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Discovery of Very High Energy Gamma Radiation from IC 443 with the MAGIC Telescope
We report the detection of a new source of very high energy (VHE;Eγ>=100 GeV) γ-ray emission located close tothe Galactic plane, MAGIC J0616+225, which is spatially coincident withsupernova remnant IC 443. The observations were carried out with theMAGIC telescope in the periods 2005 December-2006 January and 2006December-2007 January. Here we present results from this source, leadingto a VHE γ-ray signal with a statistical significance of 5.7σ in the 2006/2007 data and a measured differential γ-rayflux consistent with a power law, described asdNγ/(dAdtdE)=(1.0+/-0.2)×10-11(E/0.4TeV)-3.1+/-0.3 cm-2 s-1TeV-1. We briefly discuss the observational technique usedand the procedure implemented for the data analysis. The results areplaced in the context of the multiwavelength emission and the molecularenvironment found in the region of IC 443.
| Spitzer Spectral Line Mapping of Supernova Remnants. I. Basic Data and Principal Component Analysis
We report the results of spectroscopic mapping observations carried outtoward small (1'×1') regions within thesupernova remnants W44, W28, IC 443, and 3C 391 using the InfraredSpectrograph (IRS) of the Spitzer Space Telescope. These observations,covering the 5.2-37 μm spectral region, have led to the detection ofa total of 15 fine-structure transitions of Ne+,Ne++, Si+, P+, S, S++,Cl+, Fe+, and Fe++; the S(0)-S(7) purerotational lines of molecular hydrogen; and the R(3) and R(4)transitions of hydrogen deuteride. In addition to these 25 spectrallines, the 6.2, 7.7, 8.6, 11.3, and 12.6 μm PAH emission bands werealso observed. Most of the detected line transitions have proven strongenough to map in several sources, providing a comprehensive picture ofthe relative distribution of the various line emissions observable inthe Spitzer IRS bandpass. A principal component analysis of thespectral-line maps reveals that the observed emission lines fall intofive distinct groups, each of which may exhibit a distinct spatialdistribution: (1) lines of S and H2(J>2) (2) theH2 S(0) line; (3) lines of ions with appearance potentialsless than 13.6 eV; (4) lines of ions with appearance potentials greaterthan 13.6 eV, not including S++; (5) lines of S++.Lines of group 1 likely originate in molecular material subject to aslow, nondissociative shock that is driven by the overpressure withinthe supernova remnant, and lines in groups 3-5 are associated primarilywith dissociative shock fronts with a range of (larger) shockvelocities. The H2 S(0) line shows a low-density diffuseemission component and, in some sources, a shock-excited component.
| A search for 22-GHz H2O masers in supernova remnants
We have examined 18 known supernova remnants for evidence of the22.235-GHz water maser spectral line, using the 20-m telescope at theOnsala observatory in Sweden. No evidence of such emission wasdiscovered above the background noise in any of the observations. Wehave developed a radiative transfer water maser model for the shockedregions of supernova remnants in order to determine why this emissionwas not detected. The model indicates an insignificant amount of22.235-GHz gain; the gain lengths are far too short to allow theformation of detectable water masers from these objects. We predict thatonly in unusual environments can 22-GHz water masers be detected aroundsupernova remnants.
| The X-Ray Structure and Spectrum of the Pulsar Wind Nebula Surrounding PSR B0540-69.3
We present the first spatially resolved spectral study of anextragalactic pulsar wind nebula (PWN), that surrounding the 50 mspulsar B0540-69.3 in the Large Magellanic Cloud, using the ACISinstrument on board the Chandra X-ray Observatory. The spectralproperties of the PWN change at a radius of ~5", corresponding to ashell detected optically in [O III]. Within this radius, the spectra arewell characterized by a simple power law, whose spectral index variesstrongly with radius, so that the effective size of the nebula decreaseswith increasing photon energy. These X-ray measurements support the ideathat the [O III] shell represents an outer skin surrounding the windnebula, analogous to that seen in the Crab Nebula. We use thesize-energy relation and radial variability of the X-ray spectral indexto estimate PWN parameters, including the radial dependence of themagnetic field, and the average ratio of electromagnetic to particleflux.
| Birth Kick Distributions and the Spin-Kick Correlation of Young Pulsars
Evidence from pulsar wind nebula symmetry axes and radio polarizationobservations suggests that pulsar motions correlate with the spindirections. We assemble this evidence for young isolated pulsars andshow how it can be used to quantitatively constrain birth kickscenarios. We illustrate by computing several plausible, but idealized,models where the momentum thrust is proportional to the neutrino coolingluminosity of the proto-neutron star. Our kick simulations include theeffects of pulsar acceleration and spin-up and our maximum likelihoodcomparison with the data constrains the model parameters. The fit to thepulsar spin and velocity measurements suggests that (1) the anisotropicmomentum required amounts to ~10% of the neutrino flux, (2) while aprekick spin of the star is required, the preferred magnitude is small10-20 rad s-1, so that for the best-fit models (3) the bulkof the spin is kick-induced with Ω¯~120 rad s-1and (4) the models suggest that the anisotropy emerges on a timescaleτ~1-3 s.
