Peak Photon Flux Research Articles

Multi-messenger prospects for black hole – neutron star mergers in the O4 and O5 runs

The existence of merging black hole-neutron star (BHNS) binaries has been ascertained through the observation of their gravitational wave (GW) signals. However, to date, no definitive electromagnetic (EM) emission has been confidently associated with these mergers. Such an association could help unravel crucial information on these systems, for example, their BH spin distribution, the equation of state (EoS) of the neutron star and the rate of heavy element production. We modeled the multi-messenger (MM) emission from BHNS mergers detectable during the fourth (O4) and fifth (O5) observing runs of the LIGO-Virgo-KAGRA (LVK) GW detector network in order to provide detailed predictions that can help enhance the effectiveness of observational efforts and extract the highest possible scientific information from such remarkable events. Our methodology is based on a population synthesis approach, which includes the modeling of the signal-to-noise ratio of the GW signal in the detectors, the GW-inferred sky localization of the source, the kilonova (KN) optical and near-infrared light curves, the relativistic jet gamma-ray burst (GRB) prompt emission peak photon flux, and the GRB afterglow light curves in the radio, optical, and X-ray bands. The resulting prospects for BHNS MM detections during O4 are not promising, with an LVK GW detection rate of 15.0−8.8+15.4 yr−1, but joint MM rates of ∼10−1 yr−1 for the KN and ∼10−2 yr−1 for the jet-related emission. In O5, we found an overall increase in expected detection rates by around an order of magnitude, owing to both the enhanced sensitivity of the GW detector network and the coming online of future EM facilities. Considering variations in the NS EoS and BH spin distribution, we find that the detection rates can increase further by up to a factor of several tens. Finally, we discuss direct searches for the GRB radio afterglow with large field-of-view instruments during O5 and beyond as a new possible follow-up strategy in the context of ever-dimming prospects for KN detection due to the recession of the GW horizon.

Revisiting empirical solar energetic particle scaling relations

Aims. The possible influence of solar superflares on the near-Earth space radiation environment are assessed through the investigation of scaling laws between the peak proton flux and fluence of solar energetic particle (SEP) events with the solar flare soft X-ray peak photon flux. Methods. We compiled a catalog of 65 well-connected (W20-90) SEP events during the last three solar cycles covering a period of ∼34 yr (1984–2020) that were associated with flares of class ≥C6.0, and investigated the statistical relations between the recorded peak proton fluxes (IP) and the fluences (FP) at a set of integral energies from E > 10, > 30, and > 60 to > 100 MeV versus the associated solar flare peak soft X-ray flux in the 1–8 Å band (FSXR). Based on the inferred relations, we calculated the integrated energy dependence of the peak proton flux (IP) and fluence (FP) of the SEP events, assuming that they follow an inverse power law with respect to energy. Finally, we made use of simple physical assumptions, combining our derived scaling laws, and estimated the upper limits for IP and FP focusing on the flare associated with the strongest ground level enhancement (GLE) directly observed to date (GLE 05 on 23 February 1956), and that inferred for the cosmogenic radionuclide-based SEP event of AD774/775. Results. A scaling law relating IP and FP to the solar soft X-ray peak intensity (FSXR) as ∝ $ {F}_{\mathrm{SXR}}^{5/6} $ for a flare with a FSXR = X600 (in the revised scale) is consistent with values of FP inferred for the cosmogenic nuclide event of AD774/775.

