ABSTRACT We present near infrared narrow-band images of the supernova remnant W49B, taken with th... more ABSTRACT We present near infrared narrow-band images of the supernova remnant W49B, taken with the WIRC instrument on the Hale 200 inch telescope on Mt. Palomar. The 1.64 micron [Fe II] image reveals a barrel-shaped structure with coaxial rings, while the 2.12 micron molecular hydrogen image is external to the [Fe II] emission---capping the ends of the barrel. The detection of shocked H2 emission provides the first evidence that W49B is interacting with a molecular cloud. We also present archival Chandra images, which show that the bulk of the X-ray line emission is emitted from a central elongated region along the axis of the barrel---flaring at the ends. Interpreting the iron-rich X-ray material as the ejecta suggests that the explosion was highly bipolar. Given that no neutron star has yet been found associated with W49B, we compare our observations to what one would expect from the remnant of a collapsar (i.e. gamma ray burst) inside a preexisting wind-blown bubble located inside a molecular cloud.
We present new Chandra A01 data of the hard X-ray feature along the southern edge of the SNR IC44... more We present new Chandra A01 data of the hard X-ray feature along the southern edge of the SNR IC443. With only 10 ks of observation time we were able to extract high resolution (~1'') images that reveal a soft point source embedded in a hard comet-shaped nebula. The background-subtracted spectrum of the point source is best fit with an absorbed
Using observations and theory, we have attempted to identify and quantify shock structures in you... more Using observations and theory, we have attempted to identify and quantify shock structures in young and intermediate aged SNRs. This poster outlines several studies currently underway to study these shocks. By comparing measurements to simulations we have developed a method to classify a remnant's dynamical age according to the classical stages of free expansion through the Sedov-Taylor phase. We have found both Cas A and Kepler's SNRs to be in the intermediary phase between free expansion and Sedov-Taylor. We have utilized OH(1720) masers as a tool to find shock positions and to prove SNR-molecular cloud interactions. These masers have also allowed us to measure milliGauss magnetic fields in the shocks of two remnants. We have found spectral index variations in Cas A over a large range of frequency, which is consistent with many power-law distributions of electron energies. Preliminary expansion measurements of Cas A in the x-ray will also be presented, which will help define shock structures in this remnant. SNR research at the University of Minnesota is supported by the NASA Graduate Research Program and the National Science Foundation under grant AST 96-19438.
We present results from our analysis of a deep XMM-Newton observation of the supernova remnant IC... more We present results from our analysis of a deep XMM-Newton observation of the supernova remnant IC 443. This observation consists of six segments which cover the entire remnant. Images produced from these observations show many point-like and compact diffuse sources within the field of view. Most of these sources have not previously been associated with any class of astrophysical objects. Here we show preliminary results of our effort to identify some of these sources using their multiwavelength spectra and morphology. Taking into account not only positional agreement but also plausible source emission mechanisms, we then discuss the possibility that one of these sources may be responsible for the >100 MeV gamma-ray emission observed from the EGRET unidentified source 3EG J0617+2238.
AXAF is ideally suited to investigate the hard X-ray region of the SNR IC 443, which is currently... more AXAF is ideally suited to investigate the hard X-ray region of the SNR IC 443, which is currently thought to be X-ray synchrotron radiation as a result of a particular interaction between a shock and a molecular cloud. Alternate explanations, such as a pulsar powered nebula, have still not been completely ruled out. This proposed observation will image the currently
We present a high angular resolution Chandra observation and narrow-band optical images of the ar... more We present a high angular resolution Chandra observation and narrow-band optical images of the archetypical mixed-morphology supernova remnant (SNR) W28. The Chandra observation covered the central and southwestern regions of W28: we have augmented this dataset with a mosaicked ROSAT HRI image that samples the entire angular extent of this SNR. Previous ASCA and ROSAT studies of W28 have shown that the plasma conditions differ from other mixed-morphology SNRs in that X-ray spectral variations are seen across W28. The Chandra image reveals that the X-ray emission from the center of this SNR is very clumpy: this central emission is several arcminutes in size and irregular in shape. The spectrum of this central X-ray emission is reasonably fit by an ionization equilibrium thermal model, but two components to this model are required for an adequate fit. Among mixed-morphology SNRs, the presence of a high temperature component is still unique to W28. Also, compared to the hard X-ray emission, the soft X-ray emission from the center of W28 is associated with smaller scale structures. In addition, we find that along the northern boundary of the SNR, the X-ray emission is very soft: this result indicates that the X-ray emitting plasma has significantly cooled at the site of interaction with adjacent clouds. Our mosaicked ROSAT HRI image reveals a surprisingly clumpy structure along the northwestern rim of W28 which resembles a broken shell rather than a smooth shell: such clumpy structure has never been seen before in the shells of SNRs. Finally, our Chandra observation has resolved a hard X-ray source located 20 arcminutes southwest of the center of W28 and on the shell of the SNR: the spectrum of this source is well-fit with a power-law model, suggesting non-thermal emission, which is either pulsar nebula or a background AGN. We will compare the high resolution X-ray image of W28 with our optical images and discuss several mechanisms that may explain the center-filled X-ray emission of this SNR.
