Search

JWST observed the magnetar 4U 0142+61 with the MIRI and NIRCam instruments within a 77 min time interval on 2022 September 20-21. The low-resolution MIRI spectrum and NIRCam photometry show that the spectrum in the wavelength range 1.4-11 $\mu$m range can be satisfactorily described by an absorbed power-law model, $f_{\nu}\propto \nu^{-\alpha}$, with a spectral slope $\alpha =0.96\pm0.02$, interstellar extinction $A_V= 3.9\pm0.2$, and normalization $f_0 = 59.4\pm 0.5$ $\mu$Jy at $\lambda = 8$ $\mu$m. These observations do not support the passive disk model proposed by Wang et al. (2006), based on the Spitzer photometry, which was interpreted as evidence for a fallback disk from debris formed during the supernova explosion. We suggest a nonthermal origin for this emission and source variability as the most likely cause of discrepancies between the JWST data and other IR-optical observing campaigns. However, we cannot firmly exclude the presence of a large disk with a different dependence of the effective disk temperature on distance from the magnetar. Comparison with the power-law fit to the hard X-ray spectrum above 10 keV, measured by NuSTAR contemporaneously with JWST, shows that the X-ray spectrum is significantly harder. This may imply that the X-ray and IR nonthermal emission come from different sites in the magnetosphere of the magnetar., Comment: Accepted for publication in ApJ

We present a detailed study of the X-ray emission from PSR B1055-52 using XMM-Newton observations from 2019 and 2000. The phase-integrated X-ray emission from this pulsar is poorly described by existing neutron star atmosphere models. Instead, we confirm that, similar to other middle-aged pulsars, the best-fitting spectral model consists of two blackbody components, with substantially different temperatures and emitting areas, and a nonthermal component characterized by a power law. Our phase-resolved X-ray spectral analysis using this three-component model reveals variations in the thermal emission parameters with the pulsar's rotational phase. These variations suggest a nonuniform temperature distribution across the neutron star's surface, including the cold thermal component and probable hot spot(s). Such a temperature distribution can be caused by external and internal heating processes, likely a combination thereof. We observe very high pulse fractions, 60\%--80\% in the 0.7-1.5, keV range, dominated by the hot blackbody component. This could be related to temperature non-uniformity and potential beaming effects in an atmosphere. We find indication of a second hot spot that appears at lower energies (0.15-0.3, keV) than the first hot spot (0.5-1.5, keV) in the X-ray light curves, and is offset by about half a rotation period. This finding aligns with the nearly orthogonal rotator geometry suggested by radio observations of this interpulse pulsar. If the hot spots are associated with polar caps, a possible explanation for their temperature asymmetry could be an offset magnetic dipole and/or an additional toroidal magnetic field component in the neutron star crust, Comment: 20 pages, 14 figures, 4 tables, accepted for publication in ApJ

We present initial results from a JWST survey of the youngest Galactic core-collapse supernova remnant Cassiopeia A (Cas A), made up of NIRCam and MIRI imaging mosaics that map emission from the main shell, interior, and surrounding circumstellar/interstellar material (CSM/ISM). We also present four exploratory positions of MIRI/MRS IFU spectroscopy that sample ejecta, CSM, and associated dust from representative shocked and unshocked regions. Surprising discoveries include: 1) a web-like network of unshocked ejecta filaments resolved to 0.01 pc scales exhibiting an overall morphology consistent with turbulent mixing of cool, low-entropy matter from the progenitor's oxygen layer with hot, high-entropy matter heated by neutrino interactions and radioactivity, 2) a thick sheet of dust-dominated emission from shocked CSM seen in projection toward the remnant's interior pockmarked with small (approximately one arcsecond) round holes formed by knots of high-velocity ejecta that have pierced through the CSM and driven expanding tangential shocks, 3) dozens of light echoes with angular sizes between 0.1 arcsecond to 1 arcminute reflecting previously unseen fine-scale structure in the ISM. NIRCam observations place new upper limits on infrared emission from the neutron star in Cas A's center and tightly constrain scenarios involving a possible fallback disk. These JWST survey data and initial findings help address unresolved questions about massive star explosions that have broad implications for the formation and evolution of stellar populations, the metal and dust enrichment of galaxies, and the origin of compact remnant objects., Comment: 27 pages, 10 figures, now published in ApJL