| Tracing high energy radiation with molecular lines near deeply embedded protostars
Aims.The aim is to probe high energy radiation emitted by deeplyembedded protostars. Methods: Submillimeter lines of CN, NO,CO+ and SO^+, and upper limits on SH+ and N2O areobserved with the James Clerk Maxwell Telescope in two high-mass and upto nine low-mass young stellar objects and compared with chemicalmodels. Results: Constant fractional abundances derived from radiativetransfer modeling of the line strengths are x(CN) ≈ a few×10-11-10-8, x(NO) ≈10-9-10-8 and x(CO^+) ≈10-12-10-10. SO+ has abundances of afew × 10-11 in the high-mass objects and upper limitsof ≈10-12-10-11 in the low-mass sources. Allabundances are up to 1-2 orders of magnitude higher if the molecularemission is assumed to originate mainly from the inner region(≲1000 AU) of the envelope. For high-mass sources, the CN,SO+ and CO+ abundances and abundance ratios arebest explained by an enhanced far-ultraviolet (FUV) field impacting gasat temperatures of a few hundred K. The observed column densitiesrequire that this region of enhanced FUV has scales comparable to theobserving beam, such as in a geometry in which the enhanced FUVirradiates outflow walls. For low-mass sources, the requiredtemperatures within the FUV models of T ≳ 300 K are much higherthan found in models, so that an X-ray enhanced region close to theprotostar (r ≲ 500 AU) is more plausible. Gas-phase chemical modelsproduce more NO than observed, suggesting an additional reductionmechanism not included in current models. Conclusions: The observed CN,CO+ and SO+ abundances can be explained witheither enhanced X-rays or FUV fields from the central source. High-masssources likely have low opacity regions that allow the FUV photons toreach large distances from the central source. X-rays are suggested tobe more effective than FUV fields in the low-mass sources. The observedabundances imply X-ray fluxes for the Class 0 objects of LX≈ 1029-1031 erg s-1, comparable tothose observed from low-mass Class I protostars. Spatially resolved dataare needed to clearly distinguish the effects of FUV and X-rays forindividual species.Appendices are only available in electronic form at http://www.aanda.org
| Mrk 609: resolving the circumnuclear structure with near-infrared integral field spectroscopy
Aims.We present first results of near-infrared (NIR) J and H + KESO-SINFONI integral field spectroscopy of the compositestarburst/Seyfert 1.8 galaxy Mrk 609. The data were taken during thescience verification period of SINFONI. We aim to investigate themorphology and excitation conditions within the central 2 kpc.Additional Nobeyama 45 m CO(1-0) data are presented, which we used toestimate the molecular gas mass. The source was selected from a sampleof SDSS/ROSAT-based, X-ray bright AGN with redshifts of 0.03 < z <1 that are suitable for adaptive optics observations. This sample allowsfor a detailed study of the NIR properties of the nuclear and hostenvironments with high spectral and spatial resolution. Methods:Integral field spectroscopy with SINFONI delivers simultaneous spatialand spectral coverage of the circumnuclear environment. The NIR light isinfluenced less by dust extinction than by optical light and issensitive to mass- dominating stellar populations. Furthermore, severalNIR emission lines allow us to distinguish between Seyfert and starburstactivities. Results: Our NIR data reveal a complex emission-linemorphology that is possibly associated with a nuclear bar seen in thereconstructed continuum images. The detections of [Si VI] and a broadPaα component are clear indicators of the presence of an accretingsuper-massive black hole at the center of Mrk 609. In agreement withprevious observations, we find that the circumnuclear emission is notsignificantly extincted. Analysis of the high angular-resolution,molecular hydrogen emission and [Fe II] emission reveals the LINERcharacter of the nucleus. The large H2 gas mass deduced from the CO(1-0)observation provides the fuel needed to feed the starburst and Seyfertactivity in Mrk 609. Conclusions: High angular resolution imagingspectroscopy provides an ideal tool for resolving the nuclear andstarburst contributions in active galaxies. We show that Mrk 609exhibits LINER features that appear to be hidden in visible/NIR spectrawith larger apertures.Based on ESO-VLT SINFONI science verification 60.A-9041(A) and NobeyamaRadio Observatory 45 m telescope observations.
