Recent surveys of 2.6 mm CO emission and 100 MeV y-radiation in the ga;actic plane reveal a strik... more Recent surveys of 2.6 mm CO emission and 100 MeV y-radiation in the ga;actic plane reveal a striking correlation suggesting that both emissions may be primarily proportional to the line-of-sight column density of H 2 in the inner galaxy. Both the y-ray and CO data suggest a prominent ring or arm consisting of cool clouds of H 2 at a galactocentric distance of 1 5 kpc with a mean density of % 4 atoms/cm 3. Estimates are made of column densities of H 2 at 1I = o. The estimates at 00 are compared with estimates from infrared and x-ray absorption measurements. These estimates are all consistent and indicate that H 2 is far more abundant than HI in the inner galaxy and is the key to a more satisfactory explanation of the y-ray observations than previous suggestions, The importance of H 2 in understanding galactic y-ray observations is also reflected in the correlation of galactic latitude distribution of y-rays and dense dust clouds. This picture suggests that only small or moderate enhancements in the cosmic-ray flux in the inner galaxy would be consistent with the Y-ray observations. The cosmic-ray distribution suggested by the calculations is similar to that of galactic supernova remnants, suggesting a galactic origin for most cosmic rays. A detailed calculation of the y-ray flux distribution in the Q 0 to 180° range using the CO data to obtain the average distribution of molecular clouds in the galaxy shows that most of the enhancement in the inner galaxy is due to o-decay radiation and the the 5 kpc ring plays a major role. Detailed agreement with the y-ray data is obtained with the additional inclusion of contributions from bremsstrahlung and Compton radiation of secondary electrons and Compton radiation from the intense radiation field near the galactic center.
The observed isotropic cosmic X-and gamma-rays maybe produced by some combination of four possibl... more The observed isotropic cosmic X-and gamma-rays maybe produced by some combination of four possible types of extragalactic interactions. We show here that spectra from these interactions have important distinguishing-characteristics in the 1-100 MeV energy range. By normalizing the theoretical spectra to the observed intensities, we have determined theoretical intensities of metagalactic cosmic-ray protons and electrons needed to account for the observed radiation.
In the beginning...there was light.-Genesis, 1:1-1:3 Within the context of hot big-bang cosmology... more In the beginning...there was light.-Genesis, 1:1-1:3 Within the context of hot big-bang cosmology, a cosmic background of presently low energy neutrinos is predicted to exist in concert with the photons of the cosmic background radiation. The number density of the cosmological neutrinos is of the same order as that of the photons of the cosmic background radiation. That makes neutrinos the second most abundant particle species in the universe. In the early universe, when these neutrinos were highly relativistic, their effects in determining the ultimate structure and evolution of the universe were significant.
We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the... more We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the Swift observatory. This is a bright, short burst that shows an extended emission detected in the GeV range. Furthermore, its optical emission initially rises, a feature so far observed only in long bursts, while the X-ray flux shows an initial shallow decrease, followed by a steeper decay. This exceptional behavior enables us to investigate the physical properties of the GRB outflow, poorly known in short bursts. We discuss internal shock and external shock models for the broadband energy emission of this object.
32 33 Observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse γ-rays in a ... more 32 33 Observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse γ-rays in a mid-latitude region in the third quadrant (Galactic longitude l from 200 • to 260 • and latitude |b| from 22 • to 60 •) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of γ-ray point sources and inverse Compton scattering are
We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray B... more We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor (GBM) and Large Area Tele
The search for a theory that unifies general relativity and quantum theory has focused attention ... more The search for a theory that unifies general relativity and quantum theory has focused attention on models of physics at the Planck scale. One possible consequence of models such as string theory may be that Lorentz invariance is not an exact symmetry of nature. We discuss here some possible experimental and observational tests of Lorentz invariance involving neutrino physics and astrophysics.
