NuSTAR Observation of LS 5039 Volkov, Igor; Kargaltsev, Oleg; Younes, George ...
Astrophysical journal/The Astrophysical journal,
07/2021, Letnik:
915, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
LS 5039 is a high-mass
γ
-ray binary hosting a compact object of unknown type. NuSTAR observed LS 5039 during the entire 3.9-day binary period. We performed a periodic signal search up to ...1000 Hz, which did not produce credible period candidates. We do see the 9.05 s period candidate, originally reported by Yoneda et al. using the same data, in the Fourier power spectrum, but we find that the statistical significance of this feature is too low to claim it as a real detection. We did not find significant bursts or quasiperiodic variability either. The modulation with orbital period is clearly seen and remains unchanged over a timescale of 10 years when compared to the earlier Suzaku light curve. The joint analysis of the NuSTAR and Suzaku XIS data shows that the 0.7–70 keV spectrum can be satisfactory described by a single absorbed power-law model with no evidence of a cutoff at higher energies. The slope of the spectrum is anticorrelated with the flux during the binary orbit. If LS 5039 hosts a young neutron star, its X-ray pulsations therefore appear to be outshone by the intrabinary shock emission. The lack of spectral lines and/or an exponential cutoff at higher energies suggests that the putative neutron star is not actively accreting. Although a black hole scenario still remains a possibility, the lack of variability or Fe K
α
lines, which typically accompany accretion, makes it less likely.
Recognising the increasing accessibility and importance of patent data, the article underscores the need for standardised and transparent data analysis methods. We illustrate the construction and ...relevance of commonly used patent indicators derived from Google Patents Public Datasets. The indicators range from citation counts to more advanced metrics like patent text similarity. The BigQuery code is available in an open Kaggle notebook, explaining operational intricacies and potential data issues. By providing clear, adaptable queries and emphasising transparent methods, this article hopes to contribute to the standardisation and accessibility of patent analysis, offering a valuable resource for researchers and practitioners alike.
We present timing and time-integrated spectral analysis of 127 bursts from SGR J1935+2154. These bursts were observed with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope and the ...Burst Alert Telescope on the Neil Gehrels Swift Observatory during the source's four active episodes from 2014 to 2016. This activation frequency makes SGR J1935+2154 the most burst prolific transient magnetar. We find the average duration of all the detected bursts to be much shorter than the typical, anticipated value. We fit the burst time-integrated spectra with two blackbody functions, a Comptonized model and three other simpler models. Bursts from SGR J1935+2154 exhibit similar spectral properties to other magnetars, with the exception of the power-law index from the Comptonized model, which correlates with burst fluence. We find that the durations and both blackbody temperatures of the bursts have significantly evolved across the four active episodes. We also find that the burst time history exhibits two trends, which are strongly correlated with the decay of the persistent emission in each outburst.
4FGL J1015.5-6030 is an unidentified Fermi-LAT source hosting a bright, extended X-ray source whose X-ray spectrum is consistent with that of a young pulsar, yet no pulsations have been found. Here ...we report on XMM-Newton timing and Chandra imaging observations of the X-ray counterpart of 4FGL J1015.5-6030. We find no significant periodicity from the source and place a 3σ upper limit on its pulsed fraction of 34%. The Chandra observations resolve the point source from the extended emission. We find that the point source's spectrum is well fit by a blackbody model, with temperature kT = 0.205 ± 0.009 keV, plus a weak power-law component, which is consistent with a thermally emitting neutron star with a magnetospheric component. The extended emission spans angular scales of a few arcseconds up to about 30'' from the point source and its spectrum is well fit by a power-law model with a photon index Γ = 1.70 ± 0.05. The extended emission's spectrum and 0.5–10 keV luminosity of 4 × 1032 erg s−1 (at a plausible distance of 2 kpc) are consistent with that of a pulsar wind nebula. Based on a comparison to other GeV and X-ray pulsars, we find that this putative pulsar is likely a middle-aged (i.e., τ ∼ 0.1–1 Myr) radio-quiet pulsar with Ė~1034-1035erg s−1.
ABSTRACT Since its launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has triggered and located on average approximately two γ-ray bursts (GRBs) every three days. Here, we present the third of a ...series of catalogs of GRBs detected by GBM, extending the second catalog by two more years through the middle of 2014 July. The resulting list includes 1405 triggers identified as GRBs. The intention of the GBM GRB catalog is to provide information to the community on the most important observables of the GBM-detected GRBs. For each GRB, the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50-300 keV energy band where the maximum energy release of GRBs in the instrument reference system is observed, and also for a broader energy band from 10 to 1000 keV, exploiting the full energy range of GBM's low-energy NaiTl) detectors. Using statistical methods to assess clustering, we find that the hardness and duration of GRBs are better fit by a two-component model with short-hard and long-soft bursts than by a model with three components. Furthermore, information is provided on the settings and modifications of the triggering criteria and exceptional operational conditions during years five and six in the mission. This third catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.
