scholarly journals Low-frequency Flux Density Measurements and Pulsars with GHz-peaked Spectra

2021 ◽  
Vol 923 (2) ◽  
pp. 211
Author(s):  
J. Kijak ◽  
R. Basu ◽  
W. Lewandowski ◽  
K. Rożko
Keyword(s):  
Flux Density ◽  
High Frequency ◽  
Supernova Remnant ◽  
Low Frequency ◽  
Physical Parameters ◽  
Absorption Model ◽  
Pulsar Wind Nebulae ◽  
Entire Sample ◽  
Density Measurements ◽  
Pulsar Wind

Abstract We have estimated flux densities of several pulsars from radio interferometric observations mainly at 325 MHz using the Giant Metrewave Radio Telescope. The new observations allowed us to update the spectral nature of the observed pulsars, and in six sources we identified relatively high frequency turnovers, which can be classified as new GHz-peaked spectrum (GPS) pulsars. For such objects the turnover in the spectrum is most likely caused by absorption in the immediate vicinity of the pulsar (or in the interstellar medium). We modeled the turnover spectra using the thermal free–free absorption model and the physical parameters obtained from the fits enabled us to identify the environments that could potentially be responsible for the observed absorption, such as pulsar wind nebulae, supernova remnant nebulae or H ii regions. The discovery of 6 new GPS pulsars brings the total number of such objects to 33 and we discuss the properties of the entire sample.

scholarly journals Targeted search for young radio pulsars in the SMC: discovery of two new pulsars

2019 ◽  
Vol 487 (3) ◽  
pp. 4332-4342 ◽  
Author(s):  
N Titus ◽  
B W Stappers ◽  
V Morello ◽  
M Caleb ◽  
M D Filipović ◽  
...  
Keyword(s):  
Fourier Analysis ◽  
Flux Density ◽  
Supernova Remnant ◽  
Dispersion Measure ◽  
Small Magellanic Cloud ◽  
Radio Pulsars ◽  
Pulsar Wind Nebulae ◽  
Folding Algorithm ◽  
Main Target ◽  
Pulsar Wind

ABSTRACT We report the first rotation powered pulsars discovered in the Small Magellanic Cloud (SMC) in more than a decade. PSR J0043–73 and PSR J0052–72 were discovered during a Parkes Multi-Beam (PMB) survey of MCSNR J0127–7332, and five new, optically selected, supernova remnant (SNR) candidates identified by the XMM–Newton survey. In addition to the candidates, we adjusted the PMB rotation to include additional nine SNRs and pulsar wind nebulae. We searched for young pulsars (1–200 ms) employing a Fourier analysis with PRESTO, as well as a search for longer period pulsars (200 ms–360 s) with a fast folding algorithm. Our targeted survey had a limiting flux density of 0.039 mJy for periods greater than 50 ms. Although not the main target of this search it was also sensitive to millisecond pulsars. PSR J0043–73 has a period and dispersion measure of 937.429 37 (26) ms and 115.1 (3.4) pc cm−3, respectively, and PSR J0052–72 has a period of 191.444 328 (46) ms and a DM of 158.6 (1.6) pc cm−3.

Numerical simulation of seismic waves in porous media components

2021 ◽  
Vol 9 (1) ◽  
pp. 4-30
Author(s):  
M. Azeredo ◽  
◽  
V. Priimenko ◽  
Keyword(s):  
Numerical Simulation ◽  
Porous Medium ◽  
High Frequency ◽  
Seismic Waves ◽  
Computational Algorithm ◽  
Low Frequency ◽  
Physical Parameters ◽  
Mathematical Algorithm ◽  
Biot Equations ◽  
Attenuation And Dispersion

This work presents a mathematical algorithm for modeling the propagation of poroelastic waves. We have shown how the classical Biot equations can be put into Ursin’s form in a plane-layered 3D porous medium. Using this form, we have derived explicit for- mulas that can be used as the basis of an efficient computational algorithm. To validate the algorithm, numerical simulations were performed using both the poroelastic and equivalent elastic models. The results obtained confirmed the proposed algorithm’s reliability, identify- ing the main wave events in both low-frequency and high-frequency regimes in the reservoir and laboratory scales, respectively. We have also illustrated the influence of some physical parameters on the attenuation and dispersion of the slow wave.

scholarly journals G51.04+0.07 and its environment: Identification of a new Galactic supernova remnant at low radio frequencies

2018 ◽  
Vol 616 ◽  
pp. A98 ◽  
Author(s):  
L. Supan ◽  
G. Castelletti ◽  
W. M. Peters ◽  
N. E. Kassim
Keyword(s):  
Radio Emission ◽  
Flux Density ◽  
Supernova Remnant ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Radio Continuum ◽  
Very Large Array ◽  
Continuum Spectrum ◽  
Galactic Emission ◽  
Nonthermal Radio Emission

