Symposium Proceedings

SN, SNR and Isolated Neutron Stars

Evidence of an Inverse Compton Origin for the TeV Emission from G347.3-0.5

Glenn E. Allen, John C. Houck (MIT Kavli Institute), Thomas G. Pannuti (Caltech), Steven J. Sturner (USRA/NASA-GSFC)

Gamma-ray spectra of the supernova remnant G347.3-0.5 have been published by the CANGAROO and HESS collaborations. Several analyses of the CANGAROO data have been reported. Here we present the results of a joint spectral analysis of the HESS data, some XMM X-ray data and some ATCA radio data. The X-ray and radio data were fitted with a synchrotron radiation model. Inverse Compton scattering, nonthermal bremsstrahlung and neutral-pion decay models were fitted to the gamma-ray data. The results of these analyses suggest that the HESS spectrum is dominated by inverse Compton scattered photons.

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Fe-Rich Supernova Remnants DEM L238 and DEM L249: A Challenge for Standard Type Ia Explosion Models?

Kazimierz Borkowski (North Carolina State Univ.), Sean Hendrick (Millersville Univ.), Stephen Reynolds (North Carolina State Univ.)

We present observations of two Large Magellanic Cloud (LMC) supernova remnants (SNRs), DEM L238 and DEM L249, with CCD imaging detectors onboard Chandra and XMM-Newton X-ray satellites. Bright central emission, surrounded by a faint shell, is present in both remnants. Spectra of central emission are dominated by strong Fe L-shell lines, with the deduced Fe abundance far in excess of solar and not consistent with the LMC abundance. This Fe overabundance and a low observed O/Fe abundance ratio lead to the conclusion that DEM L238 and DEM L249 are remnants of thermonuclear (Type Ia) explosions. Elemental abundances in the shell are consistent with standard (0.4 solar) LMC abundances, and the shell emission originates in gas swept up and heated by the blast wave. The faint shells observed in these remnants are in stark contrast to the bright shells seen in the LMC remnants DEM L71 and SNR 0548-70.4 also known to be of Type Ia. A standard Sedov analysis implies about 50 solar masses in the swept-up shell, SNR ages between 10,000 and 15,000 yr, low ($<0.05$ cm$^{-3}$) preshock densities, and subluminous explosions with energies of $3 \times 10^{50}$ ergs. By modeling the central Fe-rich emission with plane-parallel heavy-element shock models, we find very long ($\sim 10^{12}$ cm$^{-3}$ s) shock ionization ages. We performed 1-D hydrodynamical simulations of the interaction of 1.4 solar masses of supernova ejecta, assumed to consist of pure Fe and distributed in an exponential density profile, with a uniform ambient interstellar medium with densities as determined from the Sedov analysis. Thermal X-ray spectra have been calculated for these hydrodynamical models using nonequilibrium ionization spectral codes. The predicted Fe L-shell emission is much weaker (by an order of magnitude or more) than observed, and ionization ages are too short. This problem persists for more realistic Type Ia 1-D explosion models of Badenes et al. These standard Type Ia SNR models cannot explain strong Fe L-shell emission with long ionization ages present within faint shells of X-ray emitting swept-up ambient gas. We discuss possible solutions to this problem, including inhomogeneous clumpy ejecta and the hypothetical presence of dense circumstellar medium around Type Ia supernova progenitors.

Images of a Moving Neutron Star

Andrea DeLuca, Patrizia Caraveo, Fabio Mattana, Alberto Pellizzoni (INAF, IASF-Milano-Italy), Giovanni Bignami (CESR, Toulouse-France),

A deep (100 ks) XMM-Newton observations of Geminga has shown two faint parallel tails of diffuse X-ray emission, extending for 2' behind the pulsar, well aligned with the proper motion (PM) direction. Such a structure is most likely due to electron synchrotron radiation in the bow-shock between the pulsar and the surrounding medium. We report here on the results of a recent 20 ks Chandra observation which enveil a new structure on a much smaller angular scale: a Trail of diffuse emission, 25'' long and 5'' thick, starting at the pulsar positionn and perfectly aligned with the PM direction, with a surface brightness 40 times higher than the Tails' one. The Trail has a remarkably hard spectrum (photon index $\sim0.9-1.4$) and a luminosity of $\sim5.5x10^{28}$ erg s$^{-1}$, comparable to the energetics of the larger Tails. Geminga is thus the first neutron star to show X-ray evidence of a large scale bow-shock as well as a jet-like, collimated short Trail.