| Diffusive synchrotron radiation from pulsar wind nebulae
Diffusive synchrotron radiation (DSR) is produced by charged particlesas they random walk in a stochastic magnetic field. The spectrum of theradiation produced by particles in such fields differs substantiallyfrom those of standard synchrotron emission because the correspondingparticle trajectories deviate significantly from gyration in a regularfield. The Larmor radius, therefore, is no longer a good measure of theparticle trajectory. In this paper, we analyse a special DSR regimewhich arises as highly relativistic electrons move through magneticfields which have only random structure on a wide range of spatialscales. Such stochastic fields arise in turbulent processes, and arelikely present in pulsar wind nebulae (PWNe). We show that DSR generatedby a single population of electrons can reproduce the observedbroad-band spectra of PWNe from the radio to the X-ray, in particularproducing relatively flat spectrum radio emission as is usually observedin PWNe. DSR can explain the existence of several break frequencies inthe broad-band emission spectrum without recourse to breaks in theenergy spectrum of the relativistic particles. The shape of theradiation spectrum depends on the spatial spectrum of the stochasticmagnetic field. The implications of the presented DSR regime for PWNphysics are discussed.
| The Radio Spectra of the Compact Sources in Arp 220: A Mixed Population of Supernovae and Supernova Remnants
We report the first detection at multiple radio wavelengths (13, 6, and3.6 cm) of the compact sources within both nuclei of the ultraluminousinfrared galaxy Arp 220, presenting radio spectra of the 18 detectedsources. In just over half of these, we find that these spectra andother properties are consistent with the standard model of powerful TypeIIn supernovae interacting with their preexplosion stellar wind. Therate of appearance of new radio sources identified with these supernovaevents suggests that an unusually large fraction of core-collapsesupernovae in Arp 220 are highly luminous, possibly implying a radicallydifferent stellar initial mass function or stellar evolution compared togalactic disks. Another possible explanation invokes very short(~3×105 yr) intense (~103 Msolaryr-1) star formation episodes with a duty cycle of ~10%. Asecond group of our detected sources, consisting of the brightest andlongest monitored sources at 18 cm, do not easily fit the radiosupernova model. These sources show a range of spectral indexes from-0.2 to -1.9. We propose that these are young supernova remnants thathave just begun interacting with a surrounding ISM with a densitybetween 104 and 105 cm-3. One source isprobably resolved at 3.6 cm wavelength with a diameter 0.9 pc. In thewestern nucleus we estimate that the ionized component of the ISM givesrise to foreground free-free absorption with opacity at 18 cm of <0.6along the majority of lines of sight. Other sources may be affected byabsorption with opacity in the range 1-2. These values are consistentwith previous models as fitted to the radio recombination lines and thecontinuum spectrum.
| [Fe II] and H2 Filaments in the Supernova Remnant G11.2-0.3: Supernova Ejecta and Presupernova Circumstellar Wind
We present the results of near-infrared imaging and spectroscopicobservations of the young core-collapse supernova remnant (SNR)G11.2-0.3. In the [Fe II] 1.644 μm image, we first discover long,clumpy [Fe II] filaments within the radio shell of the SNR, togetherwith some faint, knotty features in the interior of the remnant. Thefilaments are thick and roughly symmetric with respect to thenortheast-southwest elongation axis of the central pulsar wind nebula.We have detected several [Fe II] lines and a H I Brγ line towardthe peak position of the bright southeastern [Fe II] filament. Thederived extinction is large (AV=13 mag), and it is thebrightest [Fe II] 1.644 μm filament detected toward SNRs to date. Byanalyzing two [Fe II] 1.644 μm images obtained 2.2 yr apart, wedetect a proper motion corresponding to an expansion rate of0.035''+/-0.013'' yr-1 (830+/-310 kms-1). In addition to the [Fe II] features, we also discovertwo small H2 2.122 μm filaments. One is bright and alongthe southeastern boundary of the radio shell, while the other is faintand just outside its northeastern boundary. We have detected theH2 (2-1) S(3) line toward the former filament and derive anexcitation temperature of 2100 K. We suggest that the H2filaments are dense clumps in a presupernova circumstellar wind swept upby the SNR shock, while the [Fe II] filaments are probably composed ofboth shocked wind material and shocked supernova (SN) ejecta. Thedistribution of [Fe II] filaments may indicate that the SN explosion inG11.2-0.3 was asymmetric, as in Cassiopeia A. Our results support thesuggestion that G11.2-0.3 is a remnant of a SN IIL/b interacting with adense red supergiant wind.
| Kinematics of the Molecular Hydrogen Associated with the Supernova Remnant IC 443
We present high angular resolution (0.86") observations of thekinematics of the molecular hydrogen in one of the zones of interactionof a molecular cloud with the Galactic supernova remnant IC 443. Thishas been done using a scanning Fabry-Pérot interferometer at thenear-IR line at 2.12 μm of molecular hydrogen. The kinematics derivedfrom the Fabry-Pérot velocity cubes thus obtained allows us tohave a better insight into the type of motions (and thereby shocks) ofmolecular gas at smaller scales in this zone of interaction, taking intoaccount the complex morphology and kinematics of the knots, diffuse gas,and filaments that comprise the molecular clumps. A combination ofJ-type and C-type shocks seems to explain the kinematics, in agreementwith the conclusions of Snell et al. based on the large amount of datagathered on the line ratios and abundances of several neutral andmolecular species.Based on observations obtained at the Observatorio AstronómicoNacional at San Pedro Mártir, BC, Mexico.
