An interpretation of the evidence for TeV emission from gamma-ray burst 970417a

The Milagrito collaboration recently reported evidence for emission of very high energy gamma rays in the TeV range from one of the BATSE gamma-ray bursts, GRB 970417a. Here I discuss possible interpretations of this result. Taking into account the intergalactic absorption of TeV gamma rays by the cosmic infrared background, I found that the detection rate (one per 54 gamma-ray bursts [GRBs] observed by the Milagrito) and energy fluence can be consistently explained with the redshift of this GRB at z approximately 0.7 and the isotropic total energy in the TeV range, ETeV,iso greater, similar1054 ergs. This energy scale is not unreasonably large, but interestingly similar to the maximum total GRB energy in the sub-MeV range observed to date for GRB 990123. On the other hand, the energy emitted in the ordinary sub-MeV range becomes EMeV,iso approximately 1051 ergs for GRB 970417a, which is much smaller than the total energy in the TeV range by a factor of about 10(3). I show that the proton-synchrotron model of GRBs provides a possible explanation for these observational results. I also discuss some observational signatures expected in future experiments from this model.

In a recent paper Stecker, De Jager, & Salamon have suggested using the observed approximately MeV to TeV spectra of extragalactic gamma-ray sources as probes of the local density of the cosmic infrared background radiation (CIBR) and have subsequently claimed a first possible measurement of the CIBR from the analysis of the gamma-ray spectrum of Mrk 421 (De Jager, Stecker, & Salamon). The CIBR from normal galaxies consists of two components: a stellar emission component (CIBRs), and a thermal dust emission component (CIBRd). Photons with energies in the approximately 0.1-2 TeV range interact primarily with the CIBRs, whereas interactions with CIBRd dominate the absorption of photons in the approximately 2-100 TeV energy range. SDS 92 and DSS94 considered only the interaction of the gamma-rays with the dust emission component of the CIBR. We present here an improved analysis of the absorption of extragalactic TeV gamma rays by the CIBR, taking the dual nature of its origin into account. Applying the analysis to the observed gamma-ray spectrum of Mrk 421, a BL Lac object at z = 0.031, we find agreement with DSS94 tentative evidence for absorption by the CINRs. Our analysis therefore limits the detection of the CIBR to the approximately 15-40 micron wavelength regime which, considering the uncertainties in the highest energy (greater than 4 TeV) data and ion the possibility of absorption inside the source, many turn out to be an upper limit on its energy density. At shorter wavelengths (lambda approximately = 1-15 microns), where the gamma-ray interactions are dominated by the CIBRs, our analysis definitely yields only an upper limit on the energy density of the CIBR. In contrast, DSS94 have claimed a possible first measurement of the CIBR over the entire 1-120 micron wavelength region. The upper limit on the CIBRs and tentative detection of the CIBRd are consistent with normal galaxies contributing most of the energy to the CIBR, and constrain the contribution of some exotic sources. With careful modeling of infrared foreground emissions, these constraints on the CIBR are above the values measurable by the DIRBE experiment on board the Cosmic Background Explorer (COBE) satellite.

The thermal Sunyaev-Zel'dovich (tSZ) effect is the distortion generated in the cosmic microwave background (CMB) spectrum by the inverse-Compton scattering of CMB photons off free, energetic electrons, primarily located in the intracluster medium. Cosmic infrared background (CIB) photons from thermal dust emission in star-forming galaxies are expected to undergo the same process. In this work, we perform the first calculation of the resulting tSZ-like distortion in the CIB. Focusing on the CIB monopole, we use a halo model approach to calculate both the CIB signal and the Compton-$y$ field that generates the distortion. We self-consistently account for the redshift coevolution of the CIB and Compton-$y$ fields: they are (partially) sourced by the same dark matter halos, which introduces new aspects to the calculation as compared to the CMB case. We find that the inverse-Compton distortion to the CIB monopole spectrum has a positive (negative) peak amplitude of $\ensuremath{\approx}4\text{ }\text{ }\mathrm{Jy}/\mathrm{sr}$ ($\ensuremath{\approx}\ensuremath{-}5\text{ }\text{ }\mathrm{Jy}/\mathrm{sr}$) at 2260 GHz (940 GHz). In contrast to the usual tSZ effect, the distortion to the CIB spectrum has two null frequencies, at approximately 196 and 1490 GHz. We perform a Fisher matrix calculation to forecast the detectability of this new distortion signal by future experiments. PIXIE would have sufficient instrumental sensitivity to detect the signal at $4\ensuremath{\sigma}$, but foreground contamination reduces the projected signal-to-noise by a factor of $\ensuremath{\approx}70$. A future ESA Voyage 2050 spectrometer could detect the CIB distortion at $\ensuremath{\approx}5\ensuremath{\sigma}$ significance, even after marginalizing over foregrounds. A measurement of this signal would provide new information on the star formation history of the Universe, and the distortion anisotropies may be accessible by near-future ground-based experiments.

