arXiv subjects

J. Tomsick

Publications and source records attributed to J. Tomsick.

At least 19 recordsLinked to original sources

arXiv2025

Gamma-Ray and AntiMatter Survey(GRAMS) experiment

The Gamma-Ray and AntiMatter Survey (GRAMS) is a next-generation experiment using a Liquid Argon Time Projection Chamber (LArTPC) detector to measure MeV gamma rays and antiparticles. MeV gamma-ray observations are important for understanding multi-messenger and time-domain astronomy, enabling exploration of the universe's most potent events, such as supernovae and neutron star mergers. Despite the significance of MeV gamma-rays, GRAMS could also explore the so-called 'MeV gap' region to improve MeV gamma-ray measurement sensitivity that was restricted by the challenge of accurately reconstructing Compton events. Aside from gamma-ray detection, the GRAMS proposed method also serves as an antiparticle spectrometer, targeting the low-energy range of cosmic antinuclei measurements. This work will provide updates on the current status and progress towards the prototype balloon flight with a small-scale LArTPC (pGRAMS) scheduled for early 2026, as well as the recent progress on antihelium-3 sensitivity calculation.

hep-ex↗

arXiv2025

Unprecedentedly bright X-ray flaring in Cygnus X-1 observed by INTEGRAL

We study three extraordinarily bright X-ray flares originating from Cyg X-1 seen on 2023 July 10 detected with INTEGRAL. The flares had a duration on the order of only ten minutes each, and within seconds reached a 1-100 keV peak luminosity of $1.1-2.6\times10^{38}$ erg/s. The associated INTEGRAL/IBIS count rate was about ${\sim}$10x higher than usual for the hard state. To our knowledge, this is the first time that such strong flaring has been seen in Cyg X-1, despite the more than 21 years of INTEGRAL monitoring, with almost ${\sim}$20 Ms of exposure, and the similarly deep monitoring with RXTE/PCA that lasted from 1997 to 2012. The flares were seen in all three X-ray and $\gamma$-ray instruments of INTEGRAL. Radio monitoring by the AMI Large Array with observations 6 h before and 40 h after the X-ray flares did not detect a corresponding increase in radio flux. The shape of the X-ray spectrum shows only marginal change during the flares, i.e., photon index and cut-off energy are largely preserved. The overall flaring behavior points toward a sudden and brief release of energy, either due to the ejection of material in an unstable jet or due to the interaction of the jet with the ambient clumpy stellar wind.

astro-ph.HE↗

arXiv2025

Antihelium-3 Sensitivity for the GRAMS Experiment

The Gamma-Ray and AntiMatter Survey (GRAMS) is a next-generation balloon/satellite mission utilizing a Liquid Argon Time Projection Chamber (LArTPC) detector to measure both MeV gamma rays and antinuclei produced by dark matter annihilation or decay. The GRAMS can identify antihelium-3 events based on the measurements of X-rays and charged pions from the decay of the exotic atoms, Time of Flight (TOF), energy deposition, and stopping range. This paper shows the antihelium-3 sensitivity estimation using a GEANT4 Monte Carlo simulation. For the proposed long-duration balloon (LDB) flight program (35 days $ \times $ 3 flights) and future satellite mission (2-year observation / 10-year observation), the sensitivities become 1.47 $\times$ 10$^{-7}$ [m$^2$ s sr GeV/n]$^{-1}$ and 1.55 $\times$ 10$^{-9}$ [m$^2$ s sr GeV/n]$^{-1}$ / $3.10\times10^{-10}$ [m$^2$ s sr GeV/n]$^{-1}$, respectively. The results indicate that GRAMS can extensively investigate various dark matter models through the antihelium-3 measurements.

hep-ex↗

arXiv2024

First operation of LArTPC in the stratosphere as an engineering GRAMS balloon flight (eGRAMS)

