arXiv subjects

D. M. Smith

Publications and source records attributed to D. M. Smith.

At least 19 recordsLinked to original sources

arXiv2024

NuSTAR as an Axion Helioscope

We present a novel approach to investigating axions and axion-like particles (ALPs) by studying their potential conversion into X-rays within the Sun's atmospheric magnetic field. Utilizing high-sensitivity data from the Nuclear Spectroscopic Telescope Array (NuSTAR) collected during the 2020 solar minimum, along with advanced solar atmospheric magnetic field models, we establish a new limit on the axion-photon coupling strength $g_{a\gamma}\lesssim 7.3\times 10^{-12}$~GeV$^{-1}$ at 95\% CL for axion masses $m_a\lesssim 4\times 10^{-7}$\,eV. This constraint surpasses current ground-based experimental limits, studying previously unexplored regions of the axion-photon coupling parameter space up to masses of $m_a\lesssim 3.4\times 10^{-4}$\,eV. These findings mark a significant advancement in our ability to probe axion properties and strengthen indirect searches for dark matter candidates.

astro-ph.CO↗

arXiv2022

The Second Catalog of Interplanetary Network Localizations of Konus Short Duration Gamma-Ray Bursts

We present the catalog of Interplanetary Network (IPN) localizations for 199 short-duration gamma-ray bursts (sGRBs) detected by the Konus-Wind (KW) experiment between 2011 January 1 and 2021 August 31, which extends the initial sample of IPN localized KW sGRBs (arXiv:1301.3740) to 495 events. We present the most comprehensive IPN localization data on these events, including probability sky maps in HEALPix format.

astro-ph.HE↗

arXiv2018

Characterizing upward lightning with and without a terrestrial gamma-ray flash

We compare two observations of gamma-rays before, during, and after lightning flashes initiated by upward leaders from a tower during low-altitude winter thunderstorms on the western coast of Honshu, Japan. While the two leaders appear similar, one produced a terrestrial gamma-ray flash (TGF) so bright that it paralyzed the gamma-ray detectors while it was occurring, and could be observed only via the weaker flux of neutrons created in its wake, while the other produced no detectable TGF gamma-rays at all. The ratio between the indirectly derived gamma-ray fluence for the TGF and the 95% confidence gamma-ray upper limit for the gamma-ray quiet flash is a factor of $1\times10^7$. With the only two observations of this type providing such dramatically different results -- a TGF probably as bright as those seen from space and a powerful upper limit -- we recognize that weak, sub-luminous TGFs in this situation are probably not common, and we quantify this conclusion. While the gamma-ray quiet flash appeared to have a faster leader and more powerful initial continuous current pulse than the flash that produced a TGF, the TGF-producing flash occurred during a weak gamma-ray "glow", while the gamma-ray quiet flash did not, implying a higher electric field aloft when the TGF was produced. We suggest that the field in the high-field region approached by a leader may be more important for whether a TGF is produced than the characteristics of the leader itself.

physics.ao-ph↗

arXiv2016

First flight of the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument

The Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) is a balloon-borne telescope designed to study solar-flare particle acceleration and transport. We describe GRIPS's first Antarctic long-duration flight in Jan 2016 and report preliminary calibration and science results. Electron and ion dynamics, particle abundances and the ambient plasma conditions in solar flares can be understood by examining hard X-ray (HXR) and gamma-ray emission (20 keV to 10 MeV) with enhanced imaging, spectroscopy and polarimetry. GRIPS is specifically designed to answer questions including: What causes the spatial separation between energetic electrons producing HXRs and energetic ions producing gamma-ray lines? How anisotropic are the relativistic electrons, and why can they dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and why? GRIPS's key technological improvements over the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) include 3D position-sensitive germanium detectors (3D-GeDs) and a single-grid, multi-pitch rotating modulator (MPRM) collimator. The 3D-GeDs have spectral FWHM resolution of a few hundred keV and spatial resolution $<$1 mm$^3$. For photons that Compton scatter, usually $\gtrsim$150 keV, the energy deposition sites can be tracked, providing polarization measurements as well as enhanced background reduction. The MPRM single-grid design provides twice the throughput of a bi-grid imaging system like RHESSI. The grid is composed of 2.5 cm thick W/Cu slats with 1-13 mm variable slit pitch, achieving quasi-continuous FWHM angular coverage over 12.5-162 arcsecs. This resolution is capable of imaging the separate magnetic loop footpoint emissions in a variety of flare sizes. (Abstract edited down from source.)