| XMM-Newton Detection of the Supernova Remnant G337.2+0.1
We report the first XMM-Newton detection of the SNR candidate G337.2+0.1(=AX J1635.9-4719). The object shows centrally filled and diffuse X-rayemission. The emission peaks in the hard 3.0-10.0 keV band. A spatiallyresolved spectral study confirms that the column density of the centralpart of the SNR is about NH~5.9(+/-1.5)×1022cm-2 and its X-ray spectrum is well represented by a singlepower law with a photon index Γ=0.96+/-0.56. The nondetection ofline emission in the central spectrum is consistent with synchrotronradiation from a population of relativistic electrons. Detailed spectralanalysis indicates that the outer region is highly absorbed and quitesofter than the inner region, withNH~16.2(+/-5.2)×1022 cm-2 andkT=4.4(+/-2.8) keV. Such characteristics are already observed in otherX-ray plerions. On the basis of the morphological and spectral X-rayinformation, we confirm the SNR nature of G337.2+0.1 and suggest thatthe central region of the source is a pulsar wind nebula, originated byan energetic although yet undetected pulsar, that is currently losingenergy at a rate of ~1036 ergs s-1.
| Green Bank Telescope Observations of IC 443: The Nature of OH (1720 MHz) Masers and OH Absorption
We present spectral line observations of the ground-state transitions ofhydroxyl (OH) toward supernova remnant (SNR) IC 443 carried out with theGreen Bank Telescope. Weak, extended OH (1720 MHz) maser emission withOH (1667, 1665, 1612 MHz) absorption is detected along the southernextent of the remnant where no bright compact maser sources have beenpreviously observed. These newly detected SNR-type masers are coincidentwith well-known molecular clumps and a ridge of shocked H2emission indicative of the SNR shock front interacting with the adjacentmolecular cloud. Simultaneous observation of all four ground-statetransitions of OH permits us to fit physical conditions of the shockedgas at the interaction site. A simple two-component model for the lineprofiles yields the physical parameters for detected regions of maseremission, including excitation temperature, OH column density, andfilling factor. Observed line profiles suggest the shock is largelypropagating toward the line of sight in the region of these newlyidentified weak masers. The implications of shock geometry and physicalparameters in producing spatially extended OH maser emission in SNRs areexplored. We also present VLA radio continuum observations at 330 MHzfor comparison with OH line observations of the remnant.
| Faint X-Ray Structure in the Crab Pulsar Wind Nebula
We report on a Chandra observation of the Crab Nebula that gives thefirst clear view of the faint boundary of the Crab's X-ray-emittingpulsar wind nebula. There is structure in all directions. Fingers,loops, bays, and the south pulsar jet all indicate that eitherfilamentary material or the magnetic field is controlling therelativistic electrons. In general, spectra soften as distance from thepulsar increases but do not change rapidly along linear features. Thisis particularly true for the pulsar jet. The termination of the jet isabrupt; the east side is close to an [O III] optical filament, which maybe blocking propagation on this side. We argue that linear features haveordered magnetic fields and that the structure is determined by thesynchrotron lifetime of particles diffusing perpendicular and parallelto the magnetic field. We find no significant evidence for thermalX-rays inside the filamentary envelope.
| Chandra ACIS Spectroscopy of N157B: A Young Composite Supernova Remnant in a Superbubble
We present a Chandra ACIS observations of N157B, a young supernovaremnant (SNR) located in the 30 Doradus star formation region of theLarge Magellanic Cloud. This remnant contains the most energetic pulsarknown (PSR J053747.39-691020.2 E˙=4.8×1038 ergss-1), which is surrounded by a X-ray-bright nonthermal nebulathat likely represents a toroidal pulsar wind terminal shock observededge-on. Two of the eight pointlike X-ray sources detected in theobservation are shown to have near-IR and optical counterparts (within0.5" offsets), which are identified as massive stellar systems in theCloud. We confirm the nonthermal nature of the comet-shaped X-rayemission feature and show that the spectral steepening of this featureaway from the pulsar is quantitatively consistent with synchrotroncooling of shocked pulsar wind particles flowing downstream at a bulkvelocity close to the speed of light. Around the cometary nebula weunambiguously detect a spatially resolved thermal component, whichaccounts for about 1/3 of the total 0.5-10 keV flux from the remnant.This thermal component is distributed among various clumps ofmetal-enriched plasma embedded in the low surface brightnessX-ray-emitting diffuse gas. The relative metal enrichment patternsuggests that the mass of the supernova progenitor is >~20Msolar. A comparison of the X-ray data with Hubble SpaceTelescope optical images now suggests that the explosion site is closeto a dense cloud, against which a reflection shock is launched. Theinteraction between the reflected material and the nebula has likelyproduced both its cometary shape and the surrounding thermal emissionenhancement. SNR N157B is apparently expanding into the hot low-densityinterior of the surrounding superbubble formed by the young OBassociation LH 99, as revealed by Spitzer mid-infrared images. Thisscenario naturally explains the exceptionally large sizes of both thethermal and nonthermal components, as well as the lack of an outer shellof the SNR. However, the real situation in the region is likely to bemore complicated. We find that a partially round soft X-ray-emittingclump with distinct spectral properties may result from a separateoxygen-rich remnant. These results provide a rare glimpse into the SNRstructure and evolution in a region of recent star formation.
