Continuum Loop Research Articles

X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures

The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning across 100° on the sky, is still being debated. The northern-most part of Loop I, known as the North Polar Spur (NPS), is the brightest arm and is even clearly visible in the ROSAT X-ray sky map. In this paper, we present a comprehensive review on the X-ray observations of the Fermi bubbles and their possible association with the NPS and Loop I structures. Using uniform analysis of archival Suzaku and Swift data, we show that X-ray plasma with kT~0.3 keV and low metal abundance (Z~0.2 Z◉) is ubiquitous in both the bubbles and Loop I and is naturally interpreted as weakly shock-heated Galactic halo gas. However, the observed asymmetry of the X-ray-emitting gas above and below the GC has still not been resolved; it cannot be fully explained by the inclination of the axis of the Fermi bubbles to the Galactic disk normal. We argue that the NPS and Loop I may be asymmetric remnants of a large explosion that occurred before the event that created the Fermi bubbles, and that the soft gamma-ray emission from Loop I may be due to either π0 decay of accelerated protons or electron bremsstrahlung.

Quantum decay and amplification in a non-Hermitian unstable continuum

The decay of a bound state weakly-coupled to a non-Hermitian tight-binding unstable continuum, i.e. a continuum of states comprising energies with positive imaginary part, is theoretically investigated. As compared to quantum decay in an Hermitian continuum, in the non-Hermitian case a richer scenario can be found as a result of non-unitary dynamics. Different behaviors are observed depending on the kind of instability of the continuum. These include complete or fractional decay in convectively-unstable continua, the absence of quantum decay for a bound state with energy embedded in the continuum loop, and unstable (secular) growth with pseudo exponential amplification in the absolutely-unstable regime. Analytical results are presented for a nearest-neighboring tight-binding continuum with asymmetric hopping rates $\kappa_1$ and $\kappa_2$, which shows a transition from convective to absolute instability when the sign $\kappa_1 \kappa_2$ changes from positive to negative. In the convectively unstable regime the model describes the decay of a bound state coupled to a tight-binding lattice with an imaginary gauge field, which shows a pseudo-Hermitian dynamics. In the absolutely-unstable regime, pseudo-Hermitian dynamics is broken and a pseudo exponential secular growth is observed.

Distance to northern high-latitude HI shells

A detailed 3D distribution of interstellar matter in the solar neighborhood is increasingly necessary. As part of a 3D mapping program, we aim at assigning a precise distance to the high-latitude HI gas in particular the northern part (b \geq 55^{circ}) of the shell associated with the conspicuous radio continuum Loop I. This shell is thought to be the expanding boundary of an interstellar bubble inflated and recently reheated by the strong stellar winds of the nearby Scorpius-Centaurus OB. We recorded high-resolution spectra of 30 A-type target stars located at various distances in the direction of the northern part of Loop I. Interstellar NaI 5889-5895 and CaII K-H 3934-3968 {\AA} are modeled and compared with the HI emission spectra from the LAB Survey. About two-thirds of our stellar spectra possess narrow interstellar lines. Narrow lines are located at the velocity of the main, low-velocity Loop 1 HI shell ([-6,+1] km/s in the LSR). Using Hipparcos distances to the target stars, we show that the closest boundary of the b geq+70^{\circ} part of this low-velocity Loop I arch is located at of 98 \pm 6 pc. The corresponding interval for the lower-latitude part (55^{\circ} \leq b \leq 70^{\circ}) is 95-157 pc. However, since the two structures are apparently connected, the lower limit is more likely. At variance with this shell, the second HI structure, which is characterized by LSR Doppler velocities centered at -30 km/s, is NOT detected in any of the optical spectra. It is located beyond 200 parsecs or totally depleted in NaI and CaII. We discuss these results in the light of spherical expanding shells and show that they are difficult to reconcile with simple geometries and a nearby shell center close to the Plane. Instead, this high-latitude gas seems to extend the inclined local chimney wall to high distances from the Plane.

AN OLD SUPERNOVA REMNANT WITHIN AN H II COMPLEX AT ℓ ≈ 173°: FVW 172.8+1.5

We present the results of HI 21-cm line observations to explore the nature of the high-velocity (HV) HI gas at l ~ 173{\circ} . In low-resolution Hi surveys this HV gas appears as faint, wing-like, HI emission that extends to velocities beyond those allowed by Galactic rotation. We designate this feature FVW (Forbidden Velocity Wing) 172.8+1.5. Our high-resolution (3.'4) Arecibo HI observations show that FVW 172.8+1.5 is composed of knots, filaments, and ring-like structures distributed over an area a few degrees in extent. These HV HI emission features are confined within the limits of the HII complex G173+1.5, which is composed of five Sharpless HII regions distributed along a radio continuum loop of size 4{\circ}.4 {\times} 3{\circ}.4, or ~ 138 pc {\times} 107 pc, at a distance of 1.8 kpc. G173+1.5 is one of the largest star-forming regions in the outer Galaxy. We demonstrate that the HV HI gas is well correlated with the radio continuum loop and that the two seem to trace an expanding shell. The expansion velocity of the shell is large (55 km s-1) suggesting that it represents a supernova-remnant (SNR). We derive physical parameters for the shell and show these to be consistent with the object being a SNR. We also detect hot X-ray emitting gas inside the HII complex by analyzing the ROSAT all-sky X-ray background survey data. This also supports the SNR interpretation. We conclude that the HV HI gas and the X-rays are most likely the products of a supernova explosion(s) within the HII complex, possibly in a cluster that triggered the formation of these HII regions.

