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1.
Models of Galactic 1.275‐MeV emission produced by the decay of the radionuclide 22Na have been computed. Several frequency–spatial distributions of novae have been investigated using recent results of nova rates and spatial distributions of novae in our Galaxy. These models allow us to estimate the lower limit of the 22Na mass ejected per ONe nova detectable with the future spectrometer (SPI) of the INTEGRAL observatory as a function of the frequency–spatial distribution of ONe novae in the Galaxy. Calculations using recent estimations of the expected 22Na mass ejected per ONe nova show that the detection of the Galactic emission of 1.275‐MeV photons will be difficult with the future spectrometer of the INTEGRAL observatory, whereas the cumulative emission around the Galactic Centre has some chance of being detected during the deep survey of the central radian of the Galaxy.  相似文献   

2.
The core of planetary nebula NGC 6302 is filled with high-excitation photoionized gas at low expansion velocities. It represents a unique astrophysical situation in which to search for hyperfine structure (HFS) in coronal emission lines from highly ionized species. HFS is otherwise blended by thermal or velocity broadening. Spectra containing  [Al  vi ] 3.66 μm 3P23P1  , obtained with Phoenix on Gemini South at resolving powers of up to 75 000, resolve the line into five hyperfine components separated by 20–60 km s−1 as a result of the coupling of the   I = 5/2  nuclear spin of 27Al with the total electronic angular momentum J . The isotope 26Al has a different nuclear spin of   I = 5  , and a different HFS, which allows us to place a 3σ upper limit on the 26Al/27Al abundance ratio of 1/33. We measure the HFS magnetic dipole coupling constants for [Al  vi ], and provide the first estimates of the electric quadrupole HFS coupling constants obtained through astronomical observations of an atomic transition.  相似文献   

3.
We study the emission from an old supernova remnant (SNR) with an age of around 105 yr and that from a giant molecular cloud (GMC) encountered by the SNR. When the SNR age is around 105 yr, proton acceleration is efficient enough to emit TeV γ-rays both at the shock of the SNR and that in the GMC. The maximum energy of primarily accelerated electrons is so small that TeV γ-rays and X-rays are dominated by hadronic processes,  π0  -decay and synchrotron radiation from secondary electrons, respectively. However, if the SNR is older than several 105 yr, there are few high-energy particles emitting TeV γ-rays because of the energy-loss effect and/or the wave-damping effect occurring at low-velocity isothermal shocks. For old SNRs or SNR–GMC interacting systems capable of generating TeV γ-ray emitting particles, we calculated the ratio of TeV γ-ray (1–10 TeV) to X-ray (2–10 keV) energy flux and found that it can be more than  ∼102  . Such a source showing large flux ratio may be a possible origin of recently discovered unidentified TeV sources.  相似文献   

4.
We constrain the distance of the gamma-ray burst (GRB) prompt emission site from the explosion centre R , by determining the location of the electron's self-absorption frequency in the GRB prompt optical-to-X/γ-ray spectral energy distribution, assuming that the optical and the γ-ray emissions are among the same synchrotron radiation continuum of a group of hot electrons. All possible spectral regimes are considered in our analysis. The method has only two assumed parameters, namely the bulk Lorentz factor of the emitting source Γ and the magnetic field strength B in the emission region (with a weak dependence). We identify a small sample of four bursts that satisfy the following three criteria: (1) they all have simultaneous optical and γ-ray detections in multiple observational time intervals, (2) they all show temporal correlations between the optical and γ-ray light curves and (3) the optical emission is consistent with belonging to the same spectral component as the γ-ray emission. For all the time intervals of these four bursts, it is inferred that   R ≥ 1014  (Γ/300)3/4 ( B /105 G)1/4  cm. For a small fraction of the sample, the constraint can be pinned down to   R ≈ 1014–1015 cm  for  Γ∼ 300  . For a second sample of bursts with prompt optical non-detections, only upper limits on R can be obtained. We find no inconsistency between the R -constraints for this non-detection sample and those for the detection sample.  相似文献   

5.
We study the structure of a stationary and axisymmetric charge-deficient region (or potential gap) in the outer magnetosphere of a spinning neutron star. Assuming the existence of global current flow patterns in the magnetosphere, the charge depletion causes a large electric field along the magnetic field lines. This longitudinal electric field accelerates migratory electrons and/or positrons to ultrarelativistic energies. These relativistic electrons/positrons radiate γ -ray photons by curvature radiation. These γ -rays, in turn, produce yet more radiating particles by colliding with ambient X-ray photons, leading to a pair production cascade in the gap. The replenished charges partially screen the longitudinal electric field, which is self-consistently solved together with the distribution of e± and γ -ray photons. We find the voltage drop in the gap as a function of the soft photon luminosity. It is demonstrated that the voltage drop is less than 3×1013 V when the background X-ray radiation is as luminous as Vela . However, this value increases with decreasing X-ray luminosity and attains 3×1015 V when the X-ray luminosity is as low as L X=1031 erg s−1.  相似文献   

