Γ-ray Pulsars Research Articles

Pulsed high-energy γ-rays from the radio pulsar PSRI706–44

OF the more than 500 known radio pulsars, only three have been detected as γ-ray sources. Using the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory satellite, we have detected pulsed γ-radiation, above 100 MeV in energy, from a fourth radio pulsar, PSR1706–44. Within the pulse period of 102 ms, the γ-emission forms a single broad peak, in contrast to the two narrow peaks seen in the other high-energy γ-ray pulsars. The emission mechanism in all cases is probably the same, the differences arising from the geometry of the magnetic and rotation axes and the line of sight. In these pulsars, γ-ray emission accounts for as much as 1% of the total neutron star spin-down energy, much more than emerges at optical or radio frequencies, so study of this emission is important in understanding pulsar emission and evolution.

Is it advantageous to use a commercial CCD for data acquisition in pulsed experiments? (abstract)

We found that a CCD compared favorably with the film currently used to record gated XUV camera images from plasma physics experiments. The CCD was 20 times as sensitive as the film, indicating that the CCD has an effective ISO of 40 000. The camera was successfully shielded from electromagnetic pulses with electric field strengths of 0.7–1 kV/m and pulse widths of 30–65 ns. The CCD also survived the γ-ray pulse, and no degradation in performance was seen after an accumulated dose of 10–20 rad. We also successfully acquired optical light images of a Z pinch using a commercial camcorder.

Pulsed high-energy γ-radiation from Geminga (1E0630+178)

HALPERN and Holt1 have recently reported the detection of coherent pulsations with a period of 237 ms from the soft X-ray source 1E0630 +178, which lies in the error box of the γ-ray source known as Geminga (2GC195 + 04). This observation provides compelling evidence that Geminga, an object whose nature has hitherto been mysterious, is an X-ray pulsar. Prompted by this discovery, we have searched the data from EGRET, the Energetic Gamma Ray Experiment Telescope on the Compton Gamma Ray Observatory, for a comparable signal in the γ-radiation from this part of the sky. We now report the detection of pulsed γ-rays, with energy >50MeV, from 1E0630 + 178, confirming the identification of Geminga with this X-ray source. The period derivative, (11.4 ± 1.7) x 10−15ss−1, suggests that Geminga is a nearby, isolated, rotating neutron star with a magnetic field of 1.6 x1012 gauss, a characteristic age of 3 x 105 yr and a spin-down energy loss rate of 3.5 x 1034 erg s−1.

Photoinduced formation and reaction of benzalaniline radical anions: comparison with the radiation-induced reaction

Photoirradiation of benzalaniline ( 1) and its derivatives in a tetrahydrofuran (THF) solution yielded a THF adduct regioselectively. The reaction efficiency is strongly dependent on the substituent of both benzene rings, and photoexcitation of the intramolecular charge transfer (CT) band is effective for the product formation. In the case of the 4′-CN derivative, this reaction appears to proceed via the radical anion, the transient absorption of which was clearly observed upon the irradiation of a 2-methyltetrahydrofuran matrix at 77 K. Thus the CT excited state may be quenched by THF to form the radical anion of 1. The following reaction of the radical anion was also studied by γ-ray irradiation and pulse radiolysis techniques, and a regioselective protonation at a nitrogen atom of 1 − was observed.

Gamma-ray emission from pulsars

We have attempted to devise a scheme by which it may be possible to identify pulsars which are likely to be γ-ray pulsars. We apply this test to a representative population of pulsars and identify the likely candidates for γ emission. We also discuss some individual cases including the Crab and Vela pulsars.

Shall we Observe a Radio Binary Pulsar in SN 1987A?

