Western Lobe Research Articles

Turbulent circumnuclear disc and cold gas outflow in the newborn radio source 4C 31.04

We present deep kiloparsec- and parsec-scale neutral atomic hydrogen (H I) absorption observations of a very young radio source (≤5000 years), 4C 31.04, using the Westerbork Synthesis Radio Telescope (WSRT) and the Global Very Long Baseline Interferometry (VLBI) array. Using z = 0.0598, derived from molecular gas observations, we detect, at both kpc and pc scales, a broad absorption feature (FWZI = 360 km s−1) centred at the systemic velocity, and narrow absorption (FWZI = 6.6 km s−1) redshifted by 220 km s−1, both previously observed. Additionally, we detect a new blueshifted, broad, shallow absorption wing. At pc scales, the broad absorption at the systemic velocity is detected across the entire radio source while the shallow wing is only seen against part of the eastern lobe. The gas has higher H I column density along the eastern lobe than along the western one. The velocity dispersion of the gas is high (≥40 km s−1) along the entire radio continuum, and is highest (≥60 km s−1) in the region including the outflow and the radio hot spot. While we detect a velocity gradient along the western lobe and parts of the eastern lobe at PA ∼ 5° −10°, most of the gas along the rest of the eastern lobe exhibits no signs of rotation. Earlier optical spectroscopy suggests that the optical AGN is very weak. We therefore conclude that the radio lobes of 4C 31.04 are expanding into a circumnuclear disc, partially disrupting it and making the gas highly turbulent. The distribution of gas is predominantly smooth at the spatial resolution of ∼4 pc studied here. However, clumps of gas are also present, particularly along the eastern lobe. This lobe appears to be strongly interacting with the clouds and driving an outflow ∼35 pc from the radio core, with a mass-outflow rate of 0.3 ≤ Ṁ ≤ 1.4 M⊙ year−1. It is likely that this interaction has caused the eastern lobe to be rebrightened, giving the source an asymmetric morphology. We compare our observations with the predictions of a recent analytical model regarding the survival of atomic gas clouds in radio-jet-driven outflows and find that the existence of a subkpc-scale outflow in this case could imply inefficient mixing of the cold gas with the hot medium and high gas density, leading to very short cooling times. Overall, our study provides further evidence of the strong impact of radio jets on the cold interstellar medium (ISM) in the early stages of their evolution and supports the predictions of numerical simulations regarding jet–ISM interactions and the nature of the circumnuclear gas into which the jets expand.

Decadal Changes (1980–2021) of Shoreline and Mangrove Cover in Sundarban Delta, India, Using Remote Sensing and GIS

Abstract Being situated in the estuary of the flood-dominated Hooghly River system, the macrotidal Indian Sundarban Delta (ISD) has become one of the most complex, dynamic, and rapidly changing landforms on Earth’s surface. To study the horizontal areal shifting of shoreline and its impact on mangrove cover in the region, the U.S. Geological Survey (USGS) satellite data of 1980, 1990, 2000, 2010, and 2021 were used. Remote sensing and geographic information system (GIS) techniques were employed in the investigation. Simultaneous prograding and retrograding shoreline shifting was distinguished almost in all the parts, although sediment-starved eastern and macrotidally more active southern lobes experienced dominantly retreating shift, and the sediment-engorged western lobe was demonstrated to be more dynamic. Net areal change over north–south tracks followed the trend of decreasing accretion to increasing erosion while going from west to east, whereas that over west–east tracks followed the trend of exponentially increasing erosion while going from north to south. Overall accretion of ∼91 km2 in the ISD accounted for the augmentation of sparse vegetation of ∼13 km2, whereas ∼243 km2 erosion called for the depletion of sparse and moderate vegetation of ∼18 and ∼174 km2, respectively, over the 41-yr period. Various oceanographic and riparian forces and actions, episodic natural events, etc., vis-a-vis several anthropogenic interventions—all together contributed to such changes. The findings may help the coastal environmentalists, professionals, planners, decision-makers, and implementers in formulating and taking up of suitable strategic measures for integrated and effective coastal zone management in this estuarine wetland forest.

Accentuating the Reservoir Potentials of Balkassar Field by Delineating the Fracture Trends and Hydrocarbon Prospects with the Aid of Seismic Attributes.

