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Post Info TOPIC: G1.9+0.3
Blobrana


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The Remarkable Remains of a Recent Supernova

g19_w11.jpg

Astronomers estimate that a star explodes as a supernova in our Galaxy, on average, about twice per century. In 2008, a team of scientists announced they discovered the remains of a supernova that is the most recent, in Earth's time frame, known to have occurred in the Milky Way.
The explosion would have been visible from Earth a little more than a hundred years ago if it had not been heavily obscured by dust and gas. Its likely location is about 28,000 light years from Earth near the center of the Milky Way. A long observation equivalent to more than 11 days of observations of its debris field, now known as the supernova remnant G1.9+0.3, with NASA's Chandra X-ray Observatory is providing new details about this important event.
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Blobrana


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Title: Supernova Ejecta in the Youngest Galactic Supernova Remnant G1.9+0.3
Authors: K. J. Borkowski, S. P. Reynolds, U. Hwang, D. A. Green, R. Petre, K. Krishnamurthy, R. Willett

G1.9+0.3 is the youngest known Galactic supernova remnant (SNR), with an estimated supernova (SN) explosion date of about 1900, and most likely located near the Galactic Center. Only the outermost ejecta layers with free-expansion velocities larger than about 18,000 km/s have been shocked so far in this dynamically young, likely Type Ia SNR. A long (980 ks) Chandra observation in 2011 allowed spatially-resolved spectroscopy of heavy-element ejecta. We denoised Chandra data with the spatio-spectral method of Krishnamurthy et al., and used a wavelet-based technique to spatially localise thermal emission produced by intermediate-mass elements (IMEs: Si and S) and iron. The spatial distribution of both IMEs and Fe is extremely asymmetric, with the strongest ejecta emission in the northern rim. Fe Kalpha emission is particularly prominent there, and fits with thermal models indicate strongly oversolar Fe abundances. In a localised, outlying region in the northern rim, IMEs are less abundant than Fe, indicating that undiluted Fe-group elements (including 56Ni) with velocities larger than 18,000 km/s were ejected by this SN. But in the inner west rim, we find Si- and S-rich ejecta without any traces of Fe, so high-velocity products of O-burning were also ejected. G1.9+0.3 appears similar to energetic Type Ia SNe such as SN 2010jn where iron-group elements at such high free-expansion velocities have been recently detected. The pronounced asymmetry in the ejecta distribution and abundance inhomogeneities are best explained by a strongly asymmetric SN explosion, similar to those produced in some recent 3D delayed-detonation Type Ia models.

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Blobrana


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Title: Expansion of the Youngest Galactic Supernova Remnant G1.9+0.3
Authors: A.K. Carlton, K.J. Borkowski, S.P. Reynolds, U. Hwang, R. Petre, D.A. Green, K. Krishnamurthy, R. Willett

We present a measurement of the expansion and brightening of G1.9+0.3, the youngest Galactic supernova remnant, comparing Chandra X-ray images obtained in 2007 and 2009. A simple uniform expansion model describes the data well, giving an expansion rate of 0.642 ±0.049 % yr^-1, and a flux increase of 1.7 ±1.0 % yr^-1. Without deceleration, the remnant age would then be 156 ±11 yr, consistent with earlier results. Since deceleration must have occurred, this age is an upper limit; we estimate an age of about 110 yr, or an explosion date of about 1900. The flux increase is comparable to reported increases at radio wavelengths. G1.9+0.3 is the only Galactic supernova remnant increasing in flux, with implications for the physics of electron acceleration in shock waves

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Blobrana


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G1.9 0.3 in 60 Seconds
G1.9+0.3 and NGC 4258



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Blobrana


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Title: X-RAY SPECTRAL VARIATIONS IN THE YOUNGEST GALACTIC SUPERNOVA REMNANT G1.9+0.3
Authors: Stephen P. Reynolds, Kazimierz J. Borkowski, David A. Green, Una Hwang, Ilana Harrus and Robert Petre

The discovery of the youngest Galactic supernova remnant (SNR) G1.9+0.3 has allowed a look at a stage of SNR evolution never before observed. We analyse the 50 ks Chandra observation with particular regard to spectral variations. The very high column density (NH   ~ 6 × 10^22 cm^-2) implies that dust scattering is important, and we use a simple scattering model in our spectral analysis. The integrated X-ray spectrum of G1.9+0.3 is well described by synchrotron emission from a power-law electron distribution with an exponential cutoff.

