427 research outputs found
The remnant of SN1987A revealed at (sub-)mm wavelengths
Context: Supernova 1987A (SN1987A) exploded in the Large Magellanic Cloud
(LMC). Its proximity and rapid evolution makes it a unique case study of the
early phases in the development of a supernova remnant. One particular aspect
of interest is the possible formation of dust in SN1987A, as SNe could
contribute significantly to the dust seen at high redshifts. Aims: We explore
the properties of SN1987A and its circumburst medium as seen at mm and sub-mm
wavelengths, bridging the gap between extant radio and infrared (IR)
observations of respectively the synchrotron and dust emission. Methods:
SN1987A was observed with the Australia Telescope Compact Array (ATCA) at 3.2
mm in July 2005, and with the Atacama Pathfinder EXperiment (APEX) at 0.87 mm
in May 2007. We present the images and brightness measurements of SN1987A at
these wavelengths for the first time. Results: SN1987A is detected as an
unresolved point source of 11.2 +/- 2.0 mJy at 3.2 mm (5" beam) and 21 +/- 4
mJy at 0.87 mm (18" beam). These flux densities are in perfect agreement with
extrapolations of the powerlaw radio spectrum and modified-blackbody dust
emission, respectively. This places limits on the presence of free-free
emission, which is similar to the expected free-free emission from the ionized
ejecta from SN1987A. Adjacent, fainter emission is observed at 0.87 mm
extending ~0.5' towards the south-west. This could be the impact of the
supernova progenitor's wind when it was still a red supergiant upon a dense
medium. Conclusions: We have established a continuous spectral energy
distribution for the emission from SN1987A and its immediate surroundings,
linking the IR and radio data. This places limits on the contribution from
ionized plasma. Our sub-mm image reveals complexity in the distribution of cold
dust surrounding SN1987A, but leaves room for freshly synthesized dust in the
SN ejecta.Comment: Accepted for publication in Astronomy and Astrophysics Letters on 28
April 2011. A better quality figure 1 can be had from
http://www.astro.keele.ac.uk/~jacco/research/SN1987A087mm.ep
Evolution of the Radio Remnant of Supernova 1987A: Morphological Changes from Day 7000
We present radio imaging observations of supernova remnant 1987A at 9 GHz,
taken with the Australia Telescope Compact Array over 21 years from 1992 to
2013. By employing a Fourier modeling technique to fit the visibility data, we
show that the remnant structure has evolved significantly since day 7000
(mid-2006): the emission latitude has gradually decreased, such that the
overall geometry has become more similar to a ring structure. Around the same
time, we find a decreasing trend in the east-west asymmetry of the surface
emissivity. These results could reflect the increasing interaction of the
forward shock with material around the circumstellar ring, and the relative
weakening of the interaction with the lower-density material at higher
latitudes. The morphological evolution caused an apparent break in the remnant
expansion measured with a torus model, from a velocity of 4600+150-200 km/s
between day 4000 and 7000 to 2400+100-200 km/s after day 7000. However, we
emphasize that there is no conclusive evidence for a physical slowing of the
shock at any given latitude in the expanding remnant, and that a change of
radio morphology alone appears to dominate the evolution. This is supported by
our ring-only fits which show a constant expansion of 3890+/-50 km/s without
deceleration between days 4000 and 9000. We suggest that once the emission
latitude no longer decreases, the expansion velocity obtained from the torus
model should return to the same value as that measured with the ring model.Comment: 11 pages, 5 figures, accepted for publication in ApJ, Figure 1 has
been scaled dow
Search for a Radio Pulsar in the Remnant of Supernova 1987A
We have observed the remnant of supernova SN~1987A (SNR~1987A), located in
the Large Magellanic Cloud (LMC), to search for periodic and/or transient radio
emission with the Parkes 64\,m-diameter radio telescope. We found no evidence
of a radio pulsar in our periodicity search and derived 8 upper bounds
on the flux density of any such source of Jy at 1.4~GHz and
Jy at 3~GHz. Four candidate transient events were detected with
greater than significance, with dispersion measures (DMs) in the
range 150 to 840\,cmpc. For two of them, we found a second pulse at
slightly lower significance. However, we cannot at present conclude that any of
these are associated with a pulsar in SNR~1987A. As a check on the system, we
also observed PSR~B054069, a young pulsar which also lies in the LMC. We
found eight giant pulses at the DM of this pulsar. We discuss the implications
of these results for models of the supernova remnant, neutron star formation
and pulsar evolution.Comment: 7 pages, 3 figures, 2 tables. Accepted for publication in MNRA