The Sunyaev–Zeldovich effect towards clusters of galaxies has become a standard probe of cosmology. It is caused by the scattering of photons from the cosmic microwave background (CMB) by the hot cluster electron gas. In a similar manner, other photon backgrounds can be scattered when passing through the cluster medium. This problem has been recently considered for the radio and the cosmic infrared background. Here, we revisit the discussion of the cosmic infrared background (CIB) including several additional effects that were omitted before. We discuss the intracluster scattering of the CIB and the role of relativistic temperature corrections to the individual cluster and all-sky averaged signals. We show that the all-sky CIB distortion introduced by the scattering of the photon field was underestimated by a factor of ≃1.5 due to neglecting the intracluster scattering contribution. The CIB photons can scatter with the thermal electrons of both the parent halo or another halo, meaning that there are two ways to gain energy. Therefore, energy is essentially transferred twice from the thermal electrons to the CIB. We carefully clarify the origin of various effects in the calculation of the average CIB and also scattered signals. The single-cluster CIB scattering signal also exhibits a clear redshift dependence, which can be used in cosmological analyses, as we describe both analytically and numerically. This may open a new way for cosmological studies with future CMB experiments.

An electron/positron pair halo is formed by electromagnetic cascades that initiate when high energy gamma-rays from extragalactic sources - i.e. Blazar AGN - interact with the cosmic infrared background (CIB), and are then absorbed via the electron/positron pair production process. The high energy electron/positron pairs produced could up-scatter the cosmic microwave background (CMB) and become gamma rays which can interact with CIB again. Thus, the process could happen continuously until the produced gamma-rays have insufficient energy to interact with the CIB. Indeed, given the presence of intergalactic magnetic field, the produced electron/positron pairs could gyrate before scattered with the CMB photons so that they emit X-ray photons via the synchrotron radiation process. In this work, we determine whether the predicted X-ray photons emitted from the halo can be detected by the current generation X-ray observatory: XMM-Newton. The Spectral Energy Distributions (SEDs) of the synchrotron radiation of the pair halo predicted to be obtained from the AGN H1426+428 are simulated by the Monte Carlo simulations method; these are used as a source model for simulating observed spectra. The spectra of the halo virtually observed by XMM-Newton are generated in three different regions: the inner region, outer region and the region out of the XMM-Newton’s field of view. The resulting spectra suggest that the outer region spectra could provide the best opportunity to detect and confirm the existence of electron/positron pair halos.

