arXiv subjects

Tomonori Totani

Publications and source records attributed to Tomonori Totani.

At least 55 records · Page 3Linked to original sources

arXiv2014

FIELD: An automated emission-line detection software for Subaru/FMOS near-infrared spectroscopy

We describe the development of automated emission line detection software for the Fiber Multi-Object Spectrograph (FMOS), which is a near-infrared spectrograph fed by $400$ fibers from the $0.2$ deg$^2$ prime focus field of view of the Subaru Telescope. The software, FIELD (FMOS software for Image-based Emission Line Detection), is developed and tested mainly for the FastSound survey, which is targeting H$α$ emitting galaxies at $z \sim 1.3$ to measure the redshift space distortion as a test of general relativity beyond $z \sim 1$. The basic algorithm is to calculate the line signal-to-noise ratio ($S/N$) along the wavelength direction, given by a 2-D convolution of the spectral image and a detection kernel representing a typical emission line profile. A unique feature of FMOS is its use of OH airglow suppression masks, requiring the use of flat-field images to suppress noise around the mask regions. Bad pixels on the detectors and pixels affected by cosmic-rays are efficiently removed by using the information obtained from the FMOS analysis pipeline. We limit the range of acceptable line-shape parameters for the detected candidates to further improve the reliability of line detection. The final performance of line detection is tested using a subset of the FastSound data; the false detection rate of spurious objects is examined by using inverted frames obtained by exchanging object and sky frames. The false detection rate is $< 1$\% at $S/N > 5$, allowing an efficient and objective emission line search for FMOS data at the line flux level of $\gtrsim 1.0 \times 10^{-16}$[erg/cm$^2$/s].

astro-ph.IM↗

arXiv2014

Unveiling the Origin of Fast Radio Bursts by Optical Follow Up Observations

We discuss how we can detect and identify counterparts of fast radio bursts (FRBs) in future optical follow up observations of FRBs if real-time alert of FRBs becomes available. We consider kilonovae as candidates of FRB optical counterparts, as expected in the case that FRBs originate from mergers of double neutron star binaries. Although theoretical predictions on luminosities of kilonovae are still highly uncertain, recent models suggest that kilonovae can be detected at redshifts up to z $\sim$ 0.3 within the range of the uncertainties. We expect $\sim$ 1--5 unrelated supernovae (SNe) down to a similar variability magnitude in 5 days interval within the typical error radius of a FRB. We show that, however, a kilonova can be distinguished from these SNe by its rapid decay and/or color evolution, making it possible to verify the existence of a kilonova associated with a FRB. We also discuss the case that SNe Ia are FRB optical counterparts, as it might be if FRBs originate from double white dwarf binaries. Verification of this scenario is also possible, since the chance probability of finding a SNe Ia having consistent explosion time with that of a FRB within the FRB error region is small (typically $\lesssim$ 0.01).

astro-ph.HE↗

arXiv2014

On the Systematic Errors of Cosmological-Scale Gravity Tests using Redshift Space Distortion: Non-linear Effects and the Halo Bias

Redshift space distortion (RSD) observed in galaxy redshift surveys is a powerful tool to test gravity theories on cosmological scales, but the systematic uncertainties must carefully be examined for future surveys with large statistics. Here we employ various analytic models of RSD and estimate the systematic errors on measurements of the structure growth-rate parameter, $fσ_8$, induced by non-linear effects and the halo bias with respect to the dark matter distribution, by using halo catalogues from 40 realisations of $3.4 \times 10^8$ comoving $h^{-3}$Mpc$^3$ cosmological N-body simulations. We consider hypothetical redshift surveys at redshifts z=0.5, 1.35 and 2, and different minimum halo mass thresholds in the range of $5.0 \times 10^{11}$ -- $2.0 \times 10^{13} h^{-1} M_\odot$. We find that the systematic error of $fσ_8$ is greatly reduced to ~5 per cent level, when a recently proposed analytical formula of RSD that takes into account the higher-order coupling between the density and velocity fields is adopted, with a scale-dependent parametric bias model. Dependence of the systematic error on the halo mass, the redshift, and the maximum wavenumber used in the analysis is discussed. We also find that the Wilson-Hilferty transformation is useful to improve the accuracy of likelihood analysis when only a small number of modes are available in power spectrum measurements.

