trieste, Italy

We present BeppoSAX   LECS, MECS, and PDS spectra of eleven X-ray selected BL Lacertae objects. Combining these sources with the ones presented elsewhere we have a sample of 21 BL Lacs from the Einstein Medium Sensitivity and Einstein Slew Survey. The sample shows strong correlations of several physical parameters with the peak frequency of the synchrotron branch of the spectral energy distribution. In particular the peak frequency is correlated to the X-ray spectral shape: objects with the peak near to the X-ray band show harder and straighter X-ray spectra than those of the low energy peaked sources. This work shows that the recently proposed unification scenario for different types of blazars can hold also within the class of high frequency peaked BL Lac objects.

Accepted by A&A

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Relation between radio core length and black hole mass for active galactic nuclei

Xinwu Cao1 and D.R. Jiang1

1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, 200030, China

We explore the relation between the linear length of radio core and the central black hole mass for a sample of radio-loud active galactic nuclei (AGNs). An empirical relation between the size of the broad line region (BLR) and optical luminosity is used to estimate the size of the BLR. The black hole mass is derived from Hb line width and the radius of the BLR on the assumption that the clouds in BLRs are orbiting with Keplerian velocities. A significant intrinsic correlation is found between the linear length of the core and the black hole mass, which implies that the jet formation is closely related with the central black hole. We also find a strong correlation between the black hole mass and the core luminosity.

Accepted by MNRAS

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A Survey of Extended Radio Jets in AGN with Chandra and HST: First Results

Rita M. Sambruna1, L. Maraschi2, F. Tavecchio2, C. Megan Urry3, C. C. Cheung4, G. Chartas5, R. Scarpa6, Jessica K. Gambill1

1 George Mason University, Fairfax, VA
2 Brera Observatory, Milano, Italy
3 Yale University, New Haven, CT
4 Brandeis Univeristy, Waltham, MA
5 Penn State University, State College, PA
6 European Southern Observatory, Santiago, Chile

We present the first results from an X-ray and optical survey of a sample of AGN radio jets with Chandra and HST. We focus here on the first six sources observed at X-rays, in four of which a bright X-ray jet was detected for the first time. In three out of four cases optical emission from the jet is also detected in our HST images. We compare the X-ray morphology with the radio as derived from improved processing of archival VLA data and we construct spectral energy distributions (SED) for the most conspicuous emission knots. In most cases the SEDs, together with the similarity of the X-ray and radio morphologies, favor an inverse Compton origin of the X-rays. The most likely origin of the seed photons is the Cosmic Microwave Background, implying the jets are still relativistic on kiloparsec scales. However, in the first knot of the PKS 1136-135 jet, X-rays are likely produced via the synchrotron process. In all four cases bulk Lorentz factors of a few are required. The radio maps of the two jets not detected by either Chandra or HST suggest that they are less beamed at large scales than the other four detected sources. Our results demonstrate that, at the sensitivity and resolution of Chandra, X-ray emission from extragalactic jets is common, yielding essential information on their physical properties.

Accepted by ApJ

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TeV candidate BL Lac objects

Luigi Costamante1,2 & Gabriele Ghisellini2

1 Università Statale di Milano, via Celoria 16, I-20133 Milano, Italy.
2 Osservatorio Astronomico di Brera, via Bianchi 46, I-23807 Merate, Italy.

The TeV emission of low power BL Lac objects has been established by the detection of an handful of them. The knowledge of the level of the TeV emission and its spectrum can shed light on the particle acceleration mechanisms, and it is especially important to assess the still uncertain level of the far infrared background radiation, which can absorb the TeV photons through photon-photon interactions. In view of these implications, it is necessary to enlarge the number of TeV detected sources, and to find them at different redshifts. To this aim, we propose a general and simple criterium to select the best TeV candidates, and produce a list of them with flux estimates above 40 GeV, 300 GeV and 1 TeV.