We have identified a new supernova remnant (SNR), G51.04+0.07, using observations at 74 MHz from the Very Large Array Low-Frequency Sky Survey Redux (VLSSr). Earlier, higher frequency radio continuum, recombination line, and infrared data had correctly inferred the presence of nonthermal radio emission within a larger, complex environment including ionised nebulae and active star formation. However, our observations have allowed us to redefine at least one SNR as a relatively small source (7.′5 × 3′in size) located at the southern periphery of the originally defined SNR candidate G51.21+0.11. The integrated flux density of G51.04+0.07 at 74 MHz is 6.1 ± 0.8 Jy, while its radio continuum spectrum has a slope α = −0.52 ± 0.05 (S v ∝ vα), typical of a shell-type remnant. We also measured spatial variations in the spectral index between 74 and 1400 MHz across the source, ranging from a steeper spectrum (α = −0.50 ± 0.04) coincident with the brightest emission to a flatter component (α = −0.30 ± 0.07) in the surrounding fainter region. To probe the interstellar medium into which the redefined SNR is likely evolving, we have analysed the surrounding atomic and molecular gas using the 21 cm neutral hydrogen (HI) and 13CO(J = 1 − 0) emissions. We found that G51.04+0.07 is confined within an elongated HI cavity and that its radio emission is consistent with the remains of a stellar explosion that occurred ~6300 yr ago at a distance of 7.7 ± 2.3 kpc. Kinematic data suggest that the newly discovered SNR lies in front of HII regions in the complex, consistent with the lack of a turnover in the low frequency continuum spectrum. The CO observations revealed molecular material that traces the central and northern parts of G51.04+0.07. The interaction between the cloud and the radio source is not conclusive and motivates further study. The relatively low flux density (~1.5 Jy at 1400 MHz) of G51.04+0.07 is consistent with this and many similar SNRs lying hidden along complex lines of sight towards inner Galactic emission complexes. It would also not be surprising if the larger complex studied here hosted additional SNRs.

scholarly journals Multifrequency radio observations of SNR J0536-6735 (N 59B) with associated pulsar

2012 ◽  
pp. 69-76 ◽  
Author(s):  
L.M. Bozzetto ◽  
M.D. Filipovic ◽  
E.J. Crawford ◽  
Horta de ◽  
M. Stupar
Keyword(s):  
Flux Density ◽  
Supernova Remnant ◽  
Optical Emission ◽  
Shell Morphology ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Density Estimates ◽  
Hii Region ◽  
Pulsar Wind ◽  
Compact Array

We present a study of new Australian Telescope Compact Array (ATCA) observations of supernova remnant, SNR J0536-6735. This remnant appears to follow a shell morphology with a diameter of D=36x29 pc (with 1 pc uncertainty in each direction). There is an embedded HII region on the northern limb of the remnant which made various analysis and measurements (such as flux density, spectral index and polarisation) difficult. The radio-continuum emission followed the same structure as the optical emission, allowing for extent and flux density estimates at 20 cm. We estimate the surface brightness at 1 GHz of 2.55x10?21 Wm?2 Hz?1 sr?1 for the SNR. Also, we detect a distinctive radio-continuum point source which confirms the previous suggestion of this remnant being associated with pulsar wind nebula (PWN). The tail of this remnant is not seen in the radio-continuum images and is only seen in the optical and X-ray images.

scholarly journals Unveiling the high-frequency radio source population with the AT20G survey

2013 ◽  
Vol 9 (S304) ◽  
pp. 205-208
Author(s):  
Elizabeth K. Mahony
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Frequency ◽  
Gamma Ray ◽  
Low Frequency ◽  
Radio Sources ◽  
Source Population ◽  
Frequency Source ◽  
Galaxy Population ◽  
5 Ghz

AbstractUntil recently, the radio sky above 5 GHz was relatively unexplored. This has changed with the completion of the Australia Telescope 20 GHz survey (AT20G; Murphy et al., 2010); a blind survey of the southern sky down to a limiting flux density of 40 mJy. The AT20G survey provides by far the largest and most complete sample of high-frequency radio sources yet obtained, offering new insights into the nature of the high-frequency active galaxy population. Whilst the radio data provides a unique sample of objects, these data alone are insufficient to completely constrain models of radio source properties and the evolution of radio galaxies. Complementary multiwavelength data is vital in understanding the physical properties of the central black hole.In this talk I will provide a brief overview of the AT20G survey, followed by a discussion of the multiwavelength properties of the high-frequency source population. In particular, I will focus on the optical properties of AT20G sources, which are very different to those of a low-frequency selected sample, along with the gamma-ray properties where we find a correlation between high-frequency radio flux density and gamma-ray flux density. By studying the multiwavelength properties of a large sample of high-frequency radio sources we gain a unique perspective on the inner dynamics of some of the most active AGN.

scholarly journals A LOFAR search for steep-spectrum pulsars in supernova remnants and pulsar wind nebulae

