Search

We have observed a sample of nine Extended Green Objects (EGOs) at 1.3 and 5 cm with the Very Large Array (VLA) with subarcsecond resolution and ∼7–14 μJy beam−1-sensitivities in order to characterize centimeter continuum emission as it first appears in these massive protoclusters. We find an EGO-associated continu um emission—within 1″ of the extended 4.5 μm emission—in every field, which is typically faint (order 101–102 μJy) and compact (unresolved at 0″.3–0″.5). The derived spectral indices of our 36 total detections are consistent with a wide array of physical processes, including both non-thermal (19% of detections) and thermal free–free processes (e.g., ionized jets and compact H ii regions, 78% of sample) and warm dust (1 source). We also find an EGO-associated 6.7 GHz CH3OH and 22 GHz H2O maser emission in 100% of the sample and a NH3 (3,3) masers in ∼45%; we do not detect any NH3 (6,6) masers at ∼5.6 mJy beam−1 sensitivity. We find statistically-significant correlations between L radio and L bol at two physical scales and three frequencies, consistent with thermal emission from ionized jets, but no correlation between L H 2 O and L radio for our sample. From these data, we conclude that EGOs likely host multiple different centimeter continuum-producing processes simultaneously. Additionally, at our ∼1000 au resolution, we find that all EGOs except G18.89−0.47 contain 1 ∼ 2 massive sources based on the presence of CH3OH maser groups, which is consistent with our previous work suggesting that these are typical massive protoclusters, in which only one to a few of the young stellar objects are massive.

(Abridged) The initial physical conditions of high-mass stars and protoclusters remain poorly characterized. To this end we present the first targeted ALMA 1.3mm continuum and spectral line survey towards high-mass starless clump candidates, selecting a sample of 12 of the most massive candidates ($400-4000\, M_\odot$) within 5 kpc. The joint 12+7m array maps have a high spatial resolution of $\sim 3000\, \mathrm{au}$ ($\sim 0.8^{\prime\prime}$) and have point source mass-completeness down to $\sim 0.3\, M_\odot$ at $6\sigma$ (or $1\sigma$ column density sensitivity of $1.1\times10^{22}\, \mathrm{cm^{-2}}$). We discover previously undetected signposts of low-luminosity star formation from CO (2-1) and SiO (5-4) bipolar outflows and other signatures towards 11 out of 12 clumps, showing that current MIR/FIR Galactic Plane surveys are incomplete to low- and intermediate-mass protostars ($\lesssim 50\, L_\odot$). We compare a subset of the observed cores with a suite of radiative transfer models of starless cores. We find a high-mass starless core candidate with a model-derived mass consistent with $29^{52}_{15}\, M_\odot$ when integrated over size scales of $2\times10^4\, \mathrm{au}$. Unresolved cores are poorly fit by starless core models, supporting the interpretation that they are protostellar even without detection of outflows. Substantial fragmentation is observed towards 10 out of 12 clumps. We extract sources from the maps using a dendrogram to study the characteristic fragmentation length scale. Nearest neighbor separations when corrected for projection are consistent with being equal to the clump average thermal Jeans length. Our findings support a hierarchical fragmentation process, where the highest density regions are not strongly supported against thermal gravitational fragmentation by turbulence or magnetic fields., Comment: 32 pages, 17 figures, and 6 tables. Accepted for publication in ApJ (August 26, 2019)

Following an eruptive accretion event in NGC6334I-MM1, flares in the various maser species, including water masers, were triggered. We report the observed relative proper motion of the highly variable water masers associated with the massive star-forming region, NGC6334I. High velocity H$_2$O maser proper motions were detected in 5 maser clusters, CM2-W2 (bow-shock structure), MM1-W1, MM1-W3, UCHII-W1 and UCHII-W3. The overall average of the derived relative proper motion is 85 km s$^{-1}$. This mean proper motion is in agreement with the previous results from VLA multi-epoch observations. Our position and velocity variance and co-variance matrix analyses of the maser proper motions show its major axis to have a position angle of $-$79.4$^\circ$, cutting through the dust cavity around MM1B and aligned in the northwest-southeast direction. We interpret this as the axis of the jet driving the CM2 shock and the maser motion. The complicated proper motions in MM1-W1 can be explained by the combined influence of the MM1 northeast-southwest bipolar outflow, CS(6-5) north-south collimated bipolar outflow, and the radio jet. The relative proper motions of the H$_2$O masers in UCHII-W1 are likely not driven by the jets of MM1B protostar but by MM3-UCHII. Overall, the post-accretion burst relative proper motions of the H$_2$O masers trace shocks of jet motion., 18 pages, 6 figures, accepted for publication by The Astrophysical Journal

