Aims. The aim of this study is to search for evidence of a common emission engine between radio giant pulses (GPs) and very-high-energy (VHE, E > 100 GeV) γ -rays from the Crab pulsar. Methods. We ...performed 16 h of simultaneous observations of the Crab pulsar at 1.4 GHz with the Effelsberg radio telescope and the Westerbork Synthesis Radio Telescope (WSRT), and at energies above 60 GeV we used the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes. We searched for a statistical correlation between the radio and VHE γ -ray emission with search windows of different lengths and different time lags to the arrival times of a radio GP. A dedicated search for an enhancement in the number of VHE γ -rays correlated with the occurrence of radio GPs was carried out separately for the P1 and P2 phase ranges, respectively. Results. In the radio data sample, 99444 radio GPs were detected. We find no significant correlation between the GPs and VHE photons in any of the search windows. Depending on phase cuts and the chosen search windows, we find upper limits at a 95% confidence level on an increase in VHE γ -ray events correlated with radio GPs between 7% and 61% of the average Crab pulsar VHE flux for the P1 and P2 phase ranges, respectively. This puts upper limits on the flux increase during a radio GP between 12% and 2900% of the pulsed VHE flux, depending on the search window duration and phase cuts. This is the most stringent upper limit on a correlation between γ -ray emission and radio GPs reported so far.
Galaxies as complex systems Shore, S N; Galli, D
Astrophysics and space science,
01/2003, Letnik:
284, Številka:
2
Journal Article
Recenzirano
... all for the want of a nail. English nursery rhyme Feedback is the essential property of multiphase models for the evolution of galaxies. In this review, we stress the generic behavior of toy ...models to highlight those features that are inevitable consequences of assumptions in the current catalog of galactic evolution calculations.PUBLICATION ABSTRACT
This paper reviews general features common to all novae, classical or recurrent, from a multi-wavelength perspective, although concentrating on the 1000 - 8000 A range, for which the greatest wealth ...of high resolution data exists. Particular information derived from line profiles are highlighted, e.g. abundances, mixing within the ejecta, fossilized instabilities and symmetries of the expanding gas, radial dependence of the velocity and density, and time dependent ionization. Energetics of the outburst, especially the prolonged constant luminosity phase following initial outburst, are discussed along with the evidence for super-Eddington phases of the later outburst. Finally, contrasts between Galactic and Magellanic Cloud novae are discussed with a view toward extending studies to extragalactic novae with future ground-based and satellite observatories. (Author)
We report the Fermi-LAT gamma-ray detection of the 2021 outburst of the symbiotic recurrent nova RS Ophiuchi. In this system, unlike classical novae from cataclysmic binaries, the ejecta from the ...white dwarf form shocks when interacting with the dense circumstellar wind environment of the red giant companion. We find the LAT spectra from 50 MeV to ~20-23 GeV, the highest-energy photons detected in some sub-intervals, are consistent with \(\pi^{\rm 0}\)-decay emission from shocks in the ejecta as proposed by Tatischeff & Hernanz (2007) for its previous 2006 outburst. The LAT light-curve displayed a fast rise to its peak >0.1 GeV flux of \(\simeq\)6x10^-6 ph cm^-2 s^-1 beginning on day 0.745 after its optically-constrained eruption epoch of 2021 August 8.50. The peak lasted for ~1 day, and exhibited a power-law decline up to the final LAT detection on day 45. We analyze the data on shorter timescales at early times and found evidence of an approximate doubling of emission over ~200 minutes at day 2.2, possibly indicating a localized shock-acceleration event. Comparing the data collected by the AAVSO, we measured a constant ratio of ~2.8x10^-3 between the gamma-ray and optical luminosities except for a ~5x smaller ratio within the first day of the eruption likely indicating attenuation of gamma rays by ejecta material and lower high-energy proton fluxes at the earliest stages of the shock development. The hard X-ray emission due to bremsstrahlung from shock-heated gas traced by the Swift-XRT 2-10 keV light-curve peaked at day ~6, later than at GeV and optical energies. Using X-ray derived temperatures to constrain the velocity profile, we find the hadronic model reproduces the observed >0.1 GeV light-curve.