Carbonates constitute a significant proportion of the world's hydrocarbon reserves, accounting for approximately 43%. Despite their substantial potential, accurately characterizing these reserves is a challenging task due to their complex and anisotropic nature. In the upper Indus basin of Pakistan, Eocene carbonates exhibit strong production capabilities. However, the Eocene reservoir (comprising the Chorgali and Sakesar formations) and the deeper Lockhart formation of the Paleocene age present a considerable challenge. The Chorgali formation is dolomitic in composition, featuring both primary and secondary porosity, while the Sakesar formation has only secondary porosity resulting from tectonic activity. The delineation of tectonically induced porosities is a highly demanding task that requires exceptional quality seismic and well data for reliable results. To address the complex heterogeneities present in the Eocene reservoir of the upper Indus basin, a variety of seismic attributes, such as sweetness, instantaneous frequency, amplitude, curvature, similarity variance, lateral continuity, and fault likelihood, have been employed in conjunction with fundamental interpreting techniques. These advanced seismic attributes greatly contribute to delineating fracture zones and identifying sweet spots with remarkable precision. They also enable a focus on high-frequency data content and differentiate between shale beds and reservoir zones based on frequency and amplitude. This helps in the concise marking of fractured zones to enhance our understanding of secondary porosity. Moreover, these attributes help delineate the continuity of reflectors and pinpoint disruptions caused by compression forces and tectonic activities. This study aims to capture the heterogeneity and complexity of reservoir zones to address a critical question regarding the Balkassar structure. The Western lobe of the field, which demonstrates promising oil production, outperforms the structurally higher Eastern part, which lags behind in production. This research seeks to recognize the geological elements contributing to the superior performance of the Western lobe and provide guidance for maximizing the potential of the Eastern lobe through advanced characterization techniques.

Initiation and Eruption of a Two-turn Helical Quiescent Filament on 2013 August 2

We investigate a quiescent filament that erupted on 2013 August 2; the eruption was observed in EUV and Hα by the Solar Dynamics Observatory and GONG. After a B9.7 flare in the nearby active region, the dark filament materials near its eastern footpoint start to move in the direction of eruption, and are followed by a counterclockwise rotation identified as the motion of a combination of dark and bright filament materials. Then the entire filament rises up and keeps rotating in a clockwise direction during the eruption. More interestingly, the filament exhibits an unusual two-helix structure near its western footpoint during the eruption, which indicates the existence of a highly twisted flux rope. This hypothesis is confirmed by magnetic field modeling using the flux rope insertion method. In the best-fit unstable model, the lower limits of the estimated maximum and average twist numbers of the erupting flux rope reach 7.5π and 4π, which suggests that kink instability plays an important role in the eruption. During these magnetically coupled sympathetic eruptions, the highly twisted filament under the western lobe of a pseudo-streamer-like structure becomes unstable and erupts due to the removal of confinement by magnetic reconnection at the overlying hyperbolic flux tube, which is initiated by the B9.7 flare in the nearby active region. The initial filament motion occurs at the more unstable eastern footpoint, where the surrounding fields are weaker and decrease with height more rapidly.

Loess chronology and composition as interpreted through the lens of fossiliferous lake sediments in central Illinois, USA

Silty lacustrine and paludal records spanning from the penultimate deglaciation (late Illinois Episode) to the present are preserved in kettles formed during marine isotope stage (MIS) 6 that lie adjacent to the MIS 2 Manito terrace along the valleys of the Sangamon and Illinois Rivers. Geochemical, mineralogical, particle-size, and chronological records from two basins, Smith Lake and Lake Ben, provide a unique opportunity to assess loess age and provenance of the south-central Laurentide ice sheet. Here, I focused on deposits of redeposited loess of the last glaciation (Wisconsin Episode). Other than subtle laminations and fossils of emergent and aquatic plants and animals, the silty texture, chemical composition, and mineralogy of the lake sediment closely resemble Peoria Silt (loess). Sediment-core records sampled from Smith Lake and Lake Ben in Mason County, Illinois, confirm rapid deposition of proximal loess derived from the nearby outwash plain of the Illinois River from ca. 30.9−18.0 calibrated (cal) k.y. B.P. From 18.0−14.7 cal k.y. B.P., deposition of proximal loess was gradually replaced by far-traveled (distal) loess chiefly derived from Superior lobe provenance and global dust. The succession is capped by a cumulic gleysol that was truncated by recent plowing. Proximal loess deposits in lakes Smith and Ben are composed primarily of very fine sand, coarse silt, and medium silt (125−16 µm) compared to the distal facies (fine silt and finer sediment: <16 µm). Proximal loess that originated from outwash of the Lake Michigan lobe contains abundant Ca, Zr, Sr, illite, and magnetic minerals. The distal facies contains relatively abundant Rb, Al, K, Si, Cu, and Pb, and it is enriched in smectite (relative to illite) and depleted in magnetic minerals. Radiocarbon ages on terrestrial gastropod aragonite in loess from the nearby New Cottonwood School and Thomas Quarry sites indicate that Peoria Silt deposition ended between 18 cal k.y. B.P. and 16 cal k.y. B.P. At these localities, the upper part of the record is complicated by the modern soil, which has altered soil organic matter and leached carbonate. At Lake Ben, the radiocarbon record of emergent aquatic vegetation indicates that sediment accumulation rates and the ratio of proximal to distal loess decreased at the correlative interval that yielded the youngest snail shell ages at Cottonwood School. The upward increase in element concentrations such as Al and decrease in coarse/fine silt ratios in the modern soil are prominent features in the Lake Ben record dating from 18−14 cal k.y. B.P. This correlation strongly suggests that many of the features of the modern soil were not developed into uniform parent material but, rather, were inherited from incremental addition of distal loess to proximal loess, collectively identified as Peoria Silt. The paucity of key elements (Cd, Hg, Se, Ag, Au) in this transition zone suggests limited contributions from western lobes (i.e., Des Moines and James lobes), but abundant Ti and Cu suggest a contribution from the Superior lobe. A new wrinkle in this interpretation is that the rise in elements such as Al, Rb, and Si suggests significant additions from generic dust from unknown sources.

