We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGNs), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when ...multi-TeV gamma-rays from an AGN interact with extragalactic background light (EBL) photons to produce electron-positron pairs, which then interact with cosmic microwave background photons via inverse-Compton scattering to produce gamma-rays. Due to the deflection of the electron-positron pairs, a non-zero intergalactic magnetic field (IGMF) would potentially produce detectable effects on the angular distribution of the cascade emission. In particular, an angular broadening compared to the unscattered emission could occur. Through non-detection of angularly broadened emission from 1ES 1218+304, the source with the largest predicted cascade fraction, we exclude a range of IGMF strengths around 10−14 G at the 95% confidence level. The extent of the exclusion range varies with the assumptions made about the intrinsic spectrum of 1ES 1218+304 and the EBL model used in the simulation of the cascade process. All of the sources are used to set limits on the flux due to extended emission.
Cosmic-ray electrons and positrons (CREs) at GeV-TeV energies are a unique probe of our local Galactic neighborhood. CREs lose energy rapidly via synchrotron radiation and inverse-Compton scattering ...processes while propagating within the Galaxy, and these losses limit their propagation distance. For electrons with TeV energies, the limit is on the order of a kiloparsec. Within that distance, there are only a few known astrophysical objects capable of accelerating electrons to such high energies. It is also possible that the CREs are the products of the annihilation or decay of heavy dark matter (DM) particles. VERITAS, an array of imaging air Cherenkov telescopes in southern Arizona, is primarily utilized for gamma-ray astronomy but also simultaneously collects CREs during all observations. We describe our methods of identifying CREs in VERITAS data and present an energy spectrum, extending from 300 GeV to 5 TeV, obtained from approximately 300 hours of observations. A single power-law fit is ruled out in VERITAS data. We find that the spectrum of CREs is consistent with a broken power law, with a break energy at 710±40stat±140syst GeV.
Blazars have traditionally been separated into two broad categories based on their optical emission characteristics. Blazars with faint or no emission lines are referred to as BL Lacertae objects (BL ...Lacs), and blazars with prominent, broad emission lines are commonly referred to as flat-spectrum radio quasars (FSRQs). The spectral energy distribution of FSRQs has generally been thought of as being more akin to the low-peaked BL Lacs, which exhibit a peak in the infrared region of the spectrum, as opposed to high-peaked BL Lacs (HBLs), which exhibit a peak in UV/X-ray region of the spectrum. All blazars that are currently confirmed as sources of TeV emission fall into the HBL category. Recent surveys have found several FSRQs that exhibit spectral properties, particularly the synchrotron peak frequency, similar to HBLs. These objects are potential sources of TeV emission according to several models of blazar jet emission and the evolution of blazars. Measurements of TeV flux or flux upper limits could impact existing theories explaining the links between different blazar types and could have a significant impact on our understanding of the nature of objects that are capable of TeV emission. In particular, the presence (or absence) of TeV emission from FSRQs could confirm (or cast doubt on) recent evolutionary models that expect intermediate objects in a transitional state between FSRQ and BL Lac. The Whipple 10 m imaging air Cerenkov gamma-ray telescope is well suited for TeV gamma-ray observations. Using the Whipple telescope, we have taken data on a small selection of nearby (z < 0.1 in most cases) high-peaked FSRQs. Although one of the objects, B2 0321+33, showed marginal evidence of flaring, no significant emission was detected. The implications of this paucity of emission and the derived upper limits are discussed.
Distraction has been shown to be an effective technique for managing pain in children; however, few investigations have examined the utility of this technique with infants. The goal of the current ...study was to investigate the effectiveness of movie distraction in reducing infants' immunization distress. Participants were 136 infants (range=1-21 months; M=7.6 months, SD=5.0 months) and their parents, all of whom were recruited when presenting for routine vaccinations. The parent-child dyads were randomly assigned to either a Distraction or Typical Care control condition. Infant and adult behaviors were assessed using a visual analog scale and a behavioral observation rating scale. Results indicated parents in the Distraction group engaged in higher rates of distraction than those in the Typical Care group, whereas there was no difference in the behavior of nurses in the Distraction and Typical Care groups. In addition, infants in the Distraction group displayed fewer distress behaviors than infants in the Typical Care group both prior to and during recovery from the injection. Findings suggest that a simple and practical distraction intervention can provide some distress relief to infants during routine injections.
RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE Arlen, T; Aune, T; BEILICKE, M ...
Astrophysical journal/The Astrophysical journal,
01/2013, Letnik:
762, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We report on the detection of a very rapid TeV gamma-ray flare from BL Lacertae on 2011 June 28 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The flaring activity was ...observed during a 34.6 minute exposure, when the integral flux above 200 GeV reached (3.4 + or - 0.6) x 10 super(-6) photons m super(-2) s super(-1), roughly 125% of the Crab Nebula flux measured by VERITAS. The light curve indicates that the observations missed the rising phase of the flare but covered a significant portion of the decaying phase. The exponential decay time was determined to be 13 + or - 4 minutes, making it one of the most rapid gamma-ray flares seen from a TeV blazar. The gamma-ray spectrum of BL Lacertae during the flare was soft, with a photon index of 3.6 + or - 0.4, which is in agreement with the measurement made previously by MAGIC in a lower flaring state. Contemporaneous radio observations of the source with the Very Long Baseline Array revealed the emergence of a new, superluminal component from the core around the time of the TeV gamma-ray flare, accompanied by changes in the optical polarization angle. Changes in flux also appear to have occurred at optical, UV, and GeV gamma-ray wavelengths at the time of the flare, although they are difficult to quantify precisely due to sparse coverage. A strong flare was seen at radio wavelengths roughly four months later, which might be related to the gamma-ray flaring activities. We discuss the implications of these multiwavelength results.
Context.
The response of imaging atmospheric Cherenkov telescopes to incident
γ
-ray-initiated showers in the atmosphere changes as the telescopes age due to exposure to light and weather. These ...aging processes affect the reconstructed energies of the events and
γ
-ray fluxes.
Aims.
This work discusses the implementation of signal calibration methods for the Very Energetic Radiation Imaging Telescope Array System (VERITAS) to account for changes in the optical throughput and detector performance over time.
Methods.
The total throughput of a Cherenkov telescope is the product of camera-dependent factors, such as the photomultiplier tube gains and their quantum efficiencies, and the mirror reflectivity and Winston cone response to incoming radiation. This document summarizes different methods to determine how the camera gains and mirror reflectivity have evolved over time and how we can calibrate this changing throughput in reconstruction pipelines for imaging atmospheric Cherenkov telescopes. The implementation is validated against seven years of observations with the VERITAS telescopes of the Crab Nebula, which is a reference object in very-high-energy astronomy.
Results.
Regular optical throughput monitoring and the corresponding signal calibrations are found to be critical for the reconstruction of extensive air shower images. The proposed implementation is applied as a correction to the signals of the photomultiplier tubes in the telescope simulation to produce fine-tuned instrument response functions. This method is shown to be effective for calibrating the acquired
γ
-ray data and for recovering the correct energy of the events and photon fluxes. At the same time, it keeps the computational effort of generating Monte Carlo simulations for instrument response functions affordably low.