Bulletin of the American Astronomical Society, May 1, 1997
Young supernova remnants are often assumed to be the source of cosmic rays up to energies approac... more Young supernova remnants are often assumed to be the source of cosmic rays up to energies approaching the slight steepening at around 1000 TeV known as the ``knee'' in the cosmic-ray energy spectrum. We show that the observed X-ray emission of seven shell remnants, including all five historical shells, can be used to put limits on E_m, the energy at which the electron energy distribution must steepen from its slope at radio-emitting energies. Six of the remnants show thermal spectra, so any nonthermal component must fall below the observed X-ray fluxes. Assuming homogeneous emitting volumes with a mean magnetic-field strength of 10 \ mu G, no object could reach 1000 TeV, and only one, Cas A, has an upper limit on E_m near 100 TeV. All the other historical shells have limits at or below 50 TeV. These limits scale as B(-1/2) , so absurdly low magnetic fields would be required to get E_m much higher. E_m is probably set by the finite remnant lifetime rather than by synchrotron losses for remnants younger than a few thousand years, so that an observed electron steepening implies that the proton spectrum should steepen at that energy as well. More complicated, inhomogeneous models could allow higher values of E_m in parts of the remnant, but the emission-weighted average value, that characteristic of typical electrons, should obey these limits. The historical remnants should be among the best in the Galaxy at producing the highest-energy Galactic cosmic rays; if they cannot do it, this picture of cosmic-ray origin may need major alteration.
Recent X-ray observations of supernova remnants have provided the first strong evidence that supe... more Recent X-ray observations of supernova remnants have provided the first strong evidence that supernova remnants accelerate particles to energies as high as 10-100 TeV, but not further. In order to investigate the role that age and other properties of supernova remnants have on the shock acceleration process, we must observe a number of supernova remnants with the hard band-pass capabilities of RXTE. We propose to observe the supernova remnant Puppis A to continue to investigate hard synchrotron emission, and by extension the supernova remnant/cosmic ray connection. In addition, Puppis A is known to house an isolated neutron star. We will attempt to discover pulsations from this object, or put stricter upper limits on its hard X-ray pulsed fraction.
Bulletin of the American Astronomical Society, May 1, 2008
At Hampden-Sydney College, we teach a one-semester introductory astronomy class targeting non-sci... more At Hampden-Sydney College, we teach a one-semester introductory astronomy class targeting non-science majors. This course fulfills the laboratory science requirement, and as such the class is obligated to teach transferable skills such as basic numeracy, quantitative reasoning and data analysis. To this end, we explicitly teach the use of the most commonly available data analysis program, which is currently Microsoft Excel. The laboratory sciences are ideally suited to teaching these skills. During each laboratory session, students explore an astronomical phenomenon related to the lectures for that week. Randomly assigned partners use computers to analyze their data in spreadsheets and to write detailed reports structured like journal articles. We present nine Excel templates, along with the corresponding laboratory instructions, that are designed to teach general data analysis techniques using spreadsheets within the context of a traditional astronomy laboratory. These exercises begin with basic calculations and move toward more complex ones such as least squares fitting of sine functions and calculating distances from measured magnitudes and assumed luminosities. <table border="1" cellpadding="1" class="DisplayTable" id="{4943485B-0043-43E5-83A5-19F9B869429C}"><caption>Laboratory Exercises with Excel Templates</caption><tr><td rowspan="1" colspan="1">Measuring Angles</td><td rowspan="1" colspan="1">This first lab uses the small angle formula.</td></tr><tr><td rowspan="1" colspan="1">Jupiter's Moons</td><td rowspan="1" colspan="1">The students take data with the CLEA lab of Jupiter's moons, but complete the data analysis using Excel. This includes least squares fitting of sine functions.</td></tr><tr><td rowspan="1" colspan="1">Astrometry and Parallax</td><td rowspan="1" colspan="1">The students complete the Astrometry of Asteroids CLEA lab, but perform the parallax calculations using Excel.</td></tr><tr><td rowspan="1" colspan="1">The Resolution of a Telescope</td><td rowspan="1" colspan="1">The students measure the resolution of their naked eyes and a telescope, using two eye charts, along with the theoretical resolution of the telescope for comparison.</td></tr><tr><td rowspan="1" colspan="1">The Light Gathering Power of a Telescope</td><td rowspan="1" colspan="1">The students observe a light bulb using a telescope equipped with a photometer and a mask of variable aperture.</td></tr><tr><td rowspan="1" colspan="1">Solar Radiation</td><td rowspan="1" colspan="1">The students measure the length of a solar day and the transparency of the earth's atmosphere, using a sundial and a calorimeter.