We have collected a new deep {\it Chandra X-ray Observatory} ({\it CXO}) exposure of PSR B2224+65 and the `Guitar Nebula', mapping the complex X-ray structure. This is accompanied by a new {\it HST} H$\alpha$ image of the head of the Guitar. Comparing the {\it HST} and {\it CXO} structures in 4 epochs over 25 years, we constrain the evolution of the TeV particles that light up the filament. Cross-field diffusion appears to be enhanced, likely by the injected particles, behind the filament's sharp leading edge, explaining the filament width and its evolving surface brightness profile., Comment: 13 pages, 10 figures, accepted for publication in ApJ

The X-ray emission of neutron stars enables a probe of their temperatures, geometries, and magnetospheric properties. The current number of X-ray emitting pulsars is insufficient to rule out observational biases that may arise from poorly known distance, age, or location of the neutron stars. One approach to overcome such biases is to create a distance-limited sample with sufficiently deep observations. With the aim of better sampling of the nearby ($\lesssim$ 2kpc) neutron stars population, we started an XMM-Newton survey of pulsars to measure their X-ray fluxes or derive respective constraining upper limits. We investigated 14 nearby pulsars for potential X-ray counterparts using different energy bands and detectors. In addition to our new XMM-Newton data, we also considered archival data and catalogs. We discuss source properties and also check for alternative counterparts to the X-ray sources. In our new XMM-Newton data, we found two pulsar counterpart candidates with significance above over $4\sigma$ and one candidate with $3.5\sigma$ by combining EPIC camera detection likelihoods. We also report the detection of potential X-ray counterparts to 8 radio pulsars in the 4XMM-DR10 catalog which have not been reported in the literature., Comment: 10 pages, 3 figures, 7 tables, accepted for publication in Astronomy and Astrophysics

We have obtained a deep 670 ks CXO ACIS image of the remarkable pulsar wind nebula (PWN) of PSR J1709-4429, in 4 epochs during 2018-2019. Comparison with an archival 2004 data set provides a pulsar proper motion mu = 13 \pm 3 mas/yr at a PA of 86 \pm 9 degree (1 sigma combined statistical and systematic uncertainties), precluding birth near the center of SNR G343.1-2.3. At the pulsar's characteristic age of 17 kyr, the association can be preserved through a combination of progenitor wind, birth kick and PWN outflow. Associated TeV emission may, however, indicate explosion in an earlier supernova. Inter-epoch comparison of the X-ray images shows that the PWN is dynamic, but we are unable to conclusively measure flow speeds from blob motion. The pulsar has generated a radio/X-ray wind bubble, and we argue that the PWN's long narrow jets are swept back by shocked pulsar wind venting from this cavity. These jets may trace the polar magnetic field lines of the PWN flow, an interesting challenge for numerical modeling., Comment: 11 pages, 8 figures. Accepted for publication in the Astrophysical Journal

PSR J1809-1917 is a young ($\tau=51$ kyr) energetic ($\dot{E}=1.8\times10^{36}$ erg s$^{-1}$) radio pulsar powering an X-ray pulsar wind nebula (PWN) that exhibits morphological variability. We report on the results of a new monitoring campaign by the Chandra X-ray Observatory (CXO), carried out across 6 epochs with a $\sim$7-week cadence. The compact nebula can be interpreted as a jet-dominated outflow along the pulsar's spin axis. Its variability can be the result of Doppler boosting in the kinked jet whose shape changes with time (akin to the Vela pulsar jet). The deep X-ray image, composed of 405 ks of new and 131 ks of archival CXO data, reveals an arcminute-scale extended nebula (EN) whose axis of symmetry aligns with both the axis of the compact nebula and the direction toward the peak of the nearby TeV source HESS J1809-193. The EN's morphology and extent suggest that the pulsar is likely moving through the ambient medium at a transonic velocity. We also resolved a faint 7$'$-long nonthermal collimated structure protruding from the PWN. It is possibly another instance of a "misaligned outflow" (also known as a "kinetic jet") produced by high-energy particles escaping the PWN's confinement and tracing the interstellar magnetic field lines. Finally, taking advantage of the 536 ks exposure, we analyzed the point sources in the J1809 field and classified them using multiwavelength data. None of the classified sources in the field can reasonably be expected to produce the extended TeV flux in the region, suggesting that PSR J1809-1917 is indeed the counterpart to HESS/eHWC J1809-193., Comment: 23 pages, 11 figures, accepted for publication in ApJ