Amide molecules produced in space could play a key role in the formation of biomolecules on a young planetary object. However, the formation and chemical network of amide molecules in space is not well understood. In this work, ALMA observations are used to study a number of amide(-like) molecules toward the high-mass star-forming region NGC 6334I. The first detections of cyanamide (NH$_{2}$CN), acetamide (CH$_{3}$C(O)NH$_{2}$) and N-methylformamide (CH$_{3}$NHCHO) are presented for this source. These are combined with analyses of isocyanic acid (HNCO) and formamide (NH$_{2}$CHO) and a tentative detection of urea (carbamide; NH$_{2}$C(O)NH$_{2}$). Abundance correlations show that most amides are likely formed in related reactions occurring in ices on interstellar dust grains in NGC 6334I. However, in an expanded sample of sources, large abundance variations are seen for NH$_{2}$CN that seem to depend on the source type, which suggests that the physical conditions within the source heavily influence the production of this species. The rich amide inventory of NGC 6334I strengthens the case that interstellar molecules can contribute to the emergence of biomolecules on planets., Accepted for publication in The Astrophysical Journal

We report the first detection of isotopic methanol (13CH3OH) maser emission in interstellar space. The emission was detected toward the high-mass young stellar object G358.93-0.03 during monitoring of a flare in the 6.7 GHz methanol (CH3OH) maser emission in this source. We find that the spectral and spatial distribution of the 13CH3OH masers differs from the CH3OH masers imaged at the same epoch, contrary to expectations from similarity of their pumping. This conclusively demonstrates that isotopic methanol masers are bright under different physical conditions and suggests that they can provide additional, complementary information to the CH3OH masers from the same source. We detect a rapid decay of the 13CH3OH maser lines suggesting that they are transient phenomena (masing for only a few months), likely associated with rapid changes in radiation field due to an accretion burst induced by massive disk fragmentation. Changes in the line flux density are faster than required to achieve equilibrium in the energy level populations, indicating that the pumping of these masers is likely variable. © 2020. The American Astronomical Society. All rights reserved..

We present (sub)millimeter imaging at 0.5'' resolution of the massive star-forming region G358.93-0.03 acquired in multiple epochs at 2 and 3 months following the recent flaring of its 6.7 GHz methanol maser emission. Using SMA and ALMA, we have discovered 14 new Class II methanol maser lines ranging in frequency from 199 GHz to 361 GHz, which originate mostly from vt=1 torsionally-excited transitions and include one vt=2 transition. The latter detection provides the first observational evidence that Class II maser pumping involves levels in the vt=2 state. The masers are associated with the brightest continuum source (MM1), which hosts a line-rich hot core. The masers present a consistent curvilinear spatial velocity pattern that wraps around MM1, suggestive of a coherent physical structure 1200 au in extent. In contrast, the thermal lines exhibit a linear pattern that crosses MM1 but at progressive position angles that appear to be a function of either increasing temperature or decreasing optical depth. The maser spectral profiles evolved significantly over one month, and the intensities dropped by factors of 3.0 to 7.2, with the vt=2 line showing the largest change. A small area of maser emission from only the highest excitation lines closest to MM1 has disappeared. There are seven additional dust continuum sources in the protocluster, including another hot core (MM3). We do not find evidence for a significant change in (sub)millimeter continuum emission from any of the sources during the one month interval, and the total protocluster emission remains comparable to prior single dish measurements., 10 pages, 2 figures, 3 tables, accepted for publication in The Astrophysical Journal Letters. All maser transitions detected in this object can be displayed via an option on the advanced interface of http://splatalogue.net

