Supernova remnants: The Crab Nebula,Cassiopeia A,and Tycho as sources of cosmic rays in our galaxy

We present the results of our observations of two types of Galactic supernova remnants with the ShALON mirror Cherenkov telescope: the plerion Crab Nebula and the shell-type supernova remnants Cassiopeia A and Tycho. The experimental data have confirmed the prediction of the theory about the hadronic generation mechanism of very high energy (0.8–100 TeV) gamma rays in Tycho’s supernova remnant. The data obtained suggest that the very high energy gamma-ray emission in the objects being discussed is different in origin.     

Neutrino synchrotron radiation

The neutrino luminosity of several models of neutron stars has been computed according to the photon-neutrino coupling theory and compared with that of the current-current coupling theory. It is shown that the NSR process alone should have cooled the core of the neutron star created in a supernova explosion in 1954 A.D. to a temperature around 2×10⁹ K according to the photon-neutrino coupling theory.The emission power of the star is greater than the emission power of the X-ray source discovered in the Crab Nebula; so the source may be interpreted as the thermal radiation of the star according to the photon-neutrino coupling theory.     

A search for compact decametric radio sources in supernova remnants using the interplanetary scintillation technique

Interplanetary scintillation observations of eleven supernova remnants and the pulsar J1939+2134, around which the existence of a supernova remnant remains obscure, were carried out with the largest in the world decameter radio telescope UTR-2 at 20, 25 and 30 MHz to determine if any of them contain compact radio sources with the angular size θ<5″. The sample included the young Galactic remnants and the other powerful SNRs. The interplanetary scintillations of the compact radio source in the Crab Nebula associated with the well-known pulsar J0534+2200 and the pulsar J1939+2134 were observed. Apart from the Crab Nebula, we have not detected a compact radio source in supernova remnants with the angular size θ<5″ and the flux density more than 10 Jy. The observations do not confirm the existence of the low frequency compact source in Cassiopeia A that has remained controversial.     

Nebular complex in the region of Cas OB2 association; ring nebula Sh157

This paper presents the results of monochromatic [Oiii], [Nii], and [Sii] observations of ring nebula Sh157 around the star (WR + B0III) HD 219460 belonging to the Ba 3 cluster. A stratification of radiation typical for photoionization excitation has been revealed. The observations suggest that the Sh157 ring structure may arise as a result of the HD 219460 stellar wind blowing the surroundingHii region, and the bubble age is found to bet(2–5)×10⁵ yr. Three outer envelopes have been distinguished: a weaker extended emission shell apparently blown out by the wind from B-stars of the Ba 3 cluster, and two dust shells which are likely to be associated with NGC 7510 and Cas OB2. The paper is also concerned with the discussion of young star aggregates Ba 3, NGC 7510, Cas OB1, OB2, OB4, OB5, OB7, and Cep OBI and the associatedHii regions, shells and supershells of gas and dust, molecular clouds, and supernova remnants which may be probable members of a single giant stellar complex where the star formation process is in progress.     

Association of the supernova remnant G 65.3+5.7 with ambient neutral hydrogen and a possible nature of the remnant

The neutral hydrogen at 21 cm has been investigated with the RATAN-600 radio telescope around the supernova remnant G 65.3+5.7, which has the largest angular sizes in the group of shell remnants. An expanding HI shell left after an old supernova explosion with an energy of ∼10⁵¹ erg and an age of 440 000 yr coincident in coordinates with the radio and optical remnant has been discovered. Since an X-ray emission from a much younger (27 000 yr) supernova remnant is observed in the same region and the shells detected by nebular lines have probably intermediate ages, we suggest that several successive supernova explosions have occurred here.     

X-rays from supernovae remants 3C 400.2 (≡ G53.7-2.2) and MSH 15-56

Detection of two new soft X-ray sources and their identification with the supernova remnants (RNRs) 3C400.2 and MSH 15-56, is reported. From the observed X-ray flux in the 0.7–2.0 keV energy range, the X-ray luminosity of 3C400.2 is derived to be in the range of (2.7–5.3)×10³⁵ ergs s^?1 and that of MSH 15-56 in the range of (0.9–1.6)×10³⁵ ergs s^?1. If we use the standard adiabatic shockwave model for the SNR's, an age of ～(1.4–3.2)×10⁴ yr is derived for 3C400.2 whereas MSH 15-56 is found to be younger of an age of (5–10)×10³ yr.     