6.
The prompt optical emission of GRB 990123 was uncorrelated to the γ-ray light curve and exhibited temporal properties similar to those of the steeply decaying, early X-ray emission observed by Swift at the end of many bursts. These facts suggest that the optical counterpart of GRB 990123 was the large-angle emission released during (the second pulse of) the burst. If the optical and γ-ray emissions of GRB 990123 have, indeed, the same origin then their properties require that (i) the optical counterpart was synchrotron emission and γ-rays arose from inverse-Compton scatterings (the 'synchrotron self-Compton model'), (ii) the peak energy of the optical-synchrotron component was at ∼20 eV and (iii) the burst emission was produced by a relativistic outflow moving at Lorentz factor  ≳450  and at a radius  ≳1015  cm, which is comparable to the outflow deceleration radius. Because the spectrum of GRB 990123 was optically thin above 2 keV, the magnetic field behind the shock must have decayed on a length-scale of  ≲1  per cent  of the thickness of the shocked gas, which corresponds to  106–107  plasma skin depths. Consistency of the optical counterpart decay rate and its spectral slope (or that of the burst, if they represent different spectral components) with the expectations for the large-angle burst emission represents the most direct test of the unifying picture proposed here for GRB 990123.  相似文献   

7.
We study the structure of a stationary and axisymmetric charge-deficient region (or a potential gap) in the outer magnetosphere of a spinning neutron star. A large electric field along the magnetic field lines is created in this potential gap and accelerates migratory electrons (e) and/or positrons (e+) to ultrarelativistic energies. Assuming that the gap is immersed in a dense soft photon field, these relativistic e± radiate γ -ray photons via inverse Compton (IC) scattering. These γ -rays, in turn, produce yet more radiating particles by colliding with ambient soft photons, leading to a pair-production cascade in the gap. The replenished charges partially screen the longitudinal electric field, which is self-consistently solved together with the distribution of e± and γ -ray photons. It is demonstrated that the voltage drop in the gap is not more than 1010 V when the background X-ray radiation is as luminous as 1037 erg s−1. However, this value increases with decreasing X-ray luminosity and attains 1012 V when the X-ray radiation is 1036 erg s−1. In addition, we find useful expressions of the spatial distribution of the particle fluxes and longitudinal electric field, together with the relationship between the voltage drop and the current density. Amazingly, these expressions are valid not only when IC scattering dominates but also when curvature radiation dominates.  相似文献   

8.
We study the contribution of young pulsars, with characteristic ages of less than 106 yr, to the diffuse γ-ray emission from the Large Magellanic Cloud (LMC). Based on the outer gap model for γ-ray emission proposed by Zhang & Cheng and pulsar properties in the LMC given by Hartmann, Brown & Schnepf, we simulate the properties of the young pulsars in the LMC. We show that γ-rays produced by the pulsars in the LMC may make an important contribution to the diffuse γ-rays in the LMC, especially in the high-energy range. We calculate the γ-ray energy spectrum of the pulsars in the LMC and show that the γ-ray component contributed by the pulsars to the diffuse γ-rays in the high-energy range (above ∼1 GeV) becomes dominant. We expect that none of the young pulsars should be detectable as an individual point source of γ-ray emission by EGRET. We also expect that pulsar contribution above ∼1 GeV in the SMC is very important.  相似文献   

9.
We present ROSAT [High Resolution Imager (HRI) and Position Sensitive Proportional Counter (PSPC)] and ASCA observations of the two luminous ( L x ∼ 1041−42 erg s−1) star-forming galaxies NGC 3310 and 3690. The HRI shows clearly that the sources are extended with the X-ray emission in NGC 3690 coming from at least three regions. The combined 0.1–10 keV spectrum of NGC 3310 can be described by two components, a Raymond–Smith plasma with temperature kT  = 0.81+0.09−0.12 keV and a hard power law, Γ = 1.44−0.20−0.11 (or alternatively a harder Raymond–Smith plasma with kT  ∼ 15 keV), while there is no substantial excess absorption above the Galactic column value. The soft component emission is probably a super wind while the nature of the hard emission is more uncertain with the likely origins being X-ray binaries, inverse Compton scattering of infrared photons, an active galactic nucleus or a very hot gas component (∼108 K). The spectrum of NGC 3690 is similar, with kT  = 0.83+0.02−0.04 keV and Γ = 1.56+0.11−0.11. We also employ more complicated models such as a multi-temperature thermal plasma, a non-equilibrium ionization code or the addition of a third softer component, which improve the fit but not at a statistically significant level (2σ). These results are similar to recent results on the archetypal star-forming galaxies M82 and NGC 253.  相似文献   