The high-frequency-peaked BL Lacertae object 1ES 0229+200 is a relatively distant (z = 0.1396), hard-spectrum (Gamma ~ 2.5), very-high-energy (VHE; E > 100 GeV) emitting gamma -ray blazar. VHE ...measurements of this active galactic nucleus have been used to place constraints on the intensity of the extragalactic background light and the intergalactic magnetic field (IGMF). A multi-wavelength study of this object centered around VHE observations by Very Energetic Radiation Imaging Telescope Array System (VERITAS) is presented. This study obtained, over a period of three years, an 11.7 standard deviation detection and an average integral flux F(E > 300 GeV) = (23.3 + or - 2.8 sub(stat) + or - 5.8 sub(sys)) x 10 super(-9) photons m super(-2) s super(-1), or 1.7% of the Crab Nebula's flux (assuming the Crab Nebula spectrum measured by H.E.S.S). Supporting observations from Swift and RXTE are analyzed. The Swift observations are combined with previously published Fermi observations and the VHE measurements to produce an overall spectral energy distribution which is then modeled assuming one-zone synchrotron-self-Compton emission. The chi super(2) probability of the TeV flux being constant is 1.6%. This, when considered in combination with measured variability in the X-ray band, and the demonstrated variability of many TeV blazars, suggests that the use of blazars such as 1ES 0229+200 for IGMF studies may not be straightforward and challenges models that attribute hard TeV spectra to secondary gamma -ray production along the line of sight.
Abstract
The Breakthrough Listen Initiative is conducting a program using multiple telescopes around the world to search for “technosignatures”: artificial transmitters of extraterrestrial origin ...from beyond our solar system. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) Collaboration joined this program in 2018 and provides the capability to search for one particular technosignature: optical pulses of a few nanoseconds in duration detectable over interstellar distances. We report here on the analysis and results of dedicated VERITAS observations of Breakthrough Listen targets conducted in 2019 and 2020 and of archival VERITAS data collected since 2012. Thirty hours of dedicated observations of 136 targets and 249 archival observations of 140 targets were analyzed and did not reveal any signals consistent with a technosignature. The results are used to place limits on the fraction of stars hosting transmitting civilizations. We also discuss the minimum pulse sensitivity of our observations and present VERITAS observations of CALIOP: a space-based pulsed laser on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations. The detection of these pulses with VERITAS, using the analysis techniques developed for our technosignature search, allows a test of our analysis efficiency and serves as an important proof of principle.
The purpose of the present study was to provide empirical evidence of system-based barriers to psychological services for pediatric brain tumor patients when they are medically indicated.
Insurance ...claims data covering 263,866 insured lives during the 1996 fiscal year were pooled from a cross-sectional national sample of adults and their families insured by private insurance companies or self-insured firms. Based on inclusion criteria, records for 209 pediatric brain tumor patients aged 18 and under were extracted and analyzed. Claims data including total amount of payments made on behalf of a member, total length of hospital stays, and total number of unique admissions were recorded for all patients, and current procedural terminology (CPT) codes were analyzed to determine frequency of payment for routinely billed psychological procedures. Results were then compared to the frequency of payment for routinely billed psychological procedures for children with other medical conditions.
Results indicate that two of the CPT codes commonly associated with neurocognitive evaluations were reimbursed by these third-party payers for pediatric brain tumor patients during the 1996 fiscal year. Additionally, seven of the CPT codes commonly associated with psychological therapy were also reimbursed.
The present findings provide empirical evidence of system-based obstacles (i.e., lack of third-party reimbursement) for medically indicated psychological services in pediatric brain tumor patients.
Abstract
Superluminous supernovae (SLSNe) are a rare class of stellar explosions with luminosities ∼ 10–100 times greater than ordinary core-collapse supernovae. One popular model to explain the ...enhanced optical output of hydrogen-poor (Type I) SLSNe invokes energy injection from a rapidly spinning magnetar. A prediction in this case is that high-energy gamma-rays, generated in the wind nebula of the magnetar, could escape through the expanding supernova ejecta at late times (months or more after optical peak). This paper presents a search for gamma-ray emission in the broad energy band from 100 MeV to 30 TeV from two Type I SLSNe, SN2015bn, and SN2017egm, using observations from Fermi-LAT and VERITAS. Although no gamma-ray emission was detected from either source, the derived upper limits approach the putative magnetar’s spin-down luminosity. Prospects are explored for detecting very-high-energy (VHE; 100 GeV–100 TeV) emission from SLSNe-I with existing and planned facilities such as VERITAS and CTA.
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