We present multi-epoch continuum observations of the Class 0 protostellar system IRAS 16293-2422 taken with the Very Large Array (VLA) at multiple wavelengths between 7 mm and 15 cm (41 GHz down to 2 GHz), as well as single-epoch Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations covering the range from 0.4 to 1.3 mm (700 GHz down to 230 GHz). The new VLA observations confirm that source A2 is a protostar driving episodic mass ejections, and reveal the complex relative motion between A2 and A1. The spectrum of component B can be described by a single power law ($S_\nu \propto \nu^{2.28}$) over the entire range from 3 to 700 GHz (10 cm down to 0.4 mm), suggesting that the emission is entirely dominated by dust even at $\lambda$ = 10 cm. Finally, the size of source B appears to increase with frequency up to 41 GHz, remaining roughly constant (at $0''.39$ $\equiv$ 55 AU) at higher frequencies. We interpret this as evidence that source B is a dusty structure of finite size that becomes increasingly optically thick at higher frequencies until, in the millimeter regime, the source becomes entirely optically thick. The lack of excess free-free emission at long wavelengths, combined with the absence of high-velocity molecular emission indicates that source B does not drive a powerful outflow, and might indicate that source B is at a particularly early stage of its evolution.

We present $\sim$0.1" resolution ($\sim$10 pc) ALMA observations of a molecular cloud identified in the merging Antennae galaxies with the potential to form a globular cluster, nicknamed the ``Firecracker.' Since star formation has not yet begun at an appreciable level, this cloud provides an example of what the birth environment of a globular cluster may have looked like before stars form and disrupt the natal conditions. Using emission from $^{12}$CO(2-1), $^{12}$CO(3-2), $^{13}$CO(2-1), HCN(4-3), and HCO$^+$(4-3), we are able to resolve the cloud's structure and find that it has a characteristic radius of 22 pc and a mass of 1--9$\times10^6 M_\odot$. We also constrain the abundance ratios of $^{12}$CO/$^{13}$CO and H$_2$/\twelveCO. Based on the calculated mass, we determine that the commonly used CO-to-H$_2$ conversion factor varies spatially, with average values in the range $X_{CO}=(0.12-1.1)\times10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$. We demonstrate that if the cloud is bound (as is circumstantially suggested by its bright, compact morphology), an external pressure of $P/k > 10^8$ K cm$^{-3}$ is required. This would be consistent with theoretical expectations that globular cluster formation requires high pressure environments. The position-velocity diagram of the cloud and its surrounding material suggests that this pressure may be produced by the collision of filaments. The radial profile of the column density can be fit with both a Gaussian and Bonnor-Ebert profile. The relative line strengths of HCN and HCO$^+$ in this region suggest that these molecular lines can be used as tracers for the evolutionary stage of a cluster., 18 pages, 14 figures, Accepted to ApJ 2019 March 4

We use Atacama Large Millimeter Array CO(3-2) observations in conjunction with optical observations from the Hubble Space Telescope to determine the ratio of stellar to gas mass for regions in the Antennae Galaxies. We adopt the term "instantaneous mass ratio" IMR(t) = M$_{stars}$/(M$_{gas}$ +M$_{stars}$), that is equivalent to the star formation efficiency for an idealized system at t = 0. We use two complementary approaches to determining the IMR(t) based on 1) the enclosed stellar and molecular mass within circular apertures centered on optically-identified clusters, and 2) a tessellation algorithm that defines regions based on CO emission. We find that only a small number of clusters appear to have IMR(0) = SFE > 0.2, which suggests that only a small fraction of these clusters will remain bound. The results suggest that by ages of $10^{6.7}$ years, some clusters will have lost all of their associated molecular gas, and by $10^{7.5}$ years this is true for the majority of clusters. There appears to be slight dependence of the IMR(t) on the CO surface brightness, which could support the idea that dense molecular environments are more likely to form bound clusters. However, the IMR(t) appears to have a strong dependence on extinction, which likely traces the evolutionary state of clusters., 17 pages, 10 figures, accepted for publication in ApJ

