Region Of Galactic Plane Research Articles

Search for Galactic PeV gamma rays with the IceCube Neutrino Observatory

Gamma-ray induced air showers are notable for their lack of muons, compared to hadronic showers. Hence, air shower arrays with large underground muon detectors can select a sample greatly enriched in photon showers by rejecting showers containing muons. IceCube is sensitive to muons with energies above ∼500 GeV at the surface, which provides an efficient veto system for hadronic air showers with energies above 1 PeV. One year of data from the 40-string IceCube configuration was used to perform a search for point sources and a Galactic diffuse signal. No sources were found, resulting in a 90% C.L. upper limit on the ratio of gamma rays to cosmic rays of 1.2×10−3 for the flux coming from the Galactic plane region (−80°≲l≲−30°; −10°≲b≲5°) in the energy range 1.2–6.0 PeV. In the same energy range, point source fluxes with E−2 spectra have been excluded at a level of (E/TeV)2dΦ/dE∼10−12–10−11 cm−2 s−1 TeV−1 depending on source declination. The complete IceCube detector will have a better sensitivity (due to the larger detector size), improved reconstruction, and vetoing techniques. Preliminary data from the nearly final IceCube detector configuration have been used to estimate the 5-yr sensitivity of the full detector. It is found to be more than an order of magnitude better, allowing the search for PeV extensions of known TeV gamma-ray emitters.9 MoreReceived 30 October 2012DOI:https://doi.org/10.1103/PhysRevD.87.062002© 2013 American Physical Society

Conducting the deepest all-sky pulsar survey ever: the all-sky High Time Resolution Universe survey

AbstractThe extreme conditions found in and around pulsars make them fantastic natural laboratories, providing insights to a rich variety of fundamental physics and astronomy. To discover more pulsars we have begun the High Time Resolution Universe (HTRU) survey: a blind survey of the northern sky with the 100-m Effelsberg radio telescope in Germany and a twin survey of the southern sky with the 64-m Parkes radio telescope in Australia. The HTRU is an international collaboration with expertise shared among the MPIfR in Germany, ATNF/CASS and Swinburne University of Technology in Australia, University of Manchester in the UK and INAF in Italy. The HTRU survey uses multi-beam receivers and backends constructed with recent advancements in technology, providing unprecedentedly high time and frequency resolution, allowing us to probe deeper into the Galaxy than ever before. While a general overview of HTRU has been given by Keith at this conference, here we focus on three further aspects of HTRU discoveries and highlights. These include the ‘Diamond-planet pulsar’ binary J1719-1438 and a second similar system recently discovered. In addition, we provide specifications of the HTRU-North survey and an update of its status. In the last section we give an overview of the search for highly-accelerated binaries in the Galactic plane region. We discuss the computational challenges arising from the processing of the petabyte-sized HTRU survey data. We present an innovative segmented search technique which aims to increase our chances of discovering highly accelerated relativistic binary systems, potentially including pulsar-black-hole binaries.

DIRECT MEASUREMENT OF THE ANGULAR POWER SPECTRUM OF COSMIC MICROWAVE BACKGROUND TEMPERATURE ANISOTROPIES IN THEWMAPDATA

Angular power spectrum of the cosmic microwave background (CMB) temperature anisotropies is one of the most important on characteristics of the Universe such as its geometry and total density. Using flat sky approximation and Fourier analysis, we estimate the angular power spectrum from an ensemble of least foreground-contaminated square patches from WMAP W and V frequency band map. This method circumvents the issue of foreground cleaning and that of breaking orthogonality in spherical harmonic analysis due to masking out the bright Galactic plane region, thereby rendering a direct measurement of the angular power spectrum. We test and confirm Gaussian statistical characteristic of the selected patches, from which the first and second acoustic peak of the power spectrum are reproduced, and the third peak is clearly visible albeit with some noise residual at the tail.