We report on the energy-resolved timing and phase-resolved spectral analysis of X-ray emission from PSR J0659+1414 observed with XMM-Newton and NuSTAR. We find that the new data rule out the previously suggested model of the phase-dependent spectrum as a three-component (2 blackbodies + power-law) continuum, which shows large residuals between $0.3-0.7$ keV. Fitting neutron star atmosphere models or several blackbodies to the spectrum does not provide a better description of the spectrum, and requires spectral model components with unrealistically large emission region sizes. The fits improve significantly if we add a phase-dependent absorption feature with central energy $0.5-0.6$ keV and equivalent width up to $\approx 50$ eV. We detected the feature for about half of the pulse cycle. Energy-resolved pulse profiles support the description of the spectrum with a three-component continuum and an absorption component. The absorption feature could be interpreted as an electron cyclotron line originating in the pulsar magnetosphere and broadened by the non-uniformity of the magnetic field along the line of sight. The significant phase-variability in the thermal emission from the entire stellar surface may indicate multi-polar magnetic fields and a non-uniform temperature distribution. The strongly pulsed non-thermal spectral component detected with NuSTAR in the $3-20$ keV range is well fit by a power-law model with a photon index $\Gamma=1.5\pm0.2$., Comment: 25 pages, 17 figure. Accepted by the Astrophysical Journal

PSR J1809-1917 is a young ($\tau=51$ kyr) energetic ($\dot{E}=1.8\times10^{36}$ erg s$^{-1}$) radio pulsar powering a pulsar wind nebula (PWN). We report on the results of three Chandra X-ray Observatory observations which show that the PWN consists of a small ($\sim 20''$) bright compact nebula (CN) and faint extended emission seen up to $2'$ from the pulsar. The CN is elongated in the northeast-southwest direction and exhibits morphological and flux variability on a timescale of a few months. We also find evidence of small arcsecond-scale jets extending from the pulsar along the same direction, and exhibiting a hard power-law (PL) spectrum with photon index $\Gamma_{\rm jet}=1.2\pm0.1$. The more extended emission and CN share the same symmetry axis, which is also aligned with the direction toward the TeV $\gamma$-ray source HESS J1809--193, supporting their association. The spectrum of the extended nebula (EN) fits an absorbed PL with about the same slope as that of the CN, $\Gamma_{\rm CN}\approx\Gamma_{\rm EN}=1.55\pm0.09$; no spectral changes across the EN's 2 pc extent are seen. The total PWN 0.5-8 keV luminosity is $L_{\rm PWN}\approx 9\times10^{32}$ erg s$^{-1}$, about half of which is due to the EN., Comment: 10 pages, 6 figures, accepted for publication in ApJ

We report on Chandra X-ray Observatory (CXO) observations of the pulsar wind nebula (PWN) associated with PSR B0355+54 (eight observations with a 395 ks total exposure, performed over an 8 month period). We investigated the spatial and spectral properties of the emission coincident with the pulsar, compact nebula (CN), and extended tail. We find that the CN morphology can be interpreted in a way that suggests a small angle between the pulsar spin axis and our line-of-sight, as inferred from the radio data. On larger scales, emission from the 7' (2 pc) tail is clearly seen. We also found hints of two faint extensions nearly orthogonal to the direction of the pulsar's proper motion. The spectrum extracted at the pulsar position can be described with an absorbed power-law + blackbody model. The nonthermal component can be attributed to magnetospheric emission, while the thermal component can be attributed to emission from either a hot spot (e.g., a polar cap) or the entire neutron star surface. Surprisingly, the spectrum of the tail shows only a slight hint of cooling with increasing distance from the pulsar. This implies either a low magnetic field with fast flow speed, or particle re-acceleration within the tail. We estimate physical properties of the PWN and compare the morphologies of the CN and the extended tail with those of other bow shock PWNe observed with long CXO exposures., Comment: 11 pages, 8 figures

