Observations of the supernova remnants HB 9 and 1C 443 at 34.5MHz

We have observed the extended supernova remnants HB 9 (G 160.5 + 2.8) and IC 443 (G 189.1 + 2.9) at 34.5 MHz with a resolution of 26 arcmin × 40 arcmin. A map of HB 9 is presented. The integrated flux density of HB 9 at 34.5 MHz is 750 ± 150 Jy. The spectral index in the frequency range from 34.5 MHz to 2700 MHz is found to be constant (- 0.58 ± 0.06) without any spectral break such as was reported earlier by Willis (1973). There is no significant variation of the spectral index across the remnant. The integrated flux density of IC 443 at 34.5 MHz is 440 ± 88 Jy. The spectral index in the frequency range from 20 MHz to 10700 MHz is - 0.36 ± 0.04. The reduction in flux at very low frequencies (10 MHz) is attributable to free-free absorption in the interstellar medium and/or in the H II region S 249.     

The structure of the Cygnus loop at 34.5 MHz

We have observed the large supernova remnant Cygnus Loop at 34.5 MHz with the low frequency radio telescope at Gauribi-danur, India. A radio map of the region with a resolution of 26 arcmin × 40 arcmin (α × δ) is presented. The integrated flux density of the Cygnus Loop at this frequency is 1245 ± 195 Jy. The radio fluxes of different parts of the nebula at this frequency were also measured and used to construct their spectra. It is found that the spectrum of the region associated with the optical nebulosity NGC 6992/5 is not flat at low frequencies, and also exhibits a break at a frequency around 400 MHz. The spectrum of the region associated with NGC 6960 also shows a break but around 1000 MHz, while the spectrum of the region associated with NGC 6974 is straight in the entire frequency range 25 to 5000 MHz. The implication of these results on the basis of existing theories of the origin of radio emission from supernova remnants is discussed.     

Radio Observations at 232 MHz and Multifrequency Spectral Studies of SNR HB21

Radio observational results at 232 MHz and multifrequency studies of supernova remnant (SNR) HB21 are presented. Its integrated flux density at 232 MHz is about 390 ± 30 Jy. Both the integrated spectral index and the spatial variations of spectral index of the remnant were calculated by combining the new map at 232 MHz with previously published maps made at 408, 1420, 2695, and 4750 MHz. The SNR has an integrated spectral index of about α = -0.43(S _ν ∝ ν^α) between 232 and 4750 MHz. In general the spectral index varies from –0.5 in southeast and west regions of the remnant to –0.3 in the central region and near the northwest edge. The new data of 232 MHz reveals that there is interaction between the remnant and the surrounding gas along the east edge of the remnant which causes the spectrum flattening at low frequency, while the very good agreement between the structure of X-ray emission and the central flat spectrum area suggests that the existence of thermal emission is the reason of spectrum flattening in the area. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Radio-continuum study of MCSNR J0536–7038 (DEM L249)

We present a detailed radio-continuum study on Australia Telescope Compact Array (ATCA) observations of Large Magellanic Cloud (LMC) supernova remnant (SNR), MCSNR J0536–7038. This Type Ia SNR follows a horseshoe morphology, with a size 32 pc × 32 pc (1-pc uncertainty in each direction). It exhibits a radio spectrum α=?0.52±0.07 between λ=73 and 6 cm. We report detections of regions showing moderately high fractional polarisation at 6 cm, with a peak value of 71±25 % and a mean fractional polarisation of 35±8 %. We also estimate an average rotation measure across the remnant of –237 rad m^?2. The intrinsic magnetic field appears to be uniformly distributed, extending in the direction of the two brightened limbs of the remnant.     

No detectable supernova remnant near the pulsar PSR 1930 + 22

No supernova remnant has been found near the third youngest pulsar PSR 1930+22 down to a -limiting brightness temperature of 1·4 K at 610 MHz. This is 6–8 times less than expected of a typical remnant whose age is that of the pulsar (3·60×10⁴ years).     

Terrestrial paleoenvironmental effects of a late quaternary-age supernova

A chronology of the γ and X radiation incident upon the Earth from discrete supernova occurences is desirable for two reasons: (1) large but short-lived γ flashes should result in episodically increased atmospheric ¹⁴C production, and thus affect the ¹⁴C dating method, and (2) modeling of the other atmospheric effects to be expected from nearby supernovas indicates their possible importance as independent variables capable of causing climatic or other environmental changes. Presented here is a preliminary chronology of the larger inferred radiation events experienced by the Earth during the past 15, 000 years. This chronology illustrates the possible importance of the Vela optical-, radio-, and X-emitting supernova remnant (G263.9-3.3), and its associated pulsar (PSR-0833-45), which together record an unusually close (d = 500 pc supernova occuring sometime between 11,300 and 8,400 years B.P. The predicted terrestrial effects of a 10⁴⁹?1 10⁵⁰-erg γ- and X-emitting supernova at this distance include short-term increases in ¹⁴C activity (+3 to +6%), increases in aquatic productivity at some localities, and a brief global cooling. Such effects appear to be documented by many late Quaternary paleoenvironmental records dated between 11,000 and 10,000 ¹⁴C yr B.P.     