The Chandra/XMM-Newton View of the Eastern Cygnus Loop Supernova Remnant

Terrance Gaetz (SAO), William Blair (Johns Hopkins), Richard Edgar, Paul Plucinsky, Manami Sasaki, John Raymond (SAO)

The XA region in eastern Cygnus Loop supernova remnant is the site of an advanced cloud-shock interaction, including a range of shocks from radiative to partially radiative to nonradiative shocks. It has been well studied in the optical, UV, and IR, and is the target of upcoming Spitzer observations. It is also one of the brightest soft X-ray regions in the remnant, dominated by OVII and OVIII emission and even softer emission in places. We have imaged the region with Chandra, providing a deep, high spatial resolution image. We also observed it with the XMM-Newton RGS (and simultaneously with EPIC-MOS), providing low spatial resolution but high spectral resolution data. The Chandra data shows the structure of the bright, compact ``XA'' knot, and details of the the shock-cloud interaction. The RGS spectrum shows the distribution of CVI Ly$\alpha$ alpha emission, and partially resolves the OVII He-like triplet for the bright, compact X-ray knot. We analyze and compare these complementary datasets making use of the recent improvements in the calibration of the low energy responses.

This work was supported by NASA grants G01-2060X and NAG5-9978, and by NASA contract NAS8-03060.

Chandra Observations of Several Radio Pulsars

Oleg Kargaltsev, George Pavlov, Gordon Garmire (Penn State Univ.), Divas Sanwal (Johns Hopkins Univ.)

X-ray observations of spin-powered pulsars (PSRs) provide valuable diagnostics of emission mechanisms and acceleration processes operating in pulsar magnetospheres and winds. We present the results from ACIS observations of several radio pulsars that belong to different categories of the diverse pulsar population. These include the 5-Myr-old "nulling" pulsar B1133+16, 200-kyr-old PSR J1825-1446, 20-kyr-old PSR B1800-21 with a pulsar-wind nebula (PWN), the famous 1-Gyr-old PSR B1257+12 with a planetary system, and a few others. The pulsars exhibit different X-ray spectral slopes suggesting that the contribution of polar cap thermal emission may become more important as pulsar ages. although the pulsar X-ray luminosities generally correlate with the spin-down power $\dot{E}$, a strong scatter in the $L_{x}$ vs. $\dot{E}$ dependence suggests that other factors (e.g., the magnetic field geometry and orientation of magnetic and spin axes) are equally important. A compact 10''-size PWN around PSR B1800-21 shows a bow-shock-like morphology reminiscent of those found for several other PWNe. To provide a more complete picture, we compare our results with those from other Chandra observations of spin-powered pulsars.

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HETGS Observation of Cas A: Looking at the Trees in the Forest

Jasmina Lazendic, Daniel Dewey (MIT Kavli Institute)

Cas A is the largest supernova remnant (SNR) observed with the Chandra High Energy Transmission Grating Spectrometer (HETGS) to date. High resolution X-ray spectra extracted for many bright, narrow regions of Cas A provide unique insights into their kinematics and plasma state. From the dominant emission lines of H- and He-like silicon and sulfur we derived unambiguous, accurate Doppler shifts of up to 4000 km/s which agree well with transverse-velocity measurements (DeLaney 2004.) Plasma diagnostics of these regions indicate temperatures largely around 1 keV, which we model as O-rich reverse-shocked ejecta using as well the non-dispersed zeroth-order data. In this poster we present and discuss our results including some of the challenges we face in HETGS data reduction of such an extended, complex object.