</td></tr><tr><td rowspan="1" colspan="1">Binary Stars</td><td rowspan="1" colspan="1">The students use photodiodes and oscilloscopes to measure the light curve of a model eclipsing binary star.</td></tr><tr><td rowspan="1" colspan="1">Distance and Age of the Pleiades</td><td rowspan="1" colspan="1">The students gather data using the CLEA lab of the same name, but they plot an HR diagram along with a distance dependent standard main sequence using Excel. This lab uses luminosities and the inverse square law, instead of absolute magnitudes and the distance modulus.</td></tr><tr><td rowspan="1" colspan="1">Hubble's Law</td><td rowspan="1" colspan="1">The students gather data using the CLEA lab of the same name, but they use Excel for all the analysis. This lab also favors the inverse square law over the distance modulus to calculate distances.</td></tr></table>
We present Chandra spectra and high-resolution images of the hard X-ray feature in the southern e... more We present Chandra spectra and high-resolution images of the hard X-ray feature in the southern edge of the supernova remnant (SNR) IC 443 that reveal a comet-shaped nebula of hard emission that contains a softer point source at its apex. We also present 20, 6, and 3.5 cm Very Large Array maps that clearly show the cometary nebula. Based on the radio and X-ray morphology and spectrum, and the radio polarization properties, we argue that this object is a synchrotron nebula powered by the compact source that is physically associated with IC 443. The spectrum of the soft point source is adequately but not uniquely fitted by a blackbody model [kT=0.71+/-0.08 keV, L=(6.5+/-0.9)×1031 ergs s-1]. The morphology of the nebula can be explained by the supersonic motion of the neutron star (VNS~=250+/-50 km s-1), which causes the relativistic wind of the pulsar to terminate in a bow shock and trail behind as a synchrotron tail. This velocity is consistent with an age of 30,000 yr for the SNR and its associated neutron star.
We have analyzed VLA polarization data on the supernova remnant Cas A at multiple frequencies in ... more We have analyzed VLA polarization data on the supernova remnant Cas A at multiple frequencies in the lambda lambda 20cm and 6cm bands. This allows us to determine the rotation measures, depolarizations, and magnetic field orientations in the remnant. We find that the depolarization is strongly anti-correlated with the X-ray emitting shell of thermal material. The relativistic plasma, especially the bright radio ring, is therefore found mostly within the thermal shell. At the same time, a number of blobs of relativistic plasma have ``broken out'' beyond this thermal shell, and show little depolarization. However, a wide range of observed rotation measures suggests that these break-out features are still accompanied by a substantial local thermal plasma. Correcting for the rotation measures observed at high frequencies, we derive the direction of the remnant's magnetic field, and find it to be radial, to first order, as previously known. However, we find an additional, quasi-sinusoidal modulation of the field direction as a function of azimuthal angle, with an amplitude of approximately 30 degrees. This modulation can be simply modelled as due to the presence of the compressed local interstellar magnetic field within the relativistic plasma. This is not due to small scale clumps of interstellar plasma mixed with clumps of ejected plasma. Each relativistic electron actually finds itself in a local magnetic field that is the vector sum of the heavily amplified remnant field and the compressed ISM field. This result has important, but still not understood, consequences for the evolution of magnetic fields in Cas A and other supernova remnants. This work is supported in part by NSF grant AST 9100486 to the University of Minnesota.
An archival ROSAT XRT/HRI image of the Cassiopeia A supernova remnant was corrected for absorptio... more An archival ROSAT XRT/HRI image of the Cassiopeia A supernova remnant was corrected for absorption, on 30\arcsec \ (0.5 pc) scales, using existing OH and H I absorption data (Bieging & Crutcher 1986, Goss unpublished data), and theoretical effective x-ray cross-sections for the ISM. A much stronger correlation was discovered than had been previously seen between the x-ray and radio emission. We observe (log (radio))/(log (x-ray)) values between 0.26 and 0.37. The implications of these data for physical parameters in the relativistic and thermal plasmas of the supernova remnant will be discussed. Assuming the relation above, the lambda20 cm radio emission, which is free from absorption effects, was then used as a predictor of the actual x-ray emission. By comparing the predicted values to the uncorrected x-ray image, an empirical x-ray optical depth was derived. A good linear correlation exists between this empirical x-ray optical depth and the column density of hydrogen as calculated using the OH and H I absorption data. The effective cross-section of the interstellar medium was then calculated and found to be consistent with the theoretical models. This work is supported in part by NSF grant AST 9100486 to the University of Minnesota.