High-resolution radio observations of SNR 1987A at high frequencies
We present new imaging observations of the remnant of Supernova (SN) 1987A at
44 GHz, performed in 2011 with the Australia Telescope Compact Array (ATCA).
The 0\farcs35\times0\farcs23 resolution of the diffraction-limited image is
the highest achieved to date in high-dynamic range. We also present a new ATCA
image at 18 GHz derived from 2011 observations, which is super-resolved to
0\farcs25. The flux density is 402 mJy at 44 GHz and 816 mJy at 18
GHz. At both frequencies, the remnant exhibits a ring-like emission with two
prominent lobes, and an east-west brightness asymmetry that peaks on the
eastern lobe. A central feature of fainter emission appears at 44 GHz. A
comparison with previous ATCA observations at 18 and 36 GHz highlights higher
expansion velocities of the remnant eastern side. The 18-44 GHz spectral index
is (). The spectral index map
suggests slightly steeper values at the brightest sites on the eastern lobe,
whereas flatter values are associated with the inner regions. The remnant
morphology at 44 GHz generally matches the structure seen with contemporaneous
X-ray and H observations. Unlike the H emission, both the radio
and X-ray emission peaks on the eastern lobe. The regions of flatter spectral
index align and partially overlap with the optically-visible ejecta. Simple
free-free absorption models suggest that emission from a pulsar wind nebula or
a compact source inside the remnant may now be detectable at high frequencies,
or at low frequencies if there are holes in the ionised component of the
ejecta.Comment: References updated. High resolution version may be found at
http://ict.icrar.org/store/staff/gio/Papers/Zanardo_2013.pd
Detection and whole genome sequencing of CPMMV in common bean resistant to BGMV from Paraná State.
Cowpea mild mottle virus (CPMMV) is a Carlavirus from the family Betaflexiviridae which has a linear single stranded positive sense rna genome of approximately 8,200 nt and infects a wide range of cultivated plants from the Fabaceae family. It is transmitted by the whitefly Bemisia tabaci
Expected gamma-ray emission of supernova remnant SN 1987A
A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants is employed to re-examine the nonthermal properties of the remnant of
SN 1987A for an extended evolutionary period of 5--100 yr. It is shown that an
efficient production of nuclear CRs leads to a strong modification of the outer
supernova remnant shock and to a large downstream magnetic field
mG. The shock modification and the strong field are
required to yield the steep radio emission spectrum observed, as well as to
considerable synchrotron cooling of high energy electrons which diminishes
their X-ray synchrotron flux. These features are also consistent with the
existing X-ray observations. The expected \gr energy flux at TeV-energies at
the current epoch is nearly erg cms under reasonable assumptions about the overall
magnetic field topology and the turbulent perturbations of this field. The
general nonthermal strength of the source is expected to increase roughly by a
factor of two over the next 15 to 20 yrs; thereafter it should decrease with
time in a secular form.Comment: 7 pages, 5 figures, accepted for publication in ApJ, a number of
changes have been made, even though these are not changing the main results
of the pape
Detection of linear polarization in the radio remnant of supernova 1987A
Supernova 1987A in the Large Magellanic Cloud has proven a unique laboratory to investigate particle acceleration in young supernova remnants. Here we report the �rst detection of linear polarization of the supernova's synchrotron emission from imaging observations at frequencies spanning from 20 to 50GHz, carried out with the Australia Telescope Compact Array between October 2015 and May 2016. The direction of the radio polarization, corrected for Faraday rotation, points to a primarily radial magnetic �eld across the inner ring, encompassing both the reverse and forward shocks. The magnetic eld strength peaks over the high-emissivity eastern sites, where e�cient cosmic ray acceleration likely takes place under quasi-parallel shocks at high Mach numbers. The mean fraction of polarized emission in the brightest sites is 2:7 � 0:2% at 22 GHz and 3:5 � 0:7% at 44 GHz. In the inner remnant, non-radial components of the polarized emission appear to be more prevalent. However, the low signi�cance
detection in the central regions limits interpretation
The radio remnant of supernova 1987A- A broader view
Supernova remnants (SNRs) are powerful particle accelerators. As a supernova (SN) blast wave propagates through the circumstellar medium (CSM), electrons and protons scatter across the shock and gain energy by entrapment in the magnetic field. The accelerated particles generate further magnetic field fluctuations and local amplification, leading to cosmic ray production. The wealth of data from Supernova 1987A is providing a template of the SN-CSM interaction, and an important guide to the radio detection and identification of core-collapse SNe based on their spectral properties. Thirty years after the explosion, radio observations of SNR 1987A span from 70 MHz to 700 GHz. We review extensive observing campaigns with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and follow-ups with other radio telescopes. Observations across the radio spectrum indicate rapid changes in the remnant morphology, while current ATCA and ALMA observations show that the SNR has entered a new evolutionary phase
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