astro-ph.CO↗

arXiv2014

Galaxy luminosity function and its cosmological evolution: Testing a new feedback model depending on galaxy-scale dust opacity

We present a new version of a semi-analytic model of cosmological galaxy formation, incorporating a star formation law with a feedback depending on the galaxy-scale mean dust opacity and metallicity, motivated by recent observations of star formation in nearby galaxies and theoretical considerations. This new model is used to investigate the effect of such a feedback on shaping the galaxy luminosity function and its evolution. Star formation activity is significantly suppressed in dwarf galaxies by the new feedback effect, and the faint-end slope of local luminosity functions can be reproduced with a reasonable strength of supernova feedback, which is in contrast to the previous models that require a rather extreme strength of supernova feedback. Our model can also reproduce the early appearance of massive galaxies manifested in the bright-end of high redshift K-band luminosity functions. Though some of the previous models also succeeded in reproducing this, they assumed a star formation law depending on the galaxy-scale dynamical time, which is not supported by observations. We argue that the feedback depending on dust opacity (or metal column density) is essential, rather than that simply depending on gas column density, to get these results.

astro-ph.CO↗

arXiv2014

Probing Intergalactic Neutral Hydrogen by the Lyman Alpha Red Damping Wing of Gamma-Ray Burst 130606A Afterglow Spectrum at z = 5.913

The unprecedentedly bright optical afterglow of GRB 130606A located by Swift at a redshift close to the reionization era (z = 5.913) provides a new opportunity to probe the ionization status of intergalactic medium (IGM). Here we present an analysis of the red Ly alpha damping wing of the afterglow spectrum taken by Subaru/FOCAS during 10.4-13.2 hr after the burst. We find that the minimal model including only the baseline power-law and HI absorption in the host galaxy does not give a good fit, leaving residuals showing concave curvature in 8400-8900 A with an amplitude of about 0.6% of the flux. Such a curvature in the short wavelength range cannot be explained either by extinction at the host with standard extinction curves, intrinsic curvature of afterglow spectra, or by the known systematic uncertainties in the observed spectrum. The red damping wing by intervening HI gas outside the host can reduce the residual by about 3 sigma statistical significance. We find that a damped Ly alpha system is not favored as the origin of this intervening HI absorption, from the observed Ly beta and metal absorption features. Therefore absorption by diffuse IGM remains as a plausible explanation. A fit by a simple uniform IGM model requires HI neutral fraction of f_HI ~ 0.1-0.5 depending on the distance to the GRB host, implying high f_HI IGM associated with the observed dark Gunn-Peterson (GP) troughs. This gives a new evidence that the reionization is not yet complete at z ~ 6.

astro-ph.HE↗

arXiv2014

The Type Ia supernovae rate with Subaru/XMM-Newton Deep Survey

We present measurements of the rates of high-redshift Type Ia supernovae derived from the Subaru/XMM-Newton Deep Survey (SXDS). We carried out repeat deep imaging observations with Suprime-Cam on the Subaru Telescope, and detected 1040 variable objects over 0.918 deg$^2$ in the Subaru/XMM-Newton Deep Field. From the imaging observations, light curves in the observed $i'$-band are constructed for all objects, and we fit the observed light curves with template light curves. Out of the 1040 variable objects detected by the SXDS, 39 objects over the redshift range $0.2 < z < 1.4$ are classified as Type Ia supernovae using the light curves. These are among the most distant SN Ia rate measurements to date. We find that the Type Ia supernova rate increase up to $z \sim 0.8$ and may then flatten at higher redshift. The rates can be fitted by a simple power law, $r_V(z)=r_0(1+z)^α$ with $r_0=0.20^{+0.52}_{-0.16}$(stat.)$^{+0.26}_{-0.07}$(syst.)$\times 10^{-4} {\rm yr}^{-1}{\rm Mpc}^{-3}$, and $α=2.04^{+1.84}_{-1.96}$(stat.)$^{+2.11}_{-0.86}$(syst.).

astro-ph.CO↗

arXiv2013

A Study of Selection Methods for H alpha Emitting Galaxies at z~1.3 for the Subaru/FMOS Galaxy Redshift Survey for Cosmology (FastSound)