A Sino-Germanλ6 cm polarization survey of the Galactic plane

Linearly polarized Galactic synchrotron emission provides valuable information about the properties of the Galactic magnetic field and the interstellar magneto-ionic medium, when Faraday rotation along the line of sight is properly taken into account. We aim to survey the Galactic plane at 6 cm including linear polarization. At such a short wavelength Faraday rotation effects are in general small and the Galactic magnetic field properties can be probed to larger distances than at long wavelengths. The Urumqi 25-m telescope is used for a sensitive 6 cm survey in total and polarized intensities. WMAP K-band (22.8 GHz) polarization data are used to restore the absolute zero-level of the Urumqi U and Q maps by extrapolation. Total intensity and polarization maps are presented for a Galactic plane region of 129 degree < l < 230 degree and |b| < 5 degree in the anti-centre with an angular resolution of 9'5 and an average sensitivity of 0.6 mK and 0.4 mK Tb in total and polarized intensity, respectively. We briefly discuss the properties of some extended Faraday Screens detected in the 6 cm polarization maps. The Sino-German 6 cm polarization survey provides new information about the properties of the magnetic ISM. The survey also adds valuable information for discrete Galactic objects and is in particular suited to detect extended Faraday Screens with large rotation measures hosting strong regular magnetic fields.

Ultra- and hyper-compact H ii regions at 20 GHz

We present radio and infrared observations of 4 hyper-compact HII regions and 4 ultra-compact HII regions in the southern Galactic plane. These objects were selected from a blind survey for UCHII regions using data from two new radio surveys of the southern sky; the Australia Telescope 20 GHz survey (AT20G) and the 2nd epoch Molonglo Galactic Plane Survey (MGPS-2) at 843 MHz. To our knowledge, this is the first blind radio survey for hyper- and ultra-compact HII regions. We have followed up these sources with the Australia Telescope Compact Array to obtain H70-alpha recombination line measurements, higher resolution images at 20 GHz and flux density measurements at 30, 40 and 95 GHz. From this we have determined sizes and recombination line temperatures as well as modeling the spectral energy distributions to determine emission measures. We have classified the sources as hyper-compact or ultra-compact on the basis of their physical parameters, in comparison with benchmark parameters from the literature. Several of these bright, compact sources are potential calibrators for the Low Frequency Instrument (30-70 GHz) and the 100-GHz channel of the High Frequency Instrument of the Planck satellite mission. They may also be useful as calibrators for the Australia Telescope Compact Array, which lacks good non-variable primary flux calibrators at higher frequencies and in the Galactic plane region. Our spectral energy distributions allow the flux densities within the Planck bands to be determined, although our high frequency observations show that several sources have excess emission at 95 GHz (3 mm) that can not be explained by current models.

MIDCOURSE SPACE EXPERIMENTVERSUSIRASTWO-COLOR DIAGRAMS AND THE CIRCUMSTELLAR ENVELOPE-SEQUENCE OF OXYGEN-RICH LATE-TYPE STARS

We present MSX two-color diagrams that can be used to characterize circumstellar environments of sources with good quality MSX colors in terms of IRAS color regions for oxygen-rich stars. With these diagrams we aim to provide a new tool that can be used to study circumstellar environments and to improve detection rates for targeted surveys for circumstellar maser emission similar to the IRAS two-color diagram. This new tool is especially useful for regions in the sky where IRAS was confused, in particular in the Galactic plane and bulge region. Unfortunately, using MSX colors alone does not allow to distinguish between carbon-rich and oxygen-rich objects. An application of this tool on 86 GHz SiO masers shows that for this type of masers an instantaneous detection rate of 60% to 80% can be achieved if target sources are selected according to MSX color (region). Our investigations may have revealed an error in the MSX point source catalog version 2.3. That is, the photometry of the 21.3 $\mu$m (MSX E filter) band for most weak 8.28 $\mu$m (or MSX A filter) band sources seems off by about a factor two (0.5--1 magnitude too bright).