astro-ph.IM↗

arXiv2016

The first X-ray imaging spectroscopy of quiescent solar active regions with NuSTAR

We present the first observations of quiescent active regions (ARs) using NuSTAR, a focusing hard X-ray telescope capable of studying faint solar emission from high temperature and non-thermal sources. We analyze the first directly imaged and spectrally resolved X-rays above 2~keV from non-flaring ARs, observed near the west limb on 2014 November 1. The NuSTAR X-ray images match bright features seen in extreme ultraviolet and soft X-rays. The NuSTAR imaging spectroscopy is consistent with isothermal emission of temperatures $3.1-4.4$~MK and emission measures $1-8\times 10^{46}$~cm$^{-3}$. We do not observe emission above 5~MK but our short effective exposure times restrict the spectral dynamic range. With few counts above 6~keV, we can place constraints on the presence of an additional hotter component between 5 and 12~MK of $\sim 10^{46}$cm$^{-3}$ and $\sim 10^{43}$ cm$^{-3}$, respectively, at least an order of magnitude stricter than previous limits. With longer duration observations and a weakening solar cycle (resulting in an increased livetime), future NuSTAR observations will have sensitivity to a wider range of temperatures as well as possible non-thermal emission.

astro-ph.SR↗

arXiv2015

High-energy radiation from thunderstorms and lightning with LOFT

This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of high-energy radiation from thunderstorms and lightning. For a summary, we refer to the paper.

astro-ph.HE↗

arXiv2013

Solar Eruptive Events (SEE) 2020 Mission Concept

Major solar eruptive events (SEEs), consisting of both a large flare and a near simultaneous large fast coronal mass ejection (CME), are the most powerful explosions and also the most powerful and energetic particle accelerators in the solar system, producing solar energetic particles (SEPs) up to tens of GeV for ions and hundreds of MeV for electrons. The intense fluxes of escaping SEPs are a major hazard for humans in space and for spacecraft. Furthermore, the solar plasma ejected at high speed in the fast CME completely restructures the interplanetary medium (IPM) - major SEEs therefore produce the most extreme space weather in geospace, the interplanetary medium, and at other planets. Thus, understanding the flare/CME energy release process(es) and the related particle acceleration processes are major goals in Heliophysics. To make the next major breakthroughs, we propose a new mission concept, SEE 2020, a single spacecraft with a complement of advanced new instruments that focus directly on the coronal energy release and particle acceleration sites, and provide the detailed diagnostics of the magnetic fields, plasmas, mass motions, and energetic particles required to understand the fundamental physical processes involved.

astro-ph.SR↗

arXiv2013

IPN localizations of Konus short gamma-ray bursts

Between the launch of the \textit{GGS Wind} spacecraft in 1994 November and the end of 2010, the Konus-\textit{Wind} experiment detected 296 short-duration gamma-ray bursts (including 23 bursts which can be classified as short bursts with extended emission). During this period, the IPN consisted of up to eleven spacecraft, and using triangulation, the localizations of 271 bursts were obtained. We present the most comprehensive IPN localization data on these events. The short burst detection rate, $\sim$18 per year, exceeds that of many individual experiments.

astro-ph.HE↗

arXiv2013

The Interplanetary Network Supplement to the Fermi GBM Catalog of Cosmic Gamma-Ray Bursts

We present Interplanetary Network (IPN) data for the gamma-ray bursts in the first Fermi Gamma-Ray Burst Monitor (GBM) catalog. Of the 491 bursts in that catalog, covering 2008 July 12 to 2010 July 11, 427 were observed by at least one other instrument in the 9-spacecraft IPN. Of the 427, the localizations of 149 could be improved by arrival time analysis (or triangulation). For any given burst observed by the GBM and one other distant spacecraft, triangulation gives an annulus of possible arrival directions whose half-width varies between about 0.4' and 32 degrees, depending on the intensity, time history, and arrival direction of the burst, as well as the distance between the spacecraft. We find that the IPN localizations intersect the 1 sigma GBM error circles in only 52% of the cases, if no systematic uncertainty is assumed for the latter. If a 6 degree systematic uncertainty is assumed and added in quadrature, the two localization samples agree about 87% of the time, as would be expected. If we then multiply the resulting error radii by a factor of 3, the two samples agree in slightly over 98% of the cases, providing a good estimate of the GBM 3 sigma error radius. The IPN 3 sigma error boxes have areas between about 1 square arcminute and 110 square degrees, and are, on the average, a factor of 180 smaller than the corresponding GBM localizations. We identify two bursts in the IPN/GBM sample that did not appear in the GBM catalog. In one case, the GBM triggered on a terrestrial gamma flash, and in the other, its origin was given as uncertain. We also discuss the sensitivity and calibration of the IPN.