Accepted by A&A

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For preprints via ftp or WWW:, astro-ph/0112201

BL Lacertae: complex spectral variability and rapid synchrotron flare detected with BeppoSAX

M. Ravasio1, G. Tagliaferri1, G. Ghisellini1, P. Giommi2, R. Nesci3, E. Massaro3, L. Chiappetti4, A. Celotti5, L. Costamante1, L. Maraschi6, F. Tavecchio6, G. Tosti7, A. Treves8, A. Wolter6, T. Balonek9, M. Carini10, T. Kato11, O. Kurtanidze12, F. Montagni3, M. Nikolashvili12, J. Noble13, G. Nucciarelli7, C.M. Raiteri14, S. Sclavi3, M. Uemura11 and M. Villata14

1 Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate, Italy
2 BeppoSAX Science Data Center, ASI, Via Corcolle, 19, I-00131 Roma, Italy
3 Dipartimento di Fisica, Universitá La Sapienza, P.le Aldo Moro 2, 00185 Roma, Italy
4 Istituto di Fisica Cosmica G.Occhialini, CNR, Via Bassini 15, I-20133 Milano, Italy
5 SISSA/ISAS, via Beirut 2-4, 34014 Trieste, Italy
6 Osservatorio Astronomico di Brera, Via Brera, 28, I-20121 Milano, Italy
7 Osservatorio Astronomico, Università di Perugia, Via A. Pascoli, I-06100 Perugia, Italy
8 Dipartimento di Scienze, Università dell'Insubria, Via Valleggio 11, I-22100 Como, Italy
9 Foggy Bottom Observatory, Colgate University, 13 Oak Drive 13346, Hamilton NY, USA
10 Dept. of Physics and Astronomy, Western Kentucky University, 1 Big Red Way, Bowling Green, KY 42102-3576, USA
11 Dept. of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakio-ku, Kyoto 606-8502, Japan
12 Abastumani Astrophysical Observatory, 383762, Abastumani, Republic of Georgia
13 Dept. of Astronomy, Boston University, 725 Commonwealth Avenue, Boston MA 02215, USA
14 Osservatorio Astronomico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese, Italy

We report on two BeppoSAX observations of BL  Lac (2200+420) performed respectively in June and December 1999, as part of a ToO program to monitor blazars in high states of activity. During both runs the source has been detected up to 100 keV, but it showed quite different spectra: in June it was concave with a very hard component above 5-6 keV (a1 ~ 1.6; a2 ~ 0.15); in December it was well fitted by a single power law (a ~ 0.6). During the first BeppoSAX observation BL  Lac showed an astonishing variability episode: the 0.3 - 2 keV flux doubled in ~ 20 minutes, while the flux above 4 keV was almost contant. This frequency-dependent event is one of the shortest ever recordered for BL Lac objects and places lower limits on the dimension and magnetic field of the emitting region and on the energy of the synchrotron radiating electrons. A similar but less extreme behaviour is detected also in optical light curves, that display non-simultaneous, smaller fluctuations of ~ 20 % in 20 min. We fit the spectral energy distributions with a homogeneous, one-zone model to constrain the emission region in a very simple but effective SSC + external Compton scenario, highlighting the importance of the location of the emitting region with respect to the Broad Line Region and the relative spectral shape dependence. We compare our data with historical radio to g-ray Spectral Energy Distributions.

Accepted by A&A

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An AGN Identification for 3EG J2006-2321

P. M. Wallace1, J. P. Halpern2, A. M. Magalhães3  and D. J. Thompson4

1 Berry College, Rome, GA 30149, USA
2 Columbia University, New York, NY 10027, USA
3 Universidade de São Paulo, São Paulo-SP 01060-970, Brazil
4 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

We present a multiwavelength analysis of the high-energy gamma-ray source 3EG J2006-2321 (l = 18.82, b = -26.26). The flux of this source above 100 MeV is shown to be variable on time scales of days and months. Optical observations and careful examination of archived radio data indicate that its most probable identification is with PMN J2005-2310, a flat-spectrum radio quasar with a 5-GHz flux density of 260 mJy. Study of the V = 19.3 optical counterpart indicates a redshift of 0.833 and variable linear polarization. No X-ray source has been detected near the position of PMN J2005-2310, but an X-ray upper limit is derived from ROSAT data. This upper limit provides for a spectral energy distribution with global characteristics similar to those of known gamma-ray blazars. Taken together, these data indicate that 3EG J2006-2321, listed as unidentified in the 3rd EGRET Catalog, is a member of the blazar class of AGN. The 5-GHz radio flux density of this blazar is the lowest of the 68 EGRET-detected AGN. The fact that EGRET has detected such a source has implications for unidentified EGRET sources, particularly those at high latitudes (|b| > 30), many of which may be blazars.

Accepted by ApJ

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Abstract Guidelines

Abstracts for ``The Blazar Times" are solicited for papers that have been recently accepted for publication by a refereed journal, and for recent Ph.D. theses. Please do not submit an abstract before it has been accepted, nor after it is published. Abstracts from papers which are not refereed (e.g., conference proceedings) are not accepted.

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On 5 Feb 2002, 10:57.