180 research outputs found
A search for very high energy gamma rays from PSR1706-44 using the Atmospheric Cerenkov Imaging Technique / by Gavin Peter Rowell.
No full textIncludes bibliographical references.ix, 159 p. : ill. ; 30 cm.Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 199
Analysis of the optical-depth-corrected molecular line and diffuse TeV gamma-ray correlation in the Galactic centre
No full textWe explore the correlation of diffuse TeV gamma rays in the Galactic centre with optical-depth-corrected CO(1-0) emission. We present our analysis of the data, in which the 12CO(1-0) molecular line emission is corrected for optical-depth by using the the 13C and 18O isotopes of the CO(1-0) line. Using simple scatter plots, we find no evidence of a correlation with the lower-density tracer. © 2012 American Institute of Physics.David I. Jones, Michael Burton, Paul Jones, Gavin Rowell, and Felix A. Aharonia
A new template background estimate for source searching in TeV gamma-ray astronomy
No full textA new method is described that permits quickly and easily, a 2-dimensional search for TeV -ray sources over large fields of view ( 6 ) with instruments utilising the imaging atmospheric ˇCerenkov technique. It employs as a background estimate, events normally rejected according to a cosmic-ray background rejection criterion based on image shape, but with reconstructed directions overlapping the source of interest. This so-called template background model is demonstrated using example data taken with the stereoscopic HEGRA System of ˇC erenkov Telescopes. Discussion includes comparisons with a conventional background estimate and limitations of the model. The template model is well suited to the search for point-like, moderately extended sources and combinations thereof, and compensates well for localised systematic changes in cosmic-ray background responseG. P. Rowellhttp://www.aanda.org/content/view/98/102/lang,en
Dense gas towards the RXJ1713.7-3946 supernova remnant
No full textA summary of results from a 7 mm-wavelength survey towards the young X-ray and γ-ray-bright supernova remnant, RXJ1713.7-3946 (SNR G347.3-0.5) is presented. Using the Mopra telescope, the high critical density tracer CS(1-0) was targeted, complementing previous Nanten2 molecular gas studies of CO transitions. In hadronic γ-ray emission scenarios (p-p interactions), the mass of cosmic ray target material available is an important factor, so we estimate the mass of dense gas towards RX J1713.7-3946. Also of interest was the shock-tracing molecule, SiO. Although there was no evidence of SiO emission physically excited by the RXJ1713.7-3946 shock, a chance-discovery of vibrationallyexcited SiO(1-0) emission is likely to be a maser that is associated with an evolved star. © 2012 American Institute of Physics.Nigel I. Maxted, Gavin P. Rowell, Bruce R. Dawson, Michael G. Burton, Yasuo Fukui, Andrew J. Walsh, Akiko Kawamura, Hidetoshi Sano and Jasmina Lazendi
Eleanor & Park by R. Rowell
No full textRowell, Rainbow. Eleanor & Park. New York, NY: St. Martin’s Press, 2013. Print.“Disintegrated. Like something had gone wrong beaming her onto the Starship Enterprise. If you’ve ever wondered what that feels like, it’s a lot like melting, but more violent. Even in a million different pieces, Eleanor could still feel Park holding her hand. Could still feel his thumb exploring her palm. She sat completely still because she didn’t have any other option. She tried to remember what kind of animals paralyzed their prey before they ate them...Maybe Park had paralyzed her with his ninja magic, his Vulcan handhold, and now he was going to eat her. That would be awesome” (p. 72).Eleanor & Park is a smart, funny young adult romance that takes place over one school year in 1986. Told in alternating voices, this is the story of two teenagers who don’t quite fit in. Eleanor comes from the wrong side of the tracks and has big red hair and wears all the wrong clothes. Park is half Asian, loves comic books and alternative music. Eleanor has had a rough life, living with her mother, her mother’s new husband, and her four siblings in a rundown house without even a door on the bathroom. Park’s family is much more stable, yet his military veteran father and immigrant mother do not quite know what to make of Park, with his black clothes, eye makeup and love of music. Pushed together on Eleanor’s first day of school when she takes the only seat left on the bus, the one beside Park, they bond over comic books and mixed tapes and help each other survive the tumult that is high school, and life. The characters, young and old, in Eleanor & Park are far from perfect, and their imperfections and weirdness make them likeable. Young adult readers will identify with these outsiders and will be cheering for them from the beginning. Some of the pop culture references may not be recognized by today’s young adults; however, the specific music and comic book references are less important than what they represent in the story. Rowell has written a nuanced and balanced story that will