Performances across Time and Space: Drama in the Global Households of Filipina Transmigrant Workers

AbstractThe separation of transnational domestic workers from their kinship households and their inclusion into new ones is a conflict situation that creates social drama. Contradictions in their positions in these two global households highlight this drama, for example, in their contrasting roles as breadwinners in one household and as domestic workers in the other, as transnational mothers and live‐in caregivers, and as international migrants and domestically confined workers. In this article, I employ Erving Goffman’s (1959) dramaturgical approach, particularly “contrived” and “real” performances, to examine the everyday performances of migrant workers across time and space, that is, vis‐à‐vis their contradictory roles as breadwinners in their left‐behind kinship households in the Philippines and as “maids” in their co‐residential global households in Singapore, over a period of time. I offer the time‐performance continuum loop as a context explaining the variations of domestic workers’ performances. This model captures the initial years of employment as overwhelming the migrants with hardships and poor performances whereas long‐term employment as equipping them with mastery in their performances. My research draws from conventional ethnographic fieldwork among Filipina domestic workers in Singapore, supplemented by a virtual ethnography in an online forum among Singapore employers.

Comments on the D-instanton calculus in [formula omitted] minimal string theory

The FZZT and ZZ branes in ( p , p + 1 ) minimal string theory are studied in terms of continuum loop equations. We show that systems in the presence of ZZ branes (D-instantons) can be easily investigated within the framework of the continuum string field theory developed by Yahikozawa and one of the present authors [M. Fukuma, S. Yahikozawa, Phys. Lett. B 396 (1997) 97, hep-th/9609210]. We explicitly calculate the partition function of a single ZZ brane for arbitrary p. We also show that the annulus amplitudes of ZZ branes are correctly reproduced.

Continuum methods in lattice perturbation theory

We show how methods of continuum perturbation theory can be used to simplify perturbative lattice calculations. We use the technique of asymptotic expansions to expand lattice loop integrals around the continuum limit. After the expansion, all nontrivial dependence on momenta and masses is encoded in continuum loop integrals and the only genuine lattice integrals left are tadpole integrals. Using integration-by-parts relations all of these can be expressed in terms of a small number of master integrals. Four master integrals are needed for bosonic one loop integrals, sixteen in QCD with Wilson or staggered fermions.

Asymptotic expansion of lattice loop integrals around the continuum limit

We present a method of computing any one-loop integral in lattice perturbation theory by systematically expanding around its continuum limit. At any order in the expansion in the lattice spacing, the result can be written as a sum of continuum loop integrals in analytic regularization and a few genuine lattice integrals (``master integrals''). These lattice master integrals are independent of external momenta and masses and can be computed numerically. At the one-loop level, there are four master integrals in a theory with only bosonic fields, seven in HQET and sixteen in QED or QCD with Wilson fermions.

Further results on geometric operators in quantum gravity

We investigate some properties of geometric operators in canonical quantum gravity in the connection approach à la Ashtekar, which are associated with the volume, area and length of spatial regions. We give the motivations for the construction of analogous discretized lattice quantities, compute various quantum commutators of the type [area, volume], [area, length] and [volume, length], and find that they are generally non-vanishing. Although our calculations are performed mostly within a lattice-regularized approach, some are - for special, fixed spin-network configurations - identical to corresponding continuum computations. Comparison with the structure of the discretized theory leads us to conclude that anomalous commutators may be a general feature of operators constructed along similar lines within a continuum loop representation of quantum general relativity; the validity of the lattice approach remains unaffected.

DOUBLE SCALING LIMIT OF THE SUPER-VIRASORO CONSTRAINTS

We obtain the double scaling limit of a set of superloop equations recently proposed to describe the coupling of two-dimensional supergravity to minimal superconformal matter of type (2,4m). The continuum loop equations are described in terms of a [Formula: see text] theory with a Z2-twisted scalar field and a Weyl–Majorana fermion in the Ramond sector. We have computed correlation functions in genus zero, one and partially in genus two. An integrable supersymmetric hierarchy describing our model has not yet been found. We present a heuristic argument showing that the purely bosonic part of our model is described by the KdV hierarchy.

A Giant Stellar-Wind Shell and Star Formation Near the H II Region M16

A large radio continuum loop of diameter was discovered at G16.5+0.7 on the Bonn 2.7 GHz and NRO 10 GHz galactic plane surveys. The loop is associated with the H II region M16, and the diameter is 60 pc at a distance of 2.8 kpc. Figure 1 shows the loop at 2.7 GHz in gray scale. The spectrum is thermal and the total H II mass is estimated at 3×103 M⊙. If the loop is due to a shell of the same diameter, the mean electron density on the shell is about 4 cm−3. The total thermal energy is about 6×1048ergs. The characteristics are summarized in Table 1.