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"Lord, R T"
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Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event
The Galactic Centre contains a supermassive black hole with a mass of four million Suns
1
within an environment that differs markedly from that of the Galactic disk. Although the black hole is essentially quiescent in the broader context of active galactic nuclei, X-ray observations have provided evidence for energetic outbursts from its surroundings
2
. Also, although the levels of star formation in the Galactic Centre have been approximately constant over the past few hundred million years, there is evidence of increased short-duration bursts
3
, strongly influenced by the interaction of the black hole with the enhanced gas density present within the ring-like central molecular zone
4
at Galactic longitude |
l
| < 0.7 degrees and latitude |
b
| < 0.2 degrees. The inner 200-parsec region is characterized by large amounts of warm molecular gas
5
, a high cosmic-ray ionization rate
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, unusual gas chemistry, enhanced synchrotron emission
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,
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, and a multitude of radio-emitting magnetized filaments
9
, the origin of which has not been established. Here we report radio imaging that reveals a bipolar bubble structure, with an overall span of 1 degree by 3 degrees (140 parsecs × 430 parsecs), extending above and below the Galactic plane and apparently associated with the Galactic Centre. The structure is edge-brightened and bounded, with symmetry implying creation by an energetic event in the Galactic Centre. We estimate the age of the bubbles to be a few million years, with a total energy of 7 × 10
52
ergs. We postulate that the progenitor event was a major contributor to the increased cosmic-ray density in the Galactic Centre, and is in turn the principal source of the relativistic particles required to power the synchrotron emission of the radio filaments within and in the vicinity of the bubble cavities.
Radio observations show a bipolar bubble structure of size 140 parsecs by 430 parsecs both above and below the Galactic Centre.
Journal Article
The MeerKAT Galaxy Cluster Legacy Survey I. Survey Overview and Highlights
MeerKAT's large number of antennas, spanning 8 km with a densely packed 1 km core, create a powerful instrument for wide-area surveys, with high sensitivity over a wide range of angular scales. The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a programme of long-track MeerKAT L-band (900-1670 MHz) observations of 115 galaxy clusters, observed for \\(\\sim\\)6-10 hours each in full polarisation. The first legacy product data release (DR1), made available with this paper, includes the MeerKAT visibilities, basic image cubes at \\(\\sim\\)8\" resolution, and enhanced spectral and polarisation image cubes at \\(\\sim\\)8\" and 15\" resolutions. Typical sensitivities for the full-resolution MGCLS image products are \\(\\sim\\)3-5 {\\mu}Jy/beam. The basic cubes are full-field and span 4 deg^2. The enhanced products consist of the inner 1.44 deg^2 field of view, corrected for the primary beam. The survey is fully sensitive to structures up to \\(\\sim\\)10' scales and the wide bandwidth allows spectral and Faraday rotation mapping. HI mapping at 209 kHz resolution can be done at \\(0
Paper
Prescribed burning in the oak-pine forest of the New Jersey Pine Barrens: effects on growth and nutrient dynamics of two Quercus species
To determine the effect of the transient increase in nutrient availability which follows prescribed burning in the New Jersey Pine Barrens, we monitored growth and foliar nutrient dynamics of white oak (Quercus alba) and chestnut oak (Q. prinus) in neighboring burned and unburned plots. Growth rates of oak trees in the burned plot were significantly higher in 1985 (the postburn year) than in the 4 years prior to the fire. Growth increases in the burned site averaged 55% for white oak and 38% for chestnut oak. In contrast, relative growth rates of reference site Quercus trees did not differ between preburn and postburn years. Phosphorus resorption and calcium deposition in chestnut oak were greater in the burned site, though growth efficiencies did not differ between chestnut oak trees in the burned and reference sites. Calcium deposition and phosphorus growth efficiency of white oak were greater in the burned site; no differences in white oak N or P resorption were noted. These oaks showed rapid growth responses to the transient increases in nutrient supply produced by prescribed burning. Pinus rigida growth also increased slightly, though the increase was less than those of the oaks. These results contradict earlier assertions of the efficacy of sporadic prescribed burning as a management tool in these oak-pine forests and suggest that sporadic prescribed burning may accelerate, not retard, succession toward oak dominance.
Journal Article
101 Reasons for Using Cooperative Learning in Biology Teaching
An assessment is presented on cooperative learning, or students working together in small teams under the supervision of a teacher, and its successful application to instruction in biology. Benefits of cooperative learning include improved student understanding of practical relationships, enhanced social skills, and presents students with a model of real-world problem solving.
Journal Article
The SARAO MeerKAT 1.3 GHz Galactic Plane Survey
We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251\\deg \\(\\le l \\le\\) 358\\deg and 2\\deg \\(\\le l \\le\\) 61\\deg at \\(|b| \\le 1.5\\deg \\)). SMGPS is the largest, most sensitive and highest angular resolution 1 GHz survey of the Plane yet carried out, with an angular resolution of 8\" and a broadband RMS sensitivity of \\(\\sim\\)10--20 \\(\\mu\\) Jy/beam. Here we describe the first publicly available data release from SMGPS which comprises data cubes of frequency-resolved images over 908--1656 MHz, power law fits to the images, and broadband zeroth moment integrated intensity images. A thorough assessment of the data quality and guidance for future usage of the data products are given. Finally, we discuss the tremendous potential of SMGPS by showcasing highlights of the Galactic and extragalactic science that it permits. These highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-IR classification of rare Luminous Blue Variables and discovery of associated extended radio nebulae; new radio stars identified by Bayesian cross-matching techniques; the realisation that many of the largest radio-quiet WISE HII region candidates are not true HII regions; and a large sample of previously undiscovered background HI galaxies in the Zone of Avoidance.
Paper
Revival of the magnetar PSR J1622-4950: observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR
New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a quiescent state since at least early 2015, reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100x larger than during its dormant state. The X-ray flux one month after reactivation was at least 800x larger than during quiescence, and has been decaying exponentially on a 111+/-19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3-6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6-8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation.
Paper
Engineering and Science Highlights of the KAT-7 Radio Telescope
The construction of the KAT-7 array in the Karoo region of the Northern Cape in South Africa was intended primarily as an engineering prototype for technologies and techniques applicable to the MeerKAT telescope. This paper looks at the main engineering and scien- tific highlights from this effort, and discusses their applicability to both MeerKAT and other next-generation radio telescopes. In particular we found that the composite dish surface works well, but it becomes complicated to fabricate for a dish lacking circular symmetry; the Stir- ling cycle cryogenic system with ion pump to achieve vacuum works but demands much higher maintenance than an equivalent Gifford-McMahon cycle system; the ROACH (Recon- figurable Open Architecture Computing Hardware)-based correlator with SPEAD (Stream- ing Protocol for Exchanging Astronomical Data) protocol data transfer works very well and KATCP (Karoo Array Telescope Control Protocol) control protocol has proven very flexible and convenient. KAT-7 has also been used for scientific observations where it has a niche in mapping low surface-brightness continuum sources, some extended HI halos and OH masers in star-forming regions. It can also be used to monitor continuum source variability, observe pulsars, and make VLBI observations
Paper