The efficient selection of high-redshift emission galaxies is important for future large galaxy redshift surveys for cosmology. Here we describe the target selection methods for the FastSound project, a redshift survey for H alpha emitting galaxies at z=1.2-1.5 using Subaru/FMOS to measure the linear growth rate fσ8 via Redshift Space Distortion (RSD) and constrain the theory of gravity. To select ~400 target galaxies in the 0.2 deg^2 FMOS field-of-view from photometric data of CFHTLS-Wide (u*g'r'i'z'), we test several different methods based on color-color diagrams or photometric redshift estimates from spectral energy distribution (SED) fitting. We also test the improvement in selection efficiency that can be achieved by adding near-infrared data from the UKIDSS DXS (J). The success rates of H alpha detection with FMOS averaged over two observed fields using these methods are 11.3% (color-color, optical), 13.6% (color-color, optical+NIR), 17.3% (photo-z, optical), and 15.1% (photo-z, optical+NIR). Selection from photometric redshifts tends to give a better efficiency than color-based methods, although there is no significant improvement by adding J band data within the statistical scatter. We also investigate the main limiting factors for the success rate, by using the sample of the HiZELS H alpha emitters that were selected by narrow-band imaging. Although the number density of total H alpha emitters having higher H alpha fluxes than the FMOS sensitivity is comparable with the FMOS fiber density, the limited accuracy of photometric redshift and H alpha flux estimations have comparable effects on the success rate of <~20% obtained from SED fitting.

astro-ph.CO↗

arXiv2013

Cosmological Fast Radio Bursts from Binary Neutron Star Mergers

Fast radio bursts (FRBs) at cosmological distances have recently been discovered, whose duration is about milliseconds. We argue that the observed short duration is difficult to explain by giant flares of soft gamma-ray repeaters, though their event rate and energetics are consistent with FRBs. Here we discuss binary neutron star (NS-NS) mergers as a possible origin of FRBs. The FRB rate is within the plausible range of NS-NS merger rate and its cosmological evolution, while a large fraction of NS-NS mergers must produce observable FRBs. A likely radiation mechanism is coherent radio emission like radio pulsars, by magnetic braking when magnetic fields of neutron stars are synchronized to binary rotation at the time of coalescence. Magnetic fields of the standard strength (~ 10^{12-13} G) can explain the observed FRB fluxes, if the conversion efficiency from magnetic braking energy loss to radio emission is similar to that of isolated radio pulsars. Corresponding gamma-ray emission is difficult to detect by current or past gamma-ray burst satellites. Since FRBs tell us the exact time of mergers, a correlated search would significantly improve the effective sensitivity of gravitational wave detectors.

astro-ph.HE↗

arXiv2013

Constraints on f(R) theory and Galileons from the latest data of galaxy redshift surveys

The growth rate of matter density perturbations has been measured from redshift-space distortion (RSD) in the galaxy power spectrum. We constrain the model parameter space for representative modified gravity models to explain the dark energy problem, by using the recent data of f_m(z)sigma_8(z) at the redshifts z = 0.06--0.8 measured by WiggleZ, SDSS LRG, BOSS, and 6dFGRS. We first test the Hu-Sawicki's f(R) dark energy model, and find that only the parameter region close to the standard Lambda Cold Dark Matter (Lambda-CDM) model is allowed (lambda > 12 and 5 for n = 1.5 and 2, respectively, at 95% CL). We then investigate the covariant Galileon model and show that the parameter space consistent with the background expansion history is excluded by the RSD data at more than 10 sigma because of the too large growth rate predicted by the theory. Finally, we consider the extended Galileon scenario, and we find that, in contrast to the covariant Galileon, there is a model parameter space for a tracker solution that is consistent with the RSD data within a 2 sigma level.

astro-ph.CO↗

arXiv2013

Extragalactic Background Light from Hierarchical Galaxy Formation: Gamma-ray Attenuation up to the Epoch of Cosmic Reionization and the First Stars

