1,045 research outputs found
Broadband study of blazar 1ES 1959+650 during flaring state in 2016
Aim : The nearby TeV blazar 1ES 1959+650 (z=0.047) was reported to be in
flaring state during June - July 2016 by Fermi-LAT, FACT, MAGIC and VERITAS
collaborations. We studied the spectral energy distributions (SEDs) in
different states of the flare during MJD 57530 - 57589 using simultaneous
multiwaveband data to understand the possible broadband emission scenario
during the flare. Methods : The UV/optical and X-ray data from UVOT and XRT
respectively on board Swift and high energy -ray data from Fermi-LAT
are used to generate multiwaveband lightcurves as well as to obtain high flux
states and quiescent state SEDs. The correlation and lag between different
energy bands is quantified using discrete correlation function. The synchrotron
self Compton (SSC) model was used to reproduce the observed SEDs during flaring
and quiescent states of the source. Results : A decent correlation is seen
between X-ray and high energy -ray fluxes. The spectral hardening with
increase in the flux is seen in X-ray band. The powerlaw index vs flux plot in
-ray band indicates the different emission regions for 0.1 - 3 GeV and
3-300 GeV energy photons. Two zone SSC model satisfactorily fits the observed
broadband SEDs. The inner zone is mainly responsible for producing synchrotron
peak and high energy -ray part of the SED in all states. The second
zone is mainly required to produce less variable optical/UV and low energy
-ray emission. Conclusions : Conventional single zone SSC model does
not satisfactorily explain broadband emission during observation period
considered. There is an indication of two emission zones in the jet which are
responsible for producing broadband emission from optical to high energy
-rays.Comment: 11 pages, 12 figures, Accepted in A&
An implantable compound-releasing capsule triggered on demand by ultrasound
Implantable devices have a large potential to improve human health, but they are often made of biofouling materials that necessitate special coatings, rely on electrical connections for external communication, and require a continuous power source. This paper demonstrates an alternative platform, which we call iTAG (implantable thermally actuated gel), where an implanted capsule can be wirelessly controlled by ultrasound to trigger the release of compounds. We constructed a millimetersized capsule containing a co-polymer gel (NiPAAm-co-AAm) that contracts above body temperature (i.e. at 45°C) to release compounds through an opening. This gel-containing capsule is biocompatible and free of toxic electronic or battery components. An ultrasound hardware, with a focused ultrasound (FUS) transducer and a co-axial A-mode imaging transducer, was used to image the capsule (to monitor in real time its position, temperature, and effectiveness of dose delivery), as well as to trigger a rapid local rise in temperature, contraction of gel, and release of compounds in vitro and in vivo. The combination of this gel-based capsule and compact ultrasound hardware can serve as a platform for triggering local release of compounds, including potentially in deep tissue, to achieve tailored personalized therapy
X-ray variability of AGNs in the soft and the hard X-ray bands
We investigate the X-ray variability characteristics of hard X-ray selected
AGNs (based on Swift/BAT data) in the soft X-ray band using the RXTE/ASM data.
The uncertainties involved in the individual dwell measurements of ASM are
critically examined and a method is developed to combine a large number of
dwells with appropriate error propagation to derive long duration flux
measurements (greater than 10 days). We also provide a general prescription to
estimate the errors in variability derived from rms values from unequally
spaced data. Though the derived variability for individual sources are not of
very high significance, we find that, in general, the soft X-ray variability is
higher than those in hard X-rays and the variability strengths decrease with
energy for the diverse classes of AGN. We also examine the strength of
variability as a function of the break time scale in the power density spectrum
(derived from the estimated mass and bolometric luminosity of the sources) and
find that the data are consistent with the idea of higher variability at time
scales longer than the break time scale.Comment: 17 pages, 15 Postscript figures, 3 tables, accepted for publication
in Ap
Multi-frequency, Multi-Epoch Study of Mrk 501: Hints for a two-component nature of the emission
Since the detection of very high energy (VHE) -rays from Mrk 501, its
broad band emission of radiation was mostly and quite effectively modeled using
one zone emission scenario. However, broadband spectral and flux variability
studies enabled by the multiwavelength campaigns carried out during the recent
years have revealed rather complex behavior of Mrk 501. The observed emission
from Mrk 501 could be due to a complex superposition of multiple emission
zones. Moreover new evidences of detection of very hard intrinsic -ray
spectra obtained from {\it Fermi}--LAT observations have challenged the
theories about origin of VHE -rays. Our studies based on {\it
Fermi}--LAT data indicate the existence of two separate components in the
spectrum, one for low energy -rays and the other for high energy
-rays. Using multiwaveband data from several ground and space based
instruments, in addition to HAGAR data, the spectral energy distribution of
Mrk~501 is obtained for various flux states observed during 2011. In the
present work, this observed broadband spectral energy distribution is
reproduced with a leptonic, multi-zone Synchrotron Self-Compton model.Comment: Published in Astrophysical Journal (ApJ
Single-Photon Counting Receivers for Optical Wireless Communications in Future 6G Networks
International audienceOptical wireless communication (OWC) offers several complementary advantages to radio-frequency wireless networks such as its massive available spectrum. Hence, it is widely anticipated that OWC will assume a pivotal role in the forth-coming sixth generation wireless communication networks. Although significant progress has been achieved in OWC over the past decades, the outage induced by occasionally low received optical power continues to pose a key limiting factor for its deployment. In this work, we discuss the potential role of single-photon counting (SPC) receivers as a promising solution to overcome this limitation. We present an overview of the applications of SPC-based OWC systems in 6G networks, introduce their major performance-limiting factors, propose a performance-enhancement frame-work to tackle these issues, and identify critical areas of open problems for future research
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A Monte Carlo Simulation Approach to the Reliability Modeling of the Beam Permit System of the Relativistic Heavy Ion Collider (RHIC) at BNL
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