AbstractAn induced-collapse model [hereafter IC model; He et al. (1990)] can overcome the problems of the single star model of SN1987A. According to the IC model, there is a possibility that the SN1987A remnant will be a binary system with two neutron stars, one of them (SK-69 202) will have a strong magnetic field and a high surface temperature which favors detection as an X-ray or γ-ray pulsar. If the surface temperature of the neutron star cools down to T = 107 K, a radio binary pulsar is expected. There is also the possibility that an X-ray or γ-ray pulsar will be observed first, and only later will a radio pulsar will be detected.A newly formed neutron star is thought to have a short (millisecond) period. In this case, the core emission beam is then very large (Qiao 1992) and is thus very likely to swing in the direction of the Earth.

New capabilities for the Aurora flash X-ray machine

A series of recent upgrades enable the Aurora flash X-ray machine to provide a wide variety of different radiation pulses. The original design gives a single γ-ray pulse with 50 ns risetime and 135 ns width that irradiates a volume of around 1 m 3 with up to 50 krad (Si). The upgrades allow for two pulses with arbitrary separation in time, each with half the output. The pulse widths can be shortened to around 30 ns (with reduced energy), and the risetime can be reduced to 10 ns. These upgrades are discussed in some detail. Other upgrades are described elsewhere: the moderate energy bremsstrahlung option is described by J.A. Anderson et al. [Nucl. Instr. and Meth. B40/41 (1989) 1189]; the high power microwave option is described by G.A. Huttlin et al. [IEEE Trans. Plasma Sci. PS-18 (1990) 618 and other papers in this series].

Fast Neutron Streaming through Duct in Concrete Shields

Measurements on the neutron and γ-ray attenuation in multi-legged air filled ducts have been carried out using a Cockroft-Walton type neutron generator. The measured spectra were obtained with an NE-213 liquid scintillator using pulse shape discrimination to resolve neutron and γ-ray pulse height data and using a spectral unfolding code to convert these data to energy spectra. Results are given for two rectangular duct geometries. A series of integral measurements have also been carried out with a long counter for fast neutrons and a radiation survey meter to measure the γ-ray dose. The biological dose arising due to the streaming of neutrons was measured with a rem counter. The results show the relative decrement of the integral counts along the axis of the duct. The spectral measurements reveal the presence of resonant windows of oxygen present in the concrete medium. Also the 14 MeV component is found to be dominant in the first leg of the duct whereas degraded neutrons dominate in the second leg. The ...

Companion-star beam steering of high-energy particles from Hercules X-1

A recent model1 for the 1011–1015 eV γ-ray emission from the 1.24-s X-ray pulsar Hercules X-l postulates coherent charged particle beams as the photon source, through a cascade process in intervening matter in the binary system HZ Her/Her X-1. This interpretation is complicated by a 1985 observation2 of ∼1012-eV γ-ray pulsations during at least the first hour of the nominal 6-h X-ray eclipse of Her X-1 by HZ Her, which would completely absorb a particle (or photon) beam propagating along or near the line of sight to Her X-1. Here we show that the presence of even a weak dipole magnetic field around the companion star is sufficient to steer such a beam to a suitable target region for producing the observed γ-rays. We demonstrate that models such as that in ref. 1 must include such effects, and we discuss the effects of such beam steering on γ-ray and neutrino observations.