Chemistry and petrography of early 19th century basaltic andesites and basalts from the Kamakaiʻa Hills in the Southwest Rift Zone of Kīlauea volcano, Hawaiʻi

Kīlauea is a frequently active, open-system volcano on the Island of Hawaiʻi known for erupting olivine-dominated tholeiitic basalt compositions. On rare occasions it erupts more differentiated magmas (<1% of erupted volume), such as basaltic andesites and andesites, from its rift zones. These differentiated magmas offer an opportunity to understand better the petrology, magma storage, magma mixing, and eruptive triggers that occur in Kīlauea's rift zone reservoirs. This study focuses on an eruption from the Southwest Rift Zone of Kīlauea, which is dominantly basaltic andesite with subordinate basalt. This eruption originated at the Kamakaiʻa Hills during the early 19th century and has two eruptive phases: 1) an early ‘a‘ā phase that is primarily exposed in the eastern part of the flow field, with minor western lobes, and 2) a late pāhoehoe phase that makes up most of the western part of the flow field. The early ‘a‘ā phase covers at least 5.8 km2 with an erupted volume of ∼150 × 106 m3 and consists of uniform composition basaltic andesites with 3.72–4.15 wt% MgO over its ∼7 km flow length. The late pāhoehoe phase reached >10 km from its vent, covers an area of ∼7.1 km2, has a volume of ∼100 × 106 m3, and initially erupted basaltic andesite near its vent (4.50–5.64 wt% MgO extending to 3.8 km from vent) with channel and tube-fed basalt (6.21–12.38 wt% MgO sampled at >3.8 km from vent) emplaced during its waning stages. Most Kamakaiʻa Hills lavas are crystal-poor, containing ≤1.5% glomerocrysts and individual phenocrysts of plagioclase + clinopyroxene + FeTi oxides ± orthopyroxene, as well as olivine in lavas with >6 wt% MgO.Major-oxide and trace-element concentrations throughout the Kamakaiʻa Hills lavas demonstrate the involvement of three distinct magmatic processes. First, the basaltic andesites of the early ‘a‘ā phase are the products of fractionation of plagioclase + clinopyroxene + FeTi oxides ± orthopyroxene, indicative of magmas that have been stored in rift zone reservoirs for decades or longer. Second, the near-vent (within ∼400 m of vent) basaltic andesites of the late pāhoehoe phase yield chemical concentrations that indicate magma mixing with a more differentiated magma (of a similar evolved composition to basaltic andesites at ∼55–56 wt% SiO2 and ∼3.4–4.1 wt% MgO that erupted in the lower East Rift Zone in 2018). Third, the progressively more mafic magma (containing olivine + plagioclase + clinopyroxene) that continued to erupt throughout the waning stages of activity suggests an eruptive triggering process whereby an intruding summit or uprift reservoir basalt overpressurized and forced out the stored, differentiated magma of the Kamakaiʻa Hills rift zone reservoir.