Iron Emission Lines on the Galactic Ridge Observed with Suzaku

In order to elucidate the origin of galactic ridge X-ray emission, we analyzed Suzaku data taken at various regions along the galactic plane, and studied their Fe-K emission line features. Suzaku resolved the Fe line complex into three narrow lines at $\sim$ 6.4 keV, $\sim$ 6.7 keV and $\sim$ 6.97 keV, which are K-lines from neutral (or low-ionized), He-like, and H-like iron respectively. The 6.7 keV line is clearly seen in all of the observed regions, and its longitudinal distribution is consistent with that determined from previous observations. The 6.4 keV emission line was also found in various galactic plane regions ($b\sim0^{\circ}$). Differences in the flux ratios of the 6.4 keV$/$6.7 keV and 6.97 keV$/$6.7 keV lines between the galactic plane and the galactic center regions were studied and its implication was discussed.

Optical identifications of five INTEGRAL hard X-ray sources in the Galactic plane

The results of optical identifications of five hard X-ray sources in the Galactic plane region from the INTEGRAL all-sky survey are presented. The X-ray data on one source (IGRJ20216+4359) are published for the first time. The optical observations were performed with 1.5-m RTT-150 telescope (TUBITAK National Observatory, Antalya, Turkey) and 6-m BTA telescope (Special Astrophysical Observatory, Nizhny Arkhyz, Russia). A blazar, three Seyfert galaxies, and a high-mass X-ray binary are among the identified sources.

Large Scale Structure and Turbulence: The Mopra G333 Survey

We have used the new broadband capabilities of the Mopra telescope to map the distribution of 26 different molecular transitions in an approximately 1 degree square region of the southern Galactic plane (the G333/RCW106 giant molecular cloud complex). The aim is to addresss observationally some of the key questions about the dynamical processes surrounding massive star formation ( e.g. massive stellar winds and large-scale galactic flows) and their relative importance in regulating the star formation process. These dynamical processes help drive the turbulent motions, which are ubiquitous in giant molecular clouds (GMCs). The multi-molecular line nature of this survey is what distinguishes it from similar surveys and is crucial for gaining a clear picture of the energetics and dynamics of the gas. Investigating and understanding the chemistry of this region is a necessary part of the project if the molecular line observations are to be interpreted physically.

On the contribution of point sources to the Galactic ridge X-ray emission

We analyzed deep Chandra observations of the Galactic plane region centered at l=28.55, b=-0.03 with the aim to obtain the best possible constraints on the contribution of weak point sources to the Galactic ridge X-ray emission (GRXE) in this region. We demonstrate that the vast majority of the detected sources are Galactic in origin and are probably cataclysmic variables and coronally active stars. We use the number-flux function of detected sources to constrain the luminosity function of Galactic X-ray sources in the range 1e30--1e32 erg/s and find good agreement with the luminosity function of sources in the Solar vicinity. The fraction of the total flux at energies 1--7 keV resolved into point sources at the current sensitivity level is ~25%. Excluding the expected contribution of extragalactic sources, ~19% of the GRXE is due to point Galactic sources with interstellar absorption corrected fluxes higher than 1.2e-15 erg/s/cm^2in the energy band 1-7 keV.

Common Correlations between 60, 100, and 140$\, {\mu \mathrm {m}}$ Intensities in the Galactic Plane and Magellanic Clouds

Abstract We investigated the far-infrared SED of the Galaxy and the Magellanic Clouds by using the COBE (COsmic Background Explorer)/DIRBE (Diffuse InfraRed Background Experiment) ZSMA (Zodi-Subtracted Mission Average) maps at wavelengths of 60$\, {\mu \mathrm {m}}$, 100$\, {\mu \mathrm {m}}$, and 140$\, {\mu \mathrm {m}}$. We analyzed three regions: the galactic plane region with the galactic latitude $\vert b\vert &amp;lt; 5^{\circ}$, the Large Magellanic Cloud region, and the Small Magellanic Cloud region. Because the dust optical depth is much smaller in the far-infrared than in the visible, we could observe cumulative far-infrared radiation from regions with various interstellar radiation field in the line of sight. As a consequence of considering such an effect, we found a common far-infrared color correlation between the 140–100$\, {\mu \mathrm {m}}$ and 100–60$\, {\mu \mathrm {m}}$ intensity ratios in all three galaxies. Although this color correlation cannot be explained by any existing model, it fits very well the far-infrared color of nearby star-forming galaxies.

