445 research outputs found
Letter to Nature: An ultra-relativistic outflow from a neutron star accreting gas from a companion.
No full textCollimated relativistic outflows—also known as jets—are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei1, accreting stellar-mass black holes and neutron stars in binary systems2 and are believed to be responsible for gamma-ray bursts3. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downstream in the flow, which are themselves moving at mildly relativistic bulk velocities and are the sites of the observed synchrotron emission from the jet. We conclude that the generation of highly relativistic outflows does not require properties that are unique to black holes, such as an event horizon
Examples of extreme intraday variability
No full textThe original publication can be found at www.springerlink.comLucyna Kedziora-Chudczer, David L. Jauncey, Mark A. Wieringa, Anastasios K. Tzioumis and Hayley E. Bignal
Revisiting the relativistic ejection event in XTE J1550-564 during the 1998 outburst
No full textWe revisit the discovery outburst of the X-ray transient XTE J1550−564 during which relativistic jets were observed in 1998 September, and review the radio images obtained with the Australian Long Baseline Array, and light curves obtained with the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array. Based on Hi spectra, we constrain the source distance to between 3.3 and 4.9 kpc. The radio images, taken some 2 d apart, show the evolution of an ejection event. The apparent separation velocity of the two outermost ejecta is at least 1.3c and may be as large as 1.9c; when relativistic effects are taken into account, the inferred true velocity is ≥ 0.8c. The flux densities appear to peak simultaneously during the outburst, with a rather flat (although still optically thin) spectral index of −0.2
Variability in GPS sources
No full textCopyright © CSIRO 2003D. L. Jauncey, Edward A. King, Hayley E. Bignall, J. E. J. Lovell, Lucyna Kedziora-Chudczer, A. K. Tzioumis, S. J. Tingay, Jean-Pierre Macquart and P. M. McCulloc
Radio observations of NGC 6388: an upper limit on the mass of its central black hole
No full textWe present the results of deep radio observations with the Australia Telescope Compact Array (ATCA) of the globular cluster NGC 6388. We show that there is no radio source detected (with an rms noise level of 27 μJy) at the cluster centre of gravity or at the locations of any of the Chandra X-ray sources in the cluster. Based on the fundamental plane of accreting black holes which is a relationship between X-ray luminosity, radio luminosity and black hole mass, we place an upper limit of ∼1500 M⊙ on the mass of the putative intermediate-mass black hole located at the centre of NGC 6388. We discuss the uncertainties of this upper limit and the previously suggested black hole mass of 5700 M⊙ based on surface density profile analysis
Constraints on black hole accretion in V Puppis
No full textIn light of the recent suggestion that the nearby eclipsing binary star system V Puppis has a dark companion on a long orbit, we present the results of radio and X-ray observations of it. We find an upper limit on its radio flux of about 300 ?Jy and a detection of it in the X-rays with a luminosity of about 3 × 1031 erg s?1, a value much lower than what had been observed in some of the low angular resolution surveys of the past. These data are in good agreement with the idea that the X-ray emission from V Puppis comes from mass transfer between the two B stars in the system, but can still accommodate the idea that the X-ray emission comes from the black hole accreting stellar wind from one or both of the B star
The Radio Remnant of Supernova 1987A − A Broader View
No full textSupernova remnants (SNRs) are powerful particle accelerators. As a supernova (SN) blast wave propagates through the circumstellar medium (CSM), electrons and protons scatter across the shock and gain energy by entrapment in the magnetic field. The accelerated particles generate further magnetic field fluctuations and local amplification, leading to cosmic ray production. The wealth of data from Supernova 1987A is providing a template of the SN-CSM interaction, and an important guide to the radio detection and identification of core-collapse SNe based on their spectral properties. Thirty years after the explosion, radio observations of SNR 1987A span from 70 MHz to 700 GHz. We review extensive observing campaigns with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and follow-ups with other radio telescopes. Observations across the radio spectrum indicate rapid changes in the remnant morphology, while current ATCA and ALMA observations show that the SNR has entered a new evolutionary phase.postprin
Interstellar scintillation and annual cycles in the BL Lac source PKS 1519-273
No full textThe original publication can be found at www.springerlink.comWe have measured annual cycles in the time scales of the rapid, intra-day variability of the total and circularly polarized flux density, of the unusual BL Lac source PKS 1519–273 at 4.8 and 8.6 GHz. This data was collected at the ATCA over the last seven years, and establishes unequivocally interstellar scintillation as the principal mechanism responsible for this cm-wavelength intra-day variability.David L. Jauncey, Helen M. Johnston, Hayley E. Bignall, J.E.J. Lovell, Lucyna Kedziora-Chudczer, A.K. Tzioumis and Jean-Pierre Macquar
Addressing Access to Healthy Food Among Mothers, Pregnant Women, Infants, and Children Under 5 in Cleveland County, North Carolina Through a WIC-Authorized Mobile Market
No full textMothers, infants, and children under five in Cleveland County, North Carolina (priority population) have limited access to healthy foods due to the neighborhood and built environment consisting of a lack of public transportation, a rural geography, and a scarcity of grocery stores that offer a wide selection of healthy foods, including fresh fruits and vegetables. An unhealthy diet lacking in fresh fruits and vegetables can increase the risk of poor health consequences including decreased immunity, poor maternal health and/or fetal outcomes, obesity, and diabetes. We will implement a mobile market stocked with healthy foods including fresh fruits and vegetables, serving rural areas of the county, accepting WIC, SNAP, or cash/credit payments. To evaluate the program's outcomes, a study will be conducted to assess participants' fruit and vegetable intakes, pre- and post-intervention. This program strives to improve access to healthy food and increase the priority population’s overall fruit and vegetable intake.Master of Public Healt
Breakfast After the Bell - A Nutrition-Based Solution to Improving Education Access and Quality in Cleveland County Secondary Schools
No full textThis proposal describes a school nutrition program that will improve education access and quality by addressing chronic absenteeism for the secondary students at Cleveland County Schools (CCS). Chronic absenteeism or missing more than 10% of school days, is linked to poor academic performance and serious health issues that persist into adulthood. Nationally, rural schools, like those in Cleveland County, have higher absence rates compared to suburban schools. Breakfast After the Bell (BAB) is an evidence-based program proven to improve school attendance and provides school breakfast through three different, school-dependent models. This program would incorporate an interdisciplinary approach between CCS and the Cleveland County Public Health Department (CCPHD), while focusing on primary stakeholders like students and families. Addressing nutrition and school attendance will result in improved school attendance, graduation rates, educational attainment, and health outcomes.Master of Public Healt
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