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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Magnetar-like X-Ray Bursts Suppress Pulsar Radio Emission

Rotation-powered pulsars and magnetars are two different observational manifestations of neutron stars: rotation-powered pulsars are rapidly spinning objects that are mostly observed as pulsating radio sources, while magnetars, neutron stars with the highest known magnetic fields, often emit short-duration X-ray bursts. Here, we report simultaneous observations of the high-magnetic-field radio pulsar PSR J1119−6127 at X-ray, with XMM-Newton and NuSTAR , and at radio energies with the Parkes radio telescope, during a period of magnetar-like bursts. The rotationally powered radio emission shuts off coincident with the occurrence of multiple X-ray bursts and recovers on a timescale of ∼70 s. These observations of related radio and X-ray phenomena further solidify the connection between radio pulsars and magnetars and suggest that the pair plasma produced in bursts can disrupt the acceleration mechanism of radio-emitting particles.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Chandra and very large array observations of the nearby Sd galaxy NGC 45

We present an analysis of high angular resolution observations made in the X-ray and the radio with the Chandra X-ray Observatory and the Karl Jansky Very Large Array (VLA), respectively, of the nearby spiral galaxy NGC 45. This galaxy is the third that we have considered in a study of the supernova remnant (SNR) populations of nearby spiral galaxies and the present work represents the first detailed analysis of the discrete X-ray and radio source populations of this galaxy. We analyzed data sets from the three pointed observations made of this galaxy with Chandra along with a merged data set obtained from combining these data sets: the total effective exposure time of the merged data set is 63515 s. A total of 25 discrete X-ray sources are found in the entire field of view of the ACIS-S3 chip, with 16 sources found within the visual extent of the galaxy. We estimate that as many as half of the sources detected in the entire field of view of the ACIS-S3 chip and seven of the sources detected in the optical extent of NGC 45 may be background sources. We analyzed the spectral properties of the discrete X-ray sources within the galaxy and conclude that the majority of these sources are X-ray binaries. We have searched for counterparts at different wavelengths to the discrete X-ray sources and we find two associations: one with a star cluster and the other with a background galaxy. We have found one source that is clearly variable within one observation and seven that are seen to vary from one observation to another. We also conduct a photometric analysis to determine the near-infrared fluxes of the discrete X-ray sources in Spitzer Infrared Array Camera channels. We constructed a cumulative luminosity function of the discrete X-ray sources seen toward NGC 45: taking into account simultaneously the luminosity function of background sources, the fitted slope of the cumulative luminosity function Γ = –1.3{sub −1.6}{sup +0.7} (all error bounds correspond to 90% confidence intervals). The VLA observations reveal seven discrete radio sources: we find no overlaps between these sources and the X-ray detected sources. Based on their measured spectral indices and their locations with respect to the visible extent of NGC 45, we classify one source as a candidate radio SNR associated with the galaxy and the others as likely background galaxies seen in projection toward NGC 45. Finally, we discuss the properties of a background cluster of galaxies (denoted as CXOU J001354.2–231254.7) seen in projection toward NGC 45 and detected by the Chandra observations. The fit parameters to the extracted Chandra spectra of this cluster are a column density N{sub H} = 0.07(<0.14) × 10{sup 22} cm{sup −2}, a temperature kT = 4.22{sub −1.42}{sup +2.08} keV, an abundance Z = 0.30(<0.75) relative to solar and a redshift z = 0.28 ± 0.14. From the fit parameters we derive an electron number density n{sub e} = 4(±1) × 10{sup −3} cm{sup −3}, an unabsorbed X-ray luminosity L{sub 0.5−7.0 keV} ∼ 8.77(±0.96) × 10{sup 43} erg s{sup −1} for the cluster and an X-ray emitting mass M = 2.32(±1.75) × 10{sup 12} M{sub ⊙}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Extremely energetic outflow and decelerated expansion in W49N

