Stars that pass too close to a supermassive black hole are disrupted by the black hole's tidal gravity and leads to some debris being ejected while the remainder accretes into the black hole. To better study the physics of this debris, we use the moving mesh code MANGA to follow the evolution of the star from its initial encounter to its complete destruction. By varying the impact parameter ($beta$) of the star, we studied the energy distribution of the remaining material and the fallback rate of the material into the black hole as a function of time. We show that the spread of energy in the debris and peak luminosity time ($t_{rm peak}$) are both directly related to the impact parameter. In particular, we find a $beta^{1/2}$ scaling for the energy spread for $beta=2-10$ and a frozen evolution for $betagtrsim 10$. We provide analytic arguments for the spread of energy, rise time of the light curve, and broadness of the luminosity peak for these lower $beta$'s. These relationships provide a possible means of inferring the impact parameters for observed TDEs.
{"title":"The effect of impact parameter on tidal disruption events","authors":"A. Spaulding, P. Chang","doi":"10.1093/mnras/staa3627","DOIUrl":"https://doi.org/10.1093/mnras/staa3627","url":null,"abstract":"Stars that pass too close to a supermassive black hole are disrupted by the black hole's tidal gravity and leads to some debris being ejected while the remainder accretes into the black hole. To better study the physics of this debris, we use the moving mesh code MANGA to follow the evolution of the star from its initial encounter to its complete destruction. By varying the impact parameter ($beta$) of the star, we studied the energy distribution of the remaining material and the fallback rate of the material into the black hole as a function of time. We show that the spread of energy in the debris and peak luminosity time ($t_{rm peak}$) are both directly related to the impact parameter. In particular, we find a $beta^{1/2}$ scaling for the energy spread for $beta=2-10$ and a frozen evolution for $betagtrsim 10$. We provide analytic arguments for the spread of energy, rise time of the light curve, and broadness of the luminosity peak for these lower $beta$'s. These relationships provide a possible means of inferring the impact parameters for observed TDEs.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84132086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Vallely, C. Kochanek, K. Stanek, M. Fausnaugh, B. Shappee
We present observations from the Transiting Exoplanet Survey Satellite (TESS) of twenty bright core-collapse supernovae with peak TESS-band magnitudes $lesssim18$ mag. We reduce this data with an implementation of the image subtraction pipeline used by the All-Sky Automated Survey for Supernovae (ASAS-SN) optimized for use with the TESS images. In empirical fits to the rising light curves, we do not find strong correlations between the fit parameters and the peak luminosity. Existing semi-analytic models fit the light curves of the Type II supernovae well, but do not yield reasonable estimates of the progenitor radius or explosion energy, likely because they are derived for use with ultraviolet observations while TESS observes in the near-infrared. If we instead fit the data with numerically simulated light curves, the rising light curves of the Type~II SNe are consistent with the explosions of red supergiants. While we do not identify shock breakout emission for any individual event, when we combine the fit residuals of the Type II supernovae in our sample, we do find a $>5sigma$ flux excess in the $sim 0.5$~day before the start of the light curve rise. It is likely that this excess is due to shock breakout emission, and that during its extended mission TESS will observe a Type II supernova bright enough for this signal to be detected directly.
