arXiv subjects

Laura A. Lopez

Publications and source records attributed to Laura A. Lopez.

83 records · Page 5Linked to original sources

arXiv2013

Unraveling the Origin of Overionized Plasma in the Galactic Supernova Remnant W49B

Recent observations have shown several supernova remnants (SNRs) have overionized plasmas, those where ions are stripped of more electrons than they would be if in equilibrium with the electron temperature. Rapid electron cooling is necessary to produce this situation, yet the physical origin of that cooling remains uncertain. To assess the cooling scenario responsible for overionization, in this paper, we identify and map the overionized plasma in the Galactic SNR W49B based on a 220 ks Chandra Advanced CCD Imaging Spectrometer (ACIS) observation. We performed a spatially-resolved spectroscopic analysis, measuring the electron temperature by modeling the continuum and comparing it to the temperature given by the flux ratio of the He-like and H-like lines of sulfur and of argon. Using these results, we find that W49B is overionized in the west, with a gradient of increasing overionization from east to west. As the ejecta expansion is impeded by molecular material in the east but not in the west, our overionization maps suggest the dominant cooling mechanism is adiabatic expansion of the hot plasma.

astro-ph.HE↗

arXiv2013

Constraining Explosion Type of Young Supernova Remnants Using 24 Micron Emission Morphology

Determination of the explosion type of supernova remnants (SNRs) can be challenging, as SNRs are hundreds to thousands of years old and supernovae (SNe) are classified based on spectral properties days after explosion. Previous studies of thermal X-ray emission from Milky Way and Large Magellanic Cloud (LMC) SNRs have shown that Type Ia and core-collapse (CC) SNRs have statistically different symmetries, and thus these sources can be typed based on their X-ray morphologies. In this paper, we extend the same technique, a multipole expansion technique using power ratios, to infrared (IR) images of SNRs to test whether they can be typed using the symmetry of their warm dust emission as well. We analyzed archival Spitzer Space Telescope Multiband Imaging Photometer (MIPS) 24 micron observations of the previously used X-ray sample, and we find that the two classes of SNRs separate according to their IR morphologies. The Type Ia SNRs are statistically more circular and mirror symmetric than the CC SNRs, likely due to the different circumstellar environments and explosion geometries of the progenitors. Broadly, our work indicates that the IR emission retains information of the explosive origins of the SNR and offers a new method to type SNRs based on IR morphology.

astro-ph.HE↗

arXiv2013

What Shapes Supernova Remnants?

Evidence has mounted that Type Ia and core-collapse (CC) supernovae (SNe) can have substantial deviations from spherical symmetry; one such piece of evidence is the complex morphologies of supernova remnants (SNRs). However, the relative role of the explosion geometry and the environment in shaping SNRs remains an outstanding question. Recently, we have developed techniques to quantify the morphologies of SNRs, and we have applied these methods to the extensive X-ray and infrared archival images available of Milky Way and Magellanic Cloud SNRs. In this proceeding, we highlight some results from these studies, with particular emphasis on SNR asymmetries and whether they arise from "nature" versus "nurture".

astro-ph.HE↗

arXiv2013

The Burst Cluster: Dark Matter in a Cluster Merger Associated with the Short Gamma Ray Burst, GRB 050509B

We have identified a merging galaxy cluster with evidence of two distinct sub-clusters. The X-ray and optical data suggest that the subclusters are moving away from each other after closest approach. This cluster merger was discovered from observations of the well localized short-duration gamma-ray burst (GRB), GRB 050509B. The Swift/Burst Alert Telescope (BAT) source position is coincident with a cluster of galaxies ZwCl 1234.0+02916. The subsequent Swift/X-Ray Telescope (XRT) localization of the X-ray afterglow found the GRB coincident with 2MASX J12361286+2858580, a giant red elliptical galaxy in the cluster. Deep multi-epoch optical images were obtained to constrain the evolution of the GRB afterglow, including a 27480s exposure in the F814W band with Hubble Space Telescope Advanced Camera for Surveys (ACS), among the deepest imaging ever obtained towards a known galaxy cluster in a single passband. We perform a weak gravitational lensing analysis, including mapping the total mass distribution of the merger system. Combined with Chandra X-ray Observatory and Swift/XRT observations, we investigate the dynamical state of the merger to probe the nature of the dark matter component. Our weak gravitational lensing measurements reveal a separation of the X-ray centroid of the western subcluster from the center of the mass and galaxy light distributions, similar to that of the famous "Bullet cluster". We conclude that the "Burst cluster" is another candidate merger system for determining the nature of dark matter and for studying the environment of short GRBs. We discuss connections between the cluster dynamical state and/or matter composition and compact object mergers, the leading model for the origin of short GRBs. Finally, we present results from a weak lensing survey based on archival Very Large Telescope (VLT) images in the areas of 5 other short GRBs.

