Science Highlights from VERITAS Staszak, D; Abeysekara, A U; Archambault, S ...
arXiv (Cornell University),
10/2015
Paper, Journal Article
Odprti dostop
The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a ground-based array located at the Fred Lawrence Whipple Observatory in southern Arizona and is one of the world's most ...sensitive gamma-ray instruments at energies of 85 GeV to \(>\)30 TeV. VERITAS has a wide scientific reach that includes the study of extragalactic and Galactic objects as well as the search for astrophysical signatures of dark matter and the measurement of cosmic rays. In this paper, we will summarize the current status of the VERITAS observatory and present some of the scientific highlights from the last two years, focusing in particular on those results shown at the 2015 ICRC in The Hague, Netherlands.
ApJ 817 L7 2016 The TeV binary system LS I +61$^\circ$ 303 is known for its regular,
non-thermal emission pattern which traces the orbital period of the compact
object in its 26.5 day orbit around ...its B0 Ve star companion. The system
typically presents elevated TeV emission around apastron passage with flux
levels between 5% and 15% of the steady flux from the Crab Nebula (> 300 GeV).
In this article, VERITAS observations of LS I +61$^\circ$ 303 taken in late
2014 are presented, during which bright TeV flares around apastron at flux
levels peaking above 30% of the Crab Nebula flux were detected. This is the
brightest such activity from this source ever seen in the TeV regime. The
strong outbursts have rise and fall times of less than a day. The short
timescale of the flares, in conjunction with the observation of 10 TeV photons
from LS I +61$^\circ$ 303 during the flares, provides constraints on the
properties of the accelerator in the source.
Young core-collapse supernovae with dense-wind progenitors may be able to accelerate cosmic-ray hadrons beyond the knee of the cosmic-ray spectrum, and this may result in measurable gamma-ray ...emission. We searched for gamma-ray emission from ten supernovae observed with the High Energy Stereoscopic System (H.E.S.S.) within a year of the supernova event. Nine supernovae were observed serendipitously in the H.E.S.S. data collected between December 2003 and December 2014, with exposure times ranging from 1.4 to 53 h. In addition we observed SN 2016adj as a target of opportunity in February 2016 for 13 h. No significant gamma-ray emission has been detected for any of the objects, and upper limits on the >1 TeV gamma-ray flux of the order of $~10^{−13}$ $cm^{−2}s$$^{−1}$ are established, corresponding to upper limits on the luminosities in the range $~2 × 10^{39}$ to $~1 × 10^{42}$ erg $s^{−1}$. These values are used to place model-dependent constraints on the mass-loss rates of the progenitor stars, implying upper limits between $~2 × 10^{−5}$ and $~2 × 10^{−3}$ $M_⊙ yr^{−1}$ under reasonable assumptions on the particle acceleration parameters.
Issu d’une thèse de doctorat réalisée sous la direction de Christian Biet (†) et soutenue en 2019, La scène égyptienne en révolution, propose une étude de ce que Pauline Donizeau, nomme « la ...production théâtrale révolutionnaire ». Cette étude commence dans les années 1950-1960 lorsque les politiques culturelles nassériennes ont posé les fondations et l’architecture de la vie culturelle en Égypte. L’ouvrage se ferme sur la période directement contemporaine, en 2019, au moment où le travail do...
We report an analysis and modelling of new Suzaku observations of the Seyfert 1 galaxies Mrk509 and Mrk841, taken between April and November 2006,for Mrk509,and between January and July 2007,for ...Mrk841,for a total exposure time of ~100 ks each.Data from XIS and HXD/PIN instruments,going from 0.5 to 60 keV,represent the highest spectral resolution simultaneous broad-band X-ray spectrum for these objects.We fitted the broad-band spectrum of both sources with a double Comptonisation model,adding neutral reflection from distant material and a two-phase warm absorber.We then studied the two competing models developed to explain the soft excess in terms of atomic processes:a blurred ionised disc reflection and an ionised absorption by a high velocity material.When fitting the data in the 3-10 keV range with a power law spectrum,and extrapolating this result to low energies,a soft excess is clearly observed below 2 keV:its strength is however weak compared to previous observations of both sources.A moderate hard excess is seen at energies greater than 10 keV,together with a neutral Fe K_a narrow emission line at E~6.4 keV and a broad Fe emission line.For Mrk509,the broad Fe emission line is required in all the three physical models in order to have a good fit to the data:this finding suggests that the blurred reflection model correctly describes the soft excess,but that it underestimates the broad Fe emission line.For the smeared absorption model,this suggests instead that the continuum spectrum absorbed by the outflowing gas should contain indeed a reflected component.For Mrk841,all three models that we tested provide a good fit to the data,and we cannot invalidate any of them.A broad emission line is required in the double Comptonisation and smeared absorption models,while the blurred reflection model consistently fits the broad-band spectrum,without adding any extra emission-line component.