10.
Calculations are made of the resonance contribution to electron-impact excitation of H-like 13C and Li-like 23Na, 25Mg, 27Al and 29Si to the upper hyperfine levels that produce millimetre (mm) lines of likely astrophysical interest. The resonance contribution is found to be very important for these Li-like ions, considerably more important than for Li-like 57Fe considered previously. However, resonances are found to be rather unimportant for H-like 13C. The effect of radiative decay on the resonance contribution is found to be insignificant in all of the present calculations.  相似文献   

11.
We use a new self-consistent model to derive the conversion efficiency from rotation power to γ-ray power for pulsars (εth). Our result indicates that εth∝τ6/7 P 2, where τ and P are the characteristic age and period of the pulsar, which shows that although the efficiency increases with the characteristic age of the pulsar, it also depends on the pulsar period. We test our model results with the survey of high-energy γ-rays from pulsars by EGRET. Our model not only successfully explains the efficiency of the confirmed γ-ray pulsars but also explains why the γ-ray efficiency of millisecond pulsars is so low.  相似文献   

12.
In the neutron-rich internal shocks model for γ-ray bursts (GRBs), the Lorentz factors (LFs) of ion shells are variable, and so are the LFs of accompanying neutron shells. For slow neutron shells with a typical LF of approximate tens, the typical β-decay radius is  ∼1014–1015 cm  . As GRBs last long enough  [ T 90 > 14(1 + z ) s]  , one earlier but slower ejected neutron shell will be swept successively by later ejected ion shells in the range  ∼1013–1015 cm  , where slow neutrons have decayed significantly. Part of the thermal energy released in the interaction will be given to the electrons. These accelerated electrons will mainly be cooled by the prompt soft γ-rays and give rise to GeV emission. This kind of GeV emission is particularly important for some very long GRBs and is detectable for the upcoming satellite Gamma-Ray Large Area Space Telescope (GLAST).  相似文献   

13.
Chandra X-ray Observatory observations of the powerful, peculiar radio galaxy 3C 123 have resulted in an X-ray detection of the bright eastern hotspot, with a 1-keV flux density of ∼5 nJy. The X-ray flux and spectrum of the hotspot are consistent with the X-rays being inverse-Compton scattering of radio synchrotron photons by the population of electrons responsible for the radio emission ('synchrotron self-Compton emission') if the magnetic fields in the hotspot are close to their equipartition values. 3C 123 is thus the third radio galaxy to show X-ray emission from a hotspot which is consistent with being in equipartition. Chandra also detects emission from a moderately rich cluster surrounding 3C 123, with L X(2–10 keV)=2×1044 erg s−1 and kT ∼5 keV, and absorbed emission from the active nucleus, with an inferred intrinsic column density of 1.7×1022 cm−2 and an intrinsic 2–10 keV luminosity of 1044 erg s−1.  相似文献   

14.
We have used echelle spectra of resolving power 35 000 to derive chemical abundances and the 12C/13C ratio in the 1.9-d carbon Cepheid RT TrA and the Cepheid U TrA, employed as a comparison star. We confirm that RT TrA is very metal-rich with [Fe/H]=+0.4. In addition, C and N are substantially in excess, and a small deficiency in O is present. We interpret these anomalies as resulting from the appearance on the stellar surface of material enriched in 12C by the 3- α process, followed by CNO cycling to convert 12C to 13C and 14N. In addition, some 16O has been processed to 14N. The partial processing of 16O to 14N indicates that substantial 17O may be present. Proton capture seems to have enhanced 23Na from the Ne isotopes.  相似文献   

15.
We solve for the structure of a hot accretion disc with unsaturated thermal Comptonization of soft photons and with advection, generalizing the classical model of Shapiro et al. The upper limit on the accretion rate due to advection constrains the luminosity to ≲ 0.15 y3/5 α7/5 of the Eddington limit, where y and α are the Compton and viscosity parameters, respectively. The characteristic electron temperature and Thomson optical depth of the inner flow at accretion rates within an order of magnitude of that upper limit are ∼ 109 K and ∼ 1, respectively. The resulting spectra are then in close agreement with the X-ray and soft γ-ray spectra from black hole binaries in the hard state and Seyferts. At low accretion rates, bremsstrahlung becomes the dominant radiative process.  相似文献   