We present a new model of the extragalactic background light (EBL) and corresponding gamma-gamma opacity for intergalactic gamma-ray absorption from z = 0 up to z = 10, based on a semi-analytical model of hierarchical galaxy formation that reproduces key observed properties of galaxies at various redshifts. Including the potential contribution from Population III stars and following the cosmic reionization history in a simplified way, the model is also broadly consistent with available data concerning reionization, particularly the Thomson scattering optical depth constraints from WMAP. In comparison with previous EBL studies up to z ~ 3-5, our predicted gamma-gamma opacity is in general agreement for observed gamma-ray energy below 400/(1 + z) GeV, whereas it is a factor of ~ 2 lower above this energy because of a correspondingly lower cosmic star formation rate, even though the observed UV luminosity is well reproduced by virtue of our improved treatment of dust obscuration and direct estimation of star formation rate. The horizon energy at which the gamma-ray opacity is unity does not evolve strongly beyond z ~ 4 and approaches ~ 20 GeV. The contribution of Population III stars is a minor fraction of the EBL at z = 0, and is also difficult to distinguish through gamma-ray absorption in high-z objects, even at the highest levels allowed by the WMAP constraints. Nevertheless, the attenuation due to Population II stars should be observable in high-z gamma-ray sources by telescopes such as Fermi or CTA and provide a valuable probe of the evolving EBL in the rest-frame UV. The detailed results of our model are publicly available in numerical form at the URL http://www.slac.stanford.edu/~yinoue/Download.html.

astro-ph.CO↗

arXiv2013

Potential of EBL and cosmology studies with the Cherenkov Telescope Array

Very high energy (VHE, E >100 GeV) gamma-rays are absorbed via interaction with low-energy photons from the extragalactic background light (EBL) if the involved photon energies are above the threshold for electron-positron pair creation. The VHE gamma-ray absorption, which is energy dependent and increases strongly with redshift, distorts the VHE spectra observed from distant objects. The observed energy spectra of the AGNs carry, therefore, an imprint of the EBL. The detection of VHE gamma-ray spectra of distant sources (z = 0.11 - 0.54) by current generation Imaging Atmospheric Cherenkov Telescopes (IACTs) enabled to set strong upper limits on the EBL density, using certain basic assumptions about blazar physics. In this paper it is studied how the improved sensitivity of the Cherenkov Telescope Array (CTA) and its enlarged energy coverage will enlarge our knowledge about the EBL and its sources. CTA will deliver a large sample of AGN at different redshifts with detailed measured spectra. In addition, it will provide the exciting opportunity to use gamma ray bursts (GRBs) as probes for the EBL density at high redshifts.

astro-ph.CO↗

arXiv2013

Supernova Neutrino Light Curves and Spectra for Various Progenitor Stars: From Core Collapse to Proto-neutron Star Cooling

We present a new series of supernova neutrino light curves and spectra calculated by numerical simulations for a variety of progenitor stellar masses (13-50Msolar) and metallicities (Z = 0.02 and 0.004), which would be useful for a broad range of supernova neutrino studies, e.g., simulations of future neutrino burst detection by underground detectors, or theoretical predictions for the relic supernova neutrino background. To follow the evolution from the onset of collapse to 20 s after the core bounce, we combine the results of neutrino-radiation hydrodynamic simulations for the early phase and quasi-static evolutionary calculations of neutrino diffusion for the late phase, with different values of shock revival time as a parameter that should depend on the still unknown explosion mechanism. We here describe the calculation methods and basic results including the dependence on progenitor models and the shock revival time. The neutrino data are publicly available electronically.

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arXiv2012

Suzaku Observation of Abell 1555 and Abell 1558: Searching for Non-thermal Emission from Large Scale Structure Formation

We report X-ray observations of two galaxy clusters Abell 1555 and Abell 1558 with Suzaku, which are included in a large scale filamentary structure and a supercluster, to search for non-thermal emission driven by shocks produced in structure formation. These two clusters are detected by Suzaku/XIS for the first time in the X-ray band of 0.5-7 keV. No significant flux is detected by HXD in the energy band of 13-40 keV, and upper limits are reported. From the analysis of the XIS data, we find that the spectrum of A1555 is fit by a thermal plus power-law model, significantly better than a single-temperature pure thermal spectrum. If this power-law component is due to inverse-Compton scattering, the fraction of total baryon energy imparted to non-thermal electrons is consistent with the typical value inferred from the observation of other clusters. However, other scenarios (e.g., under lying AGNs, multi-temperature thermal models) cannot be excluded and further investigation of this system is desired. Basic physical properties of A1555 (e.g., total mass) are also reported.

astro-ph.CO↗

arXiv2012

Infrared Spectral Energy Distribution of Galaxies in the AKARI All Sky Survey: Correlations with Galaxy Properties, and Their Physical Origin