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The Massive, Young, Galactic Star Cluster Westerlund 1

Michael Muno (UCLA) J. Simon Clark (Open University), Paul Crowther (Sheffield), Sean Dougherty (Dominion Radio Astr. Obs.), Richard de Grijs (Sheffield), Casey Law (Northwestern), Stephen McMillan (Drexel), Mark Morris (UCLA), Ignacio Negueruela (Universidad de Alicante), David Pooley (Berkeley), Simon Portegies Zwart (Astronomical Institute Anton Pannekoek), Farhad Yusef-Zadeh (Northwestern),

We report Chandra observations of the massive, young Galactic star cluster, Westerlund 1. First, we describe a slowly-rotating X-ray pulsar (period 10.6 s) that we discovered within the cluster. Optical spectroscopy reveals that the cluster contains main sequence stars with initial masses of 35 Msun, and that the cluster is no older than 5 Myr. At this age, only stars with initial masses $>40$ Msun could have undergone supernova. Therefore, the progenitor to the neutron star was initially at least this massive. Second, describe a search for diffuse X-rays from recent supernovae, from shocks produced by the collective winds of the $>25$ member WR stars, and from unresolved pre-main sequence stars with $M<3$ Msun. Very little diffuse emission is seen, which suggests that the initial mass function of the cluster is truncated at low masses.

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Reverse Shock Processing of Ejecta in Cassiopeia A

Daniel Patnaude (Harvard-Smithsonian Center for Astrophysics), Robert Fesen (Dartmouth College)

Cassiopeia A was observed with Chandra for 50 ksec in 2000 and 2002, and for 1 Msec in 2004. We note several X-ray knots located at the reverse shock which exhibit measurable intensity changes over the 4 years worth of observations. I will summarize the results from our spectral analyses of these regions and compare them to hydrodynamical models for reverse shock interactions with non-uniform ejecta.

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CHANDRA Observations of the Eastern Limb of the Vela Supernova Remnant

Paul Plucinsky (Harvard-Smithsonian Center for Astrophysics), Randall Smith (JHU/GSFC), Terrance Gaetz (Harvard-Smithsonian Center for Astrophysics), William Blair (Johns Hopkins Univ.), Patrick Slane, Richard Edgar (Harvard-Smithsonian Center for Astrophysics)

We present results from two Chandra/ACIS observations of the so-called Vela Bullet D region on the eastern limb of the Vela supernova remnant. The Bullet D region is a bright X-ray feature identified in the ROSAT All-Sky Survey, which protrudes beyond the blast wave on the eastern side of the remnant. It has been suggested that this feature is a fragment of supernova ejecta which is just now pushing beyond the position of the main blast wave. An alternate explanation is that the feature is a break-out of the shock in which inhomogeneities in the ambient medium cause the shock to be non-spherical. The Chandra image shows a fragmented, filamentary morphology within this region. The Chandra spectra show strong emission lines of O, Ne, and Mg. Equilibrium ionization models indicate that the O and Ne abundances are significantly enhanced compared to solar values. However, non-equilibrium ionization models can fit the data with solar O abundances and Ne abundances enhanced by only a factor of two. We will discuss the implications of the Chandra spectral results for these two possible explanations and compare to recent theoretical work on the structure and evolution of large fragments of ejecta.

Chandra Observations of the Compact Shell Supernova Remnant G15.9+0.2

Stephen Reynolds, Kazimierz Borkowski (NC State Univ.), Ilana Harrus, Una Hwang, Robert Petre (NASA/GSFC)