MHD simulations of rayleigh-taylor instability in young supernova remnants

Radio observations shows that young supernova remnants such as Tycho and Cas A generally exhibit a circular clumpy shell. This shell shows a radial magnetic field whose equipartition strength is 2 to 3 orders of magnitude higher than the interstellar field. A simple compression of the ambient field by the shock can explain neither of these observations. We show that the Rayleigh-Taylor instability which occurs at the ejecta/ISM interface can explain these observations. We have done MHD simulations of the instability in the shell of Type-I supernova remnants for the first time by utilizing moving grid technique. Our simulation shows that Rayleigh-Taylor and Kelvin-Helmholtz instabilities amplify ambient magnetic fields locally and produce the clumpy radio shell. Strong magnetic field lines draped around the Rayleigh-Taylor fingers produce the radial B-vector polarization, whereas thermal bremsstrahlung from the dense fingers themselves produce the clumpy X-ray emission.     

The Crab Nebula revisited

The evolution of pulsar driven supernova remnants is briefly reviewed with special reference to the Crab Nebula. Simple models account for the integral properties of the Nebula. New data on the optical synchrotron continuum show strong spectral variations over the Nebula which will require more complex models of the particle diffusion.     

Long-term monitoring of the long-period variable Y Cassiopeiae in the 1.35-cm water-vapor line

Observations of the circumstellar maser emission from the long-period variable star Y Cas in the 1.35-cm water-vapor line are presented. The observations were performed with the RT-22 radio telescope at the Pushchino Radio Astronomy Observatory (Astrospace Center, Lebedev Physical Institute, Russian Academy of Sciences) in the period 1982–2005. The variations in the integrated flux F_int in the H₂O line correlate with the visual light curve of the star. The phase delay Δ? between the F_int variations and the light curve is 0.2–0.4P (P is the period of the star). The H₂O maser Y Cas belongs to transient sources: peaks of high maser activity alternate with intervals of a low emission level when the H₂O-line flux does not exceed (0.1–0.5) × 10^?20 W m^?2. A “superperiod” of ～5.7 yr was found in the occurrence of activity peaks. A particularly strong maximum of maser radio emission took place at the end of 1997, when the flux F_int reached 15.6 × 10^?20 W m^?2. A model for the H₂O maser variability in Y Cas is discussed. The variability is caused by a periodic action of shock waves driven by stellar pulsations. The H₂O maser flares may be associated with short-lived episodes of enhanced mass loss by the star or with the propagation of a particularly strong shock wave when a planet orbiting the star passes through its periastron.     

The Crab Nebula's dynamical age as measured from its northern filamentary jet

We present a deep [O  iii ]λλ4959,5007 image of the northern filamentary jet in the Crab Nebula taken with the 8.2-m Subaru telescope. Using this image and an image taken with the Kitt Peak National Observatory (KPNO) 4-m in 1988, we have computed proper motions for 35 locations in the jet. The results suggest that when compared to the main body of the remnant, the jet experienced less outward acceleration from the central pulsar's rapidly expanding synchrotron nebula. The jet's apparent expansion rate yields an undecelerated explosion date for the Crab Nebula of 1055 ± 24 CE, a date much closer to the appearance of the historic 1054 CE guest star than the 1120–1140 CE dates estimated in previous studies using filaments located within the remnant's main nebula. Our proper motion measurements suggest the jet likely formed during the 1054 supernova explosion and represents the remnant's highest velocity knots possibly associated with a suspected N–S bipolar outflow from the supernova explosion.     

Bimodality of anomalous pulsars?