ChandraDeep X‐Ray Observation of a Typical Galactic Plane Region and Near‐Infrared Identification

Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I), we have carried out a deep hard X-ray observation of the Galactic plane region at (l,b) approx. (28.5 deg,0.0 deg), where no discrete X-ray source has been reported previously. We have detected 274 new point X-ray sources (4 sigma confidence) as well as strong Galactic diffuse emission within two partidly overlapping ACIS-I fields (approx. 250 sq arcmin in total). The point source sensitivity was approx. 3 x 10(exp -15)ergs/s/sq cm in the hard X-ray band (2-10 keV and approx. 2 x 10(exp -16) ergs/s/sq cm in the soft band (0.5-2 keV). Sum of all the detected point source fluxes account for only approx. 10 % of the total X-ray fluxes in the field of view. In order to explain the total X-ray fluxes by a superposition of fainter point sources, an extremely rapid increase of the source population is required below our sensitivity limit, which is hardly reconciled with any source distribution in the Galactic plane. Therefore, we conclude that X-ray emission from the Galactic plane has truly diffuse origin. Only 26 point sources were detected both in the soft and hard bands, indicating that there are two distinct classes of the X-ray sources distinguished by the spectral hardness ratio. Surface number density of the hard sources is only slightly higher than observed at the high Galactic latitude regions, strongly suggesting that majority of the hard X-ray sources are active galaxies seen through the Galactic plane. Following the Chandra observation, we have performed a near-infrared (NIR) survey with SOFI at ESO/NTT to identify these new X-ray sources. Since the Galactic plane is opaque in NIR, we did not see the background extragalactic sources in NIR. In fact, only 22 % of the hard sources had NIR counterparts which are most likely to be Galactic origin. Composite X-ray energy spectrum of those hard X-ray sources having NIR counterparts exhibits a narrow approx. 6.7 keV iron emission line, which is a signature of Galactic quiescent cataclysmic variables (CVs).

INTEGRAL insight into the inner parts of the Galaxy. High mass X-ray binaries

Since its launch INTEGRAL has devoted a significant fraction of its observing time to the Galactic plane region. We present the results of INTEGRAL observations of the inner spiral arms of the Galaxy (Norma, Scutum and Sagittarius) with attention to high mass X-ray binaries. The increased sensitivity of the survey and possibility to detect absorbed sources significantly enlarged our sample of HMXBs in comparison with previous studies. For some absorbed sources we present for the first time high quality broadband (1-100 keV) energy spectra. We confirm pulsations of the X-ray flux of IGR J16358-4726, discovered by CHANDRA, and report discovery of pulsations with a period of $228\pm6$ sec from IGR J16465-4507. We confirm that the Galactic high mass X-ray binary distribution is significantly different from the distribution of low mass X-ray binaries concentrated in the Galactic Center. A large fraction of detected high mass X-ray binaries are absorbed sources.