Multi-messenger Observations of Binary Neutron Star Mergers in the O4 Run

We present realistic expectations for the number and properties of neutron star binary mergers to be detected as multi-messenger sources during the upcoming fourth observing run (O4) of the LIGO-Virgo-KAGRA gravitational-wave (GW) detectors, with the aim of providing guidance for the optimization of observing strategies. Our predictions are based on a population synthesis mode, which includes the GW signal-to-noise ratio, the kilonova (KN) optical and near-infrared light curves, the relativistic jet gamma-ray burst (GRB) prompt emission peak photon flux, and the afterglow light curves in radio, optical, and X-rays. Within our assumptions, the rate of GW events to be confidently detected during O4 is yr−1 (calendar year), 78% of which will produce a KN, and a lower 52% will also produce a relativistic jet. The typical depth of current optical electromagnetic search and follow-up strategies is still sufficient to detect most of the KNæ in O4, but only for the first night or two. The prospects for detecting relativistic jet emission are not promising. While closer events (within z ≲ 0.02) will likely still have a detectable cocoon shock breakout, most events will have their GRB emission (both prompt and afterglow) missed unless seen under a small viewing angle. This reduces the fraction of events with detectable jets to 2% (prompt emission, serendipitous) and 10% (afterglow, deep radio monitoring), corresponding to detection rates of and yr−1, respectively. When considering a GW subthreshold search triggered by a GRB detection, our predicted rate of joint GW+GRB prompt emission detections increases up to a more promising yr−1.

Bimodal distribution of short gamma-ray bursts: Evidence for two distinct types of short gamma-ray bursts

GRB 170817A was confirmed to be associated with GW170817, which was produced by a neutron star - neutron star merger. It indicates that at least some short gamma-ray bursts come from binary neutron star mergers. Theoretically, it is widely accepted that short gamma-ray bursts can be produced by two distinctly different mechanisms, binary neutron star mergers and neutron star - black hole mergers. These two kinds of bursts should be different observationally due to their different trigger mechanisms. Motivated by this idea, we collect a universal data set constituted of 51 short gamma-ray bursts observed by Swift/BAT, among which 14 events have extended emission component. We study the observational features of these 51 events statistically. It is found that our samples consist of two distinct groups. They clearly show a bimodal distribution when their peak photon fluxes at 15–150 keV band are plotted against the corresponding fluences. Most interestingly, all the 14 short bursts with extended emission lie in a particular region of this plot. When the fluences are plotted against the burst durations, short bursts with extended emission again tend to concentrate in the long duration segment. These features strongly indicate that short gamma-ray bursts really may come from two distinct types of progenitors. We argue that those short gamma-ray bursts with extended emission come from the coalescence of neutron stars, while the short gamma-ray bursts without extended emission come from neutron star - black hole mergers.

Hydrogen Peroxide Cycling in High-Temperature Acidic Geothermal Springs and Potential Implications for Oxidative Stress Response

Hydrogen peroxide (H2O2), superoxide (O2•-), and hydroxyl radicals (OH•) are produced in natural waters via ultraviolet (UV) light-induced reactions between dissolved oxygen (O2) and organic carbon, and further reaction of H2O2 and Fe(II) (i.e., Fenton chemistry). The temporal and spatial dynamics of H2O2 and other dissolved compounds (Fe(II), Fe(III), H2S, O2) were measured during a diel cycle (dark/light) in surface waters of three acidic geothermal springs (Beowulf Spring, One Hundred Springs Plain, and Echinus Geyser Spring; pH = 3-3.5, T = 68-80 °C) in Norris Geyser Basin, Yellowstone National Park. In situ analyses showed that H2O2 concentrations were lowest (ca. 1 μM) in geothermal source waters containing high dissolved sulfide (and where oxygen was below detection) and increased by two-fold (ca. 2-3 μM) in oxygenated waters corresponding to Fe(III)-oxide mat formation down the water channel. Small increases in dissolved oxygen and H2O2 were observed during peak photon flux, but not consistently across all springs sampled. Iron-oxide microbial mats were sampled for molecular analysis of ROS gene expression in two primary autotrophs of acidic Fe(III)-oxide mat ecosystems: Metallosphaera yellowstonensis (Archaea) and Hydrogenobaculum sp. (Bacteria). Expression (RT-qPCR) assays of specific stress-response genes (e.g., superoxide dismutase, peroxidases) of the primary autotrophs were used to evaluate possible changes in transcription across temporal, spatial and/or seasonal samples. Data presented here documented the presence of H2O2 and general correlation with dissolved oxygen. Moreover, two dominant microbial populations expressed ROS response genes throughout the day, but showed less expression of key genes during peak sunlight. Oxidative stress response genes (especially external peroxidases) were highly-expressed in microorganisms within Fe(III)-oxide mat communities, suggesting a significant role for these proteins during survival and growth in situ.