Modelling the anisotropies in the cosmic infrared background (CIB) on all the scales is a challenging task because the nature of the galaxy evolution is complex and too many parameters are therefore often required to fit the observational data. We present a new halo model for the anisotropies of the CIB using only four parameters. Our model connects the mass accretion on the dark matter haloes to the star formation rate. Despite its relative simplicity, it is able to fit both the Planck and Herschel CIB power spectra and is consistent with the external constraints for the obscured star formation history derived from infrared deep surveys used as priors for the fit. Using this model, we find that the halo mass with the maximum efficiency for converting the accreted baryons into stars is log10Mmax = 12.94-0.02+0.02 M⊙, consistent with other studies. Accounting for the mass loss through stellar evolution, we find for an intermediate-age galaxy that the star formation efficiency defined as M⋆(z)/Mb(z) is equal to 0.19 and 0.21 at redshift 0.1 and 2, respectively, which agrees well with the values obtained by previous studies. A CIB model is used for the first time to simultaneously fit Planck and Herschel CIB power spectra. The high angular resolution of Herschel allows us to reach very small scales, making it possible to constrain the shot noise and the one-halo term separately, which is difficult to do using the Planck data alone. However, we find that large angular scale Planck and Herschel data are not fully compatible with the small-scale Herschel data (for ℓ > 3000). The CIB is expected to be correlated with the thermal Sunyaev-Zel’dovich (tSZ) signal of galaxy clusters. Using this halo model for the CIB and a halo model for the tSZ with a single parameter, we also provide a consistent framework for calculating the CIB × tSZ cross correlation, which requires no additional parameter. To a certain extent, the CIB at high frequencies traces galaxies at low redshifts that reside in the clusters contributing to the tSZ, giving rise to the one-halo term of this correlation, while the two-halo term comes from the overlap in the redshift distribution of the tSZ clusters and CIB galaxies. The CIB × tSZ correlation is thus found to be higher when inferred with a combination of two widely spaced frequency channels (e.g. 143 × 857 GHz). We also find that even at ℓ ∼ 2000, the two-halo term of this correlation is still comparable to the one-halo term and has to be accounted for in the total cross-correlation. The CIB, tSZ, and CIB × tSZ act as foregrounds when the kinematic SZ (kSZ) power spectrum is measured from the cosmic microwave background power spectrum and need to be removed. Because of its simplistic nature and the low number of parameters, the halo model formalism presented here for these foregrounds is quite useful for such an analysis to measure the kSZ power spectrum accurately.

When Very High Energy (VHE) gamma-rays (E>100 GeV) transverse low energy photon fields, the production of electron-positron pairs leads to the attenuation of the intrinsic gamma-ray flux. This phenomena is well know for VHE radiation from extragalactic sources, like e.g. blazars, interacting with the cosmic infrared background. In this contribution the absorption of VHE gamma-rays due to the interaction with localized low energy radiation fields, e.g. the Milky Way diffuse radiation field, cluster radiation fields and radiation fields in voids and filaments is discussed. While the photon field densities of these inhomogeneous radiation fields can be several orders of magnitude higher compared to the homogeneous background, the distances are in general shorter leading to an overall smaller effect. On the other hand, the detection of such an attenuation could be used to study the IR emission on different scales, measure the distance of galactic sources, or investigate particle physics phenomena beyond the standard model. It is investigated how forthcoming imaging air Cherenkov telescopes, like CTA, and wide angle Cherenkov arrays, like HiSCORE, with their improved sensitivities up to several hundred TeV will measure this absorption feature.

Gravitational lensing deflects the paths of cosmic infrared background (CIB) photons, leaving a measurable imprint on CIB maps. The resulting statistical anisotropy can be used to reconstruct the matter distribution out to the redshifts of CIB sources. To this end, we generalize the CMB lensing quadratic estimator to any weakly non-Gaussian source field, by deriving the optimal lensing weights. We point out the additional noise and bias caused by the non-Gaussianity and the `self-lensing' of the source field. We propose methods to reduce, subtract or model these non-Gaussianities. We show that CIB lensing should be detectable with Planck data, and detectable at high significance for future CMB experiments like CCAT-Prime. The CIB thus constitutes a new source image for lensing studies, providing constraints on the amplitude of structure at intermediate redshifts between galaxies and the CMB. CIB lensing measurements will also give valuable information on the star formation history in the universe, constraining CIB halo models beyond the CIB power spectrum. By laying out a detailed treatment of lens reconstruction from a weakly non-Gaussian source field, this work constitutes a stepping stone towards lens reconstruction from continuum or line intensity mapping data, such as the Lyman-alpha emission, absorption, and the 21cm radiation.