appeal to young adult fans of realistic and romantic fiction. The ending is satisfying without being easy and Rowell has created characters that are believable and heartwarming. Eleanor & Park won the 2013 Boston Globe Horn Book Award for Best Fiction Book. Rainbow Rowell is the author of Attachments (2011) and the recently released Fangirl (2013). The book contains some scenes with some mild sexuality, violence, and language. It will make an excellent addition to any school or public library collection for young adult readers ages 14 and up.Highly Recommended: 4 out of 4 starsReviewed by: Joanne de GrootJoanne de Groot is a teacher, librarian and mom who loves to read children\u27s literature (especially with her two kids!). She is an Adjunct Assistant Professor in the Department of Elementary Education at the University of Alberta and teaches primarily in the Teacher-Librarianship by Distance Learning program. Joanne teaches courses on resources for children and young adults, children\u27s literature, educational technology and Web 2.0, and contemporary literacies
Ammonia excitation imaging of shocked gas towards the W28 gamma-ray source HESS J1801-233
No full textWe present 12 mm Mopra observations of the dense (>103 cm−3) molecular gas towards the north-east of the W28 supernova remnant (SNR). This cloud is spatially well matched to the TeV gamma-ray source HESS J1801−233 and is known to be an SNR-molecular cloud interaction region. Shock-disruption is evident from broad NH3 (1,1) spectral linewidths in regions towards the W28 SNR, while strong detections of spatially extended NH3 (3,3), NH3(4,4) and NH3(6,6) inversion emission towards the cloud strengthen the case for the existence of high temperatures within the cloud. Velocity dispersion measurements and NH3(n,n)/(1,1) ratio maps, where n = 2, 3, 4 and 6, indicate that the source of disruption is from the side of the cloud nearest to the W28 SNR, suggesting that it is the source of cloud-disruption. Towards part of the cloud, the ratio of ortho to para-NH3 is observed to exceed 2, suggesting gas-phase NH3 enrichment due to NH3 liberation from dust-grain mantles. The measured NH3 abundance with respect to H2 is ∼(1.2 ± 0.5) × 10−9, which is not high, as might be expected for a hot, dense molecular cloud enriched by sublimated grain-surface molecules. The results are suggestive of NH3 sublimation and destruction in this molecular cloud, which is likely to be interacting with the W28 SNR shock.Nigel I. Maxted, Phoebe de Wilt, Gavin P. Rowell, Brent P. Nicholas, Michael. G. Burton, Andrew Walsh, Yasuo Fukui and Akiko Kawamur
The Milky Way Heart: Investigating molecular gas and gamma-ray morphologies in the Central Molecular Zone
No full textSince the discovery of a broad distribution of very high energy (VHE; > 0:1 TeV) gamma-rays in the Central Molecular Zone (CMZ) of the Galaxy in 2006 by the HESS collaboration, the correlation of this emission with the integrated intensity of the CS(1-0) molecular line emission has inferred a hadronic origin for the gamma-rays. Here we describe the beginning of our investigation into the strength of this correlation utilising new multi-line millimeter data from the Mopra CMZ and HOP surveys and multi-wavelength GBT radio continuum observations towards the CMZ and compare these in detail with the diffuse TeV g-ray emission from HESS. The benefit of these new data is that they allow us to simultaneously observe and analyse correlations using a large number (> 10) of molecular species, some of which contain their isotopologue pairs. The use of isotopologue pairs is especially powerful, since it allows one to analyse the optical depth of a number of different molecular species, thus investigating the nature of the correlation over a range of different physical conditions. Here we begin by comparing the integrated line emission and continuum radio emission with the diffuse g-ray emission, and, by using isotopologue pairs such as HCN/H13CN, obtain optical depths throughout the CMZ corresponding to regions of both strong and weak g-ray emission. We find that the radio continuum better matches the peak of the g-ray emission, which corresponds to the more compact – compared to the relatively coarse resolution of the g-ray images – sources in the CMZ. Using the isotopologue pairs, we find that the optical depth at all positions and velocities within the CMZ are about t 2 4. This is similar to that found for the CS(1–0) line and would underestimate the mass of the CMZ, potentially explaining why molecular line emission peaks appear offset from the g-ray peaks.David I. Jones, Michael Burton, Paul Jones, Andrew Walsh, Gavin Rowell, and Felix Aharonia
TeV gamma-ray observations of three X-ray selected BL Lacs