| Supernova Remnants in the Magellanic Clouds. VII. Infrared Emission from Supernova Remnants
We have used the instruments on the Spitzer Space Telescope to study theLarge Magellanic Cloud supernova remnants (SNRs) N11L, N44, N49, N206,N63A, and N157B. The two large SNRs N44 and N206 were not detected inany Spitzer IRAC or MIPS wave bands; the remainder were detected at oneor more wavelengths. In particular, the SNRs N49 and N63A each hadfeatures that were evident in all available IRAC and MIPS bands. Each ofthese two also displayed faint limb emission in the MIPS 24 μm bandonly. Spitzer IRS spectra obtained for the N49 SNR showed a number ofprominent lines, with little continuum contribution. We thereforesuggest that N49, and possibly N63A, are dominated by line emission,with thermal emission from hot dust being at most a secondary component.
| Radio emission from shell-type supernova remnants
The evolution of the radio emission of shell-type Supernova remnants(SNRs) is modeled within the framework of the simple and commonly usedassumptions that the mechanism of diffusive shock acceleration (DSA) isresponsible for generating radio emitting electrons and that themagnetic field is the typical interstellar field compressed at theshock. It is considered that electrons are injected into the mechanismin test-particle regime directly from the high energy tail of thedownstream Maxwellian distribution function. The model can be applied tomost of the observed SNRs because the majority of detected SNRs areshell-types and have a more or less spherical shape and are sources ofnonthermal radio emission. It is shown that the model successfullyexplains the many averaged observational properties of evolvedshell-type SNRs. In particular, the radio surface brightness (Σ)evolves with diameter as ˜ D-(0.3 div 0.5), while thebounding shock is strong (Mach number is M ≥10), followed by steepdecrease (steeper than ˜ D-4.5) for M <10. Suchevolution of the surface brightness with diameter and its strongdependence on the environmental parameters strongly reduce theusefulness of Σ - D relations as a tool for determining thedistances to SNRs. The model predicts no radio emission from SNRs in thelate radiative stage of evolution and the existence of radio-quiet butrelatively active SNRs is possible. Our model easily explains verylarge-diameter radio sources such as the Galactic Loops and thecandidates for Hypernova radio remnants. The model predicts that most ofthe observed SNRs with Σ1 GHz ⪉ 10 - 20W m{- 2} sr{- 1} Hz{- 1} are located ina tenuous phase of the ISM. The model also predicts the existence of apopulation of 150-250 pc SNRs with Σ 1 GHz ⪉10 - 22 W m{- 2} sr{- 1} Hz{-1} if the kinetic energy of the explosion is ˜1051 erg. From the comparison of the model results with thestatistics of evolved shell-type SNRs, we were able to estimate thefraction of electrons accelerated from the thermal pool in the range(3div 11) × 10 - 4. If acceleration takes placedirectly from the high energy tail of the downstream Maxwelliandistribution function, then the corresponding injection momentum isestimated as p_inj˜ (2.7-3)\cdot p_th.
| XMM-Newton Observations of the Supernova Remnant IC 443. I. Soft X-Ray Emission from Shocked Interstellar Medium
The shocked interstellar medium around IC 443 produces strong X-rayemission in the soft energy band (E<~1.5 keV). We present an analysisof such emission as observed with the EPIC MOS cameras on board the XMM-Newton observatory, with the purpose to find clear signatures of theinteractions with the interstellar medium (ISM) in the X-ray band, whichmay complement results obtained in other wavelengths. We found that thegiant molecular cloud mapped in CO emission is located in the foregroundand gives an evident signature in the absorption of X-rays. This cloudmay have a torus shape, and the part of torus interacting with the IC443 shock gives rise to 2MASS Ks emission in the southeast.The measured density of emitting X-ray-shocked plasma increases towardthe northeastern limb, where the remnant is interacting with an atomiccloud. We found an excellent correlation between emission in the 0.3-0.5keV band and bright optical/radio filament on large spatial scales. Thepartial shell structure seen in this band therefore traces the encounterwith the atomic cloud.