{"title":"High-cadence, early-time observations of core-collapse supernovae from the TESS prime mission","authors":"P. Vallely, C. Kochanek, K. Stanek, M. Fausnaugh, B. Shappee","doi":"10.1093/mnras/staa3675","DOIUrl":"https://doi.org/10.1093/mnras/staa3675","url":null,"abstract":"We present observations from the Transiting Exoplanet Survey Satellite (TESS) of twenty bright core-collapse supernovae with peak TESS-band magnitudes $lesssim18$ mag. We reduce this data with an implementation of the image subtraction pipeline used by the All-Sky Automated Survey for Supernovae (ASAS-SN) optimized for use with the TESS images. In empirical fits to the rising light curves, we do not find strong correlations between the fit parameters and the peak luminosity. Existing semi-analytic models fit the light curves of the Type II supernovae well, but do not yield reasonable estimates of the progenitor radius or explosion energy, likely because they are derived for use with ultraviolet observations while TESS observes in the near-infrared. If we instead fit the data with numerically simulated light curves, the rising light curves of the Type~II SNe are consistent with the explosions of red supergiants. While we do not identify shock breakout emission for any individual event, when we combine the fit residuals of the Type II supernovae in our sample, we do find a $>5sigma$ flux excess in the $sim 0.5$~day before the start of the light curve rise. It is likely that this excess is due to shock breakout emission, and that during its extended mission TESS will observe a Type II supernova bright enough for this signal to be detected directly.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"44 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77130109","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Keto D. Zhang, Wei Zheng, T. de Jaeger, B. Stahl, T. Brink, Xuhui Han, D. Kasen, K. Shen, Kevin Tang, A. Filippenko
The ejecta velocity is a very important parameter in studying the structure and properties of Type Ia supernovae (SNe Ia). It is also a candidate key parameter in improving the utility of SNe Ia for cosmological distance determinations. Here we study the velocity distribution of a sample of 311 SNe Ia from the kaepora database. The velocities are derived from the Si II $lambda$6355 absorption line in optical spectra measured at (or extrapolated to) the time of peak brightness. We statistically show that the observed velocity has a bimodal Gaussian distribution consisting of two groups of SNe Ia: Group I with a lower but narrower scatter ($mu_1 = 11000 text{km s}^{-1}$, $sigma_1 = 700 text{km s}^{-1}$), and Group II with a higher but broader scatter ($mu_2 = 12300 text{km s}^{-1}$, $sigma_2 = 1800 text{km s}^{-1}$). The population ratio of Group I to Group II is 201:110 (65%:35%). There is substantial degeneracy between the two groups, but for SNe Ia with velocity $v > 12000 text{km s}^{-1}$, the distribution is dominated by Group II. The true origin of the two components is unknown, though there could be that naturally there exist two intrinsic velocity distributions as observed. However, we try to use asymmetric geometric models through statistical simulations to reproduce the observed distribution assuming all SNe Ia share the same intrinsic distribution. In the two cases we consider, 35% of SNe Ia are considered to be asymmetric in Case 1, and all SNe Ia are asymmetric in Case 2. Simulations for both cases can reproduce the observed velocity distribution but require a significantly large portion ($>35%$) of SNe Ia to be asymmetric. In addition, the Case 1 result is consistent with recent polarization observations that SNe Ia with higher Si II $lambda$6355 velocity tend to be more polarized.
在研究Ia型超新星(SNe Ia)的结构和性质时，喷射速度是一个非常重要的参数。它也是提高超新星Ia在宇宙距离测定中的效用的候选关键参数。本文研究了kaepora数据库311 Ia震源的速度分布。速度是由测量(或外推)峰值亮度时间的光谱中的Si II $lambda$ 6355吸收线导出的。我们统计表明，观测到的速度具有双峰高斯分布，由两组Ia型SNe组成:第一组具有较低但较窄的散点($mu_1 = 11000 text{km s}^{-1}$, $sigma_1 = 700 text{km s}^{-1}$)，第二组具有较高但较宽的散点($mu_2 = 12300 text{km s}^{-1}$, $sigma_2 = 1800 text{km s}^{-1}$)。第一组和第二组的人口比例是201:110%:35%). There is substantial degeneracy between the two groups, but for SNe Ia with velocity $v > 12000 text{km s}^{-1}$, the distribution is dominated by Group II. The true origin of the two components is unknown, though there could be that naturally there exist two intrinsic velocity distributions as observed. However, we try to use asymmetric geometric models through statistical simulations to reproduce the observed distribution assuming all SNe Ia share the same intrinsic distribution. In the two cases we consider, 35% of SNe Ia are considered to be asymmetric in Case 1, and all SNe Ia are asymmetric in Case 2. Simulations for both cases can reproduce the observed velocity distribution but require a significantly large portion ($>35%$) of SNe Ia to be asymmetric. In addition, the Case 1 result is consistent with recent polarization observations that SNe Ia with higher Si II $lambda$6355 velocity tend to be more polarized.
