Blazar Times - No. 41 - March 2002
The Blazar Times
A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena
No. 41 - March 2002 Editor: Travis A. Rector (


Journal Abstracts 1

Abstract Guidelines 4

Journal Abstracts

TeV gamma rays from the blazar H 1426+428 and the diffuse extragalactic background radiation

F. Aharonian1, A. Akhperjanian7, J. Barrio3, M. Beilicke4, K. Bernlöhr1, H. Börst5, H. Bojahr6, O. Bolz1, J. Contreras2, R. Cornils4, J. Cortina2, S. Denninghoff2, V. Fonseca3, M. Girma1, J. Gonzalez3, N. Götting4, G. Heinzelmann4, G. Hermann1, A. Heusler1, W. Hofmann1, D. Horns1, I. Jung1, R. Kankanyan1, M. Kestel2, J. Kettler1, A. Kohnle1, A. Konopelko1, H. Kornmeyer2, D. Kranich2, H. Krawczynski1,9, H. Lampeitl1, M. Lopez3, E. Lorenz2, F. Lucarelli3, N. Magnussen6, O. Mang5, H. Meyer6, R. Mirzoyan2, A. Moralejo3, E. Ona3, L. Padilla3, M. Panter1, R. Plaga2, A. Plyasheshnikov1,8, G. Pühlhofer1, G. Rauterberg5, A. Röhring4, W. Rhode6, J. Robrade4, G. Rowell1, V. Sahakian7, M. Samorski5, M. Schilling5, F. Schröder6, I. Sevilla3, M. Siems5, W. Stamm5, M. Tluczykont4, H.J. Völk1, C. A. Wiedner1, W. Wittek2

1 Max-Planck-Institut für Kernphysik, Postfach 103980, D-69029 Heidelberg, Germany
2 Max-Planck-Institut für Physik, Föhringer Ring 6, D-80805 München, Germany
3 Universidad Complutense, Facultad de Ciencias Físicas, Ciudad Universitaria, E-28040 Madrid, Spain
4 Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, D-22761 Hamburg, Germany
5 Universität Kiel, Institut für Experimentelle und Angewandte Physik, Leibnizstraße 15-19, D-24118 Kiel, Germany
6 Universität Wuppertal, Fachbereich Physik, Gaußstr.20, D-42097 Wuppertal, Germany
7 Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan, Armenia
8 On leave from Altai State University, Dimitrov Street 66, 656099 Barnaul, Russia
9 Now at Yale University, P.O. Box 208101, New Haven, CT 06520-8101, USA

The detection of TeV g-rays from the blazar H 1426+428 at an integral flux level of (4 2stat 1syst) ×10-12erg cm-2s-1 above 1 TeV with the HEGRA imaging atmospheric Cherenkov telescope system is reported. H 1426+428 is located at a redshift of z=0.129, which makes it the most distant source detected in TeV g-rays so far. The TeV radiation is expected to be strongly absorbed by the diffuse extragalactic background radiation (DEBRA). The observed energy spectrum of TeV photons is in good agreement with an intrinsic power law spectrum of the source E-1.9 corrected for DEBRA absorption. Statistical errors as well as uncertainties about the intrinsic source spectrum, however, do not permit strong statements about the density of the DEBRA infrared photon field.

Accepted by A&A Letters

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Four Years Monitoring of Blazar PKS 2155-304 with BeppoSAX : Probing the Dynamics of the Jet

Y.H. Zhang1, A. Treves1, A. Celotti2, L. Chiappetti3, G. Fossati4, G. Ghisellini5, L. Maraschi6, E. Pian7, G. Tagliaferri5  and F. Tavecchio6

1 Dipartimento di Scienze, Università dell'Insubria, via Valleggio 11, I-22100 Como, Italy
2 International School for Advanced Studies, SISSA/ISAS, via Beirut 2-4, I-34014 Trieste, Italy
3 Istituto di Fisica Cosmica G.Occhialini, IFCTR/CNR, via Bassini 15, I-20133 Milano, Italy
4 CASS, UCSD, 9500 Gilman Drive, La Jolla, CA 92093-0424, USA
5 Osservatorio Astronomico di Brera, via Bianchi 46, I-22055 Merate, Italy
6 Osservatorio Astronomico di Brera, via Brera 28, I-20121 Milano, Italy
7 Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, I-34131 Trieste, Italy

PKS 2155-304 is one of the brightest blazars in the X-ray band. It was repeatedly monitored with BeppoSAX  during three long campaigns of about 2 days each in November of 1996, 1997 and 1999. The source underwent different states of intensity and was clearly variable with successive flares detected. This paper presents temporal and spectral analysis to study the X-ray variability trends for a blazar. The variability shows larger amplitude and shorter timescale at higher energies. The power spectral densities have steep power-law slopes of ~  2-3, indicating shot noise variability. Structure function analysis reveals the existence of ``typical'' timescales characteristic of the half duration of the flares. From the cross-correlation analysis we find that the values of soft lags, i.e., delays of soft (0.1-1.5 keV) photons with respect to hard (3.5-10 keV) ones, differ from flare to flare, ranging from a few hundred seconds to about one hour. There is a suggestion that the flares with shorter duration show smaller soft lags. The soft lags are also energy-dependent, with longer lags of lower energy emission with respect to the emission in the 4-10 keV. The time-resolved X-ray spectral fits with a curved model show that peak energies of the synchrotron component are located in the very soft X-ray range or even below the BeppoSAX  lower energy limit, 0.1 keV. A correlation between peak energies and fluxes is marginal. Spectral evolution during some flares shows clockwise loops in the spectral index-flux plane, confirming the soft lags indicated by the cross-correlation analysis. Two flares, however, show evidence that spectral evolution follows opposite tracks in the soft and hard energy bands, respectively. The rich phenomenology is interpreted in the context of a model where relativistic electrons are accelerated through internal shocks taking place in the jets. The most important parameter turns out to be the initial time interval between the two shells ejected from the central engine to produce the flare, which may determine the structure of the shock and in turn the physical quantities of the emitting region to reproduce the observed trends of the X-ray variability.