| The X-Ray Structure of the Pulsar Bow Shock G189.22+2.90 in the Supernova Remnant IC 443
We present a deep observation with the Chandra X-Ray Observatory of theneutron star bow shock G189.22+2.90 in the supernova remnant (SNR) IC443. Our data confirm the cometary morphology and central point sourceseen previously, but also reveal considerable new structure.Specifically, we find that the X-ray nebula consists of two distinctcomponents: a ``tongue'' of bright emission close to the neutron star,enveloped by a larger, fainter ``tail.'' We interpret the tongue andtail as delineating the termination shock and the postshock flow,respectively, as previously identified also in the pulsar bow shockG359.23-0.82 (``the Mouse''). However, for G189.22+2.90 the tongue ismuch less elongated than for the Mouse, while the tail is much broader.These differences are consistent with the low Mach number, M<~2,expected for a neutron star moving through the hot gas in a SNR'sinterior, supporting the case for a physical association betweenG189.22+2.90 and IC 443. We resolve the standoff distance between thestar and the head of the bow shock, which allows us to estimate a spacevelocity for the neutron star of ~230 km s-1, independent ofdistance. We detect thermal emission from the neutron star surface at atemperature of 102+/-22 eV, which is consistent with the age of SNR IC443 for standard neutron star cooling models. We also identify twocompact knots of hard emission located 1"-2" north and south of theneutron star.
| Spitzer Observations of Hydrogen Deuteride
We report the detection of interstellar hydrogen deuteride (HD) towardthe supernova remnant IC 443, and the tentative detection of HD towardthe Herbig-Haro objects HH 54 and HH 7 and the star-forming region GGD37 (Cep A West). Our detections are based upon spectral line mappingobservations of the R(3) and R(4) rotational lines of HD, at restwavelengths of 28.502 and 23.034 μm, respectively, obtained using theInfrared Spectrograph on board the Spitzer Space Telescope. The HDR(4)/R(3) line intensity ratio promises to be a valuable probe of thegas pressure in regions where it can be observed. The derivedHD/H2 abundance ratios are(1.19+0.35-0.24)×10-5,(1.80+0.54-0.32)×10-5, and(1.41+0.46-0.33)×10-5,respectively (68.3% confidence limits, based upon statistical errorsalone) for IC 443 (clump C), HH 54, and HH 7. If HD is the onlysignificant reservoir of gas-phase deuterium in these sources, theinferred HD/H2 ratios are all consistent with a gas-phaseelemental abundance[nD/nH]gas~7.5×10-6, afactor of 2-3 below the values obtained previously from observations ofatomic deuterium in the Local Bubble and the Galactic halo. However,similarly low gas-phase deuterium abundances have been inferredpreviously for molecular gas clouds in the Orion region and in atomicclouds along sight lines within the Galactic disk to stars more distantthan 500 pc from the Sun.
| Radio Spectral Index Variations in HB 21
New observations are presented of the supernova remnant HB 21 at 408 and1420 MHz made with the Synthesis Telescope (ST) of the Dominion RadioAstrophysical Observatory. A new method of spectral index analysis ispresented that allows for removal of point-source contamination at thespatial resolution of the higher spatial resolution map. This is a greatimprovement in point-source contamination removal (by a factor >~10),and allows more detailed spectral index variation studies thanpreviously possible. Significant spatial variations in spectral indexare found in HB 21. Different physical mechanisms for spectral indexchanges are considered, including a detailed consideration of ionizationlosses in the dense molecular gas interacting with HB 21. The lack ofdetailed spatial correlation of spectral flattening with positions ofshocked clumps indicates that absorption by thermal plasma is thepreferred mechanism.
| Enhanced Abundances in Three Large-Diameter Mixed-Morphology Supernova Remnants
We present an X-ray study of three mixed-morphology (MM) supernovaremnants (SNRs)-HB 21, CTB 1, and HB 3-using archival ASCA and ROSATdata. These data are complemented by archival Chandra X-Ray Observatorydata for CTB 1 and XMM-Newton X-Ray Observatory data for HB 3. Thespectra from HB 21 and HB 3 are well described with a single-temperaturethermal plasma in ionization equilibrium, while a two-temperaturethermal plasma is found in CTB 1. We found enhanced abundances in allthree SNRs. The elemental abundance of Mg is clearly enhanced in CTB 1,while HB 21 has enhanced abundances of Si and S. The situation is not asclear in HB 3-the plasma in this SNR either has significantly enhancedabundances of O, Ne, and Mg, or has marginally enhanced abundances of Mgand underabundant Fe. We discuss the plausibility of mixed-morphologySNR models for the three SNRs, and the presence of enhanced abundances.We revise a list of MM SNRs and their properties, compare the three SNRsstudied here with other members of this class, and discuss the presenceof enhanced elemental abundances in MM SNRs. We also report the ASCAdetection of a compact source in the southern part of HB 3. The sourcespectrum is consistent with a power law with a photon index of ~2.7, andan unabsorbed X-ray flux of ~10-12 ergs cm-2s-1 in the 0.5-10.0 keV band. The column density toward thissource differs from that toward the SNR, and it is therefore unlikelythat they are related.