16.
Measurement sensitivity in the energetic γ-ray region has improved considerably and is about to increase further in the near future, motivating a detailed calculation of high-energy (HE; ≥100 MeV) and very high-energy (VHE; ≥100 GeV) γ-ray emission from the nearby starburst galaxy NGC 253. Adopting the convection–diffusion model for energetic electron and proton propagation, and accounting for all the relevant hadronic and leptonic processes, we determine the steady-state energy distributions of these particles by a detailed numerical treatment. The electron distribution is directly normalized by the measured synchrotron radio emission from the central starburst region; a commonly expected theoretical relation is then used to normalize the proton spectrum in this region. Doing so fully specifies the electron spectrum throughout the galactic disc and, with an assumed spatial profile of the magnetic field, the predicted radio emission from the full disc matches well the observed spectrum, confirming the validity of our treatment. The resulting radiative yields of both particles are calculated; the integrated HE and VHE fluxes from the entire disc are predicted to be   f (≥100 MeV) ≃ (1.8+1.5−0.8) × 10−8 cm−2 s−1  and   f (≥100 GeV) ≃ (3.6+3.4−1.7) × 10−12 cm−2 s−1  , with a central magnetic field value   B 0≃ 190 ± 10 μ  G. We discuss the feasibility of measuring emission at these levels with the space-borne Fermi and ground-based Cherenkov telescopes.  相似文献   

17.
We present the Chandra ACIS-S3 data of the old classical nova RR Pic (1925). The source has a count rate of 0.067 ± 0.002 count s−1 in the 0.3–5.0 keV energy range. We detect the orbital period of the underlying binary system in the X-ray wavelengths. We also find that the neutral hydrogen column density differs for orbital minimum and orbital maximum spectra with values  0.25+0.23−0.18× 1022  and  0.64+0.13−0.14× 1022 cm−2  at 3σ confidence level. The X-ray spectrum of RR Pic can be represented by a composite model of bremsstrahlung with a photoelectric absorption, two absorption lines centered around 1.1–1.4 keV and five Gaussian lines centered at emission lines around 0.3–1.1 keV corresponding to various transitions of S, N, O, C, Ne and Fe. The bremsstrahlung temperature derived from the fits ranges from 0.99 to 1.60 keV and the unabsorbed X-ray flux is found to be  2.5+0.4−1.2× 10−13 erg  cm−2 s−1  in the 0.3–5.0 keV range with a luminosity of 1.1 ± 0.2  1031 erg s−1  at 600 pc. We also detect excess emission in the spectrum possibly originating from the reverse shock in the ejecta. A fit with a cooling flow plasma emission model shows enhanced abundances of He, C, N, O and Ne in the X-ray emitting region indicating existence of diffusive mixing.  相似文献   

18.
19.
We present a comprehensive multiwavelength temporal and spectral analysis of the 'fast rise exponential decay' GRB 070419A. The early-time emission in the γ-ray and X-ray bands can be explained by a central engine active for at least 250 s, while at late times the X-ray light curve displays a simple power-law decay. In contrast, the observed behaviour in the optical band is complex (from 102 up to 106 s). We investigate the light-curve behaviour in the context of the standard forward/reverse shock model; associating the peak in the optical light curve at ∼450 s with the fireball deceleration time results in a Lorenz factor  Γ≈ 350  at this time. In contrast, the shallow optical decay between 450 and 1500 s remains problematic, requiring a reverse shock component whose typical frequency is above the optical band at the optical peak time for it to be explained within the standard model. This predicts an increasing flux density for the forward shock component until   t ∼ 4 × 106 s  , inconsistent with the observed decay of the optical emission from   t ∼ 104 s  . A highly magnetized fireball is also ruled out due to unrealistic microphysic parameters and predicted light-curve behaviour that is not observed. We conclude that a long-lived central engine with a finely tuned energy injection rate and a sudden cessation of the injection is required to create the observed light curves, consistent with the same conditions that are invoked to explain the plateau phase of canonical X-ray light curves of γ-ray bursts.  相似文献   

20.
We employ spectra of resolution 20–35000 of seven SC stars, four S stars, two Ba stars and two K–M stars to derive abundances of a variety of elements from Sr to Eu relative to iron. Special attention is paid to Rb and Tc, and to the ratio of the heavy s-process species to the light s-process elements. Abundances are derived in LTE, both by using model atmospheres in which the carbon and oxygen abundances are nearly equal and by using curves of growth. Spectrum synthesis is used for critical lines such as the 5924-Å line of Tc and the 7800-Å line of Rb. For most of the heavy-element stars the enhancement of the s-process elements is about a factor of 10. The ratio of the heavy to light s-process species is not far from solar, except for RR Her for which the same ratio is +0.45 dex. For Tc the blending by other lines is severe. While we have probably detected the 5924-Å line, we can only present abundances in the less-than-or-equal-to category. For Rb, whose abundance is sensitive to the 85Rb/87Rb ratio and hence to the neutron density during s-process production, we find a considerable range of abundances, indicating a neutron density from 106 to ≳108 cm−3 for the SC stars. For the four S stars the range is from 107 to ≳108 cm−3. Recent calculations by Gallino et al. show that neutron densities near 107 cm−3 favour the 13C source for neutrons, while densities greater than 108 cm−3 may be associated with neutrons from the 22Ne source.  相似文献   

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