Unraveling the relationship between a tonalitic pluton and shear zones: Insights from magnetic fabrics and microstructures of the Alto Maranhão batholith, Mineiro belt, southern São Francisco craton

The Alto Maranhão batholith (SE Brazil) comprises granitic juvenile arc-related rocks within the Paleoproterozoic Mineiro Belt. The pluton is bounded by the NE-SW sinistral Jeceaba-Bom Sucesso (JBSZ) and NW-SE dextral Congonhas-Itaverava (CISZ) shear zones. Field, microstructural and magnetic fabric studies were employed in order to constrain its emplacement model and the spatial and temporal relationships between plutons and shear zones during Paleoproterozoic orogenic events. Combined meso- and microscale fabric analyses allowed us to individualize two different domains or lobes across the intrusion. The magmatic foliation, defined by biotite and hornblende, strikes NE-SW in the western lobe and rotates to NW-SE in the eastern lobe, moderately to steeply dipping, trending accordingly with the solid-state foliation exhibited by the country rocks. Field observations show that magmatic structures are preserved, such as elongated to rounded syn-magmatic enclaves and magmatic layering. The microstructures described for both domains are a direct record that deformation occurs locally and under magmatic conditions, with limited features of solid-state deformation such as undulose extinction in quartz and plagioclase on both tonalite and dioritic enclaves. AMS data exhibits dominantly steep magnetic lineations in the eastern lobe of the intrusion, except for sampling sites close to the CISZ, whose lineations are shallowly plunging. In both cases, the magnetic lineation trends NW-SE. Towards the western lobe, the magnetic lineation becomes horizontal and randomly oriented close to its westernmost tip. The magnetic and magmatic foliations follow the same orientation, therefore striking NW-SE in the eastern lobe and NE-SW in the west. Considering the batholith's heterogeneities highlighted by the AMS measurements, we suggest that the eastern lobe of the intrusion is characterized as a feeder zone in which magma was injected along the CISZ, being subsequently spread into the pluton's western lobe, until being stopped by a rheological barrier defined by JBSZ and country rocks, controlling its boomerang-like form. The proposed emplacement model suggests that the Alto Maranhão batholith was emplaced in a contractional site, by arc-normal dextral simple shear revealing that transcurrent deformation was taking place concurrently with the growth of the São Francisco paleocontinent, and addition of mantle-derived magmas to the continental crust.

A physically-motivated perspective of Fanaroff–Riley classification of radio galaxies

A small subset of extragalactic double radio sources, termed HYbrid MOrpholgy Radio Sources (HYMORS), is distinguished by a very unusual, hybrid morphology in terms of Fanaroff–Riley (FR) classification. In HYMORS, one radio lobe appears edge-darkened (FR I), while the other shows a well-defined emission peak near its outer edge (edge-brightened, FR II). Such sources are rare, but critical for constraining the mechanism responsible for FR dichotomy, a widely debated issue in extragalactic astrophysics. Here, we highlight the need for caution in assigning FR type, in view of some upcoming observational campaigns to confirm HYMORS among the candidates. To illustrate this, we highlight the cases of three radio sources, which have been perceived to be HYMORS, including the radio galaxy 0500 $$+$$ 630 (4C $$+$$ 63.07), which has been claimed to be a good, original example of a HYMORS, with a FR I western lobe and a FR II eastern lobe marked by a prominent terminal hot spot. However, its recent VLASS map at 3 GHz has revealed that the western lobe actually extends much farther out than reported and terminates in a well-defined emission peak. This implies that the source is a regular FR II radio galaxy and not a HYMORS. We also provide a brief perspective of the HYMORS phenomenon and underscore the need to confirm a FR I classification by ruling out additional FR II characteristics, such as an inward lobe-widening and spectral steepening, as well as a lack of prominent radio jet within the lobe.

AGN feedback in an infant galaxy cluster: LOFAR-Chandra view of the giant FRII radio galaxy J103025+052430 at z = 1.7

In the nearby universe, jets from active galactic nuclei (AGN) are observed to have a dramatic impact on their surrounding extragalactic environment. The effect of jets at high redshift (z &gt; 1.5) is instead much more poorly constrained. However, studying the jet impact at cosmic noon, the epoch in which both star formation and AGN activity peak, is crucial for fully understanding galaxy evolution. Here we present a study of the giant (∼750 kpc) radio galaxy 103025+052430 located at the centre of a protocluster at redshift z = 1.7, with a focus on its interaction with the external medium. We present new LOFAR observations at 144 MHz, which we combine with VLA 1.4 GHz data and 0.5–7 keV Chandra archival data. The new radio map at 144 MHz confirms that the source has a complex morphology, which can possibly fit the hybrid morphology radio galaxy classification. The large size of the source enabled us to perform a resolved radio spectral index analysis, a very unique opportunity for a source at this high redshift. This revealed a tentative unexpected flattening of the radio spectral index at the edge of the backflow in the western lobe, which might be indicating plasma compression. The spatial coincidence between this region and the thermal X-ray bubble C suggests a causal connection between the two. In contrast to previous estimates for the bright X-ray component A, we find that inverse Compton scattering between the radio-emitting plasma of the eastern lobe and cosmic microwave background photons can account for a large fraction (∼45%–80%) of its total 0.5–7 keV measured flux. Finally, the X-ray bubble C, which is consistent with a thermal origin, is found to be significantly overpressurised with respect to the ambient medium. This suggests that it will tend to expand and release its energy into the surroundings, contributing to the overall intracluster medium heating. Overall, 103025+052430 enables us to investigate the interaction between AGN jets and the surrounding medium in a system that is likely the predecessor of the rich galaxy clusters we all know well at z = 0.