We have studied the properties of more than 1600 low-redshift galaxies by utilizing high-quality infrared flux measurements of the AKARI All-Sky Survey and physical quantities based on optical and 21-cm observations. Our goal is to understand the physics determining the infrared spectral energy distribution (SED). The ratio of the total infrared luminosity L_TIR, to the star-formation rate (SFR) is tightly correlated by a power-law to specific SFR (SSFR), and L_TIR is a good SFR indicator only for galaxies with the largest SSFR. We discovered a tight linear correlation for normal galaxies between the radiation field strength of dust heating, estimated by infrared SED fits (U_h), and that of galactic-scale infrared emission (U_TIR ~ L_TIR/R^2), where R is the optical size of a galaxy. The dispersion of U_h along this relation is 0.3 dex, corresponding to 13% dispersion in the dust temperature. This scaling and the U_h/U_TIR ratio can be explained physically by a thin layer of heating sources embedded in a thicker, optically-thick dust screen. The data also indicate that the heated fraction of the total dust mass is anti-correlated to the dust column density, supporting this interpretation. In the large U_TIR limit, the data of circumnuclear starbursts indicate the existence of an upper limit on U_h, corresponding to the maximum SFR per gas mass of ~ 10 Gyr^{-1}. We find that the number of galaxies sharply drops when they become optically thin against dust-heating radiation, suggesting that a feedback process to galaxy formation (likely by the photoelectric heating) is working when dust-heating radiation is not self-shielded on a galactic scale. Implications are discussed for the M_HI-size relation, the Kennicutt-Schmidt relation, and galaxy formation in the cosmological context.

astro-ph.GA↗

arXiv2011

Suzaku X-ray Follow-up Observations of Seven Unassociated Fermi-LAT Gamma-ray Sources at High Galactic Latitudes

We report on our second-year campaign of X-ray follow-up observations of unidentified Fermi-LAT γ-ray sources at high Galactic latitudes (|b|>10 degree) using the X-ray Imaging Spectrometer onboard the Suzaku X-ray Observatory. In this second year of the project, seven new targets were selected from the First Fermi-LAT Catalog, and studied with 20-40 ks effective Suzaku exposures. We detected an X-ray point source coincident with the position of the recently discovered millisecond pulsar PSR J2302+4442 within the 95% confidence error circle of 1FGL J2302.8+4443. The X-ray spectrum of the detected counterpart was well fit by a blackbody model with temperature of kT ~0.3 keV, consistent with an origin of the observed X-ray photons from the surface of a rotating magnetized neutron star. For four other targets which were also recently identified with a normal pulsar (1FGL J0106.7+4853) and millisecond pulsars (1FGL J1312.6+0048, J1902.0-5110, and J2043.2+1709), only upper limits in the 0.5-10 keV band were obtained at the flux levels of ~10^{-14} erg cm^{-2} s^{-1}. A weak X-ray source was found in the field of 1FGL J1739.4+8717, but its association with the variable γ-ray emitter could not be confirmed with the available Suzaku data alone. For the remaining Fermi-LAT object 1FGL J1743.8-7620 no X-ray source was detected within the LAT 95% error ellipse. We briefly discuss the general properties of the observed high Galactic-latitude Fermi-LAT objects by comparing their multiwavelength properties with those of known blazars and millisecond pulsars.

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arXiv2011

Supernovae in the Subaru Deep Field: the rate and delay-time distribution of type Ia supernovae out to redshift 2