astro-ph.HE↗

arXiv2012

Cross Sections from 800 MeV Proton Irradiation of Terbium

A single terbium foil was irradiated with 800 MeV protons to ascertain the potential for production of lanthanide isotopes of interest in medical, astrophysical, and basic science research and to contribute to nuclear data repositories. Isotopes produced in the foil were quantified by gamma spectroscopy. Cross sections for 36 isotopes produced in the irradiation are reported and compared with predictions by the MCNP6 transport code using the CEM03.03, Bertini, and INCL+ABLA event generators. Our results indicate the need to accurately consider fission and fragmentation of relatively light target nuclei like terbium in the modeling of nuclear reactions at 800 MeV. The predictive power of the code was found to be different for each event generator tested but was satisfactory for most of the product yields in the mass region where spallation reactions dominate. However, none of the event generators' results are in complete agreement with measured data.

nucl-ex↗

arXiv2011

The Interplanetary Network Supplement to the Fermi GBM Catalog - An AO-2 and AO-3 Guest Investigator Project

In the first two years of operation of the Fermi GBM, the 9-spacecraft Interplanetary Network (IPN) detected 158 GBM bursts with one or two distant spacecraft, and triangulated them to annuli or error boxes. Combining the IPN and GBM localizations leads to error boxes which are up to 4 orders of magnitude smaller than those of the GBM alone. These localizations comprise the IPN supplement to the GBM catalog, and they support a wide range of scientific investigations.

astro-ph.HE↗

arXiv2011

The Nature and Cause of Spectral Variability in LMC X-1

We present the results of a long-term observation campaign of the extragalactic wind-accreting black-hole X-ray binary LMC X-1, using the Proportional Counter Array on the Rossi X-Ray Timing Explorer (RXTE). The observations show that LMC X-1's accretion disk exhibits an anomalous temperature-luminosity relation. We use deep archival RXTE observations to show that large movements across the temperature-luminosity space occupied by the system can take place on time scales as short as half an hour. These changes cannot be adequately explained by perturbations that propagate from the outer disk on a viscous timescale. We propose instead that the apparent disk variations reflect rapid fluctuations within the Compton up-scattering coronal material, which occults the inner parts of the disk. The expected relationship between the observed disk luminosity and apparent disk temperature derived from the variable occultation model is quantitatively shown to be in good agreement with the observations. Two other observations support this picture: an inverse correlation between the flux in the power-law spectral component and the fitted inner disk temperature, and a near-constant total photon flux, suggesting that the inner disk is not ejected when a lower temperature is observed.

astro-ph.HE↗

arXiv2010

The Interplanetary Network Supplement to the HETE-2 Gamma-Ray Burst Catalog

Between 2000 November and 2006 May, one or more spacecraft of the interplanetary network (IPN) detected 226 cosmic gamma-ray bursts that were also detected by the FREGATE experiment aboard the HETE-II spacecraft. During this period, the IPN consisted of up to nine spacecraft, and using triangulation, the localizations of 157 bursts were obtained. We present the IPN localization data on these events.

astro-ph.HE↗

arXiv2010

The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs

Between 1996 July and 2002 April, one or more spacecraft of the interplanetary network detected 787 cosmic gamma-ray bursts that were also detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera experiments aboard the BeppoSAX spacecraft. During this period, the network consisted of up to six spacecraft, and using triangulation, the localizations of 475 bursts were obtained. We present the localization data for these events.

astro-ph.HE↗

arXiv2009

Integrating the Fermi Gamma-Ray Burst Monitor into the 3rd Interplanetary Network

We are integrating the Fermi Gamma-Ray Burst Monitor (GBM) into the Interplanetary Network (IPN) of Gamma-Ray Burst (GRB) detectors. With the GBM, the IPN will comprise 9 experiments. This will 1) assist the Fermi team in understanding and reducing their systematic localization uncertainties, 2) reduce the sizes of the GBM and Large Area Telescope (LAT) error circles by 1 to 4 orders of magnitude, 3) facilitate the identification of GRB sources with objects found by ground- and space-based observatories at other wavelengths, from the radio to very high energy gamma-rays, 4) reduce the uncertainties in associating some LAT detections of high energy photons with GBM bursts, and 5) facilitate searches for non-electromagnetic GRB counterparts, particularly neutrinos and gravitational radiation. We present examples and demonstrate the synergy between Fermi and the IPN. This is a Fermi Cycle 2 Guest Investigator project.