Recent microscopic and phenomenological calculations of giant dipole resonances for A ≤ 56 nuclei... more Recent microscopic and phenomenological calculations of giant dipole resonances for A ≤ 56 nuclei are presented. The derived photodisintegration cross sections are exhaustively compared to the photonuclear data available to date. An accurate description of the data is found. Our new calculations are also compared with the previous and widely-used estimates of Puget, Stecker and Bredekamp. The present calculations also include all the possible paths down the nuclear chart. The impact on the photodisintegration of ultra-high-energy cosmic rays (UHECR) is illustrated for a Fe source with typical energies of 10 20−21 eV. At energies around 10 20 eV, the new cross sections are found to modify the UHECR photodisintegration rates. At energies around 10 21 eV, it is recommended to solve a full reaction network to estimate the photodisintegration rate of the UHECR.
The MAGIC collaboration has recently reported the detection of the strong gamma-ray blazar 3C279 ... more The MAGIC collaboration has recently reported the detection of the strong gamma-ray blazar 3C279 during a 1-2 day flare. They have used their spectral observations to draw conclusions regarding upper limits on the opacity of the Universe to high energy gamma-rays and, by implication, upper limits on the extragalactic mid-infrared background radiation. In this paper we examine the effect of gamma-ray absorption by the extragalactic infrared radiation on intrinsic spectra for this blazar and compare our results with the observational data on 3C279. We find agreement with our previous results, contrary to the recent assertion of the MAGIC group that the Universe is more transparent to \gray s than our calculations indicate. Our analysis indicates that in the energy range between ~80 and ~500 GeV, 3C279 has a best-fit intrinsic spectrum with a spectral index ~1.78 using our fast evolution model and ~2.19 using our baseline model. However, we also find that spectral indices in the range ...
In the published article, Figure 9, referenced in Section 5.2, shows the results for z=0.1, 0.3... more In the published article, Figure 9, referenced in Section 5.2, shows the results for z=0.1, 0.3, 0.6, and 1.0 in order to compare with other results. The results in Figure 9 are not z=0.1, 0.5, 1, 3, 5 as erroneously stated in the text.
We consider here three dark matter models with the gauge symmetry of the standard model plus an a... more We consider here three dark matter models with the gauge symmetry of the standard model plus an additional local U(1)_D factor. One model is truly secluded and the other two models begin flipped, but end up secluded. All of these models include one dark fermion and one vector boson that gains mass via the Stueckelberg mechanism. We show that the would be flipped models provide an example dark matter composed of "almost least interacting particles" (ALIPs). Such particles are therefore compatible with the constraints obtained from both laboratory measurements and astrophysical observations.
In this paper, we explore the potential astrophysical signatures of dark matter (DM) annihilation... more In this paper, we explore the potential astrophysical signatures of dark matter (DM) annihilations in ultra-compact dwarf galaxies (UCDs) considering two of the richest known galaxy clusters within 100 million light-years, nominally, Virgo and Fornax. Fornax UCD3 is the most luminous known UCD and M59 UCD3 is the most massive known UCD. With the detection of a 3.5 million solar mass black hole (BH) in Fornax UCD3, we carefully model several dark matter (DM) enhanced profile scenarios, considering the presence of both a supermassive black hole (SMBH) and DM. For Fornax UCD3, the comparison of the stellar and dynamical masses suggests that there is little content of DM in UCDs. M59 UCD3 did not receive the same attention in simulations as Fornax UCD3, however deep radio imaging and X-ray observations were performed for M59 UCD3 and can be used to place limits in DM content of these UCDs. We take an average estimate of dark matter content and used the Salpeter and Kroupa mass functions...