The Galactic plane region near $\ell$ = 93°

New Canadian Galactic Plane Survey radio continuum, ROSAT X-ray, and optical line observations of supernova remnant (SNR) 3C 434.1 (G94.0+1.0) are presented. A radio spectrum of index $\alpha=0.4$ (where $S\propto \nu ^{-\alpha }$) confirms this SNR's emission signature as predominantly synchrotron, and suggests the SNR is in the Sedov expansion phase. The morphology of the remnant is compared in X-ray, optical, and radio continuum, and the brightest emission in all three wavelength regimes is from the eastern hemisphere of 3C 434.1, which marks where the SNR shock is interacting with the inside wall of its stellar wind bubble (SWB) home. The system is determined to be 4.5 kpc distant, residing in the Perseus Arm Spiral shock. From a deep H α mosaic of the region, $\lambda $656 nm H α line emission is observed that correlates well with radio synchrotron emission and anticorrelates with X-ray emission from the SNR. The origin of this optical emission is likely dense ($n_{\rm e}=40$ cm -3 ) cooling $\ion{H}{ii}$ from the wall of the SWB, where the SNR shock has penetrated and become radiative ($v_{\rm s}\sim 100$ km s -1 ). The X-ray spectrum of this SNR between 0.5 and 2.4 keV is well modelled by a single-temperature thermal plasma ($T_{\rm e}=4.5\times10^{6}$ K, $n_{\rm e}=0.2$ cm -3 ). The magnetic field of the bright radio synchrotron emission region is found (under the assumption of near equipartition) to be $B\sim 15$ μ G, a factor of 3 compression of the ambient ISM field (5 μ G). The westward extension of 3C 434.1 is the result of ongoing free expansion of the shock into the lower density interior of the SWB. I use multiwavelength observations to arrive at a unique solution for an interaction model of 3C 434.1 with the SWB, from which the age ($t=25\,000$ yr) and mass ejected in the explosion ($M_{\rm ej}=15.5$ $M_{\odot }$) are determined. I also find an initial blast-wave velocity of 1350 km s -1 , typical of type 1b SNe.

Hard X-ray survey of the Galactic plane region in Crux: A catalog of sources

This paper belongs to a series of papers devoted to a hard X-ray survey of the sky. We analyze a large set of observations of the Galactic plane region in Crux with the IBIS telescope onboard the INTEGRAL observatory. We have detected 47 sources. There are 12 active galactic nuclei and 11 and 6 galactic binary systems with high-mass and low-mass optical companions, respectively, among the identified objects. Thirteen objects remain unidentified.

High Galactic latitude polarized emission at 1.4 GHz and implications for cosmic microwave background observations

We analyse the polarized emission at 1.4 GHz in a 3° x 3° area at high Galactic latitude (b ∼ -40°). The region, centred in (a = 5 h , δ = -49°), was observed with the Australia Telescope Compact Array (ATCA) radio-interferometer, whose 3-30 arcmin angular sensitivity range allows the study of scales appropriate for cosmic microwave background polarization (CMBP) investigations. The angular behaviour of the diffuse emission is analysed through the E- and B-mode angular power spectra. These follow a power law C X l lβ X with slopes β E = -1.97 ± 0.08 and β B = -1.98 ± 0.07. The emission is found to be approximately a factor 25 fainter than in Galactic plane regions. The comparison of the power spectra with other surveys indicates that this area is intermediate between strong and negligible Faraday rotation effects. A similar conclusion can be reached by analysing both the frequency and Galactic latitude behaviours of the diffuse Galactic emission of the 408-1411 MHz Leiden survey data. We present an analysis of the Faraday rotation effects on the polarized power spectra and find that the observed power spectra can be enhanced by a transfer of power from large to small angular scales. The extrapolation of the spectra to 32 and 90 GHz of the cosmic microwave background (CMB) window suggests that Galactic synchrotron emission leaves the CMBP E-mode uncontaminated at 32 GHz. The level of the contamination at 90 GHz is expected to be more than 4 orders of magnitude below the CMBP spectrum. Extrapolating to the relevant angular scales, this region also appears adequate for investigation of the CMBP B-modes for models with tensor-to-scalar fluctuation power ratio T/S ≥ 0.01. We also identify polarized point sources in the field, providing a nine object list, which is complete down to the polarized flux limit of S p lim = 2 mJy.