{"title":"Distribution of Si ii λ6355 velocities of Type Ia supernovae and implications for asymmetric explosions","authors":"Keto D. Zhang, Wei Zheng, T. de Jaeger, B. Stahl, T. Brink, Xuhui Han, D. Kasen, K. Shen, Kevin Tang, A. Filippenko","doi":"10.1093/mnras/staa3191","DOIUrl":"https://doi.org/10.1093/mnras/staa3191","url":null,"abstract":"The ejecta velocity is a very important parameter in studying the structure and properties of Type Ia supernovae (SNe Ia). It is also a candidate key parameter in improving the utility of SNe Ia for cosmological distance determinations. Here we study the velocity distribution of a sample of 311 SNe Ia from the kaepora database. The velocities are derived from the Si II $lambda$6355 absorption line in optical spectra measured at (or extrapolated to) the time of peak brightness. We statistically show that the observed velocity has a bimodal Gaussian distribution consisting of two groups of SNe Ia: Group I with a lower but narrower scatter ($mu_1 = 11000 text{km s}^{-1}$, $sigma_1 = 700 text{km s}^{-1}$), and Group II with a higher but broader scatter ($mu_2 = 12300 text{km s}^{-1}$, $sigma_2 = 1800 text{km s}^{-1}$). The population ratio of Group I to Group II is 201:110 (65%:35%). There is substantial degeneracy between the two groups, but for SNe Ia with velocity $v > 12000 text{km s}^{-1}$, the distribution is dominated by Group II. The true origin of the two components is unknown, though there could be that naturally there exist two intrinsic velocity distributions as observed. However, we try to use asymmetric geometric models through statistical simulations to reproduce the observed distribution assuming all SNe Ia share the same intrinsic distribution. In the two cases we consider, 35% of SNe Ia are considered to be asymmetric in Case 1, and all SNe Ia are asymmetric in Case 2. Simulations for both cases can reproduce the observed velocity distribution but require a significantly large portion ($>35%$) of SNe Ia to be asymmetric. In addition, the Case 1 result is consistent with recent polarization observations that SNe Ia with higher Si II $lambda$6355 velocity tend to be more polarized.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75350775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-10-12DOI: 10.21203/rs.3.rs-89972/v1
J. Samsing, I. Bartos, D. D’Orazio, Z. Haiman, B. Kocsis, N. Leigh, Bin Liu, M. Pessah, H. Tagawa
Black hole mergers detected by LIGO and Virgo continue delivering transformational discoveries. The most recent example is the merger GW190521, which is the first detected with component masses exceeding the limit predicted by stellar models, and the first with non-zero orbital eccentricity. The large masses can be explained by build up through successive mergers, which has been suggested to occur efficiently in the gas disks of active galactic nuclei (AGN). The eccentricity, however, is a major puzzle. Here we show that AGN-disk environments naturally lead to a very high fraction of highly eccentric mergers, if interactions between binaries and singles are frequent, and the interactions are constrained to a plane representing the AGN-disk. By deriving a statistical solution to the chaotic 3-body problem with the inclusion of General Relativistic corrections, we find in our fiducial AGN-disk model that up to 70 percent of all black hole mergers could appear with an eccentricity >0.1 in LIGO/Virgo. Besides representing the most effective mechanism for producing eccentric mergers presented to date, our results have also profound implications for the origin of GW190521, and open up new lines of research on black hole scatterings in disk environments with far-reaching implications for gravitational wave astrophysics.
{"title":"Active Galactic Nuclei as Factories for Eccentric Black Hole Mergers","authors":"J. Samsing, I. Bartos, D. D’Orazio, Z. Haiman, B. Kocsis, N. Leigh, Bin Liu, M. Pessah, H. Tagawa","doi":"10.21203/rs.3.rs-89972/v1","DOIUrl":"https://doi.org/10.21203/rs.3.rs-89972/v1","url":null,"abstract":"\u0000 Black hole mergers detected by LIGO and Virgo continue delivering transformational discoveries. The most recent example is the merger GW190521, which is the first detected with component masses exceeding the limit predicted by stellar models, and the first with non-zero orbital eccentricity. The large masses can be explained by build up through successive mergers, which has been suggested to occur efficiently in the gas disks of active galactic nuclei (AGN). The eccentricity, however, is a major puzzle. Here we show that AGN-disk environments naturally lead to a very high fraction of highly eccentric mergers, if interactions between binaries and singles are frequent, and the interactions are constrained to a plane representing the AGN-disk. By deriving a statistical solution to the chaotic 3-body problem with the inclusion of General Relativistic corrections, we find in our fiducial AGN-disk model that up to 70 percent of all black hole mergers could appear with an eccentricity >0.1 in LIGO/Virgo. Besides representing the most effective mechanism for producing eccentric mergers presented to date, our results have also profound implications for the origin of GW190521, and open up new lines of research on black hole scatterings in disk environments with far-reaching implications for gravitational wave astrophysics.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"22 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79678567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-10-12DOI: 10.21203/rs.3.rs-91538/v1