Abstract
The present document provides the take of innovation economists on the COVID-19 pandemic. It targets the general public and focuses on questions related to the Science, Technology, and ...Innovation ecosystem. It provides a reading of current real-world developments using economic reasoning and relying on existing economic research.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We report on NICER observations of the magnetar SGR 1935+2154, covering its 2020 burst storm and long-term persistent emission evolution up to ∼90 days postoutburst. During the first 1120 s taken on ...April 28 00:40:58 UTC, we detect over 217 bursts, corresponding to a burst rate of >0.2 bursts s−1. Three hours later, the rate was 0.008 bursts s−1, remaining at a comparatively low level thereafter. The T90 burst duration distribution peaks at 840 ms; the distribution of waiting times to the next burst is fit with a lognormal with an average of 2.1 s. The 1-10 keV burst spectra are well fit by a blackbody, with an average temperature and area of kT = 1.7 keV and R2 = 53 km2. The differential burst fluence distribution over ∼3 orders of magnitude is well modeled with a power-law form dN/dF ∝ F−1.5 0.1. The source persistent emission pulse profile is double-peaked hours after the burst storm. We find that the burst peak arrival times follow a uniform distribution in pulse phase, though the fast radio burst associated with the source aligns in phase with the brighter peak. We measure the source spin-down from heavy-cadence observations covering days 21-39 postoutburst, Hz s−1, a factor of 2.7 larger than the value measured after the 2014 outburst. Finally, the persistent emission flux and blackbody temperature decrease rapidly in the early stages of the outburst, reaching quiescence 40 days later, while the size of the emitting area remains unchanged.
We analyzed broadband X-ray and radio data of the magnetar SGR J1935+2154 taken in the aftermath of its 2014, 2015, and 2016 outbursts. The source soft X-ray spectrum <10 keV is well described with a ...blackbody+power-law (BB+PL) or 2BB model during all three outbursts. Nuclear Spectroscopic Telescope Array observations revealed a hard X-ray tail, with a PL photon index Γ = 0.9, extending up to 50 keV, with flux comparable to the one detected <10 keV. Imaging analysis of Chandra data did not reveal small-scale extended emission around the source. Following the outbursts, the total 0.5-10 keV flux from SGR J1935+2154 increased in concordance to its bursting activity, with the flux at activation onset increasing by a factor of ∼7 following its strongest 2016 June outburst. A Swift/X-Ray Telescope observation taken 1.5 days prior to the onset of this outburst showed a flux level consistent with quiescence. We show that the flux increase is due to the PL or hot BB component, which increased by a factor of 25 compared to quiescence, while the cold BB component kT = 0.47 keV remained more or less constant. The 2014 and 2015 outbursts decayed quasi-exponentially with timescales of ∼40 days, while the stronger 2016 May and June outbursts showed a quick short-term decay with timescales of about four days. Our Arecibo radio observations set the deepest limits on the radio emission from a magnetar, with a maximum flux density limit of 14 Jy for the 4.6 GHz observations and 7 Jy for the 1.4 GHz observations. We discuss these results in the framework of the current magnetar theoretical models.
We present temporal and time-integrated spectral analyses of 148 bursts from the latest activation of SGR J1935+2154, observed with the Fermi/Gamma-ray Burst Monitor from 2019 October 4 through 2020 ...May 20, excluding an ∼130 s segment with a very high burst density on 2020 April 27. The 148 bursts presented here are slightly longer and softer than bursts from earlier activations of SGR J1935+2154, as well as from other magnetars. The long-term spectral evolution trend is interpreted as being associated with an increase in the average plasma loading of the magnetosphere during bursts. We also find a trend of increased burst activity from SGR J1935+2154 since its discovery in 2014. Finally, we find no association of typical radio bursts with X-ray bursts from the source. This contrasts the association of FRB 200428 with an SGR J1935+2154 X-ray burst, which is to-date unique among the magnetar population.
We report the analysis of simultaneous XMM-Newton+Nuclear Spectroscopic Telescope Array (NuSTAR) observations of two low-luminosity active galactic nuclei (LLAGNs), NGC 3998 and NGC 4579. We do not ...detect any significant variability in either source over the ∼3 day length of the NuSTAR observations. The broadband 0.5-60 keV spectrum of NGC 3998 is best fit with a cutoff power law, while the one for NGC 4579 is best fit with a combination of a hot thermal plasma model, a power law, and a blend of Gaussians to fit an Fe complex observed between 6 and 7 keV. Our main spectral results are the following: (1) neither source shows any reflection hump with 3 reflection fraction upper limits of and for NGC 3998 and NGC 4579, respectively; (2) the 6-7 keV line complex in NGC 4579 could be fit with either a narrow Fe K line at 6.4 keV and a moderately broad Fe xxv line or with three relatively narrow lines, which include contribution from Fe xxvi; (3) the NGC 4579 flux is 60% brighter than previously detected with XMM-Newton, accompanied by a hardening in the spectrum; (4) we measure a cutoff energy keV in NGC 3998, which represents the lowest and best constrained high-energy cutoff ever measured for an LLAGN; (5) the NGC 3998 spectrum is consistent with a Comptonization model with either a sphere (τ 3 1) or slab (τ 1.2 0.6) geometry, corresponding to plasma temperatures between 20 and 150 keV. We discuss these results in the context of hard X-ray emission from bright AGNs, other LLAGNs, and hot accretion flow models.
PDF