The Galactic Plane region near $\mathsf{\ell = 93\degr}$

New Canadian Galactic Plane Survey λ21 cm H  line observations towards supernova remnant (SNR) 3C 434.1 (G94.0+1.0) are presented. We find a fragmented and thin-walled atomic hydrogen shell inside which the SNR is seen to be contained at v �− 80 km s −1 , which we report to be a highly evolved stellar wind bubble (SWB) associated with the remnant. A dark area in the midst of otherwise bright line emission is also seen near −71 km s −1 . An absorption profile to the extragalactic continuum source 4C 51.45 (superimposed on the shell's north face) allows us to probe the shell's optical depth, kinetic temperature and expansion velocity. The material in the dark area has the same properties as material in the fragmented shell, suggesting that the dark area is actually the far-side cap of the shell seen absorbing emission from warm background gas, the first instance of H  Self Absorption (HISA) seen in such a structure. We show that the kinematic distance of 10 kpc derived from a flat Galactic rotation model is highly improbable, and that this bubble/SNR system is most likely resident in the Perseus Spiral Arm, lying 5.2 kpc distant. We model the SWB shell in three dimensions as a homologously expanding ellipsoid. Physical and dynamical characteristics of the bubble are determined, showing its advanced evolutionary state. Finally, from a photometric search for one or more stars associated with the SWB, we determine that three B0V stars and one O4V star currently inhabit this bubble, and that the progenitor of 3C 434.1 was at latest also an O4 type star.

MIRAX: a Brazilian X-ray astronomy satellite mission

We describe the “Monitor e Imageador de Raios-X” (MIRAX), an X-ray astronomy satellite mission proposed by the high-energy astrophysics group at the National Institute for Space Research (INPE) in Brazil to the Brazilian Space Agency. MIRAX is an international collaboration that includes, besides INPE, the University of California San Diego, the University of Tübingen in Germany, the Massachusetts Institute of Technology and the Space Research Organization Netherlands. The payload of MIRAX will consist of two identical hard X-ray cameras (10–200 keV) and one soft X-ray camera (2–28 keV), both with angular resolution of ∼5–7 ′. The basic objective of MIRAX is to carry out continuous broadband imaging spectroscopy observations of a large source sample (∼9 months/yr) in the central Galactic plane region. This will allow the detection, localization, possible identification, and spectral/temporal study of the entire history of transient phenomena to be carried out in one single mission. MIRAX will have sensitivities of ∼ 5 mCrab/day in the 2–10 keV band (∼2 times better than the All Sky Monitor on Rossi X-ray Timing Explorer) and 2.6 mCrab/day in the 10–100 keV band (∼40 times better than the Earth Occultation technique of the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory). The MIRAX spacecraft will weigh about 200 kg and is expected to be launched in a low-altitude (∼600 km) circular equatorial orbit around 2007/2008.

Near‐infrared identification of the dimmest X‐ray sources on the Galactic plane with the ESO/NTT SOFI camera

We have carried out a deep X-ray observation on a typical Galactic plane region with the Chandra ACIS-I instrument with unprecedented sensitivity and spatial resolution, and detected 274 unidentified X-ray point sources in the \~500 arcmin2 region. In order to identify these new X-ray sources, we have carried out a near infrared follow-up observation using ESO/NTT infrared camera on 2002/7/28 and 2002/7/29. Initial results are briefly reported.

Field Brown Dwarfs & GAIA

Because of their very red colours and intrinsic faintness, field brown dwarfs will represent a small but valuable subset of the GAIA catalogue. The return of the astrometric satellite is expected to be important because of the inherent difficulty of obtaining good parallaxes in general and for this class of objects in particular. Our first estimates show that, due to the photometric sensitivity of the astrometric CCD (ASM1) towards relatively blue objects, GAIA is unlikely to detect field brown dwarfs that have not been already seen is previous near-IR surveys, to the notable exception of the galactic plane region. The real advantage of GAIA over ground-based surveys will be the very accurate (to within a few percents) astrometric data for a few thousands brown dwarfs. These data should permit a detailed mapping of the transition region between stellar and substellar regimes, together with the kinematical and density patterns of the youngest brown dwarfs in our neighbourhood.