Journal of Cosmology and Astroparticle Physics, 2020
Here we investigate the possibility that some globular clusters (GCs) harbor intermediate mass bl... more Here we investigate the possibility that some globular clusters (GCs) harbor intermediate mass black holes (BH) in their centers and are also embedded in a low-mass dark matter (DM) halo. Up to date, there is no evidence on whether or not GCs have DM in their constitution. For standard cold DM cosmology, it is expected that GCs form with their own DM halos. Other studies investigate the possibility that GCs were initially embedded in massive DM halos that evolved during the cluster lifetime. An additional intriguing question is related to the existence of intermediate mass black holes (IMBH) in the of GCs. The determination of whether GCs hold IMBHs would be able to answer important questions about GCs formation and the circumstances that gave rise to the IMBHs. DM & IMBH in the context of GCs are interesting subjects to be studied and we will perform such studies here, assuming the coexistence of both of them in some GCs. Having such information, we perform the study possible DM signals from GCs. One important subject to be studied is the DM density profile. In the inner regions of GCs, the DM density profile is still an open question of fundamental importance to DM studies, specially for the study of radio and γ-ray emission from DM annihilation in such regions. Here we consider the case of IMBHs in the inner regions of three GCs: 47 Tuc, NGC 6266 and ω Cen. The existence of a black hole (BH) directly affects the matter distribution in its vicinity. These effects are significant for IMBHs as well as supermassive black holes (SMBHs) and can lead to large DM overdensities called spikes. In this paper, we direct our studies to the radio synchrotron emission from DM annihilation with spike profiles around possible IMBHs in GCs. We present our results for synchrotron emission produced by DM annihilation via bb channel. We use the best-fit DM mass of 34 GeV and annihilation channel in bb used to explain the Galactic center "excess" and perform our analysis for the estimated radio flux. We direct our attention specially to the γ-ray emission from 47 Tuc. When considering a scenario with includes a BH and the combined analysis of multi-wavelength studies, we conclude that some parameter choice as the annihilation cross section σv used to fit the γ-ray excess differs by many orders of magnitude from the one necessary to fit the radio observations for this globular cluster if we consider the BH scenario.
We describe the science motivation and development of a pair production telescope for mediumenerg... more We describe the science motivation and development of a pair production telescope for mediumenergy (~5-200 MeV) gamma-ray polarimetry. Our instrument concept, the Advanced Energetic Pair Telescope (AdEPT), takes advantage of the Three-Dimensional Track Imager, a low-density gaseous time projection chamber, to achieve angular resolution within a factor of two of the pair production kinematics limit (~0.6° at 70 MeV), continuum sensitivity comparable with the Fermi-LAT front detector (<3×10 -6 MeV cm -2 s -1 at 70 MeV), and minimum detectable polarization less than 10% for a 10 mCrab source in 10 6 seconds.
Recent surveys of 2.6 mm CO emission and 100 MeV y-radiation in the ga;actic plane reveal a strik... more Recent surveys of 2.6 mm CO emission and 100 MeV y-radiation in the ga;actic plane reveal a striking correlation suggesting that both emissions may be primarily proportional to the line-of-sight column density of H 2 in the inner galaxy. Both the y-ray and CO data suggest a prominent ring or arm consisting of cool clouds of H 2 at a galactocentric distance of 1 5 kpc with a mean density of % 4 atoms/cm 3. Estimates are made of column densities of H 2 at 1I = o. The estimates at 00 are compared with estimates from infrared and x-ray absorption measurements. These estimates are all consistent and indicate that H 2 is far more abundant than HI in the inner galaxy and is the key to a more satisfactory explanation of the y-ray observations than previous suggestions, The importance of H 2 in understanding galactic y-ray observations is also reflected in the correlation of galactic latitude distribution of y-rays and dense dust clouds. This picture suggests that only small or moderate enhancements in the cosmic-ray flux in the inner galaxy would be consistent with the Y-ray observations. The cosmic-ray distribution suggested by the calculations is similar to that of galactic supernova remnants, suggesting a galactic origin for most cosmic rays. A detailed calculation of the y-ray flux distribution in the Q 0 to 180° range using the CO data to obtain the average distribution of molecular clouds in the galaxy shows that most of the enhancement in the inner galaxy is due to o-decay radiation and the the 5 kpc ring plays a major role. Detailed agreement with the y-ray data is obtained with the additional inclusion of contributions from bremsstrahlung and Compton radiation of secondary electrons and Compton radiation from the intense radiation field near the galactic center.
The observed isotropic cosmic X-and gamma-rays maybe produced by some combination of four possibl... more The observed isotropic cosmic X-and gamma-rays maybe produced by some combination of four possible types of extragalactic interactions. We show here that spectra from these interactions have important distinguishing-characteristics in the 1-100 MeV energy range. By normalizing the theoretical spectra to the observed intensities, we have determined theoretical intensities of metagalactic cosmic-ray protons and electrons needed to account for the observed radiation.