W49N is a mini-starburst in the Milky Way and is thus an ideal laboratory for high-mass star formation studies. Due to its large distance (11.1{sub −0.7}{sup +0.9} kpc), the kinematics inside and between the dense molecular clumps in W49N are far from well-understood. The Submillimeter Array observations resolved the continuum emission into two clumps. The molecular line observation of SO{sub 2} (28{sub 4,24}–28{sub 3,25}) suggests that the two clumps have a velocity difference of ∼7 km s{sup −1}. The eastern clump is very close to two radio sources “G1” and “G2,” and the western clump coincides with a radio source “B.” The HCN (3–2) line reveals an extremely energetic outflow, which is among the most energetic molecular outflows in the Milky Way. This is the first report of high-velocity molecular outflow detection in W49N. The outflow jet might be in precession, which could account for the distribution, velocity, and rotation of water maser spots. Three absorption systems are identified in HCO{sup +} (3–2) spectra. The absorption features are blueshifted with respect to the emission of SO{sub 2} (28{sub 4,24}–28{sub 3,25}) lines, indicating that a cold layer is expanding in front of the warm gas. Further analysis indicates that the expansion is decelerated from the geometric expansion centers.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

SENSITIVE SEARCH FOR RADIO VARIABLES AND TRANSIENTS IN THE EXTENDED CHANDRA DEEP FIELD SOUTH

We report on an analysis of the Extended Chandra Deep Field South (E-CDFS) region using archival data from the Very Large Array, with the goal of studying radio variability and transients at the sub-milliJansky level. The 49 epochs of E-CDFS observations at 1.4 GHz sample timescales from 1 day to 3 months. We find that only a fraction (1%) of unresolved radio sources above 40 {mu}Jy are variable at the 4{sigma} level. There is no evidence that the fractional variability changes along with the known transition of radio-source populations below 1 mJy. Optical identifications of the sources show that the variable radio emission is associated with the central regions of an active galactic nucleus or a star-forming galaxy. After a detailed comparison of the efficacy of various source-finding algorithms, we use the best to carry out a transient search. No transients were found. This implies that the areal density of transients with peak flux density greater than 0.21 mJy is less than 0.37 deg{sup -2} (at a confidence level of 95%). This result is approximately an order of magnitude below the transient rate measured at 5 GHz by Bower et al. but it is consistent with more recent upper limits from Frail et al. Our findings suggest that the radio sky at 1.4 GHz is relatively quiet. For multi-wavelength transient searches, such as the electromagnetic counterparts to gravitational waves, this frequency may be optimal for reducing the high background of false positives.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

The search for reference sources for delta VLBI navigation of the Galileo spacecraft

A comprehensive search was made in order to identify celestial radio sources that can be used as references for navigation of the Galileo spacecraft by means of VLBI observations. The astronomical literature was seached for potential navigation sources, and several VLBI experiments were performed to determine the suitability of those sources for navigation. The results of such work performed since mid-1983 is reported. A summary is presented of the source properties required, the procedures used to identify candidate sources, and the results of the observations of these sources. The lists of souces presented are not meant to be taken directly and used for VLBI navigation, but they do provide a means of identifying the radio sources that could be used at various positions along the Galileo trajectory. Since the reference sources nearest the critical points of Jupiter encounter and probe release are rather weak, it would be extremely beneficial to use a pair of 70-m antennas for the VLBI measurements.

Ulvestad, J. S.↗
DOE OSTI2017

JVLA Observations of Young Brown Dwarfs

We present sensitive 3.0 cm JVLA radio continuum observations of six regions of low-mass star formation that include twelve young brown dwarfs (BDs) and four young BD candidates. We detect a total of 49 compact radio sources in the fields observed, of which 24 have no reported counterparts and are considered new detections. Twelve of the radio sources show variability in timescales of weeks to months, suggesting gyrosynchrotron emission produced in active magnetospheres. Only one of the target BDs, FU Tau A, was detected. However, we detected radio emission associated with two of the BD candidates, WL 20S and CHLT 2. The radio flux densities of the sources associated with these BD candidates are more than an order of magnitude larger than expected for a BD and suggest a revision of their classification. In contrast, FU Tau A falls on the well-known correlation between radio luminosity and bolometric luminosity, suggesting that the emission comes from a thermal jet and that this BD seems to be forming as a scaled-down version of low-mass stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Chandra and XMM-Newton observations of the merging cluster of galaxies PLCK G036.7+14.9