astro-ph.HE↗

arXiv2009

A new analysis of the short-duration, hard-spectrum GRB 051103, a possible extragalactic SGR giant flare

GRB 051103 is considered to be a candidate soft gamma repeater (SGR) extragalactic giant magnetar flare by virtue of its proximity on the sky to M81/M82, as well as its time history, localization, and energy spectrum. We have derived a refined interplanetary network localization for this burst which reduces the size of the error box by over a factor of two. We examine its time history for evidence of a periodic component, which would be one signature of an SGR giant flare, and conclude that this component is neither detected nor detectable under reasonable assumptions. We analyze the time-resolved energy spectra of this event with improved time- and energy resolution, and conclude that although the spectrum is very hard, its temporal evolution at late times cannot be determined, which further complicates the giant flare association. We also present new optical observations reaching limiting magnitudes of R > 24.5, about 4 magnitudes deeper than previously reported. In tandem with serendipitous observations of M81 taken immediately before and one month after the burst, these place strong constraints on any rapidly variable sources in the region of the refined error ellipse proximate to M81. We do not find any convincing afterglow candidates from either background galaxies or sources in M81, although within the refined error region we do locate two UV bright star forming regions which may host SGRs. A supernova remnant (SNR) within the error ellipse could provide further support for an SGR giant flare association, but we were unable to identify any SNR within the error ellipse. These data still do not allow strong constraints on the nature of the GRB 051103 progenitor, and suggest that candidate extragalactic SGR giant flares will be difficult, although not impossible, to confirm.

astro-ph.HE↗

arXiv2009

Near-infrared survey of High Mass X-ray Binary candidates

We combine infrared spectra in the I, J, H and K bands together with JHK photometry to characterize the spectral type, luminosity class and distance to the infrared counterparts to five INTEGRAL sources. For SAX J18186-1703 and IGR J18483-0311, we present the first intermediate-resolution spectroscopy reported. We find that four systems harbour early-type B supergiants. All of them are heavily obscured, with E(B-V) ranging between 3 and 5, implying visual extinctions of ~ 9 to 15 magnitudes. We refine the published classifications of IGR J18027-2016 and IGR J19140+0951 by constraining their luminosity class. In the first case, we confirm the supergiant nature and rule out class III. In the second case, we propose a slightly higher luminosity class (Ia instead of Iab) and give an improved value of the distance based on new optical photometry. Owing to their infrared and X-ray characteristics, IGR J18027-2016 and IGR J19140+0951, emerge as Supergiant X-ray binaries with X-ray luminosities of the order of Lx ~ [1-2] x 10^{36} erg/s, while SAX J1818.6-1703 and IGR J18483-0311, turn out to be Supergiant Fast X-ray Transients at 2 and 3 kpc, respectively. Finally, XTE J1901+014 emerges as a puzzling source: its X-ray behaviour is strongly reminiscent of the SFXTs but a supergiant nature is firmly ruled out for the counterpart. We discuss several alternative scenarios to explain its behaviour.

astro-ph.SR↗

arXiv2008

INTEGRAL long-term monitoring of the Supergiant Fast X-ray Transient XTE J1739-302

In the past few years, a new class of High Mass X-Ray Binaries (HMXRB) has been claimed to exist, the Supergiant Fast X-ray Transients (SFXT). These are X-ray binary systems with a compact companion orbiting a supergiant star which show very short and bright outbursts in a series of activity periods overimposed on longer quiescent periods. Only very recently the first attempts to model the behaviour of these sources have been published, some of them within the framework of accretion from clumpy stellar winds.Our goal is to analyze the properties of XTE J1739-302/IGR J17391-3021 within the context of the clumpy structure of the supergiant wind. We have used INTEGRAL and RXTE/PCA observations in order to obtain broad band (1-200 keV) spectra and light curves of XTE J1739-302 and investigate its X-ray spectrum and temporal variability. We have found that XTE J1739-302 follows a much more complex behaviour than expected. Far from presenting a regular variability pattern, XTE J1739-302 shows periods of high, intermediate, and low flaring activity.

astro-ph↗