X Ray and Radio Connections Santa Fe New Mexico Usa Proceedings and Presentations, 2015
G266.2-1.2 (RX J0852.0-4622) is a member of the emerging class of Galactic supernova remnants (SN... more G266.2-1.2 (RX J0852.0-4622) is a member of the emerging class of Galactic supernova remnants (SNRs) which feature X-ray spectra dominated by non-thermal emission. This X-ray emission is believed to be synchrotron radiation produced by cosmic-ray electrons accelerated to TeV energies along the expanding shock fronts of SNRs. To explore this phenomenon of high energy X-ray emission from SNRs in more
New Chandra X-Ray Observatory and Very Large Array observations of the hard X-ray feature along t... more New Chandra X-Ray Observatory and Very Large Array observations of the hard X-ray feature along the southern edge of the supernova remnant IC 443 have revealed a comet-shaped nebula of hard emission with a soft X-ray point source at its apex. Based on the X-ray spectrum, X-ray and radio morphology, and the radio polarization properties, we argue that this object
We present a new, deep (232 ks) ROSAT HRI exposure of Cas-A. This is the first X-ray image with e... more We present a new, deep (232 ks) ROSAT HRI exposure of Cas-A. This is the first X-ray image with enough photons to measure the outer, low surface brightness, shell of emission seen in the radio band. In addition 5 iterations of the Lucy-Richardson algorithm were used to deconvolve out the wings of the X-ray mirror point spread function, thus creating a image with a ``restored beam'' of 2.2" FWHM. These new data show a striking resemblance to the VLA radio continuum outside of the main shell. They clearly show the northern and southwestern radio features and the eastern jet region.
We present a new 100 ks Chandra Observation of the dim supernova remnant 3C396. These data show c... more We present a new 100 ks Chandra Observation of the dim supernova remnant 3C396. These data show clear evidence of diffuse (but compact), nebular emission slightly offset from the center of the remnant which interpret as a synchrotron wind nebula surrounding a neutron star that is physically associated with the remnant. We present images and spectra of this new neutron star/supernova remnant association and compare the results to similar objects recently discovered by Chandra.
We present the RXTE high-energy X-ray spectrum of the remnant of the supernova of 1006 AD. A prev... more We present the RXTE high-energy X-ray spectrum of the remnant of the supernova of 1006 AD. A previous analysis of the ASCA X-ray spectrum of the shell of this remnant provided the first evidence that supernova remnants accelerate cosmic-ray electrons to energies as high as 100 TeV. The recent detection of gamma rays at energies > 3 TeV from SN 1006 confirms that this remnant accelerates particles to very-high energies. We review the radio, X-ray, and gamma-ray spectral data and discuss the implications of this data for particle acceleration in the remnant.
3C397 (G41.1-0.3) is one of the brightest radio SNR's, whose classification remains ambiguous. Wh... more 3C397 (G41.1-0.3) is one of the brightest radio SNR's, whose classification remains ambiguous. While in the radio, it is classified as a `Shell'; in X-rays, it has a shell-like plus a centrally bright component, giving the remnant a `Composite' morphology. We present the ASCA & RXTE observations in order to better understand the nature of this unique SNR. The ASCA spectrum is dominated by thermal emission from Mg, Si, S, Ar, and Fe. One-temperature component models fail to account for the hard X-ray emission above ~ 4 keV; and at least two components are required: a soft component dominated by line emission from heavily enriched material, and a hot component, characterized by a prominent Fe-K emission line. The total observed flux is ~ 2.6 x 10(-11) erg cm(-2) s(-1) , which corresponds to an unabsorbed luminosity L_x (1-9 keV) = 4 x 10(36) erg s(-1) , assuming a distance of 10 kpc. The combined ASCA & RXTE PCA data favor the thermal interpretation of the hard component, and suggest the presence of a weak non-thermal third component, whose parameters are poorly determined because of the contamination of the RXTE signal with the emission from the Galactic ridge. We discuss the X-ray spectrum in the light of thermal emission from an ejecta-dominated and a blast wave component, and speculate on the nature of a compact object possibly hiding in this unusual remnant. Our broadband imaging and spectral study suggests that 3C397 is unlike the thermal or plerionic Composites, and that it is dynamically young ( ~ 1,500 yr-old), perhaps a transition object from the young Shells into the more evolved Composites.
ABSTRACT We present near infrared narrow-band images of the supernova remnant W49B, taken with th... more ABSTRACT We present near infrared narrow-band images of the supernova remnant W49B, taken with the WIRC instrument on the Hale 200 inch telescope on Mt. Palomar. The 1.64 micron [Fe II] image reveals a barrel-shaped structure with coaxial rings, while the 2.12 micron molecular hydrogen image is external to the [Fe II] emission---capping the ends of the barrel. The detection of shocked H2 emission provides the first evidence that W49B is interacting with a molecular cloud. We also present archival Chandra images, which show that the bulk of the X-ray line emission is emitted from a central elongated region along the axis of the barrel---flaring at the ends. Interpreting the iron-rich X-ray material as the ejecta suggests that the explosion was highly bipolar. Given that no neutron star has yet been found associated with W49B, we compare our observations to what one would expect from the remnant of a collapsar (i.e. gamma ray burst) inside a preexisting wind-blown bubble located inside a molecular cloud.