We present and analyze two new high-resolution (approx 0.3 arcsec), high-sensitivity (approx 50 uJy beam-1) Very Large Array 3.6 cm observations of IRAS 16293-2422 obtained in 2007 August and 2008 December. The components A2alpha and A2beta recently detected in this system are still present, and have moved roughly symmetrically away from source A2 at a projected velocity of 30-80 km s-1. This confirms that A2alpha and A2beta were formed as a consequence of a very recent bipolar ejection from A2. Powerful bipolar ejections have long been known to occur in low-mass young stars, but this is -to our knowledge-- the first time that such a dramatic one is observed from its very beginning. Under the reasonable assumption that the flux detected at radio wavelengths is optically thin free-free emission, one can estimate the mass of each ejecta to be of the order of 10^-8 Msun. If the ejecta were created as a consequence of an episode of enhanced mass loss accompanied by an increase in accretion onto the protostar, then the total luminosity of IRAS 16293-2422 ought to have increased by 10-60% over the course of at least several months. Between A2alpha and A2beta, component A2 has reappeared, and the relative position angle between A2 and A1 is found to have increased significantly since 2003-2005. This strongly suggests that A1 is a protostar rather than a shock feature, and that the A1/A2 pair is a tight binary system. Including component B, IRAS 16293-2422 therefore appears to be a very young hierarchical multiple system., Accepted for publication in The Astrophysical Journal

We report ALMA observations with resolution $\approx0.5$" at 3 mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000 AU. By ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact HII regions and young stellar objects (YSOs). Most of the newly-detected sources are YSOs with gas envelopes which, based on their luminosities, must contain objects with stellar masses $M_*\gtrsim8$ M$_\odot$. Their spatial distribution spread over a $\sim12\times3$ pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated `starburst' within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density ($N(H_2)\gtrsim2\times10^{23}$ cm$^{-2}$), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2 follow a linear $\Sigma_*-\Sigma_{gas}$ relation, shallower than that observed in local clouds. Together, these points suggest that a higher volume density threshold is required to explain star formation in CMZ clouds., Comment: Accepted to ApJ. Full resolution at http://keflavich.github.io/SgrB2_ALMA_3mm_Mosaic/sgrb2_cores_compressed.pdf, source code repository at https://github.com/keflavich/SgrB2_ALMA_3mm_Mosaic/, and data at DOI 10.11570/17.0007. 33 pages, 23 figures

We present ALMA observations of the dwarf starburst galaxy Henize 2-10 in combination with previous SMA CO observations to probe the molecular environments of natal super star clusters. These observations include the HCO$^+$(1-0), HCN(1-0), HNC(1-0), and CCH(1-0) molecular lines, as well as 88 GHz continuum with a spatial resolution of $1''.7\times 1''.6$. After correcting for the contribution from free-free emission to the 88 GHz continuum flux density ($\sim$ 60% of the 88 GHz emission), we derive a total gas mass for He~2-10 of $M_{gas} = 4-6\times10^8$ M$_{\odot}$, roughly 5-20% of the dynamical mass. Based on a principle component analysis, HCO$^+$ is found to be the best "general" tracer of molecular emission. The line widths and luminosities of the CO emission suggests that the molecular clouds could either be as small as $\sim 8$ pc, or alternately have enhanced line widths. The CO emission and 88 GHz continuum are anti-correlated, suggesting that either the dust and molecular gas are not cospatial, which could reflect the 88 GHz continuum is dominated by free-free emission. The CO and CCH emission are also relatively anti-correlated, which is consistent with the CCH being photo-enhanced, and/or the CO being dissociated in the regions near the natal super star clusters. The molecular line ratios of regions containing the natal star clusters are different from the line ratios observed for regions elsewhere in the galaxy. In particular, the regions with thermal radio emission all have CO(2-1)/HCO$^+(1-0) < 16$, and the HCO$^+$/CO ratio appears to be correlated with the evolutionary stage of the clusters., 15 pages, 2 tables, 13 figures, accepted for publication in ApJ