Energetic Radiation from Rapidly Spinning Pulsars. II. VELA and Crab

view Abstract Citations (427) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Energetic Radiation from Rapidly Spinning Pulsars. II. VELA and Crab Cheng, K. S. ; Ho, C. ; Ruderman, M. Abstract The growth of charge-depleted regions (gaps) in the outer magnetosphere of rapidly spinning magnetized neutron stars is limited by e± production. In the Vela pulsar a pair of e+ and e- created within the gap (primaries) are accelerated in opposite directions to extreme relativistic energies. The primary e-/e+ produce primary γ-rays through inverse Compton scattering on IR photons. Primary γ-rays are sufficiently energetic to produce (secondary) e± pairs in collisions with this same IR photon flux. Secondary synchrotron radiation by these pairs gives crossed fan beams of γ-rays and weaker ones of X-rays. Collisions of the hard secondary γ-rays with the secondary crossed beam soft X-rays give a large flux of lower energy e± (tertiary) pairs which fill much of the outer magnetosphere. It is the (tertiary) IR synchrotron radiation from tertiary pairs through the outer gap which initiates the entire series of pair production processes. For Vela, the calculated observable consequences include (a) twin cusped γ-ray pulses with photon spectrum F(ω) ≍ ω-3/2 ln (3 GeV/hω) from 3 GeV to about 102 KeV; (b) total fan beam radiated power 10-2 the pulsar spin-down energy loss rate; (c) an X-ray spectrum F(ω) ≍ ω-2/3 below 102 KeV; (d) weak, more closely spaced twin optical pulses from the tertiary radiation with power 10-5 that of the secondary γ-rays; (e) and e± outflow of 1036 s-1; (f) a double pulse of 1012 - 1013 eV γ-rays with about 10-2 the γ-ray power. Model Crab pulsar emissions are considered with emphasis on differences from those of Vela. Crab primary outer gap e+/e- lose most of their energy to curvature γ-rays, which convert to e± pairs in collisions with X-rays. These X-rays come from the synchrotron (secondary) emission from such (secondary) pairs created beyond the gap boundary. Inverse Compton scattering of secondary e± on the secondary X-rays boosts a fraction to γ-rays. The combination of secondary synchrotron and inverse Compton emission into twin fan beams gives the Crab pulsar spectrum from optical to GeV energies. Other mechanisms give the Crab's double pulsed radio and 1012 - 1013 eV emission and the possibility of 1015 eV nucleon beams. Publication: The Astrophysical Journal Pub Date: January 1986 DOI: 10.1086/163830 Bibcode: 1986ApJ...300..522C Keywords: HYDROMAGNETICS; PULSARS; RADIATION MECHANISMS; STARS: NEUTRON full text sources ADS | data products SIMBAD (3) Related Materials (1) Part 1: 1986ApJ...300..500C

Can neutrinos from Cygnus X-3 be seen by proton decay detectors?

The flux of high-energy neutrinos from Cygnus X-3 is estimated directly from the observed light curve of high-energy γ-rays from this source. These neutrinos induce an underground muon flux which can be distinguished by its characteristic direction and duration from the muon background induced by atmospheric neutrinos. For zenith angles ≥ 84° the expected rate of muon events in the IMB detector due to Cygnus X-3 is between 1 and 10 events/yr, depending on the actual duration of the γ-ray pulses from this source.

Hercules X-1—a 1,000 GeV γ-ray pulsar

An X-ray pulsar has been detected for the first time as a very high-energy (VHE) γ-ray pulsar. X-ray emission from Hercules X-1 is multiply periodic with a pulsar period of 1.24 s, a binary orbital period of 1.7 day and a 35-day amplitude modulation of unknown origin characterized by a sharp turn-on followed by a slow decline over 11 days. During a drift-scan we have detected a significant 3-min outburst of VHE γ rays, which had a 1.24-s periodicity. This outburst occurred 35 days before an observed X-ray turn-on. The γ-ray luminosity during the outburst was of the same order as the X-ray luminosity. Together with the coincidence in time, this suggests a connection between the mechanisms giving rise to the γ-ray outburst and the X-ray turn-on. Subsequent monitoring of the source during a period when the X-ray flux was decreasing yielded some evidence of much weaker pulsed γ-ray activity at the pulsar period. We note a possible similarity between this system and Cygnus X-3.

Was wissen wir �ber Neutronensterne?

There are 109±0.5 neutron stars in the Galaxy. They are born in supernova explosions. Isolated neutron stars are observed as (radio-)pulsars, in some cases also as γ-ray pulsars and as IR-, optical and X-ray pulsars. Binary neutron stars, when accreting mass from their companion, become flickering, periodic and/or bursting X-ray sources, and probably also γ-ray bursters. They may all derive from binary star systems. The masses of population-I-neutron stars are compatible with (1.4 ±0.2)M⊙; their surface magnetic fields fall almost exclusively within 1012.2 and 1013.2 Gauss (at birth). The radii of population-II-neutron stars are (10-3+6)km. Even in exotic sources like SS 433 and Cyg X-1, the compact core may well be a neutron star.