On the subclasses in Swift long gamma-ray bursts: A clue to different central engines

Abstract Analyzing light curves of a complete sample of bright Swift long gamma-ray bursts (LGRBs) of which the peak photon fluxes constructed with the bin width of one second in the Swift 15–350 keV energy band exceed 2.6 photons cm−2 s−1, we confirm that there does exist the third class of GRBs in addition to short and long GRBs. Being different from previous works based on the duration, fluence, etc., our classification method is based on two properties both quantified with light curve shapes of the prompt emission: the Absolute Deviation from the Constant Luminosity of their cumulative light curve ADCL, and the ratio of the mean counts to the maximum counts$\bar{C}/C_{\rm max}$. These are independent of the distance and the jet opening angle. A cluster analysis via the Gaussian mixture model detects three subclasses: one consisting of LGRBs with small ADCL and large $\bar{C}/C_{\rm max}$ values referred to as Type I, one with large ADCL and large $\bar{C}/C_{\rm max}$ referred to as Type II, and one with intermediate ADCL and small $\bar{C}/C_{\rm max}$, which is composed of contaminating short GRBs with the extended emission. This result is reinforced by different temporal and spectral indices of their X-ray afterglows. The difference is prominent in the temporal index of the steep decay phase in particular; the indices for Type I LGRBs distribute between −6 and −3 while those for Type II LGRBs are between −3 and −2. From these properties, we propose a possible scenario with different central engines: an accreting black hole and a magnetar.

Revisiting the Amati and Yonetoku correlations with Swift GRBs

We use a sample of \textit{Swift} gamma-ray bursts (GRBs) to analyze the Amati and Yonetoku correlations. The first relation is between $E_{p,i}$, the intrinsic peak energy of the prompt GRB emission, and $E_{iso}$, the equivalent isotropic energy. The second relation is between $E_{p,i}$ and $L_{iso}$, the isotropic peak luminosity. We select a sample of 71 \textit{Swift} GRBs that have a measured redshift and whose observed $E^{obs}_p$ is within the interval of energy 15-150 keV with a relative uncertainty of less than 70\%. We seek to find correlation relations for long-duration GRBs (LGRBs) with a peak photon flux $P_{ph}\geq 2.6~ \mathrm{ph/cm^{2}/s}$. Uncertainties (error bars) on the values of the calculated energy flux \textit{P}, the energy $E_{iso}$, and the peak isotropic luminosity $L_{iso}$ are estimated using a Monte Carlo approach. We find 27 \textit{Swift} LGRBs that satisfy all our constraints. Results of our analyses of the sample of 71 GRBs and the selected subsample (27 GRBs) are in good agreement with published results. The plots of the two relations for all bursts show a large dispersion around the best straight lines in the sample of 71 LGRBs but not so much in the subsample of 27 GRBs.

Susceptibility of the wild-derived inbred CAST/Ei mouse to infection by orthopoxviruses analyzed by live bioluminescence imaging

Classical inbred mice are extensively used for virus research. However, we recently found that some wild-derived inbred mouse strains are more susceptible than classical strains to monkeypox virus. Experiments described here indicated that the 50% lethal dose of vaccinia virus (VACV) and cowpox virus (CPXV) were two logs lower in wild-derived inbred CAST/Ei mice than classical inbred BALB/c mice, whereas there was little difference in the susceptibility of the mouse strains to herpes simplex virus. Live bioluminescence imaging was used to follow spread of pathogenic and attenuated VACV strains and CPXV virus from nasal passages to organs in the chest and abdomen of CAST/Ei mice. Luminescence increased first in the head and then simultaneously in the chest and abdomen in a dose-dependent manner. The spreading kinetics was more rapid with VACV than CPXV although the peak photon flux was similar. These data suggest advantages of CAST/Ei mice for orthopoxvirus studies.

Upgrade of Saga-university beamline in SAGA-LS

Saga-university beamline has been upgraded by installing a new planar-typ e undulator for advanced researches on nano-surfaces and interfaces in the soft X-ray region. The magnetic field of the undulator along the electron beam trajectory was measured at the magnetic gap width between 30 and 150 mm. After the installation of the undulator in a 2.7-m straight section of the Saga-LS storage ring, the performance of the beamline with varied line spacing plane grating monochromator was examined by measurements of peak energy, photon flux, and energy resolution. The beamline is opened for the experimental use in the energy region between 32 and 800 eV using fundamental and the higher harmonics.