PSR J1509-5850 is a middle-aged pulsar with the period P ~ 89 ms, spin-down power Edot = 5.1 x 10^35 erg/s, at a distance of about 3.8 kpc. We report on deep Chandra X-ray Observatory observations of this pulsar and its pulsar wind nebula (PWN). In addition to the previously detected tail extending up to 7' southwest from the pulsar (the southern outflow), the deep images reveal a similarly long, faint diffuse emission stretched toward the north (the northern outflow) and the fine structure of the compact nebula (CN) in the pulsar vicinity. The CN is resolved into two lateral tails and one axial tail pointing southwest (a morphology remarkably similar to that of the Geminga PWN), which supports the assumption that the pulsar moves towards the northeast. The luminosities of the southern and northern outflows are about 1 x 10^33 and 4 x 10^32 erg/s, respectively. The spectra extracted from four regions of the southern outflow do not show any softening with increasing distance from the pulsar. The lack of synchrotron cooling suggests a high flow speed or in-situ acceleration of particles. The spectra extracted from two regions of the northern outflow show a hint of softening with distance from the pulsar, which may indicate slower particle propagation. We speculate that the northern outflow is associated with particle leakage from the bow shock apex into the ISM, while the southern outflow represents the tail of the shocked pulsar wind behind the moving pulsar. We estimate the physical parameters of the observed outflows and compare the J1509-5850 PWN with PWNe of other supersonically moving pulsars., Comment: accepted by ApJ, 13 pages, 15 figures

Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods ($P_{\rm rot}$). M37 was observed almost continuously for five days, for a total of 440.5 ksec, to measure stellar X-ray luminosities ($L_{\mathrm{X}}$), a proxy for coronal activity, across a wide range of masses. The cluster's membership catalog was revisited to calculate updated membership probabilities from photometric data and each star's distance to the cluster center. The result is a comprehensive sample of 1699 M37 members: 426 with $P_{\rm rot}$, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, $R_o = P_{\rm rot}/\tau$, where $\tau$ is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, $L_{\rm X}/L_{\rm bol}$, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500 Myr. We find that fast rotators, for which $R_o<0.09\pm0.01$, show saturated levels of activity, with log($L_{\rm X}/L_{\rm bol}$)$=-3.06\pm0.04$. For $R_o\geq0.09\pm0.01$, activity is unsaturated and follows a power law of the form $R_o^\beta$, where $\beta$=$-2.03_{-0.14}^{+0.17}$. This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4$-$1.3 $M_{\odot}$, $P_{\rm rot}$ in the range 0.4$-$12.8 d, and $L_{\rm X}$ in the range 10$^{28.4-30.5}$ erg s$^{-1}$. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of $\approx$500 Myr., Comment: 21 pages, 22 figures, 8 tables, 2 machine-readable tables (MRT)

We obtained six observations of PSR J1741-2054 using the $Chandra$ ACIS-S detector totaling $\sim$300 ks. By registering this new epoch of observations to an archival observation taken 3.2 years earlier using X-ray point sources in the field of view, we have measured the pulsar proper motion at $\mu =109 \pm 10 {\rm mas\ yr}^{-1}$ in a direction consistent with the symmetry axis of the observed H$\alpha$ nebula. We investigated the inferred past trajectory of the pulsar but find no compelling association with OB associations in which the progenitor may have originated. We confirm previous measurements of the pulsar spectrum as an absorbed power law with photon index $\Gamma$=2.68$\pm$0.04, plus a blackbody with an emission radius of (4.5$^{+3.2}_{-2.5})d_{0.38}$ km, for a DM-estimated distance of $0.38d_{0.38}$ kpc and a temperature of $61.7\pm3.0$ eV. Emission from the compact nebula is well described by an absorbed power law model with a photon index of $\Gamma$ = 1.67$\pm$0.06, while the diffuse emission seen as a trail extending northeast of the pulsar shows no evidence of synchrotron cooling. We also applied image deconvolution techniques to search for small-scale structures in the immediate vicinity of the pulsar, but found no conclusive evidence for such structures., Comment: 7 pages, 8 figures, 4 Tables; Accepted by ApJ

HESS J1809-193 is an extended TeV gamma-ray source in the Galactic Plane. Multiwavelength observations of the HESS J1809-193 field reveal a complex picture. We present results from three CXO and two Suzaku observations of a region in the northeastern outskirts of HESS J1809-193, where enhanced TeV emission has been reported. Our analysis also includes GeV gamma-ray and radio data. One of the X-ray sources in the field is the X-ray binary XTE J1810-189, for which we present the outburst history from multiple observatories and confirm that XTE J1810-189 is a strongly variable type I X-ray burster, which can hardly produce TeV emission. We investigate whether there is any connection between the possible TeV extension of HESS J1809-193 and the sources seen at lower energies. We find that another X-ray binary candidate, Suzaku J1811-1900, and a radio supernova remnant, SNR G11.4-0.1, can hardly be responsible for the putative TeV emission. Our multiwavelength classification of fainter X-ray point sources also does not produce a plausible candidate. We conclude that the northeast extension of HESS J1809-193, if confirmed by deeper observations, can be considered as a dark accelerator - a TeV source without visible counterpart at lower energies., Comment: Accepted for publication in the Astrophysical Journal