A Model of the Vela Supernova Remnant

A model of the Vela supernova remnant (SNR) based on a cavity explosion of a supernova (SN) star is proposed. It is suggested that the general structure of the remnant is determined by the interaction of the SN blast wave with a massive shell created by the SN progenitor (15-20 M_⊙) star. A possible origin of the nebula of hard X-ray emission detected around the Velapulsar is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A review of some radio and microwave searches for transient phenomena in relation to Vela gamma-ray bursts and supernovae

Radio systems with all sky viewing antennas at 151 MHz were operating at 5 widely spaced stations over the period 1970–1973, during which 19 Vela -ray bursts were detected. The records were analysed for each Vela time but no radio coincidences were recorded. A new experiment in the radio band operating at 408 MHz with similar objectives is now under construction and will be described.Five radiometers at 10 GHz have been tracking the Perseus cluster of galaxies for over one year. The supernova reported on 1 March in Perseus occurred during our oberving time but failed to give evidence from prompt emission in excess to 8×10^–11 erg cm^–2 event^–1, for event durations 0.3–100 s.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

Diffuse radio emission from the Coma cluster of galaxies at decametre wavelengths

We have observed the region of the Coma cluster at 34.5 MHz with a resolution of 26 arcmin × 40 arcmin. A map of the diffuse halo (Coma C) is presented. The size of the halo is found to be 54 arcmin × 30 arcmin. The position angle is 50° ± 10° and the integrated flux is 60 ± 11 Jy. We have also found an extended source to the south of Coma A. The measured half-power widths of this source are 30 arcmin × 40 arcmin. The position angle is 135° and the integrated flux is ~ 15 Jy at 34.5 MHz. The spectral index in the frequency range 408 to 34.5 MHz is -1.0. It is suggested that this source also belongs to the Coma cluster.     

Electron temperatures in W51 complex from high resolution,low frequency radio observations

W51 is a giant radio complex lying along the tangent to the Sagitarius arm at a distance of about 7 kpc from the Sun, with an extension of about 1° in the sky. It is divided into three components A, B, C where W51A and W51B consist of many compact HII regions while W51C is a supernova remnant. We have made continuum radio observations of these HII regions of the W51 complex at 240, 610, 1060 and 1400 MHz using GMRT with lower resolution (20″ × 15″) at the lowest frequency. The observed spectra of the prominent thermal subcomponents of W51 have been fitted to a free-free emission spectrum and their physical properties like electron temperatures and emission measures have been estimated. The electron temperatures from continuum spectra are found to be lower than the temperatures reported from radio recombination line (RRL) studies of these HII regions indicating the need for a filling factor even at this resolution. Also, the observed brightness at 240 MHz is found to be higher than expected from the best fits suggesting the need for a multicomponent model for the region.     

SN2015bh in NGC 2770: LBV core collapse in merging of binary system components

We present spectroscopy and multicolor photometry for the optical transient PSN J09093496+3307204 in the galaxy NGC2770, which has afterwards been transferred into the supernova phase and got the name SN2015bh. Medium-resolution spectral observations were carried out between February 2015 to May 2016 using the focal reducer SCORPIO at the 6-m Russian telescope BTA. They were followed by by photometric observations at the BTA and six other telescopes with 0.5–1m apertures. Both at the phase of the SN impostor (2015a) and at the supernova phase (2015b), besides Balmer emissions, the strong Fe II emissions are seen in the spectrum; so, these spectra resemble those of Williams Fe II type classical novae. Taking into account circumstellar, interstellar and galactic absorption, A_V = 1.^m 14 ±0.^m 15), we determined maximum absolute magnitudes of the object to be M_V =–15.^m 0 ±0.^m 3 at the 2015a phase and of M^V =–18.^m 14 ±0.^m 30 at the 2015b phase. The light curve at the 2015b phase is similar to those of SN IIL. The supernova progenitor is a luminous blue variable (LBV) star with the powerful Hα emission. We consider several hypotheses of supernovae explosions following optical transients related with LBV. The hypothesis of core collapse of an evolved massive star interrupting the process of its merging with massive companion in a binary system (a failed luminous red nova) was chosen as the preferable one for this event.     