We present Chandra and XMM-Newton observations of PLCK G036.7+14.9 from the Chandra–Planck Legacy Program. The high resolution X-ray observations reveal two close (∼72″ = 193 kpc in projection) subclusters, G036N and G036S, which were not resolved by previous ROSAT, optical, or recent Planck observations. We perform detailed imaging and spectral analyses and use a simplified model to study the kinematics of this system. The basic picture is that PLCK G036.7+14.9 is undergoing a major merger (mass ratio close to unity) between the two massive subclusters, with the merger largely along the line of sight (∼80° between the merger axis and the plane of the sky from the simplified model) and probably at an early stage (less than ∼0.4–0.7 Gyr since the merger began). G036N hosts a small (∼27 kpc), moderate cool core (cooling time t{sub cool}∼2.6–4.7 Gyr), while G036S has at most a very weak cool core (t{sub cool}∼5.7–10.3 Gyr) in the central ∼40 kpc region. The difference in core cooling times is unlikely to be caused by the ongoing merger disrupting a pre-existing cool core in G036S. G036N also hosts an unresolved radio source in the center, which may be heating the gas if the radio source is extended. The total mass of the whole cluster determined from XMM-Newton is ∼(5.9−8.0)×10{sup 14} M{sub ⊙}, and is ∼(6.7−9.9)×10{sup 14} M{sub ⊙} from Chandra. The Planck derived mass, ∼(5.1−6.0)×10{sup 14} M{sub ⊙}, is higher than the X-ray measured mass of either subcluster, but is lower than the X-ray measured mass of the whole cluster, due to the fact that Planck does not resolve PLCK G036.7+14.9 into subclusters and interprets it as a single cluster. This mass discrepancy could induce significant bias to the mass function if such previously unresolved systems are common in the Planck cluster sample. High resolution X-ray observations are necessary to identify the fraction of such systems and correct such a bias for the purpose of precision cosmological studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

High-resolution Giant Metrewave Radio Telescope H I 21 cm Imaging of the Host Galaxy of FRB 20250316A

We report Giant Metrewave Radio Telescope (GMRT) H I 21 cm imaging of NGC 4141, the host galaxy of FRB 20250316A at z = 0.0063. Our GMRT H I 21 cm images have spatial resolutions, at z ≈ 0.0063, of ≈0.48–8.0 kpc, and provide evidence for (i) a companion galaxy, LEDA 2582852, to the southwest, (ii) a nearby (27 kpc distant) H i cloud to the southwest, (iii) disturbances in the H I distributions of both NGC 4141 and LEDA 2582852, and (iv) high H I column densities in the southwestern outskirts of NGC 4141. A Sloan Digital Sky Survey spectrum yields a low metallicity and a high star formation rate (SFR) surface density in the southwestern disk of NGC 4141, and an Hα-based SFR estimate that is significantly higher than that at the same location from the Galaxy Evolution Explorer near-ultraviolet image, indicating a recent burst of star formation. The total SFR of NGC 4141 is also found to be higher via the Hα line than from the 1.4 GHz radio continuum. The above evidence indicates that NGC 4141 has recently (within the last ≈3 Myr) acquired metal-poor gas, via either a merger or accretion, that resulted in the southwestern starburst and that may also have triggered large-scale star-formation activity in NGC 4141, resulting in the formation of the stellar progenitor of FRB 20250316A and the other transients. Our highest-resolution (480 pc) GMRT H I 21 cm image finds no H I 21 cm emission from the location of FRB 20250316A or the nearby star-forming region, suggesting that most of the H I here has been either ionized or converted into the molecular phase. Our nondetection of continuum emission at the location of FRB 20250316A yields the 3σ upper limit νL 1.38 GHz < 4.4 × 10 34 erg s −1 on the 1.38 GHz radio luminosity of a putative persistent radio source associated with FRB 20250316A, one of the strongest constraints on the radio luminosity of such an associated persistent radio source.

Kaur, Balpreet [Pune University (India)] (ORCID:00↗
NASA NTRS1987

Circumstellar interaction and a pulsar nebula in the supenova 1986j

It is shown here that the circumstellar interaction model for radio supernovae provides an adequate fit to the existing data on supernova SN1986j. The model implies a time of explosion of about January 1983 and provides a guide for the future evolution of the radio source. A shell-like source structure is expected. The model, together with VLBI observations of the radio source, implies a shock velocity of about 10,000 km/s and a presupernova mass loss rate of about 0.0001 solar mass/yr for a wind velocity of 10 km/s. The time behavior of the optical flux and its high luminosity suggest that a central pulsar nebula is the energy source. The required properties are comparable to those expected in the early phases of the Crab nebula.