K. Nimmo, J. Hessels, A. Keimpema, A. Archibald, J. Cordes, R. Karuppusamy, F. Kirsten, Dongzi Li, B. Marcote, Z. Paragi
Fast radio bursts (FRBs) exhibit a wide variety of spectral, temporal and polarimetric properties, which can unveil clues into their emission physics and propagation effects in the local medium. FRBs are challenging to study at very high time resolution due to the precision needed to constrain the dispersion measure, signal-to-noise limitations, and also scattering from the intervening medium. Here we present the high-time-resolution (down to 1 μs) polarimetric properties of four 1.7-GHz bursts from the repeating FRB 20180916B, which were detected in voltage data during observations with the European VLBI Network. In these bursts we observe a range of emission timescales spanning three orders of magnitude, the shortest component width reaching 3-4 μs (below which we are limited by scattering). We demonstrate that all four bursts are highly linearly polarised (≥ 80%), show no evidence for significant circular polarisation (≤ 15%), and exhibit a constant polarisation position angle during and between bursts. On short timescales (≤ 100 μs), however, there appear to be subtle (few degree) polarisation position angle variations across the burst profiles. These observational results are most naturally explained in an FRB model where the emission is magnetospheric in origin, as opposed to models where the emission originates at larger distances in a relativistic shock.
{"title":"Microsecond polarimetry of the repeating FRB 20180916B","authors":"K. Nimmo, J. Hessels, A. Keimpema, A. Archibald, J. Cordes, R. Karuppusamy, F. Kirsten, Dongzi Li, B. Marcote, Z. Paragi","doi":"10.21203/rs.3.rs-91538/v1","DOIUrl":"https://doi.org/10.21203/rs.3.rs-91538/v1","url":null,"abstract":"\u0000 Fast radio bursts (FRBs) exhibit a wide variety of spectral, temporal and polarimetric properties, which can unveil clues into their emission physics and propagation effects in the local medium. FRBs are challenging to study at very high time resolution due to the precision needed to constrain the dispersion measure, signal-to-noise limitations, and also scattering from the intervening medium. Here we present the high-time-resolution (down to 1 μs) polarimetric properties of four 1.7-GHz bursts from the repeating FRB 20180916B, which were detected in voltage data during observations with the European VLBI Network. In these bursts we observe a range of emission timescales spanning three orders of magnitude, the shortest component width reaching 3-4 μs (below which we are limited by scattering). We demonstrate that all four bursts are highly linearly polarised (≥ 80%), show no evidence for significant circular polarisation (≤ 15%), and exhibit a constant polarisation position angle during and between bursts. On short timescales (≤ 100 μs), however, there appear to be subtle (few degree) polarisation position angle variations across the burst profiles. These observational results are most naturally explained in an FRB model where the emission is magnetospheric in origin, as opposed to models where the emission originates at larger distances in a relativistic shock.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84314984","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Dieckmann, M. Falk, D. Folini, R. Walder, P. Steneteg, I. Hotz, A. Ynnerman
We study with a two-dimensional particle-in-cell simulation the stability of a discontinuity or piston, which separates an electron-positron cloud from a cooler electron-proton plasma. Such a piston might be present in the relativistic jets of accreting black holes separating the jet material from the surrounding ambient plasma and when pair clouds form during an X-ray flare and expand into the plasma of the accretion disk corona. We inject a pair plasma at a simulation boundary with a mildly relativistic temperature and mean speed. It flows across a spatially uniform electron-proton plasma, which is permeated by a background magnetic field. The magnetic field is aligned with one simulation direction and oriented orthogonally to the mean velocity vector of the pair cloud. The expanding pair cloud expels the magnetic field and piles it up at its front. It is amplified to a value large enough to trap ambient electrons. The current of the trapped electrons, which are carried with the expanding cloud front, drives an electric field that accelerates protons. A solitary wave grows and changes into a piston after it saturated. Our simulations show that this piston undergoes a collision-less instability similar to a Rayleigh-Taylor instability. The undular mode grows and we observe fingers in the proton density distribution. The effect of the instability is to deform the piston but it cannot destroy it.