| Cosmic ray proton spectrum below 100 TeV in the local region
The propagation of cosmic ray (CR) protons in the Galaxy is discussedunder the framework of a three-dimensional convection-diffusion model.Starting with the assumption of a uniform and continuous distribution ofCR sources injecting CRs continuously in the Galaxy and by invoking asupernova explosion at various distances from the Earth, it is foundthat only those sources located within a distance of ~1.5 kpc canproduce appreciable temporal fluctuations in the CR proton flux observednear the Earth. So, the construction of the local CR proton spectrum isdiscussed by separating the contributions of the distant sources fromthat of the nearby sources. The contribution from the distant sources istreated in the framework of a continuous source distribution model inboth space and time, but that of the nearby sources in a discretespace-time source model. The study predicts the presence of at least oneold nearby source with a characteristic age of ~105 yrlocated at a distance of ~0.1 kpc to explain the observed proton fluxbelow ~100 GeV.
| An Atomic and Molecular Study of the Interstellar Medium Around the Supernova Remnant RCW 103
We report on the detection of HCO+ and 12COemission in the rotational transition J = 1-0 in the vicinity of theshock front at the southern border of the supernova remnant RCW 103,where previous infrared observations suggest an interaction with amolecular cloud. The observations were carried out with the AustralianMillimeter Radiotelescope at Mopra. We observed a depletion ofHCO+ behind the supernova shock front. In addition, westudied the interstellar medium over an extended region towards RCW 103based on archival λ 21 cm Hi line observations from the AustraliaTelescope Compact Array (ATCA) and the Parkes Telescope. No atomic gaswas observed in emission in coincidence with the molecular feature. Thisabsence was interpreted in terms of self-absorption processes.
| Evidence for Shocked Molecular Gas in the Galactic Supernova Remnant CTB 109 (G109.1-1.0)
We report the detection of molecular clouds around the X-ray-brightinterior feature in the Galactic supernova remnant (SNR) CTB 109(G109.1-1.0). This feature, called the ``lobe,'' has been previouslysuggested to be the result of an interaction of the SNR shock wave witha molecular cloud complex. We present new high-resolution X-ray datafrom the Chandra X-Ray Observatory and new high-resolution CO data fromthe Five College Radio Astronomy Observatory that show the region ofinteraction with the cloud complex in greater detail. The CO data revealthree clouds around the lobe in the velocity interval -57 kms-1
| Ammonia in infrared dark clouds
Context: .While low mass clouds have been relatively well studied, ourpicture of high-mass star formation remains unclear. Infrared DarkClouds appear to be the long sought population of cold and denseaggregations with the potential of harbouring the earliest stages ofmassive star formation. Up to now there has been no systematic study onthe temperature distribution, velocity fields, chemical and physicalstate toward this new cloud population. Aims: .Knowing theseproperties is crucial for understanding the presence, absence and thevery potential of star formation. The present paper aims at addressingthese questions. We analyse temperature structures and velocity fieldsand gain information on their chemical evolution. Methods: .Wemapped the (J,K) = (1, 1) and (2, 2) inversion transitions of ammonia in9 infrared dark clouds. Our observations allow the most reliabledetermination of gas temperatures in IRDCs to date. Results: .Thegas emission is remarkably coextensive with the extinction seen atinfrared wavelengths and with the submillimeter dust emission. Ourresults show that IRDCs are on average cold (T < 20 K) and havevariations among the different cores. IRDC cores are in virialequilibrium, are massive (M > 100 {M}_ȯ), highly turbulent (1-3km s-1) and exhibit significant velocity structure(variations around 1-2 km s-1 over the cloud). Conclusions: .We find an increasing trend in temperature from IRDCs withhigh ammonia column density to high mass protostellar objects andUltracompact Hii regions, stages of early warm high-mass star formation.The linewidths of IRDCs are smaller than those observed in high massprotostellar objects and hot core/Ultracompact Hii regions. On basis ofthis sample, and by comparison of the ammonia gas properties within acloud and between different clouds, we infer that while active starformation is not yet pervasive in most IRDCs, local condensations mightcollapse in the future or have already begun forming stars.
| Molecular Gas Distribution around the Supernova Remnant G40.5 0.5
The distribution of dense molecular gas around the supernova remnantG40.5 0.5 has been investigated by radio spectroscopic observations inthe CO (J = 1-0) transition. The molecular gas is found to extend overthe entire region of G40.5 0.5. A molecular shell, with a diameter of~26', coincides with the ionized gas as revealed by the cm-radioobservations. This coincidence, along with the velocity discontinuityfollowing the shell, provides direct evidence for interaction betweenthe ionized gas and the dense molecular gas. No clear evidence forcosmic-ray acceleration can be identified from this SNR as previouslysuggested, due to positional uncertainty in relating the SNR shelldefined by CO to the EGRET gamma-ray sources, GRO J1904+06, from thegamma-ray observations.