We present new Chandra A01 data of the hard X-ray feature along the southern edge of the SNR IC44... more We present new Chandra A01 data of the hard X-ray feature along the southern edge of the SNR IC443. With only 10 ks of observation time we were able to extract high resolution (~1&amp;amp;amp;amp;amp;amp;#39;&amp;amp;amp;amp;amp;amp;#39;) images that reveal a soft point source embedded in a hard comet-shaped nebula. The background-subtracted spectrum of the point source is best fit with an absorbed
Using observations and theory, we have attempted to identify and quantify shock structures in you... more Using observations and theory, we have attempted to identify and quantify shock structures in young and intermediate aged SNRs. This poster outlines several studies currently underway to study these shocks. By comparing measurements to simulations we have developed a method to classify a remnant's dynamical age according to the classical stages of free expansion through the Sedov-Taylor phase. We have found both Cas A and Kepler's SNRs to be in the intermediary phase between free expansion and Sedov-Taylor. We have utilized OH(1720) masers as a tool to find shock positions and to prove SNR-molecular cloud interactions. These masers have also allowed us to measure milliGauss magnetic fields in the shocks of two remnants. We have found spectral index variations in Cas A over a large range of frequency, which is consistent with many power-law distributions of electron energies. Preliminary expansion measurements of Cas A in the x-ray will also be presented, which will help define shock structures in this remnant. SNR research at the University of Minnesota is supported by the NASA Graduate Research Program and the National Science Foundation under grant AST 96-19438.
We present results from our analysis of a deep XMM-Newton observation of the supernova remnant IC... more We present results from our analysis of a deep XMM-Newton observation of the supernova remnant IC 443. This observation consists of six segments which cover the entire remnant. Images produced from these observations show many point-like and compact diffuse sources within the field of view. Most of these sources have not previously been associated with any class of astrophysical objects. Here we show preliminary results of our effort to identify some of these sources using their multiwavelength spectra and morphology. Taking into account not only positional agreement but also plausible source emission mechanisms, we then discuss the possibility that one of these sources may be responsible for the >100 MeV gamma-ray emission observed from the EGRET unidentified source 3EG J0617+2238.
AXAF is ideally suited to investigate the hard X-ray region of the SNR IC 443, which is currently... more AXAF is ideally suited to investigate the hard X-ray region of the SNR IC 443, which is currently thought to be X-ray synchrotron radiation as a result of a particular interaction between a shock and a molecular cloud. Alternate explanations, such as a pulsar powered nebula, have still not been completely ruled out. This proposed observation will image the currently
We present a high angular resolution Chandra observation and narrow-band optical images of the ar... more We present a high angular resolution Chandra observation and narrow-band optical images of the archetypical mixed-morphology supernova remnant (SNR) W28. The Chandra observation covered the central and southwestern regions of W28: we have augmented this dataset with a mosaicked ROSAT HRI image that samples the entire angular extent of this SNR. Previous ASCA and ROSAT studies of W28 have shown that the plasma conditions differ from other mixed-morphology SNRs in that X-ray spectral variations are seen across W28. The Chandra image reveals that the X-ray emission from the center of this SNR is very clumpy: this central emission is several arcminutes in size and irregular in shape. The spectrum of this central X-ray emission is reasonably fit by an ionization equilibrium thermal model, but two components to this model are required for an adequate fit. Among mixed-morphology SNRs, the presence of a high temperature component is still unique to W28. Also, compared to the hard X-ray emission, the soft X-ray emission from the center of W28 is associated with smaller scale structures. In addition, we find that along the northern boundary of the SNR, the X-ray emission is very soft: this result indicates that the X-ray emitting plasma has significantly cooled at the site of interaction with adjacent clouds. Our mosaicked ROSAT HRI image reveals a surprisingly clumpy structure along the northwestern rim of W28 which resembles a broken shell rather than a smooth shell: such clumpy structure has never been seen before in the shells of SNRs. Finally, our Chandra observation has resolved a hard X-ray source located 20 arcminutes southwest of the center of W28 and on the shell of the SNR: the spectrum of this source is well-fit with a power-law model, suggesting non-thermal emission, which is either pulsar nebula or a background AGN. We will compare the high resolution X-ray image of W28 with our optical images and discuss several mechanisms that may explain the center-filled X-ray emission of this SNR.
Bulletin of the American Astronomical Society, May 1, 1997
Young supernova remnants are often assumed to be the source of cosmic rays up to energies approac... more Young supernova remnants are often assumed to be the source of cosmic rays up to energies approaching the slight steepening at around 1000 TeV known as the ``knee'' in the cosmic-ray energy spectrum. We show that the observed X-ray emission of seven shell remnants, including all five historical shells, can be used to put limits on E_m, the energy at which the electron energy distribution must steepen from its slope at radio-emitting energies. Six of the remnants show thermal spectra, so any nonthermal component must fall below the observed X-ray fluxes. Assuming homogeneous emitting volumes with a mean magnetic-field strength of 10 \ mu G, no object could reach 1000 TeV, and only one, Cas A, has an upper limit on E_m near 100 TeV. All the other historical shells have limits at or below 50 TeV. These limits scale as B(-1/2) , so absurdly low magnetic fields would be required to get E_m much higher. E_m is probably set by the finite remnant lifetime rather than by synchrotron losses for remnants younger than a few thousand years, so that an observed electron steepening implies that the proton spectrum should steepen at that energy as well. More complicated, inhomogeneous models could allow higher values of E_m in parts of the remnant, but the emission-weighted average value, that characteristic of typical electrons, should obey these limits. The historical remnants should be among the best in the Galaxy at producing the highest-energy Galactic cosmic rays; if they cannot do it, this picture of cosmic-ray origin may need major alteration.
