اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOn the Emergence and Discovery of Hot Spots in Supernova Remnant 1987A
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Stephen Lawrence
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We present the discovery of several new regions of interaction between the ejecta and equatorial circumstellar ring of SN1987A, an interaction leading to a much expanded development of the supernova remnant. We also trace the development of the first such hot spot, discovered in 1997, back to 1995. Later hot spots seem to have emerged by early 1999. We discuss mechanisms for the long delay between the first and later spots.
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We have been monitoring the supernova remnant (SNR) 1987A with {it Chandra} observations since 1999. Here we report on the latest change in the soft X-ray light curve of SNR 1987A. For the last $sim$1.5 yr (since day $sim$8000), the soft X-ray flux h
as significantly flattened, staying (within uncertainties) at $f_{rm X}$ $sim$ 5.7 $times$ 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$ (corresponding to $L_{rm X}$ $sim$ 3.6 $times$ 10$^{36}$ erg s$^{-1}$) in the 0.5--2 keV band. This remarkable change in the recent soft X-ray light curve suggests that the forward shock is now interacting with a decreasing density structure, after interacting with an increasing density gradient over $sim$10 yr prior to day $sim$8000. Possibilities may include the case that the shock is now propagating beyond a density peak of the inner ring. We briefly discuss some possible implications on the nature of the progenitor and the future prospects of our {it Chandra} monitoring observations.
The interaction between the ejecta from Supernova 1987A and surrounding material is producing steadily brightening radio and X-ray emission. The new-born supernova remnant has been significantly decelerated by this interaction, while its morphology r
eflects the axisymmetric nature of the progenitor wind.
We have observed the remnant of supernova SN~1987A (SNR~1987A), located in the Large Magellanic Cloud (LMC), to search for periodic and/or transient radio emission with the Parkes 64,m-diameter radio telescope. We found no evidence of a radio pulsar
in our periodicity search and derived 8$sigma$ upper bounds on the flux density of any such source of $31,mu$Jy at 1.4~GHz and $21,mu$Jy at 3~GHz. Four candidate transient events were detected with greater than $7sigma$ significance, with dispersion measures (DMs) in the range 150 to 840,cm$^{-3},$pc. 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~B0540$-$69, 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.
The proximity of core-collapse Supernova 1987A (SN1987A) in the Large Magellanic Cloud (LMC) and its rapid evolution make it a unique case study of the development of a young supernova remnant. We aim at resolving the remnant of SN1987A for the first
time in the 3-mm band (at 94 GHz). We observed the source at 3-mm wavelength with a 750-m configuration of the Australia Telescope Compact Array (ATCA). We compare the image with a recent 3-cm image and with archival X-ray images. We present a diffraction-limited image with a resolution of 0.7, revealing the ring structure seen at lower frequencies and at other wavebands. The emission peaks in the eastern part of the ring. The 3-mm image bears resemblance to early X-ray images (from 1999-2000). We place an upper limit of 1 mJy (2 sigma) on any discrete source of emission in the centre (inside of the ring). The integrated flux density at 3 mm has doubled over the six years since the previous observations at 3 mm. At 3 mm - i.e. within the operational domain of the Atacama Large Millimeter/submillimeter Array (ALMA) - SN1987A appears to be dominated by synchrotron radiation from the inner rim of the equatorial ring, characterised by moderately-weak shocks. There is no clear sign of emission of a different nature, but the current limits do not rule out such component altogether.
(Abridged) We aim at linking the dynamical and radiative properties of the remnant of SN 1987A to the geometrical and physical characteristics of the parent aspherical SN explosion and to the internal structure of its progenitor star. We performed 3D
hydrodynamic simulations which describe the long-term evolution of SN 1987A from the onset of the SN to the full-fledged remnant at the age of 50 years, accounting for the pre-SN structure of the progenitor star. The simulations include all physical processes relevant for the complex phases of SN evolution and for the interaction of the SNR with the highly inhomogeneous ambient environment around SN 1987A. From the simulations, we synthesize observables to be compared with observations. By comparing the model results with observations, we constrained the initial SN anisotropy causing Doppler shifts observed in emission lines of heavy elements from ejecta, and leading to the remnant evolution observed in the X-ray band in the last 30 years. In particular, we found that the high mixing of ejecta unveiled by high redshifts and broadenings of [FeII] and $^{44}$Ti lines require a highly asymmetric SN explosion channeling a significant fraction of energy along an axis almost lying in the plane of the central equatorial ring around SN 1987A, roughly along the line-of-sight but with an offset of 40 deg, with the lobe propagating away from the observer slightly more energetic than the other. We found unambiguously that the observed distribution of ejecta and the dynamical and radiative properties of the SNR can be best reproduced if the structure of the progenitor star was that of a blue supergiant resulted from the merging of two massive stars.
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