No full textDespite extensive surveys of extragalactic TeV gamma-ray candidates only 3 sources have so far been detected. All three are northern hemisphere objects and all three are low-redshift X-ray selected BL Lacs (XBLs). In this paper we present the results of observations of the three nearest southern hemisphere XBLs (PKS0548–322, PKS2005–489 and PKS2155–304) with the CANGAROO 3.8m imaging telescope. During the period of observation we estimate that the threshold of the 3.8m telescope was ∼1.5 TeV. Searches for both steady and short timescale emission have been performed for each source. Additionally, we are able to monitor the X-ray state of each source on a daily basis and we have made contemporaneous measurements of optical activity for PKS0548–322 and PKS2155–304.M.D. Roberts, P. McGee, S.A. Dazeley, P.G. Edwards ... Padric K. Mcgee … Gavin P. Rowell … et al
Environment Studies of Pulsar Wind Nebulae and Their Interactions with the Interstellar Medium
No full textPulsars, rapidly rotating neutron star born from the core-collapse of massive stars, convert a fraction of their rotational energy to accelerate electrons up to high energies. The generated pulsar wind eventually reaches the termination shock and creates a pulsar wind nebula (PWN). There, the particles’ trajectories become randomized, and they produce radio to X-ray emission via synchrotron radiation; and TeV γ-ray emission from the interaction of high energy electrons with the Cosmic Microwave Background; and the infra-red emission from Galactic dust. Although progress has been made towards the understanding of the structure of the pulsar environment, several issues, such as the composition of the pulsar winds, still need to be addressed. Indeed, no direct evidence of hadronic components have yet been discovered inside the PWN. However, nearby dense molecular clouds could provide sufficient target particles for the potential hadrons from the PWN and its progenitor supernova remnant (SNR) to produce significant TeV emission via proton-proton (p-p) interaction. My work thus first consists of conducting interstellar matter (ISM) studies towards several PWNe using the 22-metre Mopra and the 4-metre Nanten radio telescopes. Among the studied PWNe, I particularly focus on HESS J1825−137 and its plausible association with the nearby unidentified TeV source HESS J1826−130. I have mapped the HESS J1826−130 region with Mopra in the 7 and 12 mm bands which, combined with the Nanten CO(1–0) survey and the GRS ¹³CO(1–0), enable an accurate analysis of the morphological and physical properties of several dense molecular clouds found in the line of sight. Interestingly, I have found a massive molecular cloud adjacent to the PWN HESS J1825−137 and overlapping the HESS J1826−130 TeV emission. From our mass estimates, I suggest that the cosmic-rays originating from the progenitor SNR of the pulsar PSRJ1826−1334 can significantly contribute to the TeV emission. We then attempt to model and predict spectral and morphological properties of the TeV emission from the propagation of high energy CRs and electrons, originating from the progenitor SNR and potentially from the PWN.We find that the resulting spectral shape of the TeV γ-ray emission is very sensitive to the diffusion coefficient of high energy particles inside molecular clouds. I also find that only a ‘slow’ diffusion’ of CRs (diffusion coefficient D(E) ∼ 10²⁶ √E/10GeV cm² s⁻¹) results in a significant contribution of the gamma-ray emission towards HESS J1826−130 at all energies. We finally notice that the contribution from hypothetical CRs escaping the PWN HESS J1825−137 is expected to be overshadowed by the contribution of CRs escaping the progenitor SNR. As one expects the latter’s contribution to decrease as time evolves while the former’s contribution to remain somewhat constant, I thus argue that older PWNe may be more suitable candidates to obtain direct evidence of CRs inside PWNe. Among the studied PWNe, I find that, based on simplistic diffusion studies, the ISM surrounding HESS J1809−193 may be a good laboratory to detect CRs escaping the pulsar PSRJ1809−1917.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201
Gamma-ray burst observations with the H.E.S.S. air Cherenkov array
No full textGamma-ray bursts (GRBs) are among the potential very-high-energy (VHE) gamma-ray sources. VHE emission from GRBs is predicted by most GRB models. Despite its generally fast-fading nature in many wavebands, the time evolution of any VHE radiation is still not clear. The highest energy radiation from GRBs ever detected firmly by any instrument was a 18 GeV photon coming from GRB 940217 detected with EGRET about 1.5 hour after the onset of the GRB. There is also a tentative detection using MILAGRITO of TeV excess events from GRB 970417a. In order to probe the largely unexplored VHE spectra of GRBs, a GRB observing program has been set up by the H.E.S.S. collaboration. With the high sensitivity of the H.E.S.S. array, VHE flux levels predicted by GRB models are well within reach. Extra-galactic background light absorption is taken into account in cases where redshifts are known. We will present the H.E.S.S. observations of and results from some of the reported GRB positions during the past few years.Pak-Hin Tam, Paula Chadwick, Yves Gallant, Dieter Horns, Gerd Puhlhofer, Gavin Rowell, Stefan Wagner for the H.E.S.S. COLLABORATIO
- …