Recent X-ray observations of supernova remnants have provided the first strong evidence that supe... more Recent X-ray observations of supernova remnants have provided the first strong evidence that supernova remnants accelerate particles to energies as high as 10-100 TeV, but not further. In order to investigate the role that age and other properties of supernova remnants have on the shock acceleration process, we must observe a number of supernova remnants with the hard band-pass capabilities of RXTE. We propose to observe the supernova remnant Puppis A to continue to investigate hard synchrotron emission, and by extension the supernova remnant/cosmic ray connection. In addition, Puppis A is known to house an isolated neutron star. We will attempt to discover pulsations from this object, or put stricter upper limits on its hard X-ray pulsed fraction.
Bulletin of the American Astronomical Society, May 1, 2008
At Hampden-Sydney College, we teach a one-semester introductory astronomy class targeting non-sci... more At Hampden-Sydney College, we teach a one-semester introductory astronomy class targeting non-science majors. This course fulfills the laboratory science requirement, and as such the class is obligated to teach transferable skills such as basic numeracy, quantitative reasoning and data analysis. To this end, we explicitly teach the use of the most commonly available data analysis program, which is currently Microsoft Excel. The laboratory sciences are ideally suited to teaching these skills. During each laboratory session, students explore an astronomical phenomenon related to the lectures for that week. Randomly assigned partners use computers to analyze their data in spreadsheets and to write detailed reports structured like journal articles. We present nine Excel templates, along with the corresponding laboratory instructions, that are designed to teach general data analysis techniques using spreadsheets within the context of a traditional astronomy laboratory. These exercises begin with basic calculations and move toward more complex ones such as least squares fitting of sine functions and calculating distances from measured magnitudes and assumed luminosities. <table border="1" cellpadding="1" class="DisplayTable" id="{4943485B-0043-43E5-83A5-19F9B869429C}"><caption>Laboratory Exercises with Excel Templates</caption><tr><td rowspan="1" colspan="1">Measuring Angles</td><td rowspan="1" colspan="1">This first lab uses the small angle formula.</td></tr><tr><td rowspan="1" colspan="1">Jupiter's Moons</td><td rowspan="1" colspan="1">The students take data with the CLEA lab of Jupiter's moons, but complete the data analysis using Excel. This includes least squares fitting of sine functions.</td></tr><tr><td rowspan="1" colspan="1">Astrometry and Parallax</td><td rowspan="1" colspan="1">The students complete the Astrometry of Asteroids CLEA lab, but perform the parallax calculations using Excel.</td></tr><tr><td rowspan="1" colspan="1">The Resolution of a Telescope</td><td rowspan="1" colspan="1">The students measure the resolution of their naked eyes and a telescope, using two eye charts, along with the theoretical resolution of the telescope for comparison.</td></tr><tr><td rowspan="1" colspan="1">The Light Gathering Power of a Telescope</td><td rowspan="1" colspan="1">The students observe a light bulb using a telescope equipped with a photometer and a mask of variable aperture.</td></tr><tr><td rowspan="1" colspan="1">Solar Radiation</td><td rowspan="1" colspan="1">The students measure the length of a solar day and the transparency of the earth's atmosphere, using a sundial and a calorimeter.</td></tr><tr><td rowspan="1" colspan="1">Binary Stars</td><td rowspan="1" colspan="1">The students use photodiodes and oscilloscopes to measure the light curve of a model eclipsing binary star.</td></tr><tr><td rowspan="1" colspan="1">Distance and Age of the Pleiades</td><td rowspan="1" colspan="1">The students gather data using the CLEA lab of the same name, but they plot an HR diagram along with a distance dependent standard main sequence using Excel. This lab uses luminosities and the inverse square law, instead of absolute magnitudes and the distance modulus.</td></tr><tr><td rowspan="1" colspan="1">Hubble's Law</td><td rowspan="1" colspan="1">The students gather data using the CLEA lab of the same name, but they use Excel for all the analysis. This lab also favors the inverse square law over the distance modulus to calculate distances.</td></tr></table>
We present Chandra spectra and high-resolution images of the hard X-ray feature in the southern e... more We present Chandra spectra and high-resolution images of the hard X-ray feature in the southern edge of the supernova remnant (SNR) IC 443 that reveal a comet-shaped nebula of hard emission that contains a softer point source at its apex. We also present 20, 6, and 3.5 cm Very Large Array maps that clearly show the cometary nebula. Based on the radio and X-ray morphology and spectrum, and the radio polarization properties, we argue that this object is a synchrotron nebula powered by the compact source that is physically associated with IC 443. The spectrum of the soft point source is adequately but not uniquely fitted by a blackbody model [kT=0.71+/-0.08 keV, L=(6.5+/-0.9)×1031 ergs s-1]. The morphology of the nebula can be explained by the supersonic motion of the neutron star (VNS~=250+/-50 km s-1), which causes the relativistic wind of the pulsar to terminate in a bow shock and trail behind as a synchrotron tail. This velocity is consistent with an age of 30,000 yr for the SNR and its associated neutron star.