In the beginning...there was light.-Genesis, 1:1-1:3 Within the context of hot big-bang cosmology... more In the beginning...there was light.-Genesis, 1:1-1:3 Within the context of hot big-bang cosmology, a cosmic background of presently low energy neutrinos is predicted to exist in concert with the photons of the cosmic background radiation. The number density of the cosmological neutrinos is of the same order as that of the photons of the cosmic background radiation. That makes neutrinos the second most abundant particle species in the universe. In the early universe, when these neutrinos were highly relativistic, their effects in determining the ultimate structure and evolution of the universe were significant.
We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the... more We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the Swift observatory. This is a bright, short burst that shows an extended emission detected in the GeV range. Furthermore, its optical emission initially rises, a feature so far observed only in long bursts, while the X-ray flux shows an initial shallow decrease, followed by a steeper decay. This exceptional behavior enables us to investigate the physical properties of the GRB outflow, poorly known in short bursts. We discuss internal shock and external shock models for the broadband energy emission of this object.
32 33 Observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse γ-rays in a ... more 32 33 Observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse γ-rays in a mid-latitude region in the third quadrant (Galactic longitude l from 200 • to 260 • and latitude |b| from 22 • to 60 •) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of γ-ray point sources and inverse Compton scattering are
We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray B... more We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor (GBM) and Large Area Tele
The search for a theory that unifies general relativity and quantum theory has focused attention ... more The search for a theory that unifies general relativity and quantum theory has focused attention on models of physics at the Planck scale. One possible consequence of models such as string theory may be that Lorentz invariance is not an exact symmetry of nature. We discuss here some possible experimental and observational tests of Lorentz invariance involving neutrino physics and astrophysics.
Recent microscopic and phenomenological calculations of giant dipole resonances for A ≤ 56 nuclei... more Recent microscopic and phenomenological calculations of giant dipole resonances for A ≤ 56 nuclei are presented. The derived photodisintegration cross sections are exhaustively compared to the photonuclear data available to date. An accurate description of the data is found. Our new calculations are also compared with the previous and widely-used estimates of Puget, Stecker and Bredekamp. The present calculations also include all the possible paths down the nuclear chart. The impact on the photodisintegration of ultra-high-energy cosmic rays (UHECR) is illustrated for a Fe source with typical energies of 10 20−21 eV. At energies around 10 20 eV, the new cross sections are found to modify the UHECR photodisintegration rates. At energies around 10 21 eV, it is recommended to solve a full reaction network to estimate the photodisintegration rate of the UHECR.
The MAGIC collaboration has recently reported the detection of the strong gamma-ray blazar 3C279 ... more The MAGIC collaboration has recently reported the detection of the strong gamma-ray blazar 3C279 during a 1-2 day flare. They have used their spectral observations to draw conclusions regarding upper limits on the opacity of the Universe to high energy gamma-rays and, by implication, upper limits on the extragalactic mid-infrared background radiation. In this paper we examine the effect of gamma-ray absorption by the extragalactic infrared radiation on intrinsic spectra for this blazar and compare our results with the observational data on 3C279. We find agreement with our previous results, contrary to the recent assertion of the MAGIC group that the Universe is more transparent to \gray s than our calculations indicate. Our analysis indicates that in the energy range between ~80 and ~500 GeV, 3C279 has a best-fit intrinsic spectrum with a spectral index ~1.78 using our fast evolution model and ~2.19 using our baseline model. However, we also find that spectral indices in the range ...
In the published article, Figure 9, referenced in Section 5.2, shows the results for z=0.1, 0.3... more In the published article, Figure 9, referenced in Section 5.2, shows the results for z=0.1, 0.3, 0.6, and 1.0 in order to compare with other results. The results in Figure 9 are not z=0.1, 0.5, 1, 3, 5 as erroneously stated in the text.