Chevalier, Roger A.↗
NASA NTRS1989

Infrared and radio emission from S0 galaxies

Far-IR data are presented on 74 early-type S0 galaxies that were selected on the basis of the availability of radio-continuum measurements. Most of the galaxies are detected at IR wavelengths with IRAS, indicating the presence of a cold interstellar medium (ISM) in these galaxies. The mass of gas in these systems is estimated to lie in the range of 10 to the 7th to 10 to the 10th solar. The most massive ISM in some S0s approaches that found in some spirals. The brighter IR-emitting galaxies all lie close to a relationship established for gas-rich spiral galaxies. None of these galaxies have large ratio fluxes, suggesting that strong nuclear radio sources or extended radio lobes and jets are absent or suppressed. Strong radio emission is found among those galaxies that are either faint or not detected at IR wavelengths. The absence of an ISM suggests that these galaxies are of an earlier type that those that have large IR fluxes.

Bally, John↗
NASA NTRS2004

High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL

The authors present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3--0.5 resolution from 4.7 (micro)m to 22 (micro)m. The young stellar objects designed infrared source n and radio source I are believed to dominate the BN/KL region. They have detected extended emission from a probable accretion disk around source n but infer a stellar luminosity on the order of only 2000 L(sub (center-dot)).

STARS↗
DOE OSTI2024

Radioimaging for real-time tracking of high-voltage breakdown

Development of a radioimaging diagnostic for high-voltage component reliability testing and electrical breakdown computational model validation is described. Radioimaging has its roots in radio astronomy, where aperture synthesis (also known as synthesis imaging) has been utilized for decades to image radio sources far from Earth. Radioimaging as described herein, in contrast, seeks to image radio sources in close proximity to its receivers (i.e., in a laboratory environment). Here it is shown that corona discharge, a non-destructive precursor to catastrophic (thermal) arc discharge, electromagnetically radiates strongly within a 250 kHz – 2.5 GHz bandwidth, and is readily detected and located by postprocessing the received radio signals. The ability of radioimaging to detect both corona and arc discharge (grouped together herein as high voltage breakdown or HVB) makes it a valuable tool for 100% HVB detection in materials, components, and devices, and has the ability to indicate electrical weakness (via corona detection) prior to a destructive arc discharge event. Radioimaging enables HVB to be located both internal and external to dielectric components under test in near-real-time, with multiple and/or extended HVB events located simultaneously. In contrast, existing non-destructive diagnostics (at the time of this writing) either indicate electrical breakdown without resolving failure locations (e.g., current, voltage, and chemical measurements), locate external HVB (e.g., high-speed optical and ultraviolet (UV) measurements or photography), or locate both external and internal HVB but with low fidelity (e.g., a single HVB source can be located by existing time-of-arrival (TOA) UHF or acoustic emissions). Radioimaging instead creates a sequence of high-fidelity images similar to an optical high-speed camera but at radiofrequencies (RF), and is not limited to two-dimensions. Moreover, radioimaging has already served one internal and two external industry customers, the results of which are detailed in this report. The radioimaging results described herein were part of a three-year effort funded by the Sandia Lab Directed Research and Development (LDRD) program within the Radiation, Electromagnetic, High Energy Density Science (REHEDS) investment area.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Star Formation Under the Outflow: The Discovery of a Non-thermal Jet from OMC-2 FIR 3 and Its Relationship to the Deeply Embedded FIR 4 Protostar

We carried out multiwavelength (0.7–5 cm), multi-epoch (1994–2015) Very Large Array (VLA) observations toward the region enclosing the bright far-IR sources FIR 3 (HOPS 370) and FIR 4 (HOPS 108) in OMC-2. We report the detection of 10 radio sources, 7 of them identified as young stellar objects. We image a well-collimated radio jet with a thermal free–free core (VLA 11) associated with the Class I intermediate-mass protostar HOPS 370. The jet features several knots (VLA 12N, 12C, 12S) of non-thermal radio emission (likely synchrotron from shock-accelerated relativistic electrons) at distances of ∼7500–12,500 au from the protostar, in a region where other shock tracers have been previously identified. These knots are moving away from the HOPS 370 protostar at ∼100 km s{sup −1}. The Class 0 protostar HOPS 108, which itself is detected as an independent, kinematically decoupled radio source, falls in the path of these non-thermal radio knots. These results favor the previously proposed scenario in which the formation of HOPS 108 is triggered by the impact of the HOPS 370 outflow with a dense clump. However, HOPS 108 has a large proper motion velocity of ∼30 km s{sup −1}, similar to that of other runaway stars in Orion, whose origin would be puzzling within this scenario. Alternatively, an apparent proper motion could result because of changes in the position of the centroid of the source due to blending with nearby extended emission, variations in the source shape, and/or opacity effects.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

What bends 3C 465?