Spatially resolved study of the SS 433/W 50 west region with Chandra: X-ray structure and spectral variation of non-thermal emission

AbstractThe X-ray binary SS 433, embedded in the W 50 nebula (or supernova remnant W 50), shows bipolar jets that are ejected with mildly relativistic velocities and which extend toward the east and west out to scales of tens of parsecs. Previous X-ray observations revealed twin lobes along the jet precession axis that contain compact bright knots dominated by synchrotron radiation, which provide evidence of electron acceleration in this system. Particle acceleration in this system is substantiated by the recently detected gamma rays with energies up to at least 25 TeV. To elucidate the origin of the knots and particle acceleration sites in SS 433/W 50 further, we report here on detailed, spatially resolved X-ray spectroscopy of its western lobe with Chandra. We detect synchrotron emission along the jet precession axis, as well as optically thin thermal emission that is more spatially extended. Between the two previously known knots, w1 and w2, we discover another synchrotron knot, which we call w1.5. We find no significant synchrotron emission between SS 433 and the innermost X-ray knot (w1), suggesting that electrons only begin to be accelerated at w1. The X-ray spectra become gradually steeper from w1 to w2, and then rapidly so immediately outside of w2. Through comparison with a model taking into account electron transport and cooling along the jet, this result indicates that the magnetic field in w2 is substantially enhanced, which also explains its brightness. We discuss possible origins of the enhanced magnetic field of w2 as well as scenarios to explain the other two knots.

Long-term Variability of Class I Methanol Masers in the High-mass Star-forming Region DR21(OH)

High-mass stars play an important role in the interstellar medium, but much remains to be known about their formation. Class I methanol masers may be unique tracers of an early stage of high-mass star formation, and a better understanding of such masers will allow them to be used as more effective probes of the high-mass star-forming process. We present an investigation of the long-term variability of Class I methanol masers at 44 GHz toward the high-mass star-forming region DR21(OH). We compare observations taken in 2017 to observations from 2012, and also to 2001 data from the literature. A total of 57 maser spots were found in the 2017 data, with center velocities ranging between −8.65 to +2.56 km s−1. The masers are arranged in a western and an eastern lobe with two arcs in each lobe that look like bow shocks, consistent with previous observations. The general trend is an increase in intensity from 2001 to 2012, and a decrease from 2012 to 2017. Variability appears to be more prevalent in the inner arc of the western lobe than in the outer arc. We speculate that this may be a consequence of episodic accretion, in which a later accretion event has resulted in ejection of material whose shock reached the inner arc at some point in time after 2001. We conclude that class I methanol masers are variable on long timescales (of the order of 5–10 yr).

A depolarizing H I tidal tail in the western lobe of Fornax A

Recent MeerKAT neutral hydrogen (H I) observations of Fornax A reveal tidal material intersecting in projection the western lobe of this radio galaxy. We found a spatial coincidence between the northern H Itail and a depolarized structure observed for the first time with the Australian Square Kilometre Array Pathfinder (ASKAP) at 1.2 GHz. We analyzed the properties of the rotation measure (RM) image obtained with ASKAP data at the location of the H Itail and in its neighborhood. We modeled the observed RM structure function to investigate the magnetic field power spectrum at the location of the H Itail and in a nearby control region. We found that the observed RM, in the control region and in a region enclosing the H Itail, cannot be due to the intracluster Faraday screen caused by the Fornax cluster. An intragroup magnetized medium with a central magnetic field strength of 18.5 μG can explain the control region RM, but it is clear that there is an excess in correspondence with the H Itail region. We evaluated several scenarios in which the H Itail is either in the lobe foreground or embedded in the lobe. We determined a magnetic field strength on the order of ∼9.5−11 μG in the H Itail, a value consistent with constraints derived from narrowband Hαimaging of the ionized gas. The spatial coincidence between H Itail and depolarization analyzed in this paper could be the first observed evidence of a magnetic field that either has passed through a radio galaxy lobe or has survived the lobe expansion.