At present, it is widely believed that anomalous X-ray pulsars (AXPs), soft gamma-ray repeaters (SGRs), rotational radio transients (RRATs), compact central objects (CCOs) in supernova remnants, and X-ray dim isolated neutron stars (XDINSs) belong to different classes of anomalous objects in which the central bodies are isolated neutron stars. Previously, we have shown that AXPs and SGRs can be described in terms of the drift model for parameters of the central neutron star typical of radio pulsars (rotation periods P ～ 0.1–1 s and surface magnetic fields B ～ 10¹¹–10¹³ G). Here, we show that some of the peculiarities of the sources under consideration can be explained by their geometry (in particular, by the angle β between the rotation axis and the magnetic moment). If β ? 10° (an aligned rotator), the drift waves in the outer layers of the neutron star magnetosphere can account for the observed periodicity in the radiation. For large β (a nearly orthogonal rotator), the observed modulation of the radiation and its short bursts can be explained by mass accretion from the ambient medium (e.g., a relic disk).     

Cosmic-ray volleys from the galactic center and their recent impact on the earth environment

It is proposed that outbursts of cosmic ray electrons from the Galactic Center penetrate the Galaxy relatively undamped and are able to have a major impact on the Solar System through their ability to vaporize and inject cometary material into the interplanetary environment. It is suggested that one such superwave, passing through the Solar System toward the end of the Last Ice Age, was responsible for producing major changes in the Earth's climate and for indirectly precipitating the terminal Pleistocene extinction episode. The high concentrations of ¹⁰Be, NO₃ ^–, Ir and Ni observed in Late Wisconsin polar ice are consistent with this scenario. The intensities of the Galactic nonthermal radio background and diffuse X-ray emission ridge are shown to vary with Galactic longitude in the same manner as electron intensity along the proposed superwave event horizon. The high luminosities and unusual structural features which characterize the Crab Nebula and Cassiopeia A are shown to be attributable to the fact that these remnants happen to coincide with this event horizon and are being externally impacted by an intense volley of relativistic electrons travelling from the Galactic Center direction. The same cosmic ray volley is also shown to be able to account for the unusual structure of the extended radio source CTB 80.     

Neutral hydrogen in the vicinity of the supernova remnant HB 9

The neutral hydrogen emission at 21 cm has been investigated with the RATAN-600 radio telescope in the vicinity of the supernova remnant HB9. A clumpyHI shell with radial motions surrounding the remnant has been detected. Its measured parameters contradict the connection with a shock wave from a supernova explosion. The shell formation under the action of a wind from a star that exploded as a supernova at the end of its evolution seems more realistic. The characteristics of the star obtained from the observed shell parameters are the following: a wind power of 0.5 × 10³⁸ erg s^?1, a mass-loss rate of 3.7 × 10^?5 M _⊙ yr^?1, and an age of 3 × 10⁶ yr. Given the measurement errors, the mass of the star is estimated to be >8M _⊙.     

Remarks on the soft X-ray emission from the galactic radio spurs

It is pointed out that the all old supernova remnants are not in general sources of soft X-ray emission. Again it is pointed out that the galactic radio spur (Cetus arc) may be an old supernova remnant but it has already ceased to be a source of X-ray emission. Finally X-ray flux from Vela is ostimated from cooling rate of neutron star by neutrino emission. The results agree approximately with the observed X-ray flux from Vela X.     

Supernova remnants in the starburst galaxy M82

We have used the enhanced MERLIN at 1.5 and 5 GHz to image the central 700pc of the nearby starburst galaxy M82. Of order 40 discrete sources are detected and it appears that most of these sources are supernova remnants. Not only do many show shell structure and have a non-thermal radio spectrum, but they also follow a surface brightness/diameter relation consistent with that found in the LMC and Galactic supernova remnants. The detected M82 remnants are more compact and brighter than Galactic remnants which implies that they must be less than a few hundred years old and hence supernova rates are of order 0.05 per year. The 1.5 GHz measurements have shown that many of the remnants have low-frequency spectral turnovers which are probably due to free-free absorption in localised ionised gas with emission measures > 10⁶ pc cm^–6.     

Double-layer disk and magnetic field dynamics in the Crab Nebula

The mechanism of the large-scale magnetic field generation in the Crab Nebula is proposed. The basis for the considered fast mechanism is the model of the central region of Crab Nebula amorphous part having the form of slightly divergent double-layer disk consisting of the relativistic electron-positron plasma.The nebula toroidal magnetic field generation occurs in the double-layer disk in the immediate neighbourhood of the light cylinder of pulsar PSR 0531+21 due to the differential rotation by means of dynamo-mechanism. The generated field is transferred into the nebula by the pulsar wind which forms the double-layer disk.By use of the known parameters of pulsar PSR 0531+21, the considered mechanism yields the strength of magnetic fieldB=10^–3 G observed in the nebula. The disk structure must be destroyed toward the edges of the nebula.     

