784 research outputs found
Rapid X-ray Variability of the BL Lacertae Object PKS 2155-304
(Abridged) We present a detailed power density spectrum and cross-correlation
analysis of the X-ray light curves of the BL Lac object PKS 2155-304, observed
with BeppoSAX in 1997 and 1996, aimed at exploring the rapid variability
properties and the inter-band cross correlations in the X-rays. We also perform
the same analysis on the (archival) X-ray light curve obtained with ASCA in
1994.Comment: 47 pages, 11 figures, AAS Latex macros V4.0, accepted for publication
in the Astrophysical Journa
Spectral Evolution of PKS 2155-304 observed with BeppoSAX during an Active Gamma-ray Phase
We present the results of BeppoSAX observations of PKS 2155-304 during an
intense gamma-ray flare. The source was in a high X-ray state. A temporal
analysis of the data reveals a tendency of the amplitude of variations to
increase with energy, and the presence of a soft lag with a timescale of the
order 10^3 s. A curved continuum spectrum, with no evidence of spectral
features, extends up to ~50 keV, while there is indication of a flatter
component emerging at higher energies, consistent with the interpretation of
the broad band spectral energy distribution (SED) as due to synchrotron
self-Compton (SSC) emission from a single region. Notably, the fitting of the
SED with such a model is consistent with an interpretation of the detected soft
lag as due to radiative cooling, supporting the idea that radiation losses play
an important role in variability. The observed shifts of the SED peaks between
the lowest and highest flux levels can be accounted for by an increase of the
break energy in the relativistic particle spectrum. The model predicts emission
at TeV energies in good agreement with the recently reported detection.Comment: 36 pages (8 figures), Latex with AAS macros, etc), accepted for
publication on Astrophysical Journa
Chandra and HST observations of gamma-ray blazars: comparing jet emission at small and large scales
We present new Chandra and HST data for four gamma-ray blazars selected on
the basis of radio morphology with the aim of revealing X-ray and optical
emission from their jets at large scales. All the sources have been detected.
Spectral Energy Distributions of the large scale jets are obtained as well as
new X-ray spectra for the blazar cores. Modeling for each object the core
(sub-pc scale) and large-scale (>100 kpc) jet SEDs, we derive the properties of
the same jet at the two scales. The comparison of speeds and powers at
different scales supports a simple scenario for the dynamics and propagation of
high power relativistic jets.Comment: Accepted for publication in Ap
Detection of an X-ray jet in 3C 371 with Chandra
We report the detection at X-rays of the radio/optical jet of 3C 371, from a
short (10 ks) Chandra exposure in March 2000. We also present a new MERLIN
observation at 1.4 GHz together with a renalysis of the archival HST WFPC2
F555W image. Despite the limited signal-to-noise ratio of the Chandra data, the
X-ray morphology is clearly different from that of the radio/optical emission,
with the brightest X-ray knot at 1.7" from the nucleus and little X-ray
emission from the brightest radio/optical knot at 3.1". We construct the
spectral energy distributions for the two emission regions at 1.7" and 3.1".
Both show that the X-ray flux is below the extrapolation from the
radio-to-optical continuum, suggesting moderately beamed synchrotron from an
electron population with decreasing high energy cut-off as a plausible emission
mechanism.Comment: 6 pages, 4 figures (Figure 1 is a color GIF file); accepted for
publication in the Astrophysical Journal Letters. High resolution
(postscript) version of figure 1 at: http://www.astro.brandeis.edu/BRAG/pubs
The July 2010 outburst of the NLS1 PMN J0948+0022
We report about the multiwavelength campaign on the Narrow-Line Seyfert 1
(NLS1) Galaxy PMN J0948+0022 (z = 0.5846) performed in 2010 July-September and
triggered by high activity as measured by Fermi/LAT. The peak luminosity in the
0.1-100 GeV energy band exceeded, for the first time in this type of source,
the value of 10^48 erg/s, a level comparable to the most powerful blazars. The
comparison of the spectral energy distribution of the NLS1 PMN J0948+0022 with
that of a typical blazar - like 3C 273 - shows that the power emitted at gamma
rays is extreme.Comment: 2011 Fermi Symposium proceedings - eConf C11050
Gamma-loud quasars: a view with BeppoSAX
We present SAX observations of the -ray emitting quasars
0836+710, 1510-089 and 2230+114. All the objects have been detected in the PDS
up to 100 keV and have extremely flat power-law spectra above 2 keV (=0.3--0.5). 0836+710 shows absorption higher than the galactic value and
marginal evidence for the presence of the redshifted 6.4 keV Iron line.
1510-089 shows a spectral break around 1 keV, with the low energy spectrum
steeper (=1.6) than the high energy power-law (=0.3). The
data are discussed in the light of current Inverse Compton models for the high
energy emission.Comment: 4 pages, 2 figures, to appear in the proceedings of the conference
"X-Ray Astronomy '99", Bologna, Italy, September 199
High-Energy Neutrinos from Photomeson Processes in Blazars
An important radiation field for photomeson neutrino production in blazars is
shown to be the radiation field external to the jet. Assuming that protons are
accelerated with the same power as electrons and injected with a -2 number
spectrum, we predict that km^2 neutrino telescopes will detect about
1-to-several neutrinos per year from flat spectrum radio quasars (FSRQs) such
as 3C 279. The escaping high-energy neutron and photon beams transport inner
jet energy far from the black-hole engine, and could power synchrotron X-ray
jets and FR II hot spots and lobes.Comment: revised paper (minor revisions), accepted for publication in PR
Deep Multiwaveband Observations of the Jets of 0208-512 and 1202-262
We present deep {\it HST, Chandra, VLA} and {\it ATCA} images of the jets of
PKS 0208--512 and PKS 1202--262, which were found in a {\it Chandra} survey of
a flux-limited sample of flat-spectrum radio quasars with jets (see Marshall et
al., 2005). We discuss in detail their X-ray morphologies and spectra. We find
optical emission from one knot in the jet of PKS 1202--262 and two regions in
the jet of PKS 0208--512. The X-ray emission of both jets is most consistent
with external Comptonization of cosmic microwave background photons by
particles within the jet, while the optical emission is most consistent with
the synchrotron process. We model the emission from the jet in this context and
discuss implications for jet emission models, including magnetic field and
beaming parameters.Comment: 13 pages, 11 figures, ApJ in pres
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