The Slot Gap Model of Pulsars

A general picture of pulsar magnetospheres is outlined which suggests polar current flow should proceed within a magnetic flux tube with conducting boundaries. The dynamics of this current flow is considered, including the effect of formation of pair plasma on the potential. A slot gap surrounding the stream of pair plasma is described, and the electric fields and J·E work done in the gap are calculated. The inapplicability of curvature emission to the formation of γ-ray pulses is discussed. The dynamics of pair plasma flow is described, including electrostatic trapping of low energy positrons, polar cap bombardment and heating, and the emission of soft X-rays from the cap. The relation of this current flow and polar cap heating to the formation of fluctuations on the radio subpulse time scale is also described. The importance of the boundary layer between the pair plasma and the slot gap is illustrated by calculations of the boundary layer structure and microscopic instability, which show that this region may be the source of pulsar emission.I will describe a number of quantitative results and qualitative aspects of work in progress on the “slot gap” model for the emission regions of a pulsar, proposed by Arons and Scharlemann (1979, hereafter AS) and by Arons (1979b, hereafter I). The results and ideas concern the dynamics and emission physics of relativistic plasma and current flow along the polar field lines of an isolated, rotating magnetized neutron star with the axis of its dipole moment oblique to the rotation axis - a pulsar. The quantitative modelling is confined to the physics within a polar flux tube and is therefore “local”. Full detail will be given in papers now being written. However, development of this type of model requires the use of boundary conditions which follow from a qualitative view of the whole magnetosphere. Because this view involves some qualitative ideas not widely discussed in the literature, I describe it briefly.

Possible transfer of lunar matter to Earth due to a nearby supernova

Theories of supernova explosion (SNEs)1–3 as well as correlation of NO−3 in Antarctic ice cores with the dates of historical supernovae4, suggest that many Type I SNE may yield an intense 1050 erg emission of γ rays. Such a SNE may be expected to occur within a few tens of light years of our Solar System once every hundred million years or so5,6. A short γ-ray pulse of this magnitude would not only directly affect the terrestrial atmosphere in ways that can be important for surface life5, but also be absorbed by the lunar surface. Depending on the γ-ray energies involved, the upper centimetre of lunar surface soil can be evaporated by heating or ejected by the emergence at the surface of a rising pressure pulse. Such expelled lunar soil, moving at speeds near the 2 × 105 cm s−1 lunar escape velocity, could be captured by the Earth's gravitational field and gradually settle through the atmosphere to the Earth's surface. Geological strata for that epoch might then be expected to show an overabundance of iridium (but probably less than that found by Alvarez et al.7 in 65-Myr-old sedimentary layers at Gubbio). This would occur since the expelled lunar surface soil should be characterised by an Ir abundance greatly enriched, relative to terrestrial of lunar rocks, by micrometeorite bombardment.

A sensitive search for radio pulses from primordial black holes and distant Supernovae

THERE are two mechanisms of current theoretical interest which might generate short ( <1 ms) radio pulses detectable at interstellar or even cosmological distances. In both cases the pulse is generated by the alteration of a magnetic field by an expanding conducting shell. The phenomenon might occur either as the expanding core of a supernova ‘combs’ the star's intrinsic dipole field1,2, or as the shell of charged particles emitted in the explosion of a primordial black hole (PBH) excludes the surrounding magnetic field3. In the latter case, the resulting radio pulse would, with suitable particle physics3,4, be much easier to detect than the γ-ray pulses that might also accompany the explosion5. The best published upper limit on the frequency of such γ-ray pulses is 4 × 10−2 events pc−3 yr−1 (ref. 6). We present here the results of a radio frequency search for isolated pulses, with much higher sensitivity than achieved previously. No definitive pulses have been detected, and the implied limit on PBH explosions is 2×10−9 events pc−3 yr−1.