| An X-Ray Search for Compact Central Sources in Supernova Remnants. II. Six Large-Diameter SNRs
We present the second in a series of studies in which we have searchedfor undiscovered neutron stars in supernova remnants (SNRs). This paperdeals with the six largest SNRs in our sample, too large for Chandra orXMM-Newton to cover in a single pointing. These SNRs are nearby, withtypical distances of <1 kpc. We therefore used the ROSAT BrightSource Catalog and past observations in the literature to identify X-raypoint sources in and near the SNRs. Out of 54 sources, we wereimmediately able to identify optical/IR counterparts to 41 from existingdata. We obtained Chandra snapshot images of the remaining 13 sources.Of these, 10 were point sources with readily identified counterparts,two were extended, and one was not detected in the Chandra observationbut is likely a flare star. One of the extended sources may be a pulsarwind nebula, but if so it is probably not associated with the nearbySNR. We are then left with no identified neutron stars in these six SNRsdown to luminosity limits of ~1032 ergs s-1. Theselimits are generally less than the luminosities of typical neutron starsof the same ages, but are compatible with some lower luminosity sourcessuch as the neutron stars in the SNRs CTA 1 and IC 443.
| Subaru IR Echelle Spectroscopy of Herbig-Haro Driving Sources. I. H2 and [Fe II] Emission
We present infrared echelle spectroscopy of three Herbig-Haro (HH)driving sources (SVS 13, B5-IRS 1, and HH 34 IRS) using Subaru IRCS. Thelarge diameter of the telescope and wide spectral coverage of thespectrograph allowed us to detect several H2 and [Fe II]lines in the H and K bands. These include H2 lines arisingfrom v=1-3 and J=1-11, and [Fe II] lines with upper level energies ofE/k=(1.1-2.7)×104 K. For all objects the outflow isfound to have two velocity components: (1) a high-velocity (-70 to -130km s-1) component (HVC), seen in [Fe II] or H2emission and associated with a collimated jet; and (2) a low-velocity(-10 to -30 km s-1) component (LVC), which is seen inH2 emission only and is spatially more compact. Such akinematic structure resembles optical forbidden emission line outflowsassociated with classical T Tauri stars, whereas the presence ofH2 emission reflects the low-excitation nature of theoutflowing gas close to these protostars. The observed H 2flux ratios indicate a temperature of (2-3)×103 K and agas density of 105 cm-3 or more, supporting shocksas the heating mechanism. B5-IRS 1 exhibits faint extended emissionassociated with the H2-LVC, in which the radial velocityslowly increases with distance from the protostar (by ~20 kms-1 at ~500 AU). This is explained as warm molecular gasentrained by an unseen wide-angled wind. The [Fe II] flux ratiosindicate electron densities to be ~104 cm-3 orgreater, similar to forbidden-line outflows associated with classical TTauri stars. Finally, the kinematic structure of the [Fe II] emissionassociated with the base of the B5-IRS 1 and HH 34 IRS outflows is shownto support disk-wind models.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
| A Spitzer Space Telescope Infrared Survey of Supernova Remnants in the Inner Galaxy
Using Infrared Array Camera (IRAC) images at 3.6, 4.5, 5.8, and 8 μmfrom the GLIMPSE Legacy science program on the Spitzer Space Telescope,we searched for infrared counterparts to the 95 known supernova remnantsthat are located within Galactic longitudes65deg>|l|>10deg and latitudes|b|<1deg. Eighteen infrared counterparts were detected.Many other supernova remnants could have significant infrared emissionbut are in portions of the Milky Way too confused to allow theseparation of bright H II regions and pervasive mid-infrared emissionfrom atomic and molecular clouds along the line of sight. Infraredemission from supernova remnants originates from synchrotron emission,shock-heated dust, atomic fine-structure lines, and molecular lines. Thedetected remnants are G11.2-0.3, Kes 69, G22.7-0.2, 3C 391, W44, 3C 396,3C 397, W49B, G54.4-0.3, Kes 17, Kes 20A, RCW 103, G344.7-0.1,G346.6-0.2, CTB 37A, G348.5-0.0, and G349.7+0.2. The infrared colorssuggest emission from molecular lines (nine remnants), fine-structurelines (three remnants), polycyclic aromatic hydrocarbons (fourremnants), or a combination; some remnants feature multiple colors indifferent regions. None of the remnants are dominated by synchrotronradiation at mid-infrared wavelengths. The IRAC-detected sampleemphasizes remnants interacting with relatively dense gas, for whichmost of the shock cooling occurs through molecular or ionic lines in themid-infrared.
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