We present multi-wavelength observations of the radio magnetar PSR J1622-4950 and its environment. Observations of PSR J1622-4950 with Chandra (in 2007 and 2009) and XMM (in 2011) show that the X-ray flux of PSR J1622-4950 has decreased by a factor of ~50 over 3.7 years, decaying exponentially with a characteristic time of 360 +/- 11 days. This behavior identifies PSR J1622-4950 as a possible addition to the small class of transient magnetars. The X-ray decay likely indicates that PSR J1622-4950 is recovering from an X-ray outburst that occurred earlier in 2007, before the 2007 Chandra observations. Observations with the Australia Telescope Compact Array show strong radio variability, including a possible radio flaring event at least one and a half years after the 2007 X-ray outburst that may be a direct result of this X-ray event. Radio observations with the Molonglo Observatory Synthesis Telescope reveal that PSR J1622-4950 is 8' southeast of a diffuse radio arc, G333.9+0.0, which appears non-thermal in nature and which could possibly be a previously undiscovered supernova remnant. If G333.9+0.0 is a supernova remnant then the estimates of its size and age, combined with the close proximity and reasonable implied velocity of PSR J1622-4950, suggests that these two objects could be physically associated., Comment: 14 pages with 3 tables and 3 figures. Accepted for publication in ApJ

We report on follow-up observations of candidate X-ray bright, radio-quiet isolated neutron stars (INSs) identified from correlations of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) Data Release 4 in Ag\"ueros et al. (2006). We obtained Chandra X-ray Telescope exposures for 13 candidates in order to pinpoint the source of X-ray emission in optically blank RASS error circles. These observations eliminated 12 targets as good INS candidates. We discuss subsequent observations of the remaining candidate with the XMM-Newton X-ray Observatory, the Gemini North Observatory, and the Apache Point Observatory. We identify this object as a likely extragalactic source with an unusually high log(fX/fopt) ~ 2.4. We also use an updated version of the population synthesis models of Popov et al. (2010) to estimate the number of RASS-detected INSs in the SDSS Data Release 7 footprint. We find that these models predict ~3-4 INSs in the 11,000 square deg imaged by SDSS, which is consistent with the number of known INSs that fall within the survey footprint. In addition, our analysis of the four new INS candidates identified by Turner et al. (2010) in the SDSS footprint implies that they are unlikely to be confirmed as INSs; together, these results suggest that new INSs are not likely to be found from further correlations of the RASS and SDSS., Comment: 11 pages, 2 figures, 3 tables; accepted for publication in AJ

We have previously analyzed sensitive mid-infrared observations to establish that the Pipe Nebula has a very low star-formation efficiency. That study focused on YSOs with excess infrared emission (i.e, protostars and pre-main sequence stars with disks), however, and could have missed a population of more evolved pre-main sequence stars or Class III objects (i.e., young stars with dissipated disks that no longer show excess infrared emission). Evolved pre-main sequence stars are X-ray bright, so we have used ROSAT All-Sky Survey data to search for diskless pre-main sequence stars throughout the Pipe Nebula. We have also analyzed archival XMM-Newton observations of three prominent areas within the Pipe: Barnard 59, containing a known cluster of young stellar objects; Barnard 68, a dense core that has yet to form stars; and the Pipe molecular ring, a high-extinction region in the bowl of the Pipe. We additionally characterize the X-ray properties of YSOs in Barnard 59. The ROSAT and XMM-Newton data provide no indication of a significant population of more evolved pre-main sequence stars within the Pipe, reinforcing our previous measurement of the Pipe's very low star formation efficiency., Comment: Accepted for publication in ApJ