We report a 30 ks Chandra observation of the compact shell supernova remnant G15.9+0.2. The morphology resembles that seen in radio. High absorption ( $N_H \sim 4 \times 10^{22}$ cm$^{-2}$) suggests that the remnant is at least as distant as the Galactic Center, though no other distance information is available. The integrated spectrum shows very strong lines, and simple spectral models (single nonequilibrium-ionization component, plane shock, Sedov blast wave) all require elevated abundances, especially of sulfur, to describe the data. A plane-shock fit gives $kT = 0.9 \ (0.8, 1.0)$ keV, an ionization timescale $\tau = 6 \ (4, 9) \times 10^{10}$ cm$^{-3}$ s, and a sulfur abundance of 2.7 (1.7, 2.7) times solar. Solar sulfur is ruled out at a high level of confidence ( $\Delta \chi^2 = 72$). This requirement for enhanced sulfur persists even at the outer remnant edge. The integrated spectrum is softer toward the interior of the shell, and in the faint emission to the north. We conjecture that strong mixing in the shell has brought ejecta to near the blast wave around much of the remnant periphery. The observed X-ray flux gives an estimate of the electron density, $n_e \sim 3$ cm$^{-3}$, which implies a remnant age of order 1000 yr. A point source in the remnant interior contains about 120 counts ($\Rightarrow$ a count rate of $\sim 4 \times 10^{-3}$ ct s$^{-1}$), none below 1 keV; a simple absorbed power-law fit shows absorption consistent with that of the shell, and a photon index of $\Gamma \sim 5$. An absorbed black-body has $kT \sim 0.4$ keV with similar absorption. The unabsorbed flux is $\sim 10^{-13}$ cm$^{-2}$ s$^{-1}$ between 2 and 9.5 keV, implying a low luminosity of about $10^{33}$ erg s$^{-1}$ for a distance of 8.5 kpc. For thermal emission from a neutron star, this would represent only $\sim 0.1$% of the surface area. We suggest that this point source may be a neutron star associated with the remnant, most likely a rotation-powered pulsar. It seems clear that G15.9+0.2 is among the dozen or so youngest remnants in the Galaxy.

Chandra and CO Observations of the Shock-cloud Interaction in the Galactic SNR CTB 109

Manami Sasaki (Harvard-Smithsonian Center for Astrophysics), Roland Kothes (DRAO), Paul Plucinsky, Terrance Gaetz (Harvard-Smithsonian Center for Astrophysics), Christopher Brunt (Univ. of Massachusetts)

We report the detection of molecular clouds around the X-ray bright interior feature in the Galactic supernova remnant (SNR) CTB 109. This feature, called the Lobe, has been previously suggested to be the result of an interaction of the SNR shock wave with a molecular cloud and overlaps one of the CO clouds with significant 12CO emission located east of the Lobe. The velocity profiles of 12CO at various parts of the east cloud are well fit with a Gaussian. However, at the position where the CO cloud and the Lobe overlap, the velocity profile has an additional component towards higher negative velocities. The molecular hydrogen density in this part of the cloud is relatively high ( $N_H2 =
1.0 - 1.5e21$ cm-2), whereas the foreground absorption in X-rays ($N_H =
4.5e21$ cm-2), obtained from Chandra data, is lower than in other parts of the cloud and in other clouds. These results indicate that this cloud has been hit by the SNR blast wave on the western side, corroborating that the shock-cloud interaction caused the bright X-ray Lobe.

Hydrodynamical Studies of the Shock-Shell Interaction in the Cygnus Loop

Jonathan Slavin, Terrance Gaetz (Harvard-Smithsonian Center for Astrophysics)

The Cygnus Loop supernova remnant has been studied extensively in X-rays and in several other wavebands. The X-ray and optical morphology of the remnant indicate that it is a cavity remnant, i.e. that the explosion occurred inside a low density bubble carved out of the interstellar medium by the progenitor star's stellar wind. Previous studies of particular regions of the remnant have used steady planar shock models to compare with the X-ray, optical and UV data, yet the relatively recent encounter of the shock with the cavity wall makes such models questionable. In an attempt to improve on these models, we use a numerical hydrodynamical code that includes cooling and non-equilibrium ionization to investigate the interaction of the SNR shock with the cavity walls. We produce X-ray spectra and compare with Chandra ACIS observations of shocks in the NE region of the SNR. This modeling will provide constraints on the shock speed and the morphology of the shell in the Cygnus Loop and give us insights into the shock-shell interaction. On a global level our study promises to improve our understanding of the coupling of supernova energy to the interstellar medium.

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Dust Destruction in Type Ia SNRs in the Large Magellanic Cloud

Brian Williams, Stephen Reynolds, Kazimierz Borkowski (North Carolina State Univ.), William Blair, Parviz Ghavamian, Ravi Sankrit (Johns Hopkins Univ.), Knox Long (STScI), John Raymond (Harvard-Smithsonian Center for Astrophysics), P. Frank Winkler (Middlebury College), R. Chris Smith, Sean Points (NOAO), Sean Hendrick (Millersville Univ.)