Palaeoecologic and Palaeoclimatic Inferences from Calcareous Nannofossils in Western Lobe Offshore, Niger Delta

In support of the ongoing temporal palaeoenvironment and palaeoclimatic reconstructions of the Neogene sediments, this study attempts to detail the paleo-proxies recovered from DEL-1 Well, western offshore Niger Delta. The standard smear slide method enabled the recovery of well-preserved calcareous nannofossils that depict early to mid–Miocene (NN4–NN5) sediments. The up-hole relationships between the nannofossil accumulation rate (NAR), the relative abundance of Discoaster and coccolith size of Reticulofenestra show step by step collapse of sea surface stability from early to middle Miocene. The lower horizons (8000–9460 ft) exhibit a low NAR, relatively high Discoaster abundance and relatively large Reticulofenestra size to suggest a deep thermocline and nutricline that characterise oligotrophic conditions in less warm-water induced climate. Conversely, upper horizons (5225–6550 ft) exhibit a high NAR, relatively low Discoaster abundance and relatively small Reticulofenestra size to suggest a shallow thermocline and nutricline that characterise eutrophic conditions in warm-water induced climate. The relative abundance of Helicosphaera carteri within the mid-NN5 suggests mesotrophic conditions within a stressed environment, with the possible occurrence of carbonate crash events. The combined parameters indicate gradual eutrophication and collapse of sea surface stability favouring nutrients and influx of terrestrial sediments in the ocean water as it progressed from early to middle Miocene. The abundance of the palaeo-proxies assemblages suggests hyposaline waters in a neritic environment that prevailed during the warm climatic condition.

A SUCCESS CASE OF WIDURI AREA REJUVENATION, ASRI BASIN, OFFSHORE SE SUMATRA BLOCK, INDONESIA

INTA/B Field is one of the most producing mature fields in Widuri Area, Asri Basin, Offshore SE Sumatera, Indonesia, therefore it is subjected to rejuvenation to enhance hydrocarbon production. INTA/B Field is distinguished from other fields from its featured anticlinal structures that have the northeast-southwest trending. This structure is heavily faulted mainly in the up-thrown south side of a major normal fault. Two structural configurations with various oil-water contact have successfully been identified within the field. The most of oil reserves are preserved in the western lobe in which Intan-1 sands. One of the most important reservoirs in this field is Talangakar (TAF) sand deposited as a meandering river system that streamed from the northwest to the southeast within the basin. Two main reservoirs, Gita-34A and Gita-34B are correlated throughout the field and interpreted as Miocene fluvio-channel sands. These two channels are thickened moderately from southwest to northeast which has descriptions as follows: fine- to-coarse grains, unconsolidated to friable, and low cementing materials.INTA/B Field has been produced for 25 years and currently undergoing a watered-out phase. Therefore, an integrated study is subjected to overcome this issue for mature field rejuvenation. The integrated study ranged from geology (e.g., depositional environment and facies analysis), geophysics (e.g., revisiting and reprocessing of seismic attributes), petrophysical calculation, and reservoir engineering (e.g., water conformance plot and volumetric calculation).This integrated study has successfully rejuvenated a mature field resulting and added a significant number in oil production with an average of 300 BPOD/well. The extended project is estimated to have a similar result to the forward pilot.

PGE distribution in Merensky wide-reef facies of the Bushveld Complex, South Africa: Evidence for localized hydromagmatic control