The type Ia supernova (SN Ia) rate, when compared to the cosmic star formation history (SFH), can be used to derive the delay-time distribution (DTD) of SNe Ia, which can distinguish among progenitor models. We present the results of a SN survey in the Subaru Deep Field (SDF). Over a period of 3 years, we have observed the SDF on 4 independent epochs with Suprime-Cam on the Subaru 8.2-m telescope, with 2 nights of exposure per epoch, in the R, i', and z' bands. We have discovered 150 SNe out to redshift z~2. Using 11 photometric bands from the observer-frame far-ultraviolet to the near-infrared, we derive photometric redshifts for the SN host galaxies (for 24 we also have spectroscopic redshifts). This information is combined with the SN photometry to determine the type and redshift distribution of the SN sample. Our final sample includes 28 SNe Ia in the range 1.0<z<1.5 and 10 in the range 1.5<z<2.0. Our SN Ia rate measurements are consistent with those derived from the HST/GOODS sample, but the overall uncertainty of our 1.5<z<2.0 measurement is a factor of 2 smaller, of 35-50%. We find that the SN Ia rate evolution levels off at 1.0<z<2.0, but shows no sign of declining. Combining our SN Ia rate measurements and those from the literature, and comparing to a wide range of possible SFHs, the best-fit DTD is a power law of the form Psi(t) ~ t^beta, with beta = -1.1 +/- 0.1 (statistical) +/- 0.17 (systematic). This result is consistent with other recent DTD measurements at various redshifts and environments, and is in agreement with a generic prediction of the double-degenerate progenitor scenario for SNe Ia. By combining the contribution to iron production from core-collapse SNe, based on the wide range of SFHs, with that from SNe Ia, calculated with the best-fit DTD, we predict that the mean present-day cosmic iron abundance is in the range Z(Fe) = (0.09-0.37) Z(Fe,Sun) (abridged).

astro-ph.CO↗

arXiv2011

Unraveling the Nature of Unidentified High Galactic Latitude Fermi/LAT Gamma-ray Sources with Suzaku

We report on the results of deep X-ray follow-up observations of four unidentified Fermi/LAT gamma-ray sources at high Galactic latitudes using Suzaku. The studied objects were detected with high significance during the first 3 months of Fermi/LAT operation, and subsequently better localized in the Fermi/LAT 1 year catalog (1FGL). Possible associations with pulsars and active galaxies have subsequently been discussed, and our observations provide an important contribution to this debate. In particular, an X-ray point source was found within the 95% confidence error circle of 1FGL J1231.1-1410. X-ray spectrum is well-fitted by a blackbody with an additional power-law. This supports the recently claimed identification of this source with a millisecond pulsar (MSP) PSR J1231-1411. Concerning 1FGL J1311.7-3429, two X-ray sources were found within the LAT error circle. Even though the X-ray spectral and variability properties were accessed, their nature and relationship with the gamma-ray source remain uncertain. We found several weak X-ray sources in the field of 1FGL J1333.2+5056, one coinciding with CLASS J1333+5057. We argue the available data are consistent with the association between these two objects. Finally, we have detected an X-ray source in the vicinity of 1FGL J2017.3+0603. This object was recently suggested to be associated with a newly discovered MSP PSR J2017+0603, because of the spatial-coincidence and the gamma-ray pulse detection. We have only detected the X-ray counterpart of the CLASS J2017+0603, while we determined an X-ray flux upper limit at the pulsar position. All in all, our studies indicate while a significant fraction of unidentified high Galactic latitude gamma-ray sources is related to the pulsar and blazar phenomena, associations with other classes of astrophysical objects are still valid options.

astro-ph.HE↗

arXiv2010

Contribution from Star-Forming Galaxies to the Cosmic Gamma-Ray Background Radiation

We present a new theoretical calculation of the contribution to the extragalactic gamma-ray background radiation (EGRB) from star-forming galaxies, based on a state-of-the-art model of hierarchical galaxy formation that is in quantitative agreement with a variety of observations of local and high-redshift galaxies. Gamma-ray luminosity ($L_γ$) and spectrum of galaxies are related to star formation rate ($ψ$), gas mass ($M_gas$), and star formation mode (quiescent or starburst) of model galaxies using latest observed data of nearby galaxies. We try the two limiting cases about gamma-ray production: the escape limit ($L_γ\propto ψM_gas$) and the calorimetric limit ($L_γ\propto ψ$), and our standard model predicts 7 and 4% contribution from star-forming galaxies to the total EGRB flux (including bright resolved sources) recently reported by the Fermi Gamma-Ray Space Telescope. Systematic uncertainties do not allow us to determine the EGRB flux better than by a factor of ~2. The predicted number of nearby galaxies detectable by Fermi is consistent with the observation. Intergalactic absorption by pair-production attenuates the EGRB flux only by a modest factor of ~1.3 at the highest Fermi energy band, and the reprocessed cascade emission does not significantly alter EGRB at lower photon energies. The sum of the known contributions from AGNs and star-forming galaxies can explain a large part of EGRB, with a remarkable agreement between the predicted model spectrum and observation.

astro-ph.HE↗