This paper studies the interaction of the prototypical wide-angle tailed radio source 3C 465 with the ambient cluster gas. 3C 465 is attached to the dominant D galaxy NGC 7720 in the cluster Abell 2634. New VLA maps of the radio source are presented which reveal an inner jet and a rapid change of structure at the hot spots at the beginning of each tail. New X-ray maps of the cluster gas are also presented. It is shown that the sharp bend of the flowing radio-luminous plasma between the inner jets and the beginning of the tails cannot be explained by any of the conventional models. Neither galactic motion, buoyancy, gravitational bending, nor dynamic pressure can account for the bending of this source. Attention is also given to new possibilities for the dynamics of this type of radio tailed source: the effect of a current in the jets, and the interaction with cooling clouds in the cluster gas.

Eilek, J. A.↗
NASA NTRS1987

Variable radio emission from the 4 Draconis system

The 4 Dra system, which contains an M3 giant and a cataclysmic binary, has been detected as a 6 cm radio source with the VLA. This radio emission is variable on time scales of weeks to months. A number of possible sources of the radio emission within the 4 Dra system are considered, and the observed time variability probably rules out optically thick free-free emission from the wind of the M3 giant as the dominant source. The major source of the observed radio emission is likely to be either the cataclysmic binary or shocked regions due to the interaction between the cataclysmic binary and the red giant wind.

Brown, Alexander↗
DOE OSTI2019

GMRT Low-frequency Imaging of an Extended Sample of X-shaped Radio Galaxies

We present a low-frequency imaging study of an extended sample of X-shaped radio sources using the Giant Metrewave Radio Telescope (GMRT) at two frequencies (610 and 240 MHz). The sources were drawn from a Very Large Array Radio Images of the Sky at Twenty-Centimeters (FIRST) selected sample and extend an initial GMRT study at the same frequencies of 12 X-shaped radio galaxies predominantly from the 3CR catalog (Lal and Rao 2007). Both the intensity maps and spectral index maps of the 16 newly observed sources are presented. With the combined sample of 28 X-shaped radio sources, we found no systematic differences in the spectral properties of the higher surface brightness, active lobes versus the lower surface brightness, or off-axis emission. The properties of the combined sample are discussed, including the possible role of a twin active galactic nuclei model in the formation of such objects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

The Atacama Cosmology Telescope: likelihood for small-scale CMB data

The Atacama Cosmology Telescope has measured the angular power spectra of microwave fluctuations to arcminute scales at frequencies of 148 and 218 GHz, from three seasons of data. At small scales the fluctuations in the primordial Cosmic Microwave Background (CMB) become increasingly obscured by extragalactic foregounds and secondary CMB signals. We present results from a nine-parameter model describing these secondary effects, including the thermal and kinematic Sunyaev-Zel'dovich (tSZ and kSZ) power; the clustered and Poisson-like power from Cosmic Infrared Background (CIB) sources, and their frequency scaling; the tSZ-CIB correlation coefficient; the extragalactic radio source power; and thermal dust emission from Galactic cirrus in two different regions of the sky. In order to extract cosmological parameters, we describe a likelihood function for the ACT data, fitting this model to the multi-frequency spectra in the multipole range 500 < l < 10000. We extend the likelihood to include spectra from the South Pole Telescope at frequencies of 95, 150, and 220 GHz. Accounting for different radio source levels and Galactic cirrus emission, the same model provides an excellent fit to both datasets simultaneously, with χ{sup 2}/dof= 675/697 for ACT, and 96/107 for SPT. We then use the multi-frequency likelihood to estimate the CMB power spectrum from ACT in bandpowers, marginalizing over the secondary parameters. This provides a simplified 'CMB-only' likelihood in the range 500 < l < 3500 for use in cosmological parameter estimation.

79 ASTRONOMY AND ASTROPHYSICS↗