Remnants from Gamma-Ray Bursts

We model the intermediate time evolution of a "jetted" gamma-ray burst by two blobs of matter colliding with the interstellar medium. We follow the hydrodynamical evolution of this system numerically and calculate the bremsstrahlung and synchrotron images of the remnant. We find that for a burst energy of $10^{51}$ erg the remnant becomes spherical after $\sim 5000$ years when it collects $\sim 50M_\odot$ of interstellar mass. This result is independent of the exact details of the GRB, such as the opening angle. After this time a gamma-ray burst remnant has an expanding sphere morphology. The similarity to a supernova remnant makes it difficult distinguish between the two at this stage. The expected number of non-spherical gamma-ray burst remnants is $\sim0.05$ per galaxy for a beaming factor of 0.01 and a burst energy of $10^{51}$ erg. Our results suggest that that the double-shell object DEM L 316 is not a GRB remnant.Comment: 16 pages, 9 figures, Substantial revisions, Accepted by Ap

The Origin of X-shaped Radio Galaxies: Clues from the Z-symmetric Secondary Lobes

Existing radio images of a few X-shaped radio galaxies reveal Z-symmetric morphologies in their weaker secondary lobes which cannot be naturally explained by either the galactic merger or radio-lobe backflow scenarios, the two dominant models for these X-shaped radio sources. We show that the merger picture can explain these morphologies provided one takes into account that, prior to the coalescence of their supermassive black holes, the smaller galaxy releases significant amounts of gas into the ISM of the dominant active galaxy. This rotating gas, whose angular momentum axis will typically not be aligned with the original jets, is likely to provide sufficient ram pressure at a distance ~10 kpc from the nucleus to bend the extant jets emerging from the central engine, thus producing a Z-symmetry in the pair of radio lobes. Once the two black holes have coalesced some 10^7 yr later, a rapid reorientation of the jets along a direction close to that of the orbital angular momentum of the swallowed galaxy relative to the primary galaxy would create the younger primary lobes of the X-shaped radio galaxy. This picture naturally explains why such sources typically have powers close to the FR I/II break. We suggest that purely Z-symmetric radio sources are often en route to coalescence and the concomitant emission of substantial gravitational radiation, while X-shaped ones have already merged and radiated.Comment: 12 pages, 1 compressed figure; accepted for publication in ApJ Letter

On the origin of X-shaped radio galaxies

After a brief, critical review of the leading explanations proposed for the small but important subset of radio galaxies showing an X-shaped morphology (XRGs) we propose a generalized model, based on the jet-shell interaction and spin-flip hypotheses. The most popular scenarios for this intriguing phenomenon invoke either hydrodynamical backflows and over-pressured cocoons or rapid jet reorientations, presumably from the spin-flips of central engines following the mergers of pairs of galaxies, each of which contains a supermassive black hole (SMBH). We confront these models with a number of key observations and thus argue that none of the models is capable of explaining the entire range of salient observational properties of XRGs, although some of the arguments raised in the literature against the spin-flip scenario are probably not tenable. We then propose here a new scenario which also involves galactic mergers but would allow the spin of the central engine to maintain its direction. Motivated by the detailed multi-band observations of the nearest radio galaxy, Centaurus A, this new model emphasizes the role of interactions between the jets and the shells of stars and gas that form and rotate around the merged galaxy and can cause temporary deflections of the jets, occasionally giving rise to an X-shaped radio structure. Although each of the models is likely to be relevant to a subset of XRGs, the bulk of the evidence indicates that most of them are best explained by the jet-shell interaction or spin-flip hypotheses.Comment: 19 pages, major revision including two Appendices and a Table, accepted in Research in Astronomy and Astrophysic

Protein phosphatase 5 modulates SMAD3 function in the transforming growth factor-beta pathway