2019 ◽  
Vol 623 ◽  
pp. A90 ◽  
Author(s):  
S. M. Straal ◽  
J. van Leeuwen
Keyword(s):  
Black Hole ◽  
Supernova Remnants ◽  
Supernova Remnant ◽  
Point Sources ◽  
Pulsar Wind Nebulae ◽  
Upper Limits ◽  
Formation History ◽  
Propagation Effects ◽  
Pulsar Wind ◽  
Rule Out

Pinpointing a pulsar in its parent supernova remnant (SNR) or resulting pulsar wind nebula (PWN) is key to understanding its formation history and the pulsar wind mechanism, yet only about half the SNRs and PWNe appear associated with a pulsar. Our aim was to find the pulsars in a sample of eight known and new SNRs and PWNe. Using the LOFAR radio telescope at 150 MHz, each source was observed for 3 h. We covered the entire remnants where needed, by employing many tied-array beams to tile out even the largest objects. For objects with a confirmed point source or PWN we constrained our search to those lines of sight. We identified a promising radio pulsar candidate towards PWN G141.2+5.0. The candidate, PSR J0337+61, has a period of 94 ms and a DM of 226 pc cm−3. We re-observed the source twice with increased sensitivities of 30% and 50%, but did not re-detect it. It thus remains unconfirmed. For our other sources we obtain very stringent upper limits of 0.8 − 3.1 mJy at 150 MHz. Generally, we can rule out that the pulsars travelled out of the remnant. From these strict limits we conclude our non-detections towards point sources and PWNe are the result of beaming and propagation effects. Some of the remaining SNRs should host a black hole rather than a neutron star.

scholarly journals 20 Pairs of Real Pulsar/Supernova Remnant Associations

2004 ◽  
Vol 218 ◽  
pp. 137-138
Author(s):  
Wenwu Tian ◽  
Denis Leahy
Keyword(s):  
Supernova Remnant ◽  
Pulsar Wind Nebulae ◽  
Pulsar Wind

We trace all pulsar/SNR associations proposed in the literature, and find that 20 pairs of associations are highly likely real because the pulsar wind nebulae around the pulsars have been detected.

scholarly journals On the nature of radio filaments near the Galactic Centre

2019 ◽  
Vol 489 (1) ◽  
pp. L28-L31 ◽  
Author(s):  
Maxim V Barkov ◽  
Maxim Lyutikov
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
High Energy ◽  
Point Sources ◽  
Galactic Centre ◽  
Pulsar Wind Nebulae ◽  
Flux Tubes ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Pulsar Wind

ABSTRACT We suggest that narrow, long radio filaments near the Galactic Centre arise as kinetic jets – streams of high-energy particles escaping from ram pressure confined pulsar wind nebulae (PWNe). The reconnection between the PWN and interstellar magnetic field allows pulsar wind particles to escape, creating long narrow features. They are the low-frequency analogues of kinetic jets seen around some fast-moving pulsars, such as The Guitar and The Lighthouse PWNe. The radio filaments trace a population of pulsars also responsible for the Fermi GeV excess produced by the Inverse Compton scattering by the pulsar wind particles. The magnetic flux tubes are stretched radially by the large-scale Galactic winds. In addition to PWNe accelerated particles can be injected at supernovae remnants. The model predicts variations of the structure of the largest filaments on scales of ∼dozens of years – smaller variations can occur on shorter time-scales. We also encourage targeted observations of the brightest sections of the filaments and of the related unresolved point sources in search of the powering PWNe and pulsars.

scholarly journals The uGMRT Observations of Three New Gigahertz-peaked Spectra Pulsars

2021 ◽  
Vol 922 (2) ◽  
pp. 125
Author(s):  
K. Rożko ◽  
R. Basu ◽  
J. Kijak ◽  
W. Lewandowski
Keyword(s):  
Supernova Remnant ◽  
Maximum Energy ◽  
Wide Frequency Range ◽  
Absorption Model ◽  
Accurate Approximation ◽  
Spectral Measurements ◽  
Frequency Range ◽  
Sky Surveys ◽  
Pulsar Wind ◽  
Thermal Absorption

Abstract Using the Giant Metrewave Radio Telescope, we report the detailed spectral measurements over a wide frequency range of three pulsars (J1741−3016, J1757−2223, and J1845−0743), which allow us to identify them as new gigahertz-peaked spectra pulsars. Our results indicate that their spectra show turnovers at the frequencies of 620 MHz, 640 MHz, and 650 MHz, respectively. Our analysis proves that wideband observations improve estimations of spectral nature using a free–free thermal absorption model, and thus allow for a more accurate approximation of the maximum energy in the spectrum. While there is no evidence as yet that these objects are associated with a supernova remnant or pulsar wind nebula, they will make good targets when looking for interesting environments in the future, or when conducting more sensitive sky surveys.

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