GRAMS (Gamma-Ray and AntiMatter Survey) is a next-generation balloon/satellite experiment utilizing a LArTPC (Liquid Argon Time Projection Chamber), to simultaneously target astrophysical observations of cosmic MeV gamma-rays and conduct an indirect dark matter search using antimatter. While LArTPCs are widely used in particle physics experiments, they have never been operated at balloon altitudes. An engineering balloon flight with a small-scale LArTPC (eGRAMS) was conducted on July 27th, 2023, to establish a system for safely operating a LArTPC at balloon altitudes and to obtain cosmic-ray data from the LArTPC. The flight was launched from the Japan Aerospace Exploration Agency's (JAXA) Taiki Aerospace Research Field in Hokkaido, Japan. The total flight duration was 3 hours and 12 minutes, including a level flight of 44 minutes at a maximum altitude of 28.9 km. The flight system was landed on the sea and successfully recovered. The LArTPC was successfully operated throughout the flight, and about 0.5 million events of the cosmic-ray data including muons, protons, and Compton scattering gamma-ray candidates, were collected. This pioneering flight demonstrates the feasibility of operating a LArTPC in high-altitude environments, paving the way for future GRAMS missions and advancing our capabilities in MeV gamma-ray astronomy and dark matter research.

astro-ph.IM↗

arXiv2023

The High Energy X-ray Probe (HEX-P): Probing the physics of the X-ray corona in active galactic nuclei

The hard X-ray emission in active galactic nuclei (AGN) and black hole X-ray binaries is thought to be produced by a hot cloud of electrons referred to as the corona. This emission, commonly described by a power law with a high-energy cutoff, is suggestive of Comptonization by thermal electrons. While several hypotheses have been proposed to explain the origin, geometry, and composition of the corona, we still lack a clear understanding of this fundamental component. NuSTAR has been playing a key role improving our knowledge of X-ray coronae thanks to its unprecedented sensitivity above 10 keV. However, these constraints are limited to bright, nearby sources. The High Energy X-ray Probe (HEX-P) is a probe-class mission concept combining high spatial resolution X-ray imaging and broad spectral coverage (0.2-80 keV) with a sensitivity superior to current facilities. In this paper, we highlight the major role that HEX-P will play in further advancing our insights of X-ray coronae, notably in AGN. We demonstrate how HEX-P will measure key properties and track the temporal evolution of coronae in unobscured AGN. This will allow us to determine their electron distribution and test the dominant emission mechanisms. Furthermore, we show how HEX-P will accurately estimate the coronal properties of obscured AGN in the local Universe, helping address fundamental questions about AGN unification. In addition, HEX-P will characterize coronae in a large sample of luminous quasars at cosmological redshifts for the first time and track the evolution of coronae in transient systems in real time. We also demonstrate how HEX-P will enable estimating the coronal geometry using spectral-timing techniques. HEX-P will thus be essential to understand the evolution and growth of black holes over a broad range of mass, distance, and luminosity, and will help uncover the black holes' role in shaping the Universe.

astro-ph.HE↗

arXiv2019

Physical constraints from near-infrared fast photometry of the black-hole transient GX 339-4

We present results from the first multi-epoch X-ray/IR fast-photometry campaign on the black-hole transient GX 339--4, during its 2015 outburst decay. We studied the evolution of the power spectral densities finding strong differences between the two bands. The X-ray power spectral density follows standard patterns of evolution, plausibly reflecting changes in the accretion flow. The IR power spectral density instead evolves very slowly, with a high-frequency break consistent with remaining constant at $0.63 \pm 0.03$ Hz throughout the campaign. We discuss this result in the context of the currently available models for the IR emission in black-hole transients. While all models will need to be tested quantitatively against this unexpected constraint, we show that an IR emitting relativistic jet which filters out the short-timescales fluctuations injected from the accretion inflow appears as the most plausible scenario.

astro-ph.HE↗

arXiv2019

ESA Voyage 2050 white paper -- Faint objects in motion: the new frontier of high precision astrometry

Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of earth-massed habitable worlds around the nearest starts, and also into distant Milky way objects up to the Local Group of galaxies. As we enter the era of the James Webb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry ESA missions: NEAT for M3, micro-NEAT for S1 mission, and Theia for M4 and M5. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this white paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review quickly instrumentation and mission profiles.

astro-ph.IM↗

arXiv2019

Puzzling Blue Dips in the Black Hole Candidate Swift J1357.2-0933, from ULTRACAM, SALT, ATCA, Swift and NuSTAR