We have analyzed VLA polarization data on the supernova remnant Cas A at multiple frequencies in ... more We have analyzed VLA polarization data on the supernova remnant Cas A at multiple frequencies in the lambda lambda 20cm and 6cm bands. This allows us to determine the rotation measures, depolarizations, and magnetic field orientations in the remnant. We find that the depolarization is strongly anti-correlated with the X-ray emitting shell of thermal material. The relativistic plasma, especially the bright radio ring, is therefore found mostly within the thermal shell. At the same time, a number of blobs of relativistic plasma have ``broken out'' beyond this thermal shell, and show little depolarization. However, a wide range of observed rotation measures suggests that these break-out features are still accompanied by a substantial local thermal plasma. Correcting for the rotation measures observed at high frequencies, we derive the direction of the remnant's magnetic field, and find it to be radial, to first order, as previously known. However, we find an additional, quasi-sinusoidal modulation of the field direction as a function of azimuthal angle, with an amplitude of approximately 30 degrees. This modulation can be simply modelled as due to the presence of the compressed local interstellar magnetic field within the relativistic plasma. This is not due to small scale clumps of interstellar plasma mixed with clumps of ejected plasma. Each relativistic electron actually finds itself in a local magnetic field that is the vector sum of the heavily amplified remnant field and the compressed ISM field. This result has important, but still not understood, consequences for the evolution of magnetic fields in Cas A and other supernova remnants. This work is supported in part by NSF grant AST 9100486 to the University of Minnesota.
An archival ROSAT XRT/HRI image of the Cassiopeia A supernova remnant was corrected for absorptio... more An archival ROSAT XRT/HRI image of the Cassiopeia A supernova remnant was corrected for absorption, on 30\arcsec \ (0.5 pc) scales, using existing OH and H I absorption data (Bieging & Crutcher 1986, Goss unpublished data), and theoretical effective x-ray cross-sections for the ISM. A much stronger correlation was discovered than had been previously seen between the x-ray and radio emission. We observe (log (radio))/(log (x-ray)) values between 0.26 and 0.37. The implications of these data for physical parameters in the relativistic and thermal plasmas of the supernova remnant will be discussed. Assuming the relation above, the lambda20 cm radio emission, which is free from absorption effects, was then used as a predictor of the actual x-ray emission. By comparing the predicted values to the uncorrected x-ray image, an empirical x-ray optical depth was derived. A good linear correlation exists between this empirical x-ray optical depth and the column density of hydrogen as calculated using the OH and H I absorption data. The effective cross-section of the interstellar medium was then calculated and found to be consistent with the theoretical models. This work is supported in part by NSF grant AST 9100486 to the University of Minnesota.
X Ray and Radio Connections Santa Fe New Mexico Usa Proceedings and Presentations, 2015
G266.2-1.2 (RX J0852.0-4622) is a member of the emerging class of Galactic supernova remnants (SN... more G266.2-1.2 (RX J0852.0-4622) is a member of the emerging class of Galactic supernova remnants (SNRs) which feature X-ray spectra dominated by non-thermal emission. This X-ray emission is believed to be synchrotron radiation produced by cosmic-ray electrons accelerated to TeV energies along the expanding shock fronts of SNRs. To explore this phenomenon of high energy X-ray emission from SNRs in more
New Chandra X-Ray Observatory and Very Large Array observations of the hard X-ray feature along t... more New Chandra X-Ray Observatory and Very Large Array observations of the hard X-ray feature along the southern edge of the supernova remnant IC 443 have revealed a comet-shaped nebula of hard emission with a soft X-ray point source at its apex. Based on the X-ray spectrum, X-ray and radio morphology, and the radio polarization properties, we argue that this object
We present a new, deep (232 ks) ROSAT HRI exposure of Cas-A. This is the first X-ray image with e... more We present a new, deep (232 ks) ROSAT HRI exposure of Cas-A. This is the first X-ray image with enough photons to measure the outer, low surface brightness, shell of emission seen in the radio band. In addition 5 iterations of the Lucy-Richardson algorithm were used to deconvolve out the wings of the X-ray mirror point spread function, thus creating a image with a ``restored beam'' of 2.2" FWHM. These new data show a striking resemblance to the VLA radio continuum outside of the main shell. They clearly show the northern and southwestern radio features and the eastern jet region.
We present a new 100 ks Chandra Observation of the dim supernova remnant 3C396. These data show c... more We present a new 100 ks Chandra Observation of the dim supernova remnant 3C396. These data show clear evidence of diffuse (but compact), nebular emission slightly offset from the center of the remnant which interpret as a synchrotron wind nebula surrounding a neutron star that is physically associated with the remnant. We present images and spectra of this new neutron star/supernova remnant association and compare the results to similar objects recently discovered by Chandra.