{"title":"Collisionless Rayleigh–Taylor-like instability of the boundary between a hot pair plasma and an electron–proton plasma: The undular mode","authors":"M. Dieckmann, M. Falk, D. Folini, R. Walder, P. Steneteg, I. Hotz, A. Ynnerman","doi":"10.1063/5.0018321","DOIUrl":"https://doi.org/10.1063/5.0018321","url":null,"abstract":"We study with a two-dimensional particle-in-cell simulation the stability of a discontinuity or piston, which separates an electron-positron cloud from a cooler electron-proton plasma. Such a piston might be present in the relativistic jets of accreting black holes separating the jet material from the surrounding ambient plasma and when pair clouds form during an X-ray flare and expand into the plasma of the accretion disk corona. We inject a pair plasma at a simulation boundary with a mildly relativistic temperature and mean speed. It flows across a spatially uniform electron-proton plasma, which is permeated by a background magnetic field. The magnetic field is aligned with one simulation direction and oriented orthogonally to the mean velocity vector of the pair cloud. The expanding pair cloud expels the magnetic field and piles it up at its front. It is amplified to a value large enough to trap ambient electrons. The current of the trapped electrons, which are carried with the expanding cloud front, drives an electric field that accelerates protons. A solitary wave grows and changes into a piston after it saturated. Our simulations show that this piston undergoes a collision-less instability similar to a Rayleigh-Taylor instability. The undular mode grows and we observe fingers in the proton density distribution. The effect of the instability is to deform the piston but it cannot destroy it.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"19 6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89386500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Statistical methods are frequently built upon assumptions that limit their applicability to certain problems and conditions. Failure to recognize these limitations can lead to conclusions that may be inaccurate or biased. An example of such methods is the non-parametric Efron-Petrosian test statistic used in the studies of truncated data. We argue and show how the inappropriate use of this statistical method can lead to biased conclusions when the assumptions under which the method is valid do not hold. We do so by reinvestigating the evidence recently provided by multiple independent reports on the evolution of the luminosity/energetics distribution of cosmological Long-duration Gamma-Ray Bursts (LGRBs) with redshift. We show that the effects of detection threshold has been likely significantly underestimated in the majority of previous studies. This underestimation of detection threshold leads to severely-incomplete LGRB samples that exhibit strong apparent luminosity-redshift or energetics-redshift correlations. We further confirm our findings by performing extensive Monte Carlo simulations of the cosmic rates and the luminosity/energy distributions of LGRBs and their detection process.
{"title":"How unbiased statistical methods lead to biased scientific discoveries: A case study of the Efron–Petrosian statistic applied to the luminosity-redshift evolution of gamma-ray bursts","authors":"C. Bryant, J. A. Osborne, A. Shahmoradi","doi":"10.1093/MNRAS/STAB1098","DOIUrl":"https://doi.org/10.1093/MNRAS/STAB1098","url":null,"abstract":"Statistical methods are frequently built upon assumptions that limit their applicability to certain problems and conditions. Failure to recognize these limitations can lead to conclusions that may be inaccurate or biased. An example of such methods is the non-parametric Efron-Petrosian test statistic used in the studies of truncated data. We argue and show how the inappropriate use of this statistical method can lead to biased conclusions when the assumptions under which the method is valid do not hold. We do so by reinvestigating the evidence recently provided by multiple independent reports on the evolution of the luminosity/energetics distribution of cosmological Long-duration Gamma-Ray Bursts (LGRBs) with redshift. We show that the effects of detection threshold has been likely significantly underestimated in the majority of previous studies. This underestimation of detection threshold leads to severely-incomplete LGRB samples that exhibit strong apparent luminosity-redshift or energetics-redshift correlations. We further confirm our findings by performing extensive Monte Carlo simulations of the cosmic rates and the luminosity/energy distributions of LGRBs and their detection process.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74383526","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-10-05DOI: 10.1103/physrevd.102.103013
M. Di Mauro
The center of the Milky Way is offering one of the most striking mystery in Astroparticle Physics. An excess of gamma rays (GCE) has been measured by several groups in the data collected by the Fermi Large Area Telescope (LAT) towards the Galactic center region. The spectrum and spatial morphology of the GCE have been claimed by some groups to be compatible with a signal from the Galactic halo of dark matter (DM). Instead, other analyses have demonstrated that the GCE properties, e.g., its energy spectrum, highly depend on the choice of the Galactic interstellar emission (IEM) model source catalogs and analysis techniques. In this paper we investigate the sensitivity of Fermi-LAT to detect the characteristics of the GCE. In particular we simulate the GCE as given by DM and we verify that, with a perfect knowledge of the background components, its energy spectrum, position, spatial morphology and symmetry is properly measured. We also inspect two more realist cases for which there are imperfections in the IEM model. In the first we have an un-modeled gamma-ray source, constituted by the low-latitude component of the Fermi bubbles. In the second we simulate the data with one IEM template and analyze the data with an other. We verify that a mismodeling of the IEM introduces a systematics of about 10-15% in the GCE energy spectrum between 1-10 GeV and about 5% in the value of the slope for a NFW DM density profile, which is used to fit the GCE spatial morphology. Finally, we show how the GCE would be detected in case of alternative processes such as gamma-ray emission from a bulge population of pulsars or from electrons and positrons or protons injected from the Galactic center. We demonstrate that for each of these cases there is a distinctive smoking gun signature that would help to identify the real mechanism behind the origin of the GCE.