We report the detection of interstellar methoxymethanol (CH$_3$OCH$_2$OH) in ALMA Bands 6 and 7 toward the MM1 core in the high-mass star-forming region NGC 6334I at ~0.1" - 1" spatial resolution. A column density of 4(2) x $10^{18}$ cm$^{-2}$ at $T_{ex}$ = 200 K is derived toward MM1, ~34 times less abundant than methanol (CH$_3$OH), and significantly higher than predicted by astrochemical models. Probable formation and destruction pathways are discussed, primarily through the reaction of the CH$_3$OH photodissociation products, the methoxy (CH$_3$O) and hydroxymethyl (CH$_2$OH) radicals. Finally, we comment on the implications of these mechanisms on gas-phase vs grain-surface routes operative in the region, and the possibility of electron-induced dissociation of CH$_3$OH rather than photodissociation., Comment: Accepted in Astrophysical Journal Letters

We present a high-resolution, multi-wavelength study of the massive protostellar cluster NGC 6334I(N) that combines new spectral line data from the Submillimeter Array (SMA) and VLA with a reanalysis of archival VLA continuum data, 2MASS and Spitzer images. As shown previously, the brightest 1.3 mm source SMA1 contains substructure at subarcsecond resolution, and we report the first detection of SMA1b at 3.6 cm along with a new spatial component at 7 mm (SMA1d). We find SMA1 (aggregate of sources a, b, c, and d) and SMA4 to be comprised of free-free and dust components, while SMA6 shows only dust emission. Our 1.5" resolution 1.3 mm molecular line images reveal substantial hot-core line emission toward SMA1 and to a lesser degree SMA2. We find CH3OH rotation temperatures of 165\pm 9 K and 145\pm 12 K for SMA1 and SMA2, respectively. We estimate a diameter of 1400 AU for the SMA1 hot core emission, encompassing both SMA1b and SMA1d, and speculate that these sources comprise a >800 AU separation binary that may explain the previously-suggested precession of the outflow emanating from the SMA1 region. The LSR velocities of SMA1, SMA2, and SMA4 all differ by 1-2 km/s. Outflow activity from SMA1, SMA2, SMA4, and SMA6 is observed in several molecules including SiO(5--4) and IRAC 4.5 micron emission; 24 micron emission from SMA4 is also detected. Eleven water maser groups are detected, eight of which coincide with SMA1, SMA2, SMA4, and SMA6. We also detect a total of 83 Class I CH3OH 44GHz maser spots which likely result from the combined activity of many outflows. Our observations paint the portrait of multiple young hot cores in a protocluster prior to the stage where its members become visible in the near-infrared., Accepted to ApJ, 24 pages, a full high resolution version is available at http://www.cv.nrao.edu/~cbrogan/ms.long.pdf

We present the results of a high angular resolution Very Large Array (VLA) Class I 44 GHz and Class II 6.7 GHz methanol maser survey of a sample of ~20 massive young stellar object (MYSO) outflow candidates selected on the basis of extended 4.5 micron emission in Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) images. These 4.5 micron-selected candidates are referred to as extended green objects (EGOs), for the common coding of this band as green in three-color IRAC images. The detection rate of 6.7 GHz Class II methanol masers, which are associated exclusively with massive YSOs, towards EGOs is greater than ~64%--nearly double the detection rate of surveys using other MYSO selection criteria. The detection rate of Class I 44 GHz methanol masers, which trace molecular outflows, is ~89% towards EGOs associated with 6.7 GHz methanol masers. The two types of methanol masers exhibit different spatial distributions: 6.7 GHz masers are centrally concentrated and usually coincide with 24 micron emission, while 44 GHz masers are widely distributed and generally trace diffuse 4.5 micron features. We also present results of a complementary James Clerk Maxwell Telescope (JCMT) single-pointing molecular line survey of EGOs in the outflow tracers HCO+(3-2) and SiO(5-4). The HCO+ line profiles and high SiO detection rate (90%) are indicative of the presence of active outflows. No 44 GHz continuum emission is detected at the 5 mJy/beam (5 sigma) level towards 95% of EGOs surveyed, excluding bright ultracompact HII regions as powering sources for the 4.5 micron outflows. The results of our surveys constitute strong evidence that EGOs are young, massive YSOs, with active outflows, presumably powered by ongoing accretion.

