scholarly journals The Galactic population and properties of young, highly energetic pulsars

2020 ◽  
Vol 497 (2) ◽  
pp. 1957-1965
Author(s):  
Simon Johnston ◽  
D A Smith ◽  
A Karastergiou ◽  
M Kramer

ABSTRACT The population of young, non-recycled pulsars with spin-down energies $\dot{E} \gt 10^{35}$ erg s−1 is sampled predominantly at γ-ray and radio wavelengths. A total of 137 such pulsars are known, with partial overlap between the sources detectable in radio and γ-rays. We use a very small set of assumptions in an attempt to test whether the observed pulsar sample can be explained by a single underlying population of neutron stars. For radio emission we assume a canonical conal beam with a fixed emission height of 300 km across all spin periods and a luminosity law which depends on $\dot{E}^{0.25}$. For γ-ray emission we assume the outer-gap model and a luminosity law which depends on $\dot{E}^{0.5}$. We synthesize a population of fast-spinning pulsars with a birth rate of one per 100 yr. We find that this simple model can reproduce most characteristics of the observed population with two caveats. The first is a deficit of γ-ray pulsars at the highest $\dot{E}$ which we surmise to be an observational selection effect due to the difficulties of finding γ-ray pulsars in the presence of glitches without prior knowledge from radio frequencies. The second is a deficit of radio pulsars with interpulse emission, which may be related to radio emission physics. We discuss the implications of these findings.

2004 ◽  
Vol 218 ◽  
pp. 105-112 ◽  
Author(s):  
D. R. Lorimer

We review current understanding of the underlying, as opposed to the observed, pulsar population. The observed sample is heavily biased by selection effects, so that surveys see less than 10% of all potentially observable pulsars. We compare various techniques used to correct the sample for these biases. By far the most significant recent development has been the discovery of over 700 pulsars in the Parkes Multibeam (PM) survey. This new sample is far less affected by selection effects and we use it to make a preliminary analysis of the Galactic pulsar distribution, finding further evidence for a deficit of pulsars in the inner Galaxy.


Galaxies ◽  
2018 ◽  
Vol 7 (1) ◽  
pp. 3
Author(s):  
Stella Boula ◽  
Maria Petropoulou ◽  
Apostolos Mastichiadis

Blazars are a sub-category of radio-loud active galactic nuclei with relativistic jets pointing towards to the observer. They are well-known for their non-thermal variable emission, which practically extends over the whole electromagnetic spectrum. Despite the plethora of multi-wavelength observations, the issue about the origin of the γ -ray and radio emission in blazar jets remains unsettled. Here, we construct a parametric leptonic model for studying the connection between the γ -ray and radio emission in both steady-state and flaring states of blazars. Assuming that relativistic electrons are injected continuously at a fixed distance from the black hole, we numerically study the evolution of their population as it propagates to larger distances while losing energy due to expansion and radiative cooling. In this framework, γ -ray photons are naturally produced at small distances (e.g., 10 − 3 pc) when the electrons are still very energetic, whereas the radio emission is produced at larger distances (e.g., 1 pc), after the electrons have cooled and the emitting region has become optically thin to synchrotron self-absorption due to expansion. We present preliminary results of our numerical investigation for the steady-state jet emission and the predicted time lags between γ -rays and radio during flares.


2018 ◽  
Vol 14 (S342) ◽  
pp. 180-183
Author(s):  
R. Lico ◽  
M. Giroletti ◽  
M. Orienti ◽  
L. Costamante ◽  
V. Pavlidou ◽  
...  

AbstractAs revealed by the Fermi-LAT, blazars represent the dominant population of γ-ray emitters. An essential step for understanding blazar physics and the emission mechanisms is the investigation of a possible connection between the observed low- and high-energy emission. A number of works report on the existence of a significant correlation between radio emission and 0.1-100 GeV γ rays. How does this correlation evolve when very high energy (VHE, E > 0.1 TeV) γ rays are considered? The possible radio-VHE emission connection is still elusive mainly because of the lack of a homogeneous VHE sky coverage. In this work we explore the connection between the parsec-scale radio emission and GeV-TeV γ rays by using two unbiased blazar samples extracted from the 1FHL ( E > 10 GeV) and 2FHL (E > 50 GeV) Fermi catalogs. For comparison, we perform the same analysis by using the 3FGL 0.1-300 GeV γ-ray energy flux. Overall, we find out that there is no significant connection between radio and γ-ray emission above 10 GeV for all the blazar sub-classes with the exception of high synchrotron peaked objects. Conversely, when 0.1-300 GeV γ-ray energies are considered, a strong and significant correlation is found for all of the blazar sub-classes. We interpret these results within the context of the blazar spectral energy distribution properties.