{"title":"Investigating the \u0000Fermi\u0000 Large Area Telescope sensitivity of detecting the characteristics of the Galactic center excess","authors":"M. Di Mauro","doi":"10.1103/physrevd.102.103013","DOIUrl":"https://doi.org/10.1103/physrevd.102.103013","url":null,"abstract":"The center of the Milky Way is offering one of the most striking mystery in Astroparticle Physics. An excess of gamma rays (GCE) has been measured by several groups in the data collected by the Fermi Large Area Telescope (LAT) towards the Galactic center region. The spectrum and spatial morphology of the GCE have been claimed by some groups to be compatible with a signal from the Galactic halo of dark matter (DM). Instead, other analyses have demonstrated that the GCE properties, e.g., its energy spectrum, highly depend on the choice of the Galactic interstellar emission (IEM) model source catalogs and analysis techniques. In this paper we investigate the sensitivity of Fermi-LAT to detect the characteristics of the GCE. In particular we simulate the GCE as given by DM and we verify that, with a perfect knowledge of the background components, its energy spectrum, position, spatial morphology and symmetry is properly measured. We also inspect two more realist cases for which there are imperfections in the IEM model. In the first we have an un-modeled gamma-ray source, constituted by the low-latitude component of the Fermi bubbles. In the second we simulate the data with one IEM template and analyze the data with an other. We verify that a mismodeling of the IEM introduces a systematics of about 10-15% in the GCE energy spectrum between 1-10 GeV and about 5% in the value of the slope for a NFW DM density profile, which is used to fit the GCE spatial morphology. Finally, we show how the GCE would be detected in case of alternative processes such as gamma-ray emission from a bulge population of pulsars or from electrons and positrons or protons injected from the Galactic center. We demonstrate that for each of these cases there is a distinctive smoking gun signature that would help to identify the real mechanism behind the origin of the GCE.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"38 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90857548","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-10-05DOI: 10.1103/physrevd.102.123015
Aurore Betranhandy, E. O’Connor
In this paper, we present a careful study on the impact of neutrino pair-production on core-collapse supernovae via spherically-symmetric, general-relativistic simulations of two different massive star progenitors with energy-dependent neutrino transport. We explore the impact and consequences of both the underlying microphysics and the implementation in the radiation transport algorithms on the supernova evolution, neutrino signal properties, and the explosion dynamics. We consider the two dominant neutrino pair-production processes found in supernovae, electron-positron annihilation as well as nucleon-nucleon bremsstrahlung in combination with both a simplified and a complete treatment of the processes in the radiation transport algorithms. We find that the use of the simplified prescription quantitatively impacts the neutrino signal at the 10% level and potentially the supernova dynamics, as we show for the case of a 9.6M$_odot$ progenitor. We also show that the choice of nucleon-nucleon bremsstrahlung interaction can also have a quantitative impact on the neutrino signal. A self-consistent treatment with state-of-the-art microphysics is suggested for precision simulations of core collapse, however the simplified treatment explored here is both computationally less demanding and results in a qualitatively similar evolution.
{"title":"Impact of neutrino pair-production rates in core-collapse supernovae","authors":"Aurore Betranhandy, E. O’Connor","doi":"10.1103/physrevd.102.123015","DOIUrl":"https://doi.org/10.1103/physrevd.102.123015","url":null,"abstract":