The cosmic infrared background (CIB) sourced by infrared emission from dusty\nstar-forming galaxies is a valuable source of information on the star formation\nhistory of the Universe. In measurements of the millimeter sky at frequencies\nhigher than $\\sim 300$ GHz, the CIB and thermal emission from Galactic dust\ndominate. A limited understanding of the CIB contribution at lower frequencies\non the other hand can hinder efforts to measure the kinetic Sunyaev-Zeldovich\nspectrum on small scales as well as new physics that affects the damping tail\nof the cosmic microwave background (CMB). The Planck satellite has measured\nwith high fidelity the CIB at 217, 353, 545 and 857 GHz. On very large scales,\nthis measurement is limited by our ability to separate the CIB from Galactic\ndust, but on intermediate scales, the measurements are limited by sample\nvariance in the underlying matter field traced by the CIB. We show how\nsignificant improvements (20-100%) can be obtained on parameters of star\nformation models by cross-correlating the CIB (as measured from existing {\\it\nPlanck} maps or upcoming CCAT-prime maps) with upcoming mass maps inferred from\ngravitational lensing of the CMB. This improvement comes from improved\nknowledge of the redshift distribution of star-forming galaxies as well as\nthrough the use of the unbiased matter density inferred from CMB lensing mass\nmaps to cancel the sample variance in the CIB field. We also find that further\nimprovements can be obtained on CIB model parameters if the cross-correlation\nof the CIB with CMB lensing is measured over a wider area while restricting the\nmore challenging CIB auto-spectrum measurement to the cleanest 5% of the sky.\n

The cosmic infrared background (CIB) anisotropies and cosmic microwave background (CMB) lensing are powerful measurements for exploring cosmological and astrophysical problems. In this work, we measure the autocorrelation power spectrum of the CIB anisotropies in the Herschel–SPIRE HerMES Large Mode Survey (HeLMS) field, and the cross-power spectrum with the CMB lensing measurements from the Planck satellite. The HeLMS field covers more than 270 deg2, which is much larger than in previous analysis. We use the Herschel Level 1 time stream data to merge the CIB maps at 250, 350, and 500 μm bands, and mask the areas where the flux is greater than or there are no measured data. We obtain the final CIB power spectra at 100 ≤ ℓ ≤ 20,000 by considering several effects, such as beam function, mode coupling, transfer function, and so on. We also calculate the theoretical CIB auto- and cross-power spectra of CIB and CMB lensing by assuming that the CIB emissivity follows a Gaussian distribution in redshift. We find that, for the CIB auto-power spectra, we obtain signal-to-noise ratios (S/Ns) of 15.9, 15.7, and 15.3 at 250, 350, and 500 μm, and for the CIB ⨯ CMB lensing power spectra, S/Ns of 7.5, 7.0, and 6.2 at 250, 350, and 500 μm, respectively. Comparing to previous works, the constraints on the relevant CIB parameters are improved by factors of 2– 5 in this study.

As confusion with lensing B modes begins to limit experiments that search for primordial B-mode polarization, robust methods for delensing the cosmic microwave background (CMB) polarization sky are becoming increasingly important. We investigate in detail the possibility of delensing the CMB with the cosmic infrared background (CIB), emission from dusty star-forming galaxies that is an excellent tracer of the CMB lensing signal, in order to improve constraints on the tensor-to-scalar ratio $r$. We find that the maps of the CIB, such as current Planck satellite maps at 545 GHz, can be used to remove more than half of the lensing B-mode power. Calculating optimal combinations of different large-scale-structure tracers for delensing, we find that coadding CIB data and external arcminute-resolution CMB lensing reconstruction can lead to significant additional improvements in delensing performance. We investigate whether measurement uncertainty in the CIB power spectra will degrade the delensing performance if no model of the CIB spectra is assumed, and instead the CIB power spectra are marginalized over, when constraining $r$. We find that such uncertainty does not significantly affect B-mode surveys smaller than a few thousand degrees. Even for larger surveys it causes only a moderate reduction in CIB delensing performance, especially if the surveys have high (arcminute) resolution, which allows self calibration of the delensing procedure. Though further work on the impact of foreground residuals is required, our overall conclusions for delensing with current CIB data are optimistic: this delensing method can tighten constraints on $r$ by a factor up to $\ensuremath{\approx}2.2$, and by a factor up to $\ensuremath{\approx}4$ when combined with external lensing reconstruction for $\ensuremath{\approx}3\text{ }\text{ }\ensuremath{\mu}\mathrm{K}$-arcmin noise, without requiring the modeling of CIB properties. CIB delensing is thus a promising method for the upcoming generation of CMB polarization surveys.