We present rapid, multiwavelength photometry of the low-mass X-ray binary Swift J1357.2-0933 during its 2017 outburst. Using several sets of quasi-simultaneous ULTRACAM/NTT (optical), NuSTAR (X-ray), XRT/Swift (X-ray), SALT (optical) and ATCA (radio) observations taken during outburst decline, we confirm the frequent optical dipping that has previously been noted both in outburst and in quiescence. We also find: 1) that the dip frequency decreases as the outburst decays, similar to what was seen in the previous outburst, 2) that the dips produce a shape similar to that in binary systems with partial disc occultations, 3) that the source becomes significantly bluer during these dips, indicating an unusual geometry compared to other LMXB dippers, and 4) that dip superposition analysis confirms the lack of an X-ray response to the optical dips. These very unusual properties appear to be unique to Swift J1357.2-0933, and are likely the result of a high binary inclination, as inferred from features such as its very low outburst X-ray luminosity. From this analysis as well as X-ray/optical timing correlations, we suggest a model with multi-component emission/absorption features with differing colours. This could include the possible presence of a sporadically occulted jet base and a recessed disc. This source still hosts many puzzling features, with consequences for the very faint X-ray transients population.

astro-ph.HE↗

arXiv2019

Opportunities for Multimessenger Astronomy in the 2020s

Electromagnetic observations of the sky have been the basis for our study of the Universe for millennia, cosmic ray studies are now entering their second century, the first neutrinos from an astrophysical source were identified three decades ago, and gravitational waves were directly detected only four years ago. Detections of these messengers are now common. Astrophysics will undergo a revolution in the 2020s as multimessenger detections become routine. The 8th Astro2020 Thematic Area is Multimessenger Astronomy and Astrophysics, which includes the identification of the sources of gravitational waves, astrophysical and cosmogenic neutrinos, cosmic rays, and gamma-rays, and the coordinated multimessenger and multiwavelength follow-ups. Identifying and characterizing multimessenger sources enables science throughout and beyond astrophysics. Success in the multimessenger era requires: (i) sensitive coverage of the non-electromagnetic messengers, (ii) full coverage of the electromagnetic spectrum, with either fast-response observations or broad and deep high-cadence surveys, and (iii) improved collaboration, communication, and notification platforms.

astro-ph.HE↗

arXiv2019

Gamma Rays and Gravitational Waves

The first multimessenger observation of a neutron star merger was independently detected in gamma-rays by Fermi-GBM and INTEGRAL SPI-ACS and gravitational waves by Advanced LIGO and Advanced Virgo. Gravitational waves are emitted from systems with accelerating quadrupole moments, and detectable sources are expected to be compact objects. Nearly all distant astrophysical gamma-ray sources are compact objects. Therefore, serendipitous observations of these two messengers will continue to uncover the sources of gravitational waves and gamma-rays, and enable multimessenger science across the Astro2020 thematic areas. This requires upgrades to the ground-based gravitational wave network and ~keV-MeV gamma-ray coverage for observations of neutron star mergers, and broadband coverage in both gravitational waves and gamma-rays to monitor other expected joint sources.

astro-ph.HE↗

arXiv2018

Multiple cyclotron line-forming regions in GX 301-2

We present two observations of the high-mass X-ray binary GX 301-2 with NuSTAR, taken at different orbital phases and different luminosities. We find that the continuum is well described by typical phenomenological models, like a very strongly absorbed NPEX model. However, for a statistically acceptable description of the hard X-ray spectrum we require two cyclotron resonant scattering features (CRSF), one at ~35 keV and the other at ~50 keV. Even though both features strongly overlap, the good resolution and sensitivity of NuSTAR allows us to disentangle them at >=99.9% significance. This is the first time that two CRSFs are seen in GX 301-2. We find that the CRSFs are very likely independently formed, as their energies are not harmonically related and, if it were a single line, the deviation from a Gaussian shape would be very large. We compare our results to archival Suzaku data and find that our model also provides a good fit to those data. We study the behavior of the continuum as well as the CRSF parameters as function of pulse phase in seven phase bins. We find that the energy of the 35 keV CRSF varies smoothly as function of phase, between 30-38 keV. To explain this variation, we apply a simple model of the accretion column, taking the altitude of the line-forming region, the velocity of the in-falling material, and the resulting relativistic effects into account. We find that in this model the observed energy variation can be explained simply due to a variation of the projected velocity and beaming factor of the line forming region towards us.

