707 research outputs found
A supernova remnant coincident with the slow X-ray pulsar AX J1845-0258
We report on Very Large Array observations in the direction of the
recently-discovered slow X-ray pulsar AX J1845-0258. In the resulting images,
we find a 5-arcmin shell of radio emission; the shell is linearly polarized
with a non-thermal spectral index. We class this source as a previously
unidentified, young (< 8000 yr), supernova remnant (SNR), G29.6+0.1, which we
propose is physically associated with AX J1845-0258. The young age of G29.6+0.1
is then consistent with the interpretation that anomalous X-ray pulsars (AXPs)
are isolated, highly magnetized neutron stars ("magnetars"). Three of the six
known AXPs can now be associated with SNRs; we conclude that AXPs are young
(~<10 000 yr) objects, and that they are produced in at least 5% of
core-collapse supernovae.Comment: 4 pages, 1 embedded EPS file, uses emulateapj.sty. Accepted to ApJ
Letter
TRIS II: search for CMB spectral distortions at 0.60, 0.82 and 2.5 GHz
With the TRIS experiment we have performed absolute measurements of the sky
brightness in a sky circle at at the frequencies
0.60, 0.82 and 2.5 GHz. In this paper we discuss the techniques used to
separate the different contributions to the sky emission and give an evaluation
of the absolute temperature of the Cosmic Microwave Background. For the
black-body temperature of the CMB we get: at GHz; at GHz; at
GHz. The first error bar is statistic (1) while the second
one is systematic. These results represent a significant improvement with
respect to the previous measurements. We have also set new limits to the
free-free distortions, ,
and slightly improved the Bose-Einstein upper limit, , both at 95% confidence level.Comment: accepted for publication in The Astrophysical Journa
On the short term stability and tilting motion of a well-observed low-latitude solar coronal hole
The understanding of the solar magnetic coronal structure is tightly linked
to the shape of open field regions, specifically coronal holes. A dynamically
evolving coronal hole coincides with the local restructuring of open to closed
magnetic field, which leads to changes in the interplanetary solar wind
structure. By investigating the dynamic evolution of a fast-tilting coronal
hole, we strive to uncover clues about what processes may drive its
morphological changes, which are clearly visible in EUV filtergrams. Using
combined 193A and 195A EUV observations by AIA/SDO and EUVI/STEREO_A, in
conjunction with line-of-sight magnetograms taken by HMI/SDO, we track and
analyze a coronal hole over 12 days to derive changes in morphology, area and
magnetic field. We complement this analysis by potential field source surface
modeling to compute the open field structure of the coronal hole. We find that
the coronal hole exhibits an apparent tilting motion over time that cannot
solely be explained by solar differential rotation. It tilts at a mean rate of
~3.2{\deg}/day that accelerates up to ~5.4{\deg}/day. At the beginning of May,
the area of the coronal hole decreases by more than a factor of three over four
days (from ~13 * 10^9 km^2 to ~4 * 10^9 km^2), but its open flux remains
constant (~2 * 10^20 Mx). Further, the observed evolution is not reproduced by
modeling that assumes the coronal magnetic field to be potential. In this
study, we present a solar coronal hole that tilts at a rate that has yet to be
reported in literature. The rate exceeds the effect of the coronal hole being
advected by either photospheric or coronal differential rotation. Based on the
analysis we find it likely that this is due to morphological changes in the
coronal hole boundary caused by ongoing interchange reconnection and the
interaction with a newly emerging ephemeral region in its vicinity.Comment: Accepted in A&A September 15, 2023; 10 pages, 8 figure
A Vision for Ice Giant Exploration
From Voyager to a Vision for 2050: NASA and ESA have just completed a study of candidate missionsto Uranus and Neptune, the so-called ice giant planets. It is a Pre-Decadal Survey Study, meant to inform the next Planetary Science Decadal Survey about opportunities for missions launching in the 2020's and early 2030's. There have been no space flight missions to the ice giants since the Voyager 2 flybys of Uranus in 1986 and Neptune in 1989. This paper presents some conclusions of that study (hereafter referred to as The Study), and how the results feed into a vision for where planetary science can be in 2050. Reaching that vision will require investments in technology andground-based science in the 2020's, flight during the 2030's along with continued technological development of both ground- and space-based capabilities, and data analysis and additional flights in the 2040's. We first discuss why exploring the ice giants is important. We then summarize the science objectives identified by The Study, and our vision of the science goals for 2050. We then review some of the technologies needed to make this vision a reality
Fourier Modeling of the Radio Torus Surrounding Supernova 1987A
We present detailed Fourier modeling of the radio remnant of Supernova 1987A,
using high-resolution 9 GHz and 18 GHz data taken with the Australia Telescope
Compact Array over the period 1992 to 2008. We develop a parameterized
three-dimensional torus model for the expanding radio shell, in which the
emission is confined to an inclined equatorial belt; our model also
incorporates both a correction for light travel-time effects and an overall
east-west gradient in the radio emissivity. By deriving an analytic expression
for the two-dimensional Fourier transform of the projected three-dimensional
brightness distribution, we can fit our spatial model directly to the
interferometric visibility data. This provides robust estimates to the radio
morphology at each epoch. The best-fit results suggest a constant remnant
expansion at 4000 +/- 400 km/s over the 16-year period covered by the
observations. The model fits also indicate substantial mid-latitude emission,
extending to 40 degree on either side of the equatorial plane. This likely
corresponds to the extra-planar structure seen in H and Ly
emission from the supernova reverse shock, and broadly supports hydrodynamic
models in which the complex circumstellar environment was produced by a
progression of interacting winds from the progenitor. Our model quantifies the
clear asymmetry seen in the radio images: we find that the eastern half of the
radio remnant is consistently ~40 brighter than the western half at all epochs,
which may result from an asymmetry in the ejecta distribution between these two
hemispheres.Comment: accepted by ApJ, 11 figures, some have been scaled down in resolutio
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