Cosmic infrared background and early galaxy evolution

We explore the use of the cosmic infrared background (CIB) as a tracer of the large scale structures for cross-correlating with the cosmic microwave background (CMB) and exploit the integrated Sachs–Wolfe (ISW) effect. We used an improved linear CIB model from our previous work and derived the theoretical CIB×ISW cross-correlation for different Planck HFI frequencies (217, 353, 545 and 857 GHz) and IRAS (3000 GHz). As expected, we predict a positive cross-correlation between the CIB and the CMB whose amplitude decreases rapidly at small scales. We perform a signal-to-noise ratio (S/N) analysis of the predicted cross-correlation. In the ideal case when the cross-correlation is obtained over 70% (40%) of the sky without residual contaminants (e.g. galactic dust) in maps, the S/N ranges from 4.2 to 5.6 (3.2 to 4.3); the highest S/N comes from 857 GHz. A Fisher matrix analysis shows that an ISW signal detected with a S/N this high on the 40% sky can considerably improve the constraints on the cosmological parameters; constraints on the equation of state of the dark energy especially are improved by 80%. We then performed a more realistic analysis considering the effect of residual galactic dust contamination in CIB maps. We calculated the dust power spectra for different frequencies and sky fractions that dominate the CIB power spectra at the lower multipoles we are interested in. Considering a conservative 10% residual level of galactic dust in the CIB power spectra, we observe that the S/N drops drastically, which makes it very challenging to detect the ISW. To determine the capability of current maps to detect the ISW effect through this method, we measured the cross-correlation of the CIB and the CMB Planck maps on the so-called GASS field, which covers an area of ∼11% in the southern hemisphere. We find that with such a small sky fraction and the dust residuals in the CIB maps, we do not detect any ISW signal, and the measured cross-correlation is consistent with zero. To avoid degrading the S/N for the ISW measurement by more than 10% on the 40% sky, we find that the dust needs to be cleaned up to the 0.01% level on the power spectrum.

The cosmic infrared background (CIB) includes roughly half of the energy radiated by all galaxies at all wavelengths across cosmic time, as observed at the present epoch. The PACS Evolutionary Probe (PEP) survey is exploited here to study the CIB and its redshift differential, at 70, 100 and 160 micron, where the background peaks. Combining PACS observations of the GOODS-S, GOODS-N, Lockman Hole and COSMOS areas, we define number counts spanning over more than two orders of magnitude in flux: from ~1 mJy to few hundreds mJy. Stacking of 24 micron sources and P(D) statistics extend the analysis down to ~0.2 mJy. Taking advantage of the wealth of ancillary data in PEP fields, differential number counts and CIB are studied up to z=5. Based on these counts, we discuss the effects of confusion on PACS blank field observations and provide confusion limits for the three bands considered. The total CIB surface brightness emitted above PEP 3 sigma flux limits is 4.52 +/- 1.18, 8.35 +/- 0.95 and 9.49 +/- 0.59 [nW/m2/sr] at 70, 100, and 160 micron, respectively. These values correspond to 58 +/- 7% and 74 +/- 5% of the COBE/DIRBE CIB direct measurements at 100 and 160 micron. Employing the P(D) analysis, these fractions increase to ~65% and ~89%. More than half of the resolved CIB was emitted at redshift z<=1. The 50%-light redshifts lie at z=0.58, 0.67 and 0.73 at the three PACS wavelengths. The distribution moves towards earlier epochs at longer wavelengths: while the 70 micron CIB is mainly produced by z<=1.0 objects, the contribution of z>1.0 sources reaches 50% at 160 micron. Most of the CIB resolved in the three PACS bands was emitted by galaxies with infrared luminosities in the range 1e11-1e12 L(sun).

We show how the correlation between the thermal Sunyaev Zel'dovich effect (tSZ) from galaxy clusters and dust emission from cosmic infrared background (CIB) sources can be calculated in a halo model framework. Using recent tSZ and CIB models, we find that the size of the tSZ x CIB cross-correlation is approximately 20 per cent at 150 GHz. The contribution to the total angular power spectrum is of order -2 \mu K^2 at ell=3000, however, this value is uncertain by a factor of two to three, primarily because of CIB source modelling uncertainties. We expect the large uncertainty in this component to degrade upper limits on the kinematic Sunyaev Zel'dovich effect (kSZ), due to similarity in the frequency dependence of the tSZ x CIB and kSZ across the frequency range probed by current Cosmic Microwave Background missions. We also find that the degree of tSZ x CIB correlation is higher for mm x sub-mm spectra than mm x mm, because more of the sub-mm CIB originates at lower redshifts (z<2), where most tSZ clusters are found.