astro-ph.CO↗

arXiv2013

The Galactic Supernova Remnant W49B Likely Originates from a Jet-Driven, Core-Collapse Explosion

We present results from a 220-ks observation of the galactic supernova remnant (SNR) W49B using the Advanced CCD Imaging Spectrometer (ACIS) on board the Chanrda X-ray Observatory. We exploit these data to perform detailed spatially-resolved spectroscopic analyses across the SNR with the aim to investigate the thermodynamic properties and explosive origin of W49B. We find substantial variation in the electron temperature and absorbing column toward W49B, and we show that the mean metal abundances are consistent with the predicted yields in models of bipolar/jet-driven core-collapse SNe. Furthermore, we set strict upper limits on the X-ray luminosity of any undetected point sources, and we exclude the presence of a neutron star associated with W49B. We conclude that the morphological, spectral, and environmental characteristics of W49B are indicative of a bipolar Type Ib/Ic SN origin, making it the first of its kind to be discovered in the Milky Way.

astro-ph.HE↗

arXiv2011

Discovery of an AGN-Driven Molecular Outflow in the Local Early-Type Galaxy NGC 1266

We report the discovery of a powerful molecular wind from the nucleus of the non-interacting nearby S0 field galaxy NGC 1266. The single-dish CO profile exhibits emission to +/- 400 km/s and requires a nested Gaussian fit to be properly described. Interferometric observations reveal a massive, centrally- concentrated molecular component with a mass of 1.1x10^9 Msuns and a molecular outflow with a molecular mass of 2.4x10^7 Msuns. The molecular gas close to the systemic velocity consists of a rotating, compact nucleus with a mass of about 4.1x108 Msuns within a radius of approximately 60 pc. This compact molecular nucleus has a surface density of \approx 2.7 \times 10^4 Msuns/pc^2, more than two orders of magnitude larger than that of giant molecular clouds in the disk of the Milky Way, and it appears to sit on the Kennicutt-Schmidt relation despite its extreme kinematics and energetic activity. We interpret this nucleus as a disk that confines the outflowing wind. A mass outflow rate of 13 Msuns/yr leads to a depletion timescale of about 85 Myr. The star formation in NGC 1266 is insufficient to drive the outflow, and thus it is likely driven by the active galactic nucleus (AGN). The concentration of the majority of the molecular gas in the central 100 pc requires an extraordinary loss of angular momentum, but no obvious companion or interacting galaxy is present to enable the transfer. NGC 1266 is the first known outflowing molecular system that does not show any evidence of a recent interaction.

astro-ph.CO↗

arXiv2011

What Drives the Expansion of Giant HII Regions?: A Study of Stellar Feedback in 30 Doradus

Observations show that star formation is an inefficient and slow process. This result can be attributed to the injection of energy and momentum by stars that prevents free-fall collapse of molecular clouds. The mechanism of this stellar feedback is debated theoretically: possible sources of pressure include the classical warm HII gas, the hot gas generated by shock-heating from stellar winds and supernovae, direct radiation of stars, and the dust-processed radiation field trapped inside the HII shell. In this paper, we measure observationally the pressures associated with each component listed above across the giant HII region 30 Doradus in the Large Magellanic Cloud. We exploit high-resolution, multi-wavelengh images (radio, infrared, optical, and X-ray) to map these pressures as a function of position. We find that radiation pressure dominates within 75 pc of the central star cluster, R136, while the HII gas pressure dominates at larger radii. By contrast, the dust-processed radiation pressure and hot gas pressure are generally weak and not dynamically important, although the hot gas pressure may have played a more significant role at early times. Based on the low X-ray gas pressures, we demonstrate that the hot gas is only partially confined and must be leaking out the HII shell. Additionally, we consider the implications of a dominant radiation pressure on the early dynamics of 30 Doradus.

astro-ph.SR↗

arXiv2010

Using the X-ray Morphologies of Young Supernova Remnants to Constrain Explosion Type, Ejecta Distribution, and Chemical Mixing