On the environment of short gamma-ray bursts

In this paper we present a sample of 10 short gamma-ray bursts (GRBs) with a robust redshift determination, discovered by the Swift satellite up to January 2011. We measure their X-ray absorbing column densities and collect data on the host galaxy offsets. We find evidence for intrinsic absorption and no correlation between the intrinsic absorbing column density and the projected offset of the GRB from its host galaxy center. We find that the properties in the gamma regime (T90, fluence and 1-s peak photon flux) of short GRBs with "bright" and "faint" X-ray afterglow likely disfavour different prompt emission mechanisms. Host galaxy offset and GRB duration (T90) do not correlate. Instead, there is a hint of anti-correlation between the effective radius normalised host galaxy offset and T90. Finally, we examine the properties of short GRBs with short-lived and long-lived X-ray afterglows, finding that some short GRBs with short-lived X-ray afterglows have their optical afterglow detected. In light of this, the X-ray afterglow duration does not seem to be an unique indicator of a specific progenitor and/or environment for short GRBs.

A COMPLETE SAMPLE OF BRIGHTSWIFTLONG GAMMA-RAY BURSTS. I. SAMPLE PRESENTATION, LUMINOSITY FUNCTION AND EVOLUTION

We present a carefully selected sub-sample of Swift Long Gamma-ray Bursts (GRBs), that is complete in redshift. The sample is constructed by considering only bursts with favorable observing conditions for ground-based follow-up searches, that are bright in the 15-150 keV Swift/BAT band, i.e. with 1-s peak photon fluxes in excess to 2.6 ph s^-1 cm^-2. The sample is composed by 58 bursts, 52 of them with redshift for a completeness level of 90%, while another two have a redshift constraint, reaching a completeness level of 95%. For only three bursts we have no constraint on the redshift. The high level of redshift completeness allows us for the first time to constrain the GRB luminosity function and its evolution with cosmic times in a unbiased way. We find that strong evolution in luminosity (d_l=2.3\pm 0.6) or in density (d_d=1.7\pm 0.5) is required in order to account for the observations. The derived redshift distribution in the two scenarios are consistent with each other, in spite of their different intrinsic redshift distribution. This calls for other indicators to distinguish among different evolution models. Complete samples are at the base of any population studies. In future works we will use this unique sample of Swift bright GRBs to study the properties of the population of long GRBs.

GAMMA-RAY ACTIVITY IN THE CRAB NEBULA: THE EXCEPTIONAL FLARE OF 2011 APRIL

The Large Area Telescope on board the Fermi satellite observed a gamma-ray flare in the Crab nebula lasting for approximately nine days in April of 2011. The source, which at optical wavelengths has a size of ~11 ly across, doubled its gamma-ray flux within eight hours. The peak photon flux was (186 +- 6) 10-7 cm-2 s-1 above 100 MeV, which corresponds to a 30-fold increase compared to the average value. During the flare, a new component emerged in the spectral energy distribution, which peaked at an energy of (375 +- 26) MeV at flare maximum. The observations imply that the emission region was likely relativistically beamed toward us and that variations in its motion are responsible for the observed spectral variability.

Photon flux requirements for extreme ultraviolet reticle imaging in the 22- and 16-nm nodes

Extreme UV (EUV)-wavelength actinic microscopy yields detailed information about EUV mask patterns, architectures, defects, and the performance of defect repair strategies without the complications of photoresist imaging.To understand the pattern measurement limits of EUV mask microscopy, we investigate the effects of shot noise on aerial image linewidth measurements in the 22- and 16-nm lithography generations. Using a simple model we probe the influence of photon shot noise on measured, apparent line roughness, and find general flux density requirements independent of the specific EUV microscope configurations. Analysis reveals the trade-offs between photon energy density, effective pixel dimension on the CCD, and image log slope (ILS). We find that shot-noise-induced linewidth roughness (LWR) varies inversely with the square root of the photon energy density and is proportional to the magnification ratio. While high magnification is necessary for adequate spatial resolution, for a given flux density, higher magnification ratios have diminishing benefits. We find that to achieve an LWR (3) value of 5% of linewidth for dense, 88-nm mask features with a 2.52 normalized ILS value (image log-slope, ILS, equal to 28.6/µm) and 13.5-nm effective pixel width (1000 × magnification ratio), a peak photon flux of approximately 1400 photons/pixel per exposure is required.