Abstract
We present the first detection of the nearby (z = 0.084) low-luminosity BL Lac object 1ES 1741+196 in the very high energy (E > 100 GeV) band. This object lies in a triplet of interacting ...galaxies. Early predictions had suggested 1ES 1741+196 to be, along with several other high-frequency BL Lac sources, within the reach of MAGIC detectability. Its detection by MAGIC, later confirmed by VERITAS, helps to expand the small population of known TeV BL Lacs. The source was observed with the MAGIC telescopes between 2010 April and 2011 May, collecting 46 h of good quality data. These observations led to the detection of the source at 6.0 σ confidence level, with a steady flux F(>100 GeV) = (6.4 ± 1.7stat ± 2.6syst) × 10−12 ph cm−2s−1 and a differential spectral photon index Γ = 2.4 ± 0.2stat ± 0.2syst in the range of ∼80 GeV–3 TeV. To study the broad-band spectral energy distribution (SED) simultaneous with MAGIC observations, we use KVA, Swift/UVOT and XRT and Fermi/LAT data. One-zone synchrotron-self-Compton (SSC) modelling of the SED of 1ES 1741+196 suggests values for the SSC parameters that are quite common among known TeV BL Lacs except for a relatively low Doppler factor and slope of electron energy distribution. A thermal feature seen in the SED is well matched by a giant elliptical's template. This appears to be the signature of thermal emission from the host galaxy, which is clearly resolved in optical observations.
Aims. We aim to derive the physical properties of the recurrent nova T Pyx and the structure of the ejecta during the early stages of expansion of the 2011 outburst. Methods. The nova was observed ...with high resolution spectroscopy (R ≈ 65 000), from one day after discovery of the outburst and until the last visibility of the star at the end of May 2011. The interstellar absorption lines of Na I, Ca II, CH, CH+, and archival H I 21 cm emission line observations were used to determine a kinematical distance. Interstellar diffuse absorption features have been used to determine the extinction independent of previous assumptions. Sample Fe-peak line profiles show the optical depth and radial velocity evolution of the discrete components. Results. We propose a distance to T Pyx ≥ 4.5 kpc, with a strict lower limit of 3.5 kpc (the previously accepted distance). We derive an extinction, E(B − V) ≈ 0.5 ± 0.1, that is higher than previous estimates. The first observation, Apr. 15, displayed He I, He II, C III, and N III emission lines and a maximum velocity derived from the P Cyg profiles of the Balmer and He I lines of ≈2500 km s-1 that is characteristic of the fireball stage. These ions were undetectable in the second spectrum, Apr. 23, and we use the recombination time to estimate the mass of the ejecta, 10-5f M⊙ for a filling factor f. Numerous absorption-line systems were detected in the Balmer, Fe-peak, Ca II, and Na I lines, mirrored in broader emission-line components, that showed an “accelerated” displacement in velocity. We also show that the time sequence of these absorptions, which are common to all lines and arise only in the ejecta, can be described by a recombination front moving outward in the expanding gas without either a stellar wind or circumstellar collisions. By the end of May, the ejecta were showing signs of turning optically thin in the ultraviolet.
Postoperative atrial fibrillation in coronary artery bypass graft surgery occurs in 10-40% of patients. It is associated with a significant degree of morbidity and results in prolonged lengths of ...stay in both the intensive care unit and hospital.
The authors prospectively evaluated patients undergoing coronary artery bypass with detailed transesophageal echocardiography examinations conducted before and after cardiopulmonary bypass to study whether risk factors for atrial fibrillation could be identified. Demographic and surgical parameters were also included in the analysis. Selected variables were subjected to univariate and subsequent multivariate analyses to test for their independent or joint influence on atrial fibrillation.
Seventy-nine patients had assessable transesophageal echocardiography examinations. Significant univariate predictors of atrial fibrillation included advanced age (P = 0.002), pre-cardiopulmonary bypass left atrial appendage area (P = 0.04), and post-cardiopulmonary bypass left upper pulmonary vein systole/diastole velocity ratio (P = 0.03). When these three factors were considered together in a multiple logistic regression analysis, left upper pulmonary vein systole/diastole velocity ratio was a significant predictor (P < 0.05), as was the joint effect of age plus pre-cardiopulmonary bypass left atrial appendage area (P = 0.005). The probability of developing atrial fibrillation for the combination of age = 75 yr, post-cardiopulmonary bypass left upper pulmonary vein systole/diastole velocity ratio = 0.5, and left atrial appendage area = 4.0 cm was 0.83 (95% confidence interval, 0.51-0.96).
Early identification of patients at risk for postoperative atrial fibrillation may be feasible using the parameters identified in this study.
We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) γ -ray emission from two recent optically bright classical novae, V1369 Centauri 2013 and V5668 Sagittarii 2015. At ...early times, Fermi target-of-opportunity observations prompted by their optical discoveries provided enhanced LAT exposure that enabled the detections of γ -ray onsets beginning ∼2 days after their first optical peaks. Significant γ -ray emission was found extending to 39–55 days after their initial LAT detections, with systematically fainter and longer-duration emission compared to previous γ -ray-detected classical novae. These novae were distinguished by multiple bright optical peaks that encompassed the time spans of the observed γ -rays. The γ -ray light curves and spectra of the two novae are presented along with representative hadronic and leptonic models, and comparisons with other novae detected by the LAT are discussed.
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