Protein phosphatases play a key role in balancing the cellular responses to the transforming growth factor-beta (TGF beta) signals. Several protein phosphatases have been attributed roles in the regulation of the TGF beta pathway. Among these. PPM1A is the only phosphatase reported to dephosphorylate SMAD2/3 in the nucleus. However we observed PPM1A exclusively in the cytoplasmic fractions independently of TOM treatment in all cells tested. These observations imply that a bona fide nuclear SMAD2/3 phosphatase remains elusive. In this study, we report a role for protein phosphatase 5 (PP5) in the TGF beta pathway. We identified PP5 as an interactor of SMAD2/3. Interestingly, in mouse embryonic fibroblast cells derived from PP5-null mice, TGF beta-induced transcriptional responses were significantly enhanced. Rather surprisingly, this enhancement is due to the increased levels of SMAD3 protein observed in PP5-null MEFs compared to the wild type. No differences in the levels of SMAD3 transcripts were observed between the wild-type and PPS-null MEFs. While PP5 is capable of dephosphoiylating SMAD3-tail in overexpression assays, we demonstrate that its activity is essential in controlling SMAD3 protein levels in MEFs. We propose that PP5 regulates the TGF beta pathway in MEFs by regulating the expression of SMAD3 protein levels. (C) 2012 Elsevier Inc. All rights reserved. NOTICE: this is the author’s version of a work that was accepted for publication in Cellular Signalling. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Cellular Signalling, [VOL.24, ISSUE 11, (2012)] DOI 10.1016/j.cellsig.2012.07.003</p

Reflection confocal nanoscopy using a super-oscillatory lens

A Superoscillatory lens (SOL) is known to produce a sub-diffraction hotspot which is useful for high-resolution imaging. However, high-energy rings called sidelobes coexist with the central hotspot. Additionally, SOLs have not yet been directly used to image reflective objects due to low efficiency and poor imaging properties. We propose a novel reflection confocal nanoscope which mitigates these issues by relaying the SOL intensity pattern onto the object and use conventional optics for detection. We experimentally demonstrate super-resolution by imaging double bars with 330 nm separation using a 632.8 nm excitation and a 0.95 NA objective. We also discuss the enhanced contrast properties of the SOL nanoscope against a laser confocal microscope, and the degradation of performance while imaging large objects.Comment: 17 pages, 15 figures, supplementary include

A Study of Compact Radio Sources in Nearby Face-on Spiral Galaxies. II. Multiwavelength Analyses of Sources in M51

We report the analysis of deep radio observations of the interacting galaxy system M51 from the Very Large Array, with the goal of understanding the nature of the population of compact radio sources in nearby spiral galaxies. We detect 107 compact radio sources, 64% of which have optical counterparts in a deep H$\alpha$ Hubble Space Telescope image. Thirteen of the radio sources have X-ray counterparts from a {\em Chandra} observation of M51. We find that six of the associated H$\alpha$ sources are young supernova remnants with resolved shells. Most of the SNRs exhibit steep radio continuum spectral indices onsistent with synchrotron emission. We detect emission from the Type Ic SN 1994I nearly a decade after explosion: the emission ($160\pm22 \mu$Jy beam$^{-1}$ at 20 cm, $46\pm11 \mu$Jy beam$^{-1}$ at 6cm, $\alpha=-1.02\pm0.28$) is consistent with light curve models for Type Ib/Ic supernovae. We detect X-ray emission from the supernova, however no optical counterpart is present. We report on the analysis of the Seyfert 2 nucleus in this galaxy, including the evidence for bipolar outflows from the central black hole.Comment: 22 pages, 8 figures (5 color) in separate files, AASTeX. Full resolution figures and preprint may be obtained by contacting [email protected]. AJ accepte

Was the Cosmic Web of Protogalactic Material Permeated by Lobes of Radio Galaxies During the Quasar Era?

Evidence for extended active lifetimes (> 10^8 yr) for radio galaxies implies that many large radio lobes were produced during the `quasar era', 1.5 < z < 3, when the comoving density of radio sources was 2 -- 3 dex higher than the present level. However, inverse Compton losses against the intense microwave background substantially reduce the ages and numbers of sources that are detected in flux-limited surveys. The realization that the galaxy forming material in those epochs was concentrated in filaments occupying a small fraction of the total volume then leads to the conclusion that radio lobes permeated much of the volume occupied by the protogalactic material during that era. The sustained overpressure in these extended lobes is likely to have played an important role in triggering the high inferred rate of galaxy formation at z > 1.5 and in the magnetization of the cosmic network of filaments.Comment: 5 pages, 0 figures, submitted to ApJ Letters; uses emulateapj