A possible laser experiment for observation of photon-photon scattering in vacuum

An analysis is made of the possibility of using lasers in experimental studies of the scattering of photons by photons in vacuum. The minimum energy of each of the two lasers, required by the experimental conditions, is ~3×108 J for ultraviolet radiation if the pulse duration is 5×10–13 sec and the laser beams have the diffraction-limit divergence. The parameters obtained in this analysis indicate that the great experimental difficulties are likely to be encountered. A possibility is studied also of the formation with the aid of lasers of x- or γ-ray pulses which would collide in vacuum. It is shown that it would be much more convenient to use γ rays because it would then be sufficient to use laser systems with an energy of ~106 J per pulse and the requirements to be satisfied by such pulses would be less stringent than in the optical wavelength range.

Germanium spectrometers with internal junctions

For fabricating a spectrometer from a high purity Ge crystal with an internal junction two contact configurations are possible: p νπn or p πνn, where ν and π represent the high purity n and p portions respectively. The two configurations are compared theoretically and experimentally with respect to depletion voltages, pulse risetimes, charge collection efficiencies and γ-ray pulse height resolutions. It is shown that the p νπn configuration has advantages in depletion voltage, charge collection, and timing properties as a result of the more favorable electric field. Spectrometers with depletion depths of 3 cm at 2000 V have been made from material having a net concentration gradient of dopants of 5 × 10 −9 cm −4. The charge trapping in the Ge limited the high energy (∼1 MeV) γ-ray resolutions to about 0.4% for a 3 cm p νπn device. For spectroscopy of high energy charged particles, however, these diodes combine a thin entrance window (<50 μg/cm 2) with a large stopping power and should be very useful.

Observations of NP0532 with a wide-angle atmospheric Čerenkov system

Two 1.5 m reflectors have been used in coincidence, observing the Crab Nebula for pulsed γ-rays of about 5·1012 eV. About 600 000 showers were observed in 1972 and 1973. The overall results show no significant effect, but some runs showed anomalies, which could be consistent with a real but variable emission.

Pulsed gamma-ray emission from neutron and collapsing stars and supernovae

Three mechanisms generating pulsed γ-ray emission at late stages of stellar evolution are investigated: (1) γ-ray burst produced by the absorption of neutrino emission of a collapsing star in its envelope; (2) γ-ray burst of thermal emission when the outer layers of a compact star (R=0.01–0.1R⊙) are heated up by a powerful shock wave; and (3) γ-ray emission due to ejection of matter from neutron stars at an active stage of their existence. In case (1) the expected flux of γ-quanta with the energy 0.1 MeV amounts to about 10−4 cm−2 which is considerably less than the observed flux. However, observation of such γ-ray pulses would be an important supplement to the direct observations of neutrino emission of collapsing stars. In case (2) the outer layers of the star are heated up to the temperature of about 108 K. This results in a short burst with the emission energy ∼ 1042–43 erg whose main part is concentrated in the X-ray range (∼ 25 keV). In this case approximately 10% of the energy is emitted in the γ-ray range (≳ 0.1 MeV). Generally speaking, this mechanism is sufficient as to the energy for accounting for the observed bursts; however, probably under the condition that supernovae are exploding in our Galaxy. This involves difficulties concerning the frequency of bursts and the spectrum of emission. In case (3) ejection of chemically non-equilibrium matter from the neutron star leads to an intensive emission which is produced due to fission of superheavy nuclei, β-decay of radioactive elements and radiative capture of free neutrons. Ejection of matter from the neutron stars may be related to the observed jumps of periods of pulsars. From the observed gain of kinetic energy of the filaments of the Crab Nebula (∼ 2×1041 erg) the mass of the ejected material may be estimated (∼ 1021 g). This leads to energies of the γ-ray bursts of the order of 1038–1039 erg, which agrees fully with observations at the mean distance up to the sources 0.25 kpc. As distinct from the outbursts of supernovae it would seem that no difficulties concerning the burst frequency and the spectrum of emission are encountered. From the mechanisms of γ-ray emission examined here the mechanism connected with the ejection of matter from neutron stars seems to be the most promising as far as the interpretation of observations is concerned.