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Researchers at North Carolina State University have used a mathematical model that allows them to get a clearer picture of the galaxy's youngest supernova remnant by correcting for the distortions caused by cosmic dust.
Their new data provides evidence that this remnant is from a type Ia supernova -- the explosion of a white dwarf star -- and raises questions about the ways in which magnetic fields affect the generation of the remnant's cosmic ray particles.
NC State physicists Dr. Stephen Reynolds and Dr. Kazimierz Borkowski, with colleagues from Cambridge University and NASA, re-examined their original X-ray images of supernova remnant G1.9+0.3 in an attempt to glean more information about the remnant's origins, rate of expansion, and any cosmic particles that may have resulted from the explosion.

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SNR G1.9+0.3
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Title: An ATCA Observation of the Youngest Known Galactic SNR G1.9+0.3
Authors: A. Y. De Horta, M. D. Filipovi, E. J. Crawford, F. H. Stootman, T. G. Pannuti

We present an analysis of a previously unpublished radio-continuum observation of SNR G1.9+0.3 which at an age of <=150 years is the youngest known in the Galaxy. The observations were made in 1993 using the Australia Telescope Compact Array (ATCA) at two 6-cm frequencies. We note two previously unseen blow-out structures in the north and south directions. We estimate a flux density of 1.545Jy, an outer diameter of ~80" and confirm an expansion rate of ~0.65% per year between 1985 and 2008. No polarisation was detected in the radio emission from SNR G1.9+0.3 above the 1% level. We also present these previously unpublished results as a high resolution reference point from which to study the evolution of SNRs at times for which there is a gap in our knowledge.

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G1.9+0.3
Credit: X-ray (NASA/CXC/NCSU/S.Reynolds et al.); Radio (NSF/NRAO/VLA/Cambridge/D.Green et al.); Infrared (2MASS/UMass/IPAC-Caltech/NASA/NSF/CfA/E.Bressert)
JPEG (386.7 kb) Tiff (23 MB) PS (1.2 MB)

The expanding remains of a supernova explosion in the Milky Way are shown in this composite image, on the left, of the supernova remnant G1.9+0.3. NASA's Chandra X-ray Observatory image obtained in early 2007 is shown in orange and the radio image from NRAO's Very Large Array (VLA) from 1985 is in blue. The difference in size between the two images gives clear evidence for expansion, allowing the time since the original supernova explosion (about 140 years) to be estimated.

This makes the original explosion the most recent supernova in the Galaxy, as measured in Earth's time-frame (referring to when events are observable at Earth). Equivalently, this is the youngest known supernova remnant in the Galaxy (140 years old), easily beating the previous record of about 330 years for Cassiopeia A. The rapid expansion and young age for G1.9+0.3 was recently confirmed by a new VLA image obtained in early 2008.

Position(J2000): RA 17h 48m 45s | Dec -27° 10' 00

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-- Edited by Blobrana at 19:22, 2008-05-14

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Title: The Youngest Galactic Supernova Remnant: G1.9+0.3
Authors: S.P. Reynolds, K.J. Borkowski, D.A. Green, U. Hwang, I. Harrus, R. Petre
(Version v2)

Our 50 ks Chandra observation of the small radio supernova remnant (SNR) G1.9+0.3 shows a complete shell structure with strong bilateral symmetry, about 100'' in diameter. The radio morphology is also shell-like, but only about 84'' in diameter, based on observations made in 1985. We attribute the size difference to expansion between 1985 and our Chandra observations of 2007. Expansion is confirmed in comparing radio images from 1985 and 2008. We deduce that G1.9+0.3 is of order 100 years old -- the youngest supernova remnant in the Galaxy. Based on a very high absorbing column density of 5.5 X 10^{22} cm^{-2}, we place G1.9+0.3 near the Galactic Centre, at a distance of about 8.5 kpc, where the mean remnant radius would be about 2 pc, and the required expansion speed about 14,000 km s^{-1}. The X-ray spectrum is featureless and well-described by the exponentially cut off synchrotron model {\tt srcut}. With the radio flux at 1 GHz fixed at 0.9 Jy, we find a spectral index of 0.65 and a rolloff frequency of 1.4 \times 10^{18} Hz. The implied characteristic rolloff electron energy of about 94 (B/10 \mu{
m G})^{-1/2} TeV is the highest ever reported for a shell supernova remnant. It can easily be reached by standard diffusive shock acceleration, given the very high shock velocities; it can be well described by either age-limited or synchrotron-loss-limited acceleration. Not only is G1.9+0.3 the youngest known Galactic remnant, it is also only the fourth Galactic X-ray synchrotron-dominated shell supernova remnant.

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