Accepted by ApJ

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Detection of the BL Lac Object 1H1426+428 at TeV Gamma Ray Energies

D. Horan1,2, H. M. Badran1,7, I. H. Bond3, S. M. Bradbury3, J. H. Buckley4, M. J. Carson2, D. A. Carter-Lewis5, M. Catanese1, W. Cui10, S. Dunlea2, D. Das15, I. de la Calle Perez3, M. D'Vali3, D. J. Fegan2, S. J. Fegan1,8, J. P. Finley6, J. A. Gaidos6, K. Gibbs1, G. H. Gillanders9, T. A. Hall5,17, A. M. Hillas3, J. Holder3, M. Jordan4, M. Kertzman16, D. Kieda11, J. Kildea2, J. Knapp3, K. Kosack4, F. Krennrich5, M. J. Lang9, S. LeBohec5, R. Lessard6, J. Lloyd-Evans3, B. McKernan2, P. Moriarty13, D. Muller10, R. Ong12, R. Pallassini3, D. Petry5, J. Quinn2, N. W. Reay15, P. T. Reynolds14, H. J. Rose3, G. H. Sembroski6, R. Sidwell15, N. Stanton15, S. P. Swordy10, V. V. Vassiliev11, S. P. Wakely10, T. C. Weekes1

1 Fred Lawrence Whipple Observatory, Harvard-Smithsonian CfA, P.O. Box 97, Amado, AZ 85645
2 Experimental Physics Department, National University of Ireland, Belfield, Dublin 4, Ireland
3 Department of Physics, University of Leeds, Leeds, LS2 9JT, Yorkshire, England, UK
4 Department of Physics, Washington University, St. Louis, MO 63130
5 Department of Physics and Astronomy, Iowa State University, Ames, IA 50011
6 Department of Physics, Purdue University, West Lafayette, IN 47907
7 Physics Department, Tanta University, Tanta, Egypt
8 Department of Physics, University of Arizona, Tucson, AZ 85721
9 Physics Department, National University of Ireland, Galway, Ireland
10 Enrico Fermi Institute, University of Chicago, Chicago, IL 60637
11 High Energy Astrophysics Institute, University of Utah, Salt Lake City, UT 84112
12 Department of Physics, University of California, Los Angeles, CA 90095
13 School of Science, Galway-Mayo Institute of Technology, Galway, Ireland
14 Department of Physics, Cork Institute of Technology, Cork, Ireland
15 Department of Physics, Kansas State University, Manhattan, KS 66506
16 Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135
17 Physics & Astronomy Department, University of Arkansas at Little Rock, Little Rock, AR 72204

A very high energy g-ray signal has been detected at the 5.5s level from 1H1426+428, an x-ray selected BL Lacertae object at a redshift of 0.129. The object was monitored from 1995 - 1998 with the Whipple 10m imaging atmospheric Cerenkov telescope as part of a general blazar survey; the results of these observations, although not statistically significant, were consistently positive. X-ray observations of 1H1426+428 during 1999 with the BeppoSAX instrument revealed that the peak of its synchrotron spectrum occurs at > 100 keV, leading to the prediction of observable TeV emission from this object. 1H1426+428 was monitored extensively at the Whipple Observatory during the 1999, 2000, and 2001 observing seasons. The strongest TeV signals were detected in 2000 and 2001. During 2001, an integral flux of 2.04 0.35 x 10-11 cm-2 s-1 above 280 GeV was recorded from 1H1426+428. The detection of 1H1426+428 supports the idea that, as also seen in Markarian 501 and 1ES2344+514, BL Lacertae objects with extremely high synchrotron peak frequencies produce g-rays in the TeV range.

Accepted by ApJ

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X-ray Synchrotron Spectral Hardenings from Compton and Synchrotron Losses in Extended Chandra Jets

Charles D. Dermer1  and Armen M. Atoyan2

1 E. O. Hulburt Center for Space Research, Code 7653, Naval Research Laboratory, Washington, DC 20375-5352
2 CRM, Universite de Montreal, Montreal H3C 3J7, Canada

Chandra observations of knots and hot spots in spatially resolved X-ray jets of radio galaxies show that the X-ray fluxes often lie above an extrapolation from the radio-to-optical continuum fluxes. We show that combined synchrotron and Compton losses on a single power-law electron injection function can produce a hardening in the electron spectrum at electron Lorentz factors g 2×108/[G(1+z)] due to KN energy losses on the cosmic microwave background radiation. Here G is the bulk Lorentz factor of the outflow, and z is the source redshift. This produces a flattening in the spectrum at frequencies > 8×1016dBmG/[G2(1+z)3] Hz, where BmG is the magnetic field in the comoving plasma frame in units of micro-Gauss and d is the Doppler factor. A single population of synchrotron-emitting electrons may therefore produce the radio-to-X-ray continuum in some radio galaxy knots, such as those in 3C 273.

Accepted by ApJ Letters

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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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File translated from TEX by TTH, version 2.25.
On 5 Feb 2002, 10:57.