astro-ph.HE↗

arXiv2017

NuSTAR + XMM-Newton monitoring of the neutron star transient AX J1745.6-2901

AX J1745.6-2901 is a high-inclination (eclipsing) transient neutron star (NS) Low Mass X-ray Binary (LMXB) showcasing intense ionised Fe K absorption. We present here the analysis of 11 XMM-Newton and 15 NuSTAR new data-sets (obtained between 2013-2016), therefore tripling the number of observations of AX J1745.6-2901 in outburst. Thanks to simultaneous XMM-Newton and NuSTAR spectra, we greatly improve on the fitting of the X-ray continuum. During the soft state the emission can be described by a disk black body ($kT\sim1.1-1.2$ keV and inner disc radius $r_{DBB}\sim14$ km), plus hot ($kT\sim2.2-3.0$ keV) black body radiation with a small emitting radius ($r_{BB}\sim0.5-0.8$ km) likely associated with the boundary layer or NS surface, plus a faint Comptonisation component. Imprinted on the spectra are clear absorption features created by both neutral and ionised matter. Additionally, positive residuals suggestive of an emission Fe K$\alpha$ disc line and consistent with relativistic ionised reflection are present during the soft state, while such residuals are not significant during the hard state. The hard state spectra are characterised by a hard ($\Gamma\sim1.9-2.1$) power law, showing no evidence for a high energy cut off ($kT_e>60-140$ keV) and implying a small optical depth ($\tau<1.6$). The new observations confirm the previously witnessed trend of exhibiting strong Fe K absorption in the soft state, that significantly weakens during the hard state. Optical (GROND) and radio (GMRT) observations suggest for AX J1745.6-2901 a standard broad band SED as typically observed in accreting neutron stars.

astro-ph.HE↗

arXiv2016

Multi-wavelength observations of IGR J17544-2619 from quiescence to outburst

In this paper we report on a long multi-wavelength observational campaign of the supergiant fast X-ray transient prototype IGR J17544-2619. A 150 ks-long observation was carried out simultaneously with XMM-Newton and NuSTAR, catching the source in an initial faint X-ray state and then undergoing a bright X-ray outburst lasting about 7 ks. We studied the spectral variability during outburst and quiescence by using a thermal and bulk Comptonization model that is typically adopted to describe the X-ray spectral energy distribution of young pulsars in high mass X-ray binaries. Although the statistics of the collected X-ray data were relatively high we could neither confirm the presence of a cyclotron line in the broad-band spectrum of the source (0.5-40 keV), nor detect any of the previously reported tentative detection of the source spin period. The monitoring carried out with Swift/XRT during the same orbit of the system observed by XMM-Newton and NuSTAR revealed that the source remained in a low emission state for most of the time, in agreement with the known property of all supergiant fast X-ray transients being significantly sub-luminous compared to other supergiant X-ray binaries. Optical and infrared observations were carried out for a total of a few thousands of seconds during the quiescence state of the source detected by XMM-Newton and NuSTAR. The measured optical and infrared magnitudes were slightly lower than previous values reported in the literature, but compatible with the known micro-variability of supergiant stars. UV observations obtained with the UVOT telescope on-board Swift did not reveal significant changes in the magnitude of the source in this energy domain compared to previously reported values.

astro-ph.HE↗

arXiv2016

NuSTAR observations of the supergiant X-ray pulsar IGR J18027-2016: accretion from the stellar wind and possible cyclotron absorption line

We report on the first focused hard X-ray view of the absorbed supergiant system IGRJ18027-2016 performed with the NuSTAR observatory. The pulsations are clearly detected with a period of $P_{spin}=139.866(1)$ s and a pulse fraction of about 50-60% at energies from 3 to 80 keV. The source demonstrates an approximately constant X-ray luminosity on a time scale of more than dozen years with an average spin-down rate of $dP/dt\simeq6\times10^{-10}$ s/s. This behaviour of the pulsar can be explained in terms of the wind accretion model in the settling regime. The detailed spectral analysis at energies above 10 keV was performed for the first time and revealed a possible cyclotron absorption feature at energy ~23 keV. This energy corresponds to the magnetic field $B\simeq3\times10^{12}$ G at the surface of the neutron star, which is typical for X-ray pulsars.