2017 ◽  
Vol 12 (S331) ◽  
pp. 201-205
Author(s):  
A. J. Nayana ◽  
Poonam Chandra

AbstractHESS J1731−347 a.k.a. SNR G353.6−0.7 is one of the five known very high energy (VHE, Energy > 0.1 TeV) shell-type supernova remnants. We carried out Giant Metrewave Radio Telescope (GMRT) observations of this TeV SNR in 1390, 610 and 325 MHz bands. We detected the 325 and 610 MHz radio counterparts of the SNR G353.6−0.7 (Nayana et al. 2017). We also determined the spectral indices of individual filaments and our values are consistent with the non-thermal radio emission. We compared the radio morphology with that of VHE emission. The peak in radio emission corresponds to the faintest feature in the VHE emission. We explain this anti-correlated emission in a possible leptonic origin of the VHE γ-rays.


1997 ◽  
Vol 170 ◽  
pp. 22-24 ◽  
Author(s):  
Seth. W. Digel ◽  
Stanley D. Hunter ◽  
Reshmi Mukherjee ◽  
Eugéne J. de Geus ◽  
Isabelle A. Grenier ◽  
...  

EGRET, the high-energy γ-ray telescope on the Compton Gamma-Ray Observatory, has the sensitivity, angular resolution, and background rejection necessary to study diffuse γ-ray emission from the interstellar medium (ISM). High-energy γ rays produced in cosmic-ray (CR) interactions in the ISM can be used to determine the CR density and calibrate the CO line as a tracer of molecular mass. Dominant production mechanisms for γ rays of energies ∼30 MeV–30 GeV are the decay of pions produced in collisions of CR protons with ambient matter and Bremsstrahlung scattering of CR electrons.


2020 ◽  
Vol 4 ◽  
pp. 170
Author(s):  
N. Fotiades ◽  
Et al.

The high-spin structure of 193Hg was investigated by in-beam γ-ray spectro­scopic techniques. The tandem accelerator at Daresbury Laboratory, U. K., was used to populate excited states of 193Hg through the reaction 150Nd(48Ca,5n)193Hg at a beam energy of 213 MeV and the EUROGAM detector array was used to de­ tect the γ-rays emitted by the deexciting nuclei. The normal level scheme has been further extended and a new band has been observed. In addition two new ΔI=1 structures of competing dipole and quadrupole transitions were found which will be discussed in detail.


1970 ◽  
Vol 37 ◽  
pp. 269-279 ◽  
Author(s):  
G. W. Clark ◽  
G. P. Garmire ◽  
W. L. Kraushaar

Recent observations in the X- and γ-Ray region of the electromagnetic spectrum have given strong evidence for the existence of an extragalactic intensity with a slowly steepening power law spectrum in the region 103 to 108 eV. Further data from the OSO-III high energy γ-Ray detector are in agreement with earlier published reports, and suggest that the γ-Rays from high galactic latitudes have a softer spectrum than those from the galactic plane.


2020 ◽  
Vol 493 (3) ◽  
pp. 3608-3615 ◽  
Author(s):  
Simon Johnston ◽  
A Karastergiou ◽  
M J Keith ◽  
X Song ◽  
P Weltevrede ◽  
...  

ABSTRACT We report here on initial results from the Thousand-Pulsar-Array (TPA) programme, part of the Large Survey Project ‘MeerTime’ on the MeerKAT telescope. The interferometer is used in the tied-array mode in the band from 856 to 1712 MHz, and the wide band coupled with the large collecting area and low receiver temperature make it an excellent telescope for the study of radio pulsars. The TPA is a 5 year project, which aims at to observing (a) more than 1000 pulsars to obtain high-fidelity pulse profiles, (b) some 500 of these pulsars over multiple epochs, and (c) long sequences of single-pulse trains from several hundred pulsars. The scientific outcomes from the programme will include the determination of pulsar geometries, the location of the radio emission within the pulsar magnetosphere, the connection between the magnetosphere and the crust and core of the star, tighter constraints on the nature of the radio emission itself, as well as interstellar medium studies. First, results presented here include updated dispersion measures, 26 pulsars with Faraday rotation measures derived for the first time, and a description of interesting emission phenomena observed thus far.


1996 ◽  
Vol 165 ◽  
pp. 489-502
Author(s):  
Tsvi Piran

Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1913+16, end their life in a catastrophic merger event (denoted here NS2M). The merger releases ∼5 1053 ergs, mostly as neutrinos and gravitational radiation. A small fraction of this energy suffices to power γ-ray bursts (GRBs) at cosmological distances. Cosmological GRBs must pass, however, an optically thick fireball phase and the observed γ rays emerge only at the end of this phase. Hence, it is difficult to determine the nature of the source from present observations (the agreement between the rates of GRBs and NS2Ms providing only indirect evidence for this model). In the future a coinciding detection of a GRB and a gravitational-radiation signal could confirm this model.


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