ABSTRACT The wide-reef facies of the Merensky Reef in the eastern part of the western lobe of the Bushveld Complex was sampled in order to better resolve otherwise spatially constrained variation in highly siderophile elements across this geological unit. The platinum group element mineralogy and whole-rock highly siderophile element concentrations were measured across two vertical sections in close proximity. In one section, the Merensky Reef unit was bound by top and bottom platinum group elements-enriched horizons (reefs) with a well-developed pegmatoidal phase in the top third of the intrareef pyroxenite, but with neither a top nor a bottom chromitite present. The other drill core section featured a thin (&amp;lt;1 cm thick) chromitite layer associated with the highest platinum group element concentrations of any rock in this study as the bottom reef, but with a chromitite-absent top reef, and very poor development of the pegmatoid. Primitive mantle-normalized profiles of the main lithological units show relatively flat, primitive mantle-like highly siderophile element abundances (Cr, V, Co, Ni, platinum group elements, Au and Cu) in the Merensky pyroxenite, with modest depletion in Ir-affiliated platinum group elements. The platinum group element-rich top and bottom reefs, and the pegmatoidal upper pyroxenites, display characteristic enrichment in the Pt-affiliated platinum group elements and undepleted Ir-affiliated platinum group elements. The leuconoritic hanging wall and footwall rocks show comparable highly siderophile element profiles, distinguished from one another by relative depletion in the Pt-affiliated platinum group elements of the footwall samples. The vertical variation in highly siderophile element abundances through both sections is characterized by low platinum group element abundances through the lower reef pyroxenite, with platinum group element, Au, and Cu ± Ni concentrations increasing through the upper pegmatoidal pyroxenite, and main enrichment peaks at the top and bottom reefs. Significant localized (centimeter-scale) zones of chalcophile metal depletion are present immediately above the top reef and below the bottom reef. In addition, a wider zone of Pt-affiliated platinum group elements (with Pd more depleted than Pt)-depletion was identified within the pegmatoidal pyroxenite around one meter below the top reef. The platinum group element mineralogy of the bottom reef consists mainly of platinum group element sulfides, with minor arsenides and antimonides. In contrast, the platinum group element mineralogy of the top reef, and the small amount of data from the intrareef pyroxenite, mainly consist of Pt-affiliated platinum group elements-Bi-tellurides. The Pt-sulfides are mainly equant, relatively coarse crystals (many grains between 50 to 100 μm2 area), contrasting with the Pt-affiliated platinum group elements-Sb-As and -Bi-Te minerals that tend be high aspect-ratio grains, occurring in veinlets or as rims on earlier-forming platinum group element phases. These Te-As-Bi-Sb compounds are closely associated with chlorite, actinolite, quartz, and chalcopyrite, consistent with secondary deposition at lower temperatures and association with aqueous fluids. A model is proposed involving the emplacement of the Merensky unit as a magma pulse into at least semi-crystallized host rock, followed by aqueous fluid saturation and local migration, combined with concentration of late magmatic fluids around the top and bottom contacts of the magma pulse. Late remobilization of Pt-affiliated platinum group elements from the zones immediately (centimeter-scale) above the top reef, and from the underlying meter or two of pyroxenite, and from the centimeters underlying the bottom reef, have added additional platinum group elements to the reefs as late platinum group elements-Te-As-Bi-Sb minerals, independent of whether or not chromite is present in the reef initially.

Too large to be seen: Regional structures in Lower and Middle Group chromitites of the Bushveld Complex, South Africa

The Critical Zone of the Bushveld Complex contains thick and laterally extensive Lower, Middle and Upper Group chromitite layers (LG, MG & UG, respectively), which are exposed within many open pit and underground mines. Using field observations from these exposures throughout the Eastern and Western Lobes of the Bushveld Complex, we describe here the morphology and field relationships of the LG and MG chromitites on a regional scale. This is done to gain a new regional perspective on the formation of massive chromitites. Some prominent chromitite layers are traceable over long distances and may occur as one, two or three separate chromitite layers at different locations, with several changes in the number of layers and their thicknesses happening along a distance of a few kilometres. This can be best understood as a structure of regionally bifurcating chromitites, with small-scale bifurcation being visible even at the scale of individual outcrops. We have documented field evidence indicating magmatic erosion of the floor cumulates. Among them are large inclusions of orthopyroxenite in chromitite that are partly attached to the footwall rocks, suggesting that they are erosional remnants of these rocks. Two potholes, roughly circular depressions in the chamber floor, were also documented. They show transgressive relationships of chromitites with their footwall rocks, suggesting that magmatic erosion has occurred prior to chromitite deposition. We propose that the regionally bifurcating chromitites are best explained in the frame of the model involving erosion of the footwall rocks by chromite-only-saturated magma replenishing the evolving chamber. In this process, different locations may have experienced different degrees of magmatic erosion, causing part of the footwall, the entire footwall or even part of the underlying chromitite to have been removed. Upon cooling, the new magma would have deposited chromitite on the erosional surface. Depending on the degree of magmatic erosion, a few separate chromitite layers or a single chromitite layer would form from several influxes of fresh magma into the chamber.

Parsec-scale HI outflows in powerful radio galaxies

Massive outflows of neutral atomic hydrogen (H I) have been observed in absorption in a number of radio galaxies and are considered a signature of active galactic nucleus (AGN) feedback. These outflows on kiloparsec scales have not been investigated in great detail as they require high-angular-resolution observations to be spatially resolved. In some radio AGN, they are likely to be the result of the radio jets interacting with the interstellar medium. We have used the global very-long-baseline-interferometry (VLBI) array to map the H I outflow in a small sample of young and restarted radio galaxies that we previously observed with the Very Large Array and the Westerbork Synthesis Radio Telescope at a lower resolution. Here we report on our findings for 4C 52.37 and 3C 293 and we discuss the sample including the previously published 4C 12.50 and 3C 236. For 4C 52.37, we present the first ever H I VLBI observations, which recovered the majority of the outflowing H I gas in the form of clouds toward the central 100 pc of the AGN. The clouds are blueshifted by up to ∼600 km s−1 with respect to the systemic velocity. 3C 293 is largely resolved out in our VLBI observation, but toward the VLBI core we detect some outflowing H I gas blueshifted with respect to the systemic velocity by up to ∼300 km s−1. We also find indications of outflowing gas toward the other parts of the western lobe suggesting that the H I outflow is extended. Overall, we find that the fraction of H I gas recovered by our VLBI observations varies significantly within our sample, ranging from complete (4C 12.50) to marginal (3C 293). However, in all cases we find evidence for a clumpy structure of both the outflowing and the quiescent gas, consistent with predictions from numerical simulations. All the outflows include at least a component of relatively compact clouds with masses in the range of 104 − 105 M⊙. The outflowing clouds are often already observed at a few tens of parsecs (in projection) from the core. We find indications that the H I outflow might have a diffuse component, especially in larger sources. Our results support the interpretation that we observe these AGNs at different stages in the evolution of the interaction between the jet and the interstellar medium and this is reflected in the properties of the outflowing gas as predicted by numerical simulations.