astro-ph.HE↗

arXiv2016

NuSTAR Observations of the Black Hole GS 1354-645: Evidence of Rapid Black Hole Spin

We present the results of a NuSTAR study of the dynamically confirmed stellar-mass black hole GS 1354-645. The source was observed during its 2015 "hard" state outburst; we concentrate on spectra from two relatively bright phases. In the higher-flux observation, the broadband NuSTAR spectra reveal a clear, strong disk reflection spectrum, blurred by a degree that requires a black hole spin of a = cJ/GM^2 > 0.98 (1 sigma statistical limits only). The fits also require a high inclination: theta = 75(2) degrees. Strong "dips" are sometimes observed in the X-ray light curves of sources viewed at such an angle; these are absent, perhaps indicating that dips correspond to flared disk structures that only manifest at higher accretion rates. In the lower-flux observation, there is evidence of radial truncation of the thin accretion disk. We discuss these results in the context of spin in stellar-mass black holes, and inner accretion flow geometries at moderate accretion rates.

astro-ph.HE↗

arXiv2016

Furiously Fast and Red: Sub-second Optical Flaring in V404 Cyg during the 2015 Outburst Peak

We present observations of rapid (sub-second) optical flux variability in V404 Cyg during its 2015 June outburst. Simultaneous three-band observations with the ULTRACAM fast imager on four nights show steep power spectra dominated by slow variations on ~100-1000s timescales. Near the peak of the outburst on June 26, a dramatic change occurs and additional, persistent sub-second optical flaring appears close in time to giant radio and X-ray flaring. The flares reach peak optical luminosities of ~few x 10^{36} erg/s. Some are unresolved down to a time resolution of 24 milliseconds. Whereas the fast flares are stronger in the red, the slow variations are bluer when brighter. The redder slopes, emitted power, and characteristic timescales of the fast flares can be explained as optically-thin synchrotron emission from a compact jet arising on size scales ~140-500 Gravitational radii (with a possible additional contribution by a thermal particle distribution). The origin of the slower variations is unclear. The optical continuum spectral slopes are strongly affected by dereddening uncertainties and contamination by strong H{alpha} emission, but the variations of these slopes follow relatively stable loci as a function of flux. Cross-correlating the slow variations between the different bands shows asymmetries on all nights consistent with a small red skew (i.e., red lag). X-ray reprocessing and non-thermal emission could both contribute to these. These data reveal a complex mix of components over five decades in timescale during the outburst.

astro-ph.HE↗

arXiv2015

The physics of accretion-ejection 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 the physics of accretion and ejection around compact objects. For a summary, we refer to the paper.

astro-ph.HE↗

arXiv2014

An Ultraluminous X-ray Source Powered by An Accreting Neutron Star

Ultraluminous X-ray sources (ULX) are off-nuclear point sources in nearby galaxies whose X-ray luminosity exceeds the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass black holes. Their luminosity ranges from $10^{40}$ erg s$^{-1} < L_X$(0.5 - 10 keV) $<10^{40}$ erg s$^{-1}$. Since higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit theoretical models have focused on black hole rather than neutron star systems. The most challenging sources to explain are those at the luminous end ($L_X$ > $10^{40}$ erg s$^{-1}$), which require black hole masses MBH >50 solar masses and/or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries. Here we report broadband X-ray observations of the nuclear region of the galaxy M82, which contains two bright ULXs. The observations reveal pulsations of average period 1.37 s with a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to $L_X$(3 - 30 keV) = $4.9 \times 10^{39}$ erg s$^{-1}$. The pulsating source is spatially coincident with a variable ULX which can reach $L_X$ (0.3 - 10 keV) = $1.8 \times 10^{40}$ erg s$^{-1}$. This association implies a luminosity ~100 times the Eddington limit for a 1.4 solar mass object, or more than ten times brighter than any known accreting pulsar. This finding implies that neutron stars may not be rare in the ULX population, and it challenges physical models for the accretion of matter onto magnetized compact objects.

astro-ph.HE↗