Driver linac design for a femtosecond head-on inverse Compton scatteringX-ray source

The feasibility of generating an ultra-short relativistic electron beam with a thermionic cathode rf gun driver linac for a femtosecond head-on inverse Compton scattering (ICS) X-ray source has been examined by space charge tracking throughout the entire beamline, from the cathode to the interaction point. It has been determined that GHz-repetition-rate electron pulses as short as 49 fs can be produced by compressing the energy-chirped beam from a 2998-MHz, 1.5-cell rf gun with an alpha magnet and an rf linac operating at the injection phase near the zero crossing. These electron pulses, with a 42-pC bunch charge, are accelerated to 27 MeV with an S-band traveling-wave constant-gradient linac structure for the ICS in an interaction chamber located downstream. The driver linac design that allows the operation of an ultra-short ICS X-ray source at a 0.7-Å wavelength, with a peak photon flux of 9.08×10 17 photons/s, is presented in this paper.

INTENSITY DISTRIBUTION AND LUMINOSITY FUNCTION OF THE SWIFT GAMMA-RAY BURSTS

Using the sample of long Gamma-ray bursts (GRBs) detected by Swift-BAT before June 2007, we measure the cumulative distribution of the peak photon fluxes (log N - log P) of the Swift bursts. Compared with the BATSE sample, we find that the two distributions are consistent after correcting the band pass difference, suggesting that the two instruments are sampling the same population of bursts. We also compare the log N - log P distributions for sub-samples of the Swift bursts, and find evidence for a deficit (99.75% confident) of dark bursts without optical counterparts at high peak flux levels, suggesting different redshift or Gamma-ray luminosity distributions for these bursts. The consistency between the log N - log P distributions for the optically detected bursts with and without redshift measurements indicates that the current sample of the Swift bursts with redshift measurements, although selected heterogeneously, represents a fair sample of the non-dark bursts. We calculate the luminosity functions of this sample in two redshift bins (z<1 and z>1), and find a broken power-law is needed to fit the low redshift bin, where dN/dL \propto L^{-1.27\pm0.06} for high luminosities (L_{peak} > 5e48 erg/s) and dN/dL \propto L^{-2.3\pm0.3} at for low luminosities, confirming the results of several studies for a population of low luminosity GRBs.

An Unusual Precursor Burst with Oscillations from SAX J1808.4−3658

We report the finding of an unusual, weak precursor to a thermonuclear X-ray burst from the accreting millisecond pulsar SAX 51808.4-3658. The burst in question was observed on Oct. 19, 2002 with the Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA). The precursor began approx. equal to 1 s prior to the onset of a strong radius expansion burst, lasted for about 0.4 s, and exhibited strong oscillations at the 401 Hz spin frequency. Oscillations are not detected in the approx. equal to 0.5 s interval between the precursor and the main burst. The estimated peak photon flux and energy fluence of the precursor are about 1/25, and 1/500 that of the main burst, respectively. From joint spectral and temporal modeling, we find that an expanding burning region with a relatively low temperature on the spinning neutron star surface can explain the oscillations, as well as the faintness of the precursor with respect to the main part of the burst. We discuss some of the implications of our findings for the ignition and spreading of thermonuclear flames on neutron stars.