We consider here three dark matter models with the gauge symmetry of the standard model plus an a... more We consider here three dark matter models with the gauge symmetry of the standard model plus an additional local U(1)_D factor. One model is truly secluded and the other two models begin flipped, but end up secluded. All of these models include one dark fermion and one vector boson that gains mass via the Stueckelberg mechanism. We show that the would be flipped models provide an example dark matter composed of "almost least interacting particles" (ALIPs). Such particles are therefore compatible with the constraints obtained from both laboratory measurements and astrophysical observations.
In this paper, we explore the potential astrophysical signatures of dark matter (DM) annihilation... more In this paper, we explore the potential astrophysical signatures of dark matter (DM) annihilations in ultra-compact dwarf galaxies (UCDs) considering two of the richest known galaxy clusters within 100 million light-years, nominally, Virgo and Fornax. Fornax UCD3 is the most luminous known UCD and M59 UCD3 is the most massive known UCD. With the detection of a 3.5 million solar mass black hole (BH) in Fornax UCD3, we carefully model several dark matter (DM) enhanced profile scenarios, considering the presence of both a supermassive black hole (SMBH) and DM. For Fornax UCD3, the comparison of the stellar and dynamical masses suggests that there is little content of DM in UCDs. M59 UCD3 did not receive the same attention in simulations as Fornax UCD3, however deep radio imaging and X-ray observations were performed for M59 UCD3 and can be used to place limits in DM content of these UCDs. We take an average estimate of dark matter content and used the Salpeter and Kroupa mass functions...
Journal of Cosmology and Astroparticle Physics, 2020
Here we investigate the possibility that some globular clusters (GCs) harbor intermediate mass bl... more Here we investigate the possibility that some globular clusters (GCs) harbor intermediate mass black holes (BH) in their centers and are also embedded in a low-mass dark matter (DM) halo. Up to date, there is no evidence on whether or not GCs have DM in their constitution. For standard cold DM cosmology, it is expected that GCs form with their own DM halos. Other studies investigate the possibility that GCs were initially embedded in massive DM halos that evolved during the cluster lifetime. An additional intriguing question is related to the existence of intermediate mass black holes (IMBH) in the of GCs. The determination of whether GCs hold IMBHs would be able to answer important questions about GCs formation and the circumstances that gave rise to the IMBHs. DM & IMBH in the context of GCs are interesting subjects to be studied and we will perform such studies here, assuming the coexistence of both of them in some GCs. Having such information, we perform the study possible DM signals from GCs. One important subject to be studied is the DM density profile. In the inner regions of GCs, the DM density profile is still an open question of fundamental importance to DM studies, specially for the study of radio and γ-ray emission from DM annihilation in such regions. Here we consider the case of IMBHs in the inner regions of three GCs: 47 Tuc, NGC 6266 and ω Cen. The existence of a black hole (BH) directly affects the matter distribution in its vicinity. These effects are significant for IMBHs as well as supermassive black holes (SMBHs) and can lead to large DM overdensities called spikes. In this paper, we direct our studies to the radio synchrotron emission from DM annihilation with spike profiles around possible IMBHs in GCs. We present our results for synchrotron emission produced by DM annihilation via bb channel. We use the best-fit DM mass of 34 GeV and annihilation channel in bb used to explain the Galactic center "excess" and perform our analysis for the estimated radio flux. We direct our attention specially to the γ-ray emission from 47 Tuc. When considering a scenario with includes a BH and the combined analysis of multi-wavelength studies, we conclude that some parameter choice as the annihilation cross section σv used to fit the γ-ray excess differs by many orders of magnitude from the one necessary to fit the radio observations for this globular cluster if we consider the BH scenario.
We describe the science motivation and development of a pair production telescope for mediumenerg... more We describe the science motivation and development of a pair production telescope for mediumenergy (~5-200 MeV) gamma-ray polarimetry. Our instrument concept, the Advanced Energetic Pair Telescope (AdEPT), takes advantage of the Three-Dimensional Track Imager, a low-density gaseous time projection chamber, to achieve angular resolution within a factor of two of the pair production kinematics limit (~0.6° at 70 MeV), continuum sensitivity comparable with the Fermi-LAT front detector (<3×10 -6 MeV cm -2 s -1 at 70 MeV), and minimum detectable polarization less than 10% for a 10 mCrab source in 10 6 seconds.
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Papers by Floyd Stecker