The flat spectrum radio quasar 3C 279 is known to exhibit pronounced variability in the high-energy (100 MeV < E < 100 GeV) γ-ray band, which is continuously monitored with Fermi-LAT. During two ...periods of high activity in April 2014 and June 2015 target-of-opportunity observations were undertaken with the High Energy Stereoscopic System (H.E.S.S.) in the very-high-energy (VHE, E > 100 GeV) γ-ray domain. While the observation in 2014 provides an upper limit, the observation in 2015 results in a signal with 8.7σ significance above an energy threshold of 66 GeV. No VHE variability was detected during the 2015 observations. The VHE photon spectrum is soft and described by a power-law index of 4.2 ± 0.3. The H.E.S.S. data along with a detailed and contemporaneous multiwavelength data set provide constraints on the physical parameters of the emission region. The minimum distance of the emission region from the central black hole was estimated using two plausible geometries of the broad-line region and three potential intrinsic spectra. The emission region is confidently placed at r ≳ 1.7 × 10$^{17}$ cm from the black hole, that is beyond the assumed distance of the broad-line region. Time-dependent leptonic and lepto-hadronic one-zone models were used to describe the evolution of the 2015 flare. Neither model can fully reproduce the observations, despite testing various parameter sets. Furthermore, the H.E.S.S. data were used to derive constraints on Lorentz invariance violation given the large redshift of 3C 279.
Expression of surface adhesion molecules of the Ig superfamily (CD54 and CD58), of the integrin family (beta 1, beta 2, and beta 3 chains), of the selectin family (L-selectin), and of the lymphocyte ...homing receptor (CD44) was analyzed on B-cell chronic lymphocytic leukemia (B- CLL) cells from 74 patients. The aim of the study was the definition of phenotypically distinct disease subsets and the correlation of adhesion molecule phenotypes with clinical parameters. Expression of CD58 on B- CLL cells defined more advanced disease stages. In comparison with beta chain-positive cases, patients whose cells did not express beta 1, beta 2, and beta 3 integrin chains fell into the most favorable prognostic group, with lower lymphocytosis and the absence of splenomegaly, diffuse bone marrow infiltration, and therapy requirement. A novel finding was the expression of beta 3 chains on cells from a minority (12 of 74) of B-CLL cases. beta 3 chains were always coexpressed with beta 1 and beta 2 chains. Two-color immunofluorescence analyses of adhesion molecules such as alpha x beta 2 integrin (LeuM5) and L- selectin (Leu8) showed that these markers were detectable on variable proportions of leukemic cells, thus confirming the intraclonal phenotypic heterogeneity of B-CLL. Differences in the intensity of CD44 expression were also shown among the various B-CLL clones. Finally, no major variations were shown by comparison of adhesion molecule phenotypes of leukemic cells simultaneously obtained from blood and bone marrow, and of CD5+ versus CD5- clones.
Located between the on-detector front-end electronics and the global data acquisition system (DAQ), the off-detector electronics of the CMS electromagnetic calorimeter (ECAL) is involved in both ...detector readout and trigger system. Working at 40 MHz, the trigger part must, within 10 clock cycles, receive and deserialise the data of the front-end electronics, encode the trigger primitives using a non linear scale, assure time alignment between channels using a histogramming technique and send the trigger primitives to the regional trigger. In addition, it must classify trigger towers in three classes of interest and send this classification to the readout part. The readout part must select the zero suppression level to apply depending on the regions of interest determined from the trigger tower classification, deserialise front-end data coming from high-speed (800 Mbit/s) serial links, check their integrity, apply zero suppression, build the event and send it to the DAQ, monitor the buffer occupancy and send back pressure to the trigger system when required, provide data spying and monitoring facilities for the local DAQ. The system, and especially the data link speed, the latency constraints and the bit error rate requirements have been validated on prototypes. Part of the system is about to go to production.
During moonlit nights, observations with ground-based Cherenkov telescopes at
very high energies (VHE, $E>100$ GeV) are constrained since the photomultiplier
tubes (PMTs) in the telescope camera are ...extremely sensitive to the background
moonlight. Observations with the VERITAS telescopes in the standard
configuration are performed only with a moon illumination less than 35$\%$ of
full moon. Since 2012, the VERITAS collaboration has implemented a new
observing mode under bright moonlight, by either reducing the voltage applied
to the PMTs (reduced-high-voltage configuration, RHV), or by utilizing
UV-transparent filters. While these operating modes result in lower sensitivity
and increased energy thresholds, the extension of the available observing time
is useful for monitoring variable sources such as blazars and sources requiring
spectral measurements at the highest energies. In this paper we report the
detection of $\gamma$-ray flaring activity from the BL Lac object 1ES 1727+502
during RHV observations. This detection represents the first evidence of VHE
variability from this blazar. The integral flux is
$(1.1\pm0.2)\times10^{-11}\mathrm{cm^{-2}s^{-1}}$ above 250 GeV, which is about
five times higher than the low-flux state. The detection triggered additional
\veritas\ observations during standard dark-time. Multiwavelength observations
with the FLWO 48" telescope, and the Swift and Fermi satellites are presented
and used to produce the first spectral energy distribution (SED) of this object
during $\gamma$-ray flaring activity. The SED is then fitted with a standard
synchrotron-self-Compton model, placing constraints on the properties of the
emitting region and of the acceleration mechanism at the origin of the
relativistic particle population in the jet.
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