Supernova remnants (SNRs) are a complex class of sources, and their heterogeneous nature has hindered the characterization of their general observational properties. To overcome this challenge, we use statistical tools to analyze the Chandra X-ray images of Galactic and Large Magellanic Cloud SNRs. We apply two techniques, a power-ratio method (a multipole expansion) and wavelet-transform analysis, to measure the global and local morphological properties of the X-ray line and thermal emission in twenty-four SNRs. We find that Type Ia SNRs have statistically more spherical and mirror symmetric thermal X-ray emission than core-collapse (CC) SNRs. The ability to type SNRs based on thermal emission morphology alone enables, for the first time, the typing of SNRs with weak X-ray lines or with low-resolution spectra. We identify one source, SNR G344.7-0.1, as originating from a CC explosion that was previously unknown, and we confirm the tentative Type Ia classifications of G337.2-0.7 and G272.2-3.2. Although the global morphology is indicative of the explosion type, the relative morphology of the X-ray line emission within SNRs is not: all sources in our sample have well-mixed ejecta, irrespective of stellar origin. In particular, we find that 90% of the bright metal-line emitting substructures are spatially coincident and have similar scales, even if the metals arise from different burning processes. Moreover, the overall X-ray line morphologies within each SNR are the same, with <6% differences. These findings reinforce that hydrodynamical instabilities can efficiently mix ejecta in Type Ia and CC SNRs. The only exception is W49B, which is likely from its jet-driven/bipolar SN explosion. Finally, we describe observational constraints that can be used to test hydrodynamical models of SNR evolution; notably, the filling factor of X-ray emission decreases with SNR age.

astro-ph.HE↗

arXiv2009

Typing Supernova Remnants Using X-ray Line Emission Morphologies

We present a new observational method to type the explosions of young supernova remnants (SNRs). By measuring the morphology of the Chandra X-ray line emission in seventeen Galactic and Large Magellanic Cloud SNRs with a multipole expansion analysis (using power ratios), we find that the core-collapse SNRs are statistically more asymmetric than the Type Ia SNRs. We show that the two classes of supernovae can be separated naturally using this technique because X-ray line morphologies reflect the distinct explosion mechanisms and structure of the circumstellar material. These findings are consistent with recent spectropolarimetry results showing that core-collapse SNe are intrinsically more asymmetric.

astro-ph.HE↗

arXiv2008

Tools for Dissecting Supernova Remnants Observed with Chandra: Methods and Application to the Galactic Remnant W49B

We introduce methods to quantify the X-ray morphologies of supernova remnants observed with the Chandra X-ray Telescope. These include a power-ratio technique to measure morphological asymmetries, correlation-length analysis to probe chemical segregation and distribution, and wavelet-transform analysis to quantify X-ray substructure. We demonstrate the utility and accuracy of these techniques on relevant synthetic data. Additionally, we show the methods' capabilities by applying them to the 55-ks Chandra ACIS observation of the galactic supernova remnant W49B. We analyze the images of prominent emission lines in W49B and use the results to discern physical properties. We find that the iron morphology is very distinct from the other elements: it is statistically more asymmetric, more segregated, and has 25% larger emitting substructures than the lighter ions. Comparatively, the silicon, sulfur, argon, and calcium are well-mixed, more isotropic, and have smaller, equally-sized emitting substructures. Based on fits of XMM-Newton spectra in regions identified as iron rich and iron poor, we determine that the iron in W49B must have been anisotropically ejected. We measure the abundance ratios in many regions, and we find that large, local variations are persistent throughout the remnant. We compare the mean, global abundance ratios to those predicted by spherical and bipolar core-collapse explosions; the results are consistent with a bipolar origin from a 25 solar mass progenitor. We calculate the filling factor of iron from the volume of its emitting substructures, enabling more precise mass estimates than previous studies. Overall, this work is a first step toward rigorously describing the physical properties of supernova remnants for comparison within and between sources.

astro-ph↗

arXiv2006

Determining the Nature of the SS 433 Binary Using an X-ray Spectrum During Eclipse

We test the physical model of the relativistic jets in the galactic X-ray binary SS 433 proposed in our previous paper using additional observations from the Chandra High Energy Transmission Grating Spectrometer. These observations sample two new orbital/precessional phase combinations. In the observation near orbital phase zero, the H- and He-like Fe lines from both receding and approaching jets are comparably strong and unocculted while the He-like Si line of the receding jet is significantly weaker than that of the approaching jet. This condition may imply the cooler parts of the receding jet are eclipsed by the companion. The X-ray spectrum from this observation has broader emission lines than obtained in Paper I that may arise from the divergence of a conical outflow or from Doppler shift variations during the observation. Using recent optical results, along with the length of the unobscured portion of the receding jet assuming adiabatic cooling, we calculate the radius of the companion to be 9.6+/-1.0 R_sun, about one third of the Roche lobe radius. For a main sequence star, this corresponds to a companion mass of 35+/-7 M_sun, giving a primary source mass of 20+/-5 M_sun. If our model is correct, this calculation indicates the compact object is a black hole, and accretion occurs through a wind process. In a subsequent paper, we will examine the validity of the adiabatic cooling model of the jets and test the mode of line broadening.

astro-ph↗