M17 is one of the youngest and most massive nearby star-formation regions in the Galaxy. It features a bright H II region erupting as a blister from the side of a giant molecular cloud (GMC). Combining photometry from the Spitzer GLIMPSE survey with complementary infrared (IR) surveys, we identify candidate young stellar objects (YSOs) throughout a 1.5 deg x 1 deg field that includes the M17 complex. The long sightline through the Galaxy behind M17 creates significant contamination in our YSO sample from unassociated sources with similar IR colors. Removing contaminants, we produce a highly-reliable catalog of 96 candidate YSOs with a high probability of association with the M17 complex. We fit model spectral energy distributions to these sources and constrain their physical properties. Extrapolating the mass function of 62 intermediate-mass YSOs (M >3 Msun), we estimate that >1000 stars are in the process of forming in the extended outer regions of M17. From IR survey images from IRAS and GLIMPSE, we find that M17 lies on the rim of a large shell structure ~0.5 deg in diameter (~20 pc at 2.1 kpc). We present new maps of CO and 13CO (J=2-1) emission, which show that the shell is a coherent, kinematic structure associated with M17 at v = 19 km/s. The shell is an extended bubble outlining the photodissociation region of a faint, diffuse H II region several Myr old. We provide evidence that massive star formation has been triggered by the expansion of the bubble. The formation of the massive cluster ionizing the M17 H II region itself may have been similarly triggered. We conclude that the star formation history in the extended environment of M17 has been punctuated by successive waves of massive star formation propagating through a GMC complex., 31 pages, 15 figures, accepted for publication in ApJ. For a version with higher-quality figures, see http://www.astro.wisc.edu/glimpse/Povich2009_M17.pdf

We report the discovery of a partial ~2deg. diameter non-thermal radio shell coincident with Taz, the pulsar wind nebula (PWN) in the error box of the apparently variable gamma-ray source 3EG J1809-2328. We propose that this radio shell is a newly identified supernova remnant (SNR G7.5-1.7) associated with the PWN. The SNR surrounds an amorphous region of thermal X-rays detected in archival ROSAT and ASCA observations putting this system in the mixed-morphology class of supernova remnants. G7.5-1.7 is the fifth such supernova remnant coincident with a bright GeV source, and the fourth containing a pulsar wind nebulae., Comment: 7 pages, 3 figures, to appear in The Astrophysical Journal

We present an XMM-Newton observation of the long-overlooked radio source G350.1-0.3. The X-ray spectrum of G350.1-0.3 can be fit by a shocked plasma with two components: a high-temperature (1.5 keV) region with a low ionization time scale and enhanced abundances, plus a cooler (0.36 keV) component in ionization equilibrium and with solar abundances. The X-ray spectrum and the presence of non-thermal, polarized, radio emission together demonstrate that G350.1-0.3 is a young, luminous supernova remnant (SNR), for which archival HI and 12-CO data indicate a distance of 4.5 kpc. The diameter of the source then implies an age of only ~900 years. The SNR's distorted appearance, small size and the presence of 12-CO emission along the SNR's eastern edge all indicate that the source is interacting with a complicated distribution of dense ambient material. An unresolved X-ray source, XMMU J172054.5-372652, is detected a few arcminutes west of the brightest SNR emission. The thermal X-ray spectrum and lack of any multi-wavelength counterpart suggest that this source is a neutron star associated with G350.1-0.3, most likely a "central compact object", as seen coincident with other young SNRs such as Cassiopeia A., 6 pages, uses emulateapj. One B/W figure, one color figure. Minor text changes and update to Fig 2 following referee's report. ApJ Letters, in press

