1,511 research outputs found
Empirical multi-wavelength prediction method for very high energy gamma-ray emitting BL Lacs
Aim: We have collected the most complete multi-wavelength () dataset of very high energy (VHE) -ray emitting (TeV) BL
Lacs, which are the most numerous extragalactic VHE sources. Using significant
correlations between different bands, we aim to identify the best TeV BL Lac
candidates that can be discovered by the current and next generation of imaging
air Cherenkov telescopes.
Methods: We formed five datasets from lower energy data, i.e. radio,
mid-infrared, optical, X-rays, and GeV -ray, and five VHE -ray
datasets to perform a correlation study between different bands and to
construct the prediction method. The low energy datasets were averaged for
individual sources, while the VHE -ray data were divided into subsets
according to the flux state of the source. We then looked for significant
correlations and determined their best-fit parameters. Using the best-fit
parameters we predicted the level of VHE -ray flux for a sample of 182
BL Lacs, which have not been detected at TeV energies. We identified the most
promising TeV BL Lac candidates based on the predicted VHE -ray flux
for each source.
Results: We found 14 significant correlations between radio, mid-infrared,
optical, -ray, and VHE -ray bands. The correlation between
optical and VHE -ray luminosity is established for the first time. We
attribute this to the more complete sample and more accurate handling of host
galaxy flux in our work. We found nine BL Lac candidates whose predicted VHE
-ray flux is high enough for detection in less than 25 hours with
current imaging air Cherenkov telescopes.Comment: 10 pages, 2 figures, 4 Table
Enhanced electron transfer in composite films of reduced graphene oxide and poly(N-methylaniline)
Poly(N-methylaniline) (FNMA) has been electropolymerized for the first time from a graphene oxide (GO) dispersion containing 1.0 M HClO4. Both GO and perchlorate were incorporated in the PNMA matrix during the electropolymerization resulting in the formation of a mixed composite material of PNMA-ClO4 and PNMA-GO. Under the acidic polymerization conditions, the carboxylic groups of GO are undissociated and GO is therefore mostly mechanically entrapped in the PNMA matrix while perchlorate functions as the primary charge compensating ion. Electrochemical reduction at -0.85 V improved the election transfer of the composite film due to reduction of GO in the PNMA matrix. (C) 2013 Elsevier Ltd. All rights reserved
Redshift constraints for RGB 0136+391 and PKS 0735+178 from deep optical imaging
We present the results of deep I-band imaging of two BL Lacerate objects, RGB
0136+391 and PKS 0735+178, during an epoch when the optical nucleus was in a
faint state in both targets. In PKS 0735+178 we find a significant excess over
a point source, which, if fitted by the de Vaucouleurs model, corresponds to a
galaxy with I = 18.64 +- 0.11 and r_eff = 1.8 +- 0.4 arcsec. Interpreting this
galaxy as the host galaxy of PKS 0735+178 we derive z = 0.45 +- 0.06 using the
host galaxy as a "standard candle". We also discuss the immediate optical
environment of PKS 0735+178 and the identity of the MgII absorber at z = 0.424.
Despite of the optimally chosen epoch and deep imaging we find the surface
brightness profile of RGB 0136+391 to be consistent with a point source. By
determining a lower limit for the host galaxy brightness by simulations, we
derive z > 0.40 for this target.Comment: 6 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Synchrotron flaring behaviour of CygnusX-3 during the February-March 1994 and September 2001 outbursts
Aims: In this paper we study whether the shock-in-jet model, widely used to
explain the outbursting behaviour of quasars, can be used to explain the radio
flaring behaviour of the microquasar Cygnus X-3.
Method: We have used a method developed to model the synchrotron outbursts of
quasar jets, which decomposes multifrequency lightcurves into a series of
outbursts. The method is based on the Marscher & Gear (1985) shock model, but
we have implemented the modifications to the model suggested by Bjornsson &
Aslaksen (2000), which make the flux density increase in the initial phase less
abrupt. We study the average outburst evolution as well as specific
characteristics of individual outbursts and physical jet properties of Cyg X-3.
Results: We find that the lightcurves of the February-March 1994 and
September 2001 outbursts can be described with the modified shock model. The
average evolution shows that instead of the expected synchrotron plateau, the
flux density is still increasing during the synchrotron stage. We also find
that high frequency peaking outbursts are shorter in duration than the ones
peaking at lower frequencies. Finally, we show that the method can be used,
complementary to radio interferometric jet imaging, for deriving the physical
parameters such as the magnetic field strength and the energy density of
relativistic electrons in the jet of Cyg X-3.Comment: 8 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
MAGIC observations of Mkn 421 in 2008, and related optical/X-ray/TeV MWL study
The HBL-type blazar Markarian 421 is one of the brightest TeV gamma-ray
sources of the Northern sky. From December 2007 until June 2008 it was
intensively observed in the VHE (E>100 GeV) band by the MAGIC gamma-ray
telescope. The source showed intense and prolonged activity during the whole
period. In some nights the integral flux rose up to 3.6 Crab units (E>200 GeV).
Intra-night rapid flux variations were observed. We compared the optical (KVA)
and X-ray (RXTE-ASM, Swift-XRT) data with the MAGIC VHE data, investigating the
correlations between different energy bands.Comment: 4 pages,4figures, Contribution to the 31st ICRC, Lodz, Poland, July
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