A Wideband Polarization Study of Cygnus A with the Jansky Very Large Array. I. The Observations and Data

Abstract We present results from deep, wideband, high spatial and spectral resolution observations of the nearby luminous radio galaxy Cygnus A with the Jansky Very Large Array. The high surface brightness of this source enables detailed polarimetric imaging, providing images at , spanning 2–18 GHz, and at 0.″30 (6–18 GHz). The fractional polarization from 2000 independent lines of sight across the lobes decreases strongly with decreasing frequency, with the eastern lobe depolarizing at higher frequencies than the western lobe. The depolarization shows a considerable structure, varying from monotonic to strongly oscillatory. The fractional polarization in general increases with increasing resolution at a given frequency, as expected. However, there are numerous lines of sight with more complicated behavior. We have fitted the images with a simple model incorporating random, unresolved fluctuations in the cluster magnetic field to determine the high-resolution, high-frequency properties of the source and the cluster. From these derived properties, we generated predicted polarization images of the source at lower frequencies, convolved to 0.″75. These predictions are remarkably consistent with the observed emission. The observations are consistent with the lower-frequency depolarization being due to unresolved fluctuations on scales ≳ 300–700 pc in the magnetic field and/or electron density superposed on a partially ordered field component. There is no indication in our data of the location of the depolarizing screen or the large-scale field, either or both of which could be located throughout the cluster or in a boundary region between the lobes and the cluster.

A Small-scale Investigation of Molecular Emission toward the Tip of the Western Lobe of W50/SS 433

Abstract We perform a molecular (CO and CN) line observation using the IRAM 30 m telescope toward two small regions near the western edge of supernova remnant (SNR) W50/SS 433. CO observation reveals spatial correspondence of two molecular clumps at the local-standard-of-rest (LSR) velocity around +53 , with multiwavelength local features of the W50/SS 433 system. One of the two clumps appears to be embedded in a void of diffuse radio and X-ray emission. Toward the two clumps, asymmetric broad-line profiles of the 12CO lines are obtained, which provide kinematic evidence of the association between the clumps and the jet-related gas. The 12CO J = 2–1/J = 1–0 line ratios (≳0.9) and the kinetic temperatures (∼30 K) of the clumps are distinctively higher than all those of the clumps at other LSR velocities along the same line of sight, which may be physical signatures of the association. We show that the clump coincident with the void can survive the thermal heating if it is surrounded by hot gas, with an evaporation timescale much larger than the age of SNR W50. We also show that the thermal equilibrium in the high-temperature clumps can be maintained by the heating of the penetrating environmental cosmic rays. CN (J = 3/1–1/2) line emission is detected in the two clumps, and the CN abundances derived are much higher than that in the interstellar molecular clouds (MCs) and that in the SNR-interacting MCs.

GeV–TeV Counterparts of SS 433/W50 from Fermi-LAT and HAWC Observations

Abstract The extended jets of the microquasar SS 433 have been observed in optical, radio, X-ray, and recently very-high-energy γ-rays by High Altitude Water Cerenkov (HAWC). The detection of HAWC γ-rays with energies as great as 25 TeV motivates searches for high-energy γ-ray counterparts in the Fermi-Large Area Telescope (LAT) data in the 100 MeV–300 GeV band. In this paper, we report on the first joint analysis of Fermi-LAT and HAWC observations to study the spectrum and location of γ-ray emission from SS 433. Our analysis finds common emission sites of GeV-to-TeV γ-rays inside the eastern and western lobes of SS 433. The total flux above 1 GeV is in both lobes. The γ-ray spectrum in the eastern lobe is consistent with inverse Compton emission by an electron population that is accelerated by jets. To explain both the GeV and TeV flux, the electrons need to have a soft intrinsic energy spectrum, or undergo a quick cooling process due to synchrotron radiation in a magnetized environment.