We present the RXTE high-energy X-ray spectrum of the remnant of the supernova of 1006 AD. A prev... more We present the RXTE high-energy X-ray spectrum of the remnant of the supernova of 1006 AD. A previous analysis of the ASCA X-ray spectrum of the shell of this remnant provided the first evidence that supernova remnants accelerate cosmic-ray electrons to energies as high as 100 TeV. The recent detection of gamma rays at energies > 3 TeV from SN 1006 confirms that this remnant accelerates particles to very-high energies. We review the radio, X-ray, and gamma-ray spectral data and discuss the implications of this data for particle acceleration in the remnant.
3C397 (G41.1-0.3) is one of the brightest radio SNR's, whose classification remains ambiguous. Wh... more 3C397 (G41.1-0.3) is one of the brightest radio SNR's, whose classification remains ambiguous. While in the radio, it is classified as a `Shell'; in X-rays, it has a shell-like plus a centrally bright component, giving the remnant a `Composite' morphology. We present the ASCA & RXTE observations in order to better understand the nature of this unique SNR. The ASCA spectrum is dominated by thermal emission from Mg, Si, S, Ar, and Fe. One-temperature component models fail to account for the hard X-ray emission above ~ 4 keV; and at least two components are required: a soft component dominated by line emission from heavily enriched material, and a hot component, characterized by a prominent Fe-K emission line. The total observed flux is ~ 2.6 x 10(-11) erg cm(-2) s(-1) , which corresponds to an unabsorbed luminosity L_x (1-9 keV) = 4 x 10(36) erg s(-1) , assuming a distance of 10 kpc. The combined ASCA & RXTE PCA data favor the thermal interpretation of the hard component, and suggest the presence of a weak non-thermal third component, whose parameters are poorly determined because of the contamination of the RXTE signal with the emission from the Galactic ridge. We discuss the X-ray spectrum in the light of thermal emission from an ejecta-dominated and a blast wave component, and speculate on the nature of a compact object possibly hiding in this unusual remnant. Our broadband imaging and spectral study suggests that 3C397 is unlike the thermal or plerionic Composites, and that it is dynamically young ( ~ 1,500 yr-old), perhaps a transition object from the young Shells into the more evolved Composites.
An anthology of six important papers in the history of electrodynamics are presented, in order to... more An anthology of six important papers in the history of electrodynamics are presented, in order to illustrate the need for more primary source scientific papers to be added to what is considered the Western Canon.
The whole idea of a Western Canon is both prevalent and controversial in academia, and both for good reasons. It is controversial, because both the choice of material that is codified into the Western Canon has as more to do with mid-20th Century academic culture than it has to do with any clear definition of either The West or what it means to be canonical. However the idea still remains in the academy because the West, however it is defined, has a rich intellectual history that has greatly influenced the world as it is today.
To most scientists, however, these debates are largely moot. Nature is the way it is, regardless of our culture, so why teach the origin of the ideas? The ideas should speak for themselves. While this may be true, it perpetuates a simplistic understanding of how these ideas developed.
Unlike in most other fields, scientists tend to largely agree as to what were the most canonical experiments, and theories, throughout history. Moreover, the modern scientific method, as practiced all over the world today, was clearly of primarily European origin. Thus, if anything is a product of Western Culture, it is the modern practice of science.
In this paper, I argue for the inclusion of original scientific papers into both courses in scientific subjects and, more importantly, into a college-wide courses that trace the history of intellectual ideas. I use the field of physics, and the study of electrodynamics in particular, to show six particular examples as case studies. In each case, I have included a copy of the work, along with a short narrative designed to put it into some historical, philosophical, and scientific, context.
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Papers by Jonathan Keohane
The whole idea of a Western Canon is both prevalent and controversial in academia, and both for good reasons. It is controversial, because both the choice of material that is codified into the Western Canon has as more to do with mid-20th Century academic culture than it has to do with any clear definition of either The West or what it means to be canonical. However the idea still remains in the academy because the West, however it is defined, has a rich intellectual history that has greatly influenced the world as it is today.
To most scientists, however, these debates are largely moot. Nature is the way it is, regardless of our culture, so why teach the origin of the ideas? The ideas should speak for themselves. While this may be true, it perpetuates a simplistic understanding of how these ideas developed.
Unlike in most other fields, scientists tend to largely agree as to what were the most canonical experiments, and theories, throughout history. Moreover, the modern scientific method, as practiced all over the world today, was clearly of primarily European origin. Thus, if anything is a product of Western Culture, it is the modern practice of science.
In this paper, I argue for the inclusion of original scientific papers into both courses in scientific subjects and, more importantly, into a college-wide courses that trace the history of intellectual ideas. I use the field of physics, and the study of electrodynamics in particular, to show six particular examples as case studies. In each case, I have included a copy of the work, along with a short narrative designed to put it into some historical, philosophical, and scientific, context.