Interaction of the supernova remnant S 147 with the ambient interstellar gas

Based on RATAN-600 21-cm H I line observations with an angular resolution of 2.4', we studied the neutral-hydrogen distribution in the region of the supernova remnant (SNR) S 147 (G180.0-1.7). We detected a rotating shell of neutral gas immediately adjacent to the SNR that is expanding at a velocity of 20 km s^?1. The H I shell is less distinct in the southeastern part and at negative radial velocities. The outer shell diameter is 90 pc; the H I mass in the shell is 2.2 × 10⁴M_⊙. These data allowed us to estimate the SNR age, 6.5×10⁵ yr, and the initial explosion energy, 2.2×10⁵¹ erg.     

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 _⊙.     

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.     

26Al production in the Vela and Orion regions

The allsky image of ²⁶Al radiation at 1.809 MeV with COMPTEL suggests that clusters of massive stars dominate the Galactic production of ²⁶Al. Studies of rather well-known localized regions are most promising to further this interpretation. In the Vela region, excessive emissivity is found compared to other Galactic regions. This may be due to few prominent foreground sources, such as the Vela SNR and RX J0852.0-4622 combined; but more plausibly the star forming activity along the Vela Molecular Ridge is enhanced in general, too. In the anticenter region, the detected ²⁶Al emission appears related to nucleosynthetic activity in the Orion OB1 association: It seems plausible that ejecta are being vented into the Eridanus bubble blown by earlier massive stars’ activity.     

A search for the 53-MHz OH line near G48.4−1.4 using the National MST Radar Facility

We present the results of a search for the ground-state hyperfine transition of the OH radical near 53 MHz using the National Mesosphere–Stratosphere–Troposphere (MST) Radar Facility at Gadanki, India. The observed position was G48.4−1.4 near the Galactic plane. The OH line is not detected. We place a 3σ upper limit for the line flux density at 39 Jy from our observations. We also did not detect recombination lines (RLs) of carbon, which were within the frequency range of our observations. The 3σ upper limit of 20 Jy obtained for the flux density of carbon RLs, along with observations at 34.5 and 327 MHz, are used to constrain the physical properties of the line-forming region. Our upper limit is consistent with the line emission expected from a partially ionized region with electron temperature, density and path lengths in the range 20–300 K, 0.03–0.3 cm⁻³ and 0.1–170 pc, respectively.     

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.     

Cosmic ray diffusion at energies of 1 MeV to 105 GeV

A supernova remnant accelerates cosmic rays to energies somewhat above 10⁵ GeV by the time that the free expansion phase of its evolution has come to an end. As the remnant's outer shock slows, these highest energy cosmic rays diffuse away from the shock along a magnetic flux tube with a radius comparable to that of the remnant at the end of its free expansion phase and which eventually (over a distance of the order of a kiloparsec) bends into the Galactic halo. A similarity solution exists for the temporal and spatial variations, in such a tube, of both the number density for these ～ 10⁵ GeV cosmic rays and the energy density of the waves on which they resonantly scatter. Wave-wave interactions probably do not dominate the evolution of the energy density of these lowest frequency waves, but we assume that they do establish a Kraichnan wave spectrum at higher wavenumber. Although we cannot rigorously justify this assumption, it does receive some support from the analysis of pulsar signals. There is a large body of observations to which such a model can be applied, yielding constraints that must be met. With the model that we develop here we obtain the following results:

1. The local intensity of ～ 10⁵ GeV cosmic rays implies that the flux tube which currently surrounds the Solar System last contained a remnant in the free expansion phase several times 10⁷ years ago. We comment on the rough agreement between this age and that inferred from Be¹⁰ data.
2. The theoretical value of the cosmic ray diffusion coefficient at ～ 1 GeV in the tube corresponding to that time is in harmony with the value of the diffusion coefficient inferred from cosmic ray composition and synchrotron measurements.

In the light of our inhomogeneous cosmic ray acceleration/propagation model we re-examine our earlier work on the evidence for second order acceleration in a very old remnant. Such evidence is provided by the molecular compositions along several lines of sight to the Perseus OB2 association. We find as a third significant result that the model value of the diffusion coefficient at energies in the range of 1 MeV agrees within about an order of magnitude with that which we infer from the molecular data.     

Hard X-ray emission from the SNR G337.2+0.1

We report hard X-ray emission of the non-thermal supernova remnant G337.2+0.1. The source presents centrally filled and diffuse X-ray emission. A spectral study confirms that the column density of the central part of the object is about N _H∼5.9(±1.5)×10²² cm⁻² and its X-ray spectrum is well represented by a single power-law with a photon index Γ=0.96±0.56. Detailed spectral analysis indicates that the outer region is highly absorbed and quite softer than the inner region. Characteristics already observed in other well-known X-ray plerions. Based on the gathered information, we confirm the SNR nature of G337.2+0.1, and suggest that the central region of the source is a pulsar wind nebula (PWN), originated by an energetic though yet undetected pulsar.