The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the entire sky. While X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine the nature of an X-ray source. As a result, large-scale follow-up programs are required to construct samples of known X-ray emitters. We use optical data produced by the Sloan Digital Sky Survey (SDSS) to identify 709 stellar X-ray emitters cataloged in the RASS and falling within the SDSS Data Release 1 footprint. Most of these are bright stars with coronal X-ray emission unsuitable for SDSS spectroscopy, which is designed for fainter objects (g > 15 mag). Instead, we use SDSS photometry, correlations with the Two Micron All Sky Survey and other catalogs, and spectroscopy from the Apache Point Observatory 3.5 m telescope to identify these stellar X-ray counterparts. Our sample of 707 X-ray-emitting F, G, K, and M stars is one of the largest X-ray-selected samples of such stars. We derive distances to these stars using photometric parallax relations appropriate for dwarfs on the main sequence, and use these distances to calculate LX. We also identify a previously unknown cataclysmic variable (CV) as a RASS counterpart. Separately, we use correlations of the RASS and the SDSS spectroscopic catalogs of CVs and white dwarfs (WDs) to study the properties of these rarer X-ray-emitting stars. We examine the relationship between (fX/fg) and the equivalent width of the Hbeta emission line for 46 X-ray-emitting CVs and discuss tentative classifications for a subset based on these quantities. We identify 17 new X-ray-emitting DA (hydrogen) WDs, of which three are newly identified WDs. (abridged), Comment: 23 pages, 15 figures, 8 tables; full catalog available online only

(abridged) We study a previously discovered protostellar source that is deeply embedded and drives an energetic molecular outflow. The source, UYSO1, is located close to IRAS 07029-1215 at a distance of ~1 kpc. The multi-wavelength observations resulted in the detection of a double intermediate-mass protostar at the location of UYSO1. In addition to the associated molecular outflow, with a projected size of 0.25 pc, two intersecting near-infrared jets with projected sizes of 0.4 pc and 0.2 pc were found. However, no infrared counterparts to the driving sources could be detected in sensitive near- to far-infrared observations. In interferometric millimeter observations, UYSO1 was resolved into two continuum sources with high column densities and gas masses of 3.5 Mo and 1.2 Mo, with a linear separation of 4200 AU. We report the discovery of a H2O maser toward one of the two sources. The total luminosity is roughly estimated to be ~50 Lo, shared by the two components, one of which is driving the molecular outflow that has a dynamical timescale of less than a few thousand years. The jets of the two individual components are not aligned. Submillimeter observations show that the region lacks typical hot-core chemistry. We thus find two protostellar objects, whose associated circumstellar and parent core masses are high enough to suggest that they may evolve into intermediate-mass stars. This is corroborated by their association with a very massive and energetic CO outflow, suggesting high protostellar accretion rates. The short dynamical timescale of the outflow, the pristine chemical composition of the cloud core and absence of hot core tracers, the absence of detectable radio continuum emission, and the very low protostellar luminosity argue for an extremely early evolutionary stage., Comment: 10 pages, 10 figures, accepted for publication in A&A; minor changes: typos corrected, revised argument in Section 4

Only seven radio-quiet isolated neutron stars (INSs) emitting thermal X rays are known, a sample that has yet to definitively address such fundamental issues as the equation of state of degenerate neutron matter. We describe a selection algorithm based on a cross-correlation of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) that identifies X-ray error circles devoid of plausible optical counterparts to the SDSS g~22 magnitudes limit. We quantitatively characterize these error circles as optically blank; they may host INSs or other similarly exotic X-ray sources such as radio-quiet BL Lacs, obscured AGN, etc. Our search is an order of magnitude more selective than previous searches for optically blank RASS error circles, and excludes the 99.9% of error circles that contain more common X-ray-emitting subclasses. We find 11 candidates, nine of which are new. While our search is designed to find the best INS candidates and not to produce a complete list of INSs in the RASS, it is reassuring that our number of candidates is consistent with predictions from INS population models. Further X-ray observations will obtain pinpoint positions and determine whether these sources are entirely optically blank at g~22, supporting the presence of likely isolated neutron stars and perhaps enabling detailed follow-up studies of neutron star physics., Comment: Accepted for publication in the AJ; higher resolution figures available at http://www.astro.washington.edu/agueros/pub/

In the course of a comprehensive mm/submm survey of massive star-forming regions, the vicinities of a sample of 47 luminous IRAS sources were closely investigated with SCUBA and IRAM bolometers in order to search for massive protostellar candidates. A particularly interesting object has been found in the surroundings of the bright FIR source IRAS 07029-1215. Follow-up line observations show that the object is cold, that it has a massive envelope, and that it is associated with an energetic molecular outflow. No infrared point source has been detected at its position. Therefore, it is a very good candidate for a member of the long searched-for group of massive protostars., Comment: 17 pages, 6 figures, accepted for publication in ApJ