We present results from SMA observations of the star forming region Cepheus A-East at ~340 GHz (875 micron) with 0.7'' - 2'' resolution. At least four compact submm continuum sources have been detected, as well as a rich forest of hot core line emission. Two kinematically, chemically, and thermally distinct regions of molecular emission are present in the vicinity of the HW2 thermal jet, both spatially distinct from the submm counterpart to HW2. We propose that this emission is indicative of multiple protostars rather than a massive disk as reported by Patel et al. (2005)., Comment: 4 pages, Figures 1 and 3 are in color, latex uses emulateapj.sty. Accepted to ApJ Letters. Figures 1 and 3 have been degraded; higher quality figures available at http://www.cv.nrao.edu/~cbrogan/CepA/

We present the discovery of non-thermal radio and X-ray emission positionally coincident with the TeV $\gamma$-ray source HESS J1813--178. We demonstrate that the non-thermal radio emission is due to a young shell-type supernova remnant (SNR) G12.8--0.0, and constrain its distance to be greater than 4 kpc. The X-ray emission is primarily non-thermal and is consistent with either an SNR shell or unidentified pulsar/pulsar wind nebula origin; pulsed emission is not detected in archival ASCA data. A simple synchrotron+inverse Compton model for the broadband emission assuming that all of the emission arises from the SNR shell implies maximum energies of $(30-450)(B/10 microG)^{-0.5}$ TeV. Further observations are needed to confirm that the broadband emission has a common origin and better constrain the X-ray spectrum., Comment: Accepted to ApJ Letters; 5 pages, Figures 1 and 3 are in color. Small changes from original version

MERLIN and VLBA observations of the 1720 MHz maser emission from the OH molecule in the supernova remnant IC443 are presented. Based on MERLIN data with a resolution of 160 mas, the deconvolved sizes of the maser sources are in the range 90 to 180 mas (135 to 270 AU). The 12 mas resolution VLBA images show compact cores with sizes in the range 15 to 55 mas. The maser brightness temperatures are (2-34)x10^6 K for the MERLIN sources and (5-19)x10^8 K for the VLBA cores, in agreement with theory. Unlike the Zeeman Stokes V profiles observed in other OH (1720 MHz) SNR masers, single-handed circular polarization line profiles are observed in IC443 on all angular scales from 1000 to 10 mas resolution. For one line component, the observed line width is 0.24+/-0.07 km/s, compared to an estimated Doppler width of 0.49 km/s. This discrepancy in line widths can be accounted for if the maser emission arises from an elongated ellipsoidal region of masing gas.

We have used the NRAO Very Large Array (VLA) in conjunction with the Very Long Baseline Array (VLBA) Pie Town antenna as a real-time interferometer system to measure the size of the extragalactic source J1801-231 as a function of frequency from 1285 to 4885 MHz. These observations were made in an attempt to determine the effect interstellar scattering has on the observed sizes of OH (1720 MHz) masers in the nearby (d=2.5 kpc) supernova remnant W28. The observations clearly show that J1801-231 displays angular broadening due to turbulence in the Galaxy's interstellar medium. The minimum distance of the nearby (two arcminutes from J1801-231) pulsar PSR B1758-23 is constrained to be 9.4 +/- 2.4 kpc. This value is based on both the measured size of 220 mas for J1801-231 at 1715 MHz and the temporal broadening of the pulsar. A single thin scattering screen along the line of sight to the W28 OH(1720 MHz) masers must be at 4.7 +/- 1.2 kpc for this minimum pulsar distance. The screen may be placed closer to the Earth, but for reasonable values of the pulsar distance (i.e., the pulsar is within the Galaxy), this choice leads to a negligible scattering contribution to the sizes of the masers. Thus the OH(1720 MHz) masers, at a distance of 2.5 +/- 0.7 kpc, are unaffected by interstellar scattering, and the measured maser sizes must be intrinsic. Our measured upper limits to the size of the pulsar itself are consistent with the distance estimates to the pulsar and the scattering screen., Comment: Accepted by The Astrophysical Journal; 13 pages, 2 figures