We present early results from an extensive survey of Magellanic Clouds supernova remnants (SNRs) with the Spitzer Space Telescope. We have obtained IR images of several type Ia SNRs in the Large Magellanic Cloud (LMC), with strong 24 micron detections of DEM L71, 0509-67.5, N103B, 0519-69.0, 0534-69.9, DEM L238, and 0548-70.4. A comparison of these images to Chandra broadband images shows a clear association with the blast wave, and not with internal X-ray emission associated with ejecta. Since emission for SNRs at these infrared wavelengths is primarily thermal radiation from dust heated by the plasma, we infer that no dust has formed in the SN ejecta; we are seeing ambient interstellar dust. We employ computer models for dust emission which use plasma parameters determined from X-ray analysis to predict fluxes at Spitzer wavelengths. We find that our models can only reproduce observed flux ratios from Spitzer's 24 and 70 micron cameras if dust grain destruction (sputtering) is included. Since grains are heated and sputtered by ions and electrons in the plasma, the plasma temperature and density must be determined from X-ray analysis, which, combined with the age of the remnant, give an estimate for the amount of dust sputtered. In DEM L71, for example, we find sputtering to reduce grain radii by $\sim$3-4 nm, destroying the smallest dust grains. Without sputtering, models overpredict our observed 24/70 micron flux ratios by factors of order 2. Absolute flux measurements at 24 microns also give us a total mass of dust in the remnant. For instance, in DEM L71, we find a total dust mass of about 0.03 solar masses, significantly lower than predictions assuming a constant dust/gas ratio in the LMC, consistent with the destruction of the smaller, more numerous grains. Substantial dust destruction has implications for gas-phase abundances, and we shall present X-ray spectral analyses for some of our remnants to investigate these implications.

We acknowledge support from NASA through Chandra and Spitzer grant programs.

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Mid-Life Crisis: New Chandra Results for Middle-Aged Supernova Remnants in the Magellanic Clouds

Rosa Williams, You-Hua Chu (University of Illinois, Urbana), Fred Seward (Harvard-Smithsonian Center for Astrophysics), John Dickel (University of Illinois, Urbana)

The Chandra Observatory represents a great leap forward in sensitivity and in spatial and spectral resolution. These advances have given unprecedented opportunities for detailed studies of the structure and composition of supernova remnants (SNRs) in the neighboring Magellanic Cloud galaxies. Notably, they have enabled the study of SNRs in their advanced evolutionary stages. We discuss our findings for a number of these middle-aged remnants, including key physical properties and probable progenitor types (Type Ia vs. Type II). In particular, we have discovered two candidate pulsar-wind nebulae (PWNe) and confirmed a third; in the latter case, we have also detected an X-ray point source associated with the PWN. Additionally, we have observed regions containing multiple SNRs, which allow us to witness their contributions to the multi-phase interstellar medium.

Chandra Observations of RCW 89 at Two Epochs

Yoichi Yatsu, Nobuyuki Kawai, Jun Kataoka (Tokyo Institute of Technology), Keisuke Tamura (Nagoya Univ.), Wolfgang Brinkmann (Max-Planck-Institut fur Extraterrestische Physik)

We present two observation of the HII region RCW89 by Chandra in Aug 2000 and December 2004. RCW89 is part of the radio shell supernova remnant MSH15-52 which contains a 150 msec young pulsar PSR B1509-58. In X-ray band, RCW89 is composed of bright thermal knots embedded in tenuous non-thermal emission which extends from the pulsar wind nebula of PSR B1509-58. The location of the thermal knots at the terminus of the jet-like non-thermal feature suggests that these knots are powered by the jets from the pulsar. Based on the early Chandra observation, we found that the plasma clouds in RCW 89 aligned in a horse-shoe shape have temperatures and ionization parameters varying sequentially in clockwise direction, implying sequential heating.

We performed the second observation of RCW 89 with Chandra with RCW 89 at the aiming point, unlike the first one with RCW at 5 arcmin off-axis. The X-ray image which has higher spatial resolution and better photon statistics than the preceding observations allows us to discuss the morphology of the thermal plasma and the non-thermal emission more precisely. Furthermore, we study the dynamical evolution of the plasma clouds by comparison of the two images taken four years apart.

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