The Complete Spectral Catalog of Bright BATSE Gamma‐Ray Bursts

We present a systematic spectral analysis of 350 bright gamma-ray bursts (GRBs) observed with the Burst and Transient Source Experiment (BATSE; ~30 keV-2 MeV) with high temporal and spectral resolution. Our sample was selected from the complete set of 2704 BATSE GRBs based on their energy fluence or peak photon flux values to assure good statistics and included 17 short GRBs. To obtain well-constrained spectral parameters, several photon models were used to fit each spectrum. We compared spectral parameters resulting from the fits using different models, and the spectral parameters that best represent each spectrum were statistically determined, taking into account the parameterization differences among the models. A thorough analysis was performed on 350 time-integrated and 8459 time-resolved burst spectra, and the effects of integration times in determining the spectral parameters were explored. Using the results, we studied correlations among spectral parameters and their evolution pattern within each burst. The resulting spectral catalog is the most comprehensive study of spectral properties of GRB prompt emission to date and is available electronically from the High-Energy Astrophysics Science Archive Research Center (HEASARC). The catalog provides reliable constraints on particle acceleration and emission mechanisms in GRBs.

Constraining the Structure of Gamma‐Ray Burst Jets through the logN–logSDistribution

A general formalism is developed for calculating the luminosity function and the expected number N of observed gamma-ray bursts (GRBs) above a peak photon flux S for an arbitrary GRB jet structure. This formalism directly provides the true GRB rate for any jet model, instead of first calculating the GRB rate assuming isotropic emission and then introducing a "correction factor" to account for effects of the GRB jet structure, as was done in previous works. We apply it to the uniform jet (UJ) and universal structured jet (USJ) models for the structure of GRB jets and perform fits to the observed log N- log S distribution from the GUSBAD catalog, which contains 2204 BATSE bursts. We allow for a scatter in the peak luminosity L for a given jet half-opening angle θj (viewing angle θobs) in the UJ (USJ) model, which is implied by observations. A core angle θc and an outer edge at θmax are introduced for the structured jet, and a finite range of opening angles θmin ≤ θj ≤ θmax is assumed for the uniform jets. The efficiency for producing γ-rays, γ, and the energy per solid angle in the jet, , are allowed to vary with θj (θobs) in the UJ (USJ) model, γ ∝ θ-b and ∝ θ-a. We find that a single power-law luminosity function provides a good fit to the data. Such a luminosity function arises naturally in the USJ model, while in the UJ model it implies a power-law probability distribution for θj, P(θj) ∝ θ. The value of q cannot be directly determined from the fit to the observed log N- log S distribution, and an additional assumption on the value of a or b is required. Alternatively, an independent estimate of the true GRB rate would enable one to determine a, b, and q. The implied values of θc (or θmin) and θmax are close to the current observational limits. The true GRB rate for the USJ model is found to be RGRB(z = 0) = 0.86 Gpc-3 yr-1 (1 σ), while for the UJ model it is higher by a factor f(q), which strongly depends on the unknown value of q.

Comparison of the Gamma‐Ray Burst Sensitivity of Different Detectors

Gamma-ray burst detectors are sensitive at different energies, complicating the comparison of the burst populations that they detect. The instrument teams often report their detector sensitivities in their instruments' energy band. I propose that sensitivities be reported as the threshold peak photon flux F_T over the 1-1000 keV energy band for a specific spectral shape. The primary spectral parameter is E_p, the energy of the maximum E^2 N_E propto nu f_nu. Thus F_T vs. E_p is a useful description of a detector's sensitivity. I find that Swift will be marginally more sensitive than BATSE for E_p>100 keV, but significantly more sensitive for E_p<100 keV. Because of its low energy sensitivity, the FREGATE on HETE-2 is surprisingly sensitive below E_p=100 keV. Both the WFC on BeppoSAX and the WXM on HETE-2 are/were sensitive for low E_p. As expected, the GBM on GLAST will be less sensitive than BATSE, while EXIST will be significantly more sensitive than Swift. The BeppoSAX GRBM was less sensitive that the WFC, particularly at low E_p.

Correlations between intensity and spectral hardness in GRBs

We studied the distribution of the peak photon flux as a function of the spectral hardness (in this paper represented by the hardness-ratio) for the 4B BATSE cat- alog events. The maximum value of the peak distribution shows, for the rst part of the hardness ratio variability range, clear positive correlation with the hardness-ratio up to a given value of the hardness-ratio. On the con- trary, for higher hardness-ratio values, an anticorrelation is present. Possible interpretations of these peculiar be- haviors are briefly discussed.