Analysis of systematic errors of the ASM/RXTE monitor and GT-48 γ-ray telescope

The observational data concerning variations of light curves of supernovae remnants—the Crab Nebula, Cassiopeia A, Tycho Brahe, and pulsar Vela—over 14 days scale that may be attributed to systematic errors of the ASM/RXTE monitor are presented. The experimental systematic errors of the GT-48 γ-ray telescope in the mono mode of operation were also determined. For this the observational data of TeV J2032 + 4130 (Cyg γ-2, according to the Crimean version) were used and the stationary nature of its γ-ray emission was confirmed by long-term observations performed with HEGRA and MAGIC. The results of research allow us to draw the following conclusions: (1) light curves of supernovae remnants averaged for long observing periods have false statistically significant flux variations, (2) the level of systematic errors is proportional to the registered flux and decreases with increasing temporal scale of averaging, (3) the light curves of sources may be modulated by the year period, and (4) the systematic errors of the GT-48 γ-ray telescope, in the amount caused by observations in the mono mode and data processing with the stereo-algorithm come to 0.12 min⁻¹.     

Estimation of energy of supernovae in large and small Magellanic clouds

Based on the theory of the radio evolution of supernova remnants and the theory of x-ray emission, we have derived an expression for the energy of supernova eruption directly in terms of the observed radio flux density and x-ray luminosity. This method is used to estimate the energy of the supernova explosions in LMC and SMC. Our calculated values fall in the range 10⁴⁹ – 10⁵¹ ergs, with the values for Type I supernovae systematically smaller than those for Type II, at about 10⁴⁹ ergs. We point out that the most likely cause for the discrepancy between the statistical and theoretical N-D relations is incompletness of data. We also point out, in the two clouds, the vast majority of large sources are still in the phase of adiabatic expansion.     

Particle acceleration test with Cas A multiwavelength emission

The investigation of supernova remnants (SNRs) across the electromagnetic spectrum from radio up to very high energy gamma-rays can serve as a test of the particle acceleration and touches on one of the unresolved problems of modern astrophysics, namely the origin of cosmic rays and the Galaxy's contribution to the overall cosmic ray spectrum. The multiwavelength observations of Cas A SNR demonstrated that structure and spectral features have clear signs of young SNRs and its overall properties make this object the best target to test a hypothesis of cosmic ray origin in SNRs. Studies of Cas A at very high energies by SHALON telescope showed the location of TeV gamma-ray emission region relative to the position of reveres shock. Also, the spectral energy distribution was obtained at high and very high energies. To describe the spectral and structural features of this SNR viewed in non-thermal emission, two approaches involving reverse and also both reverse and forward shocks to the mechanism of diffusive shock acceleration of cosmic rays in Cas A were applied. It is demonstrated that the observational properties of Cas A are well reproduced by the hadronic model with significant contribution of both the forward and reverse shocks in the generation of broadband emission. Calculation results suggest that the very high efficiency of particle acceleration in Cas A, which value is up to 25% of the supernova explosion energy with energy of accelerated particles not exceeding of $$ eV. Whereas, the forward shock model predicts the spectral characteristics of the TeV-gamma-emission corresponding to ones detected at 800 GeV–40 TeV that are the evidence of acceleration of the hadronic cosmic rays in shells of SNRs up to $$ eV     

An earlier explosion date for the Crab Nebula supernova

The Chinese first reported the Crab Nebula supernova on 1054 July 5. Ecclesiastical documents from the near east reported it in April and May of 1054. More than 33 petroglyphs made by Native Americans in the US and Mexico are consistent with sightings both before and after conjunction with the Sun on 1054 May 27. We found a petroglyph showing the new star close to Venus and the Moon, which occurred on 1054 April 12 and April 13, respectively. Collins et al., using the four historical dates, derived a light curve that is like that of a Type Ia supernova. The only remaining problem with this identification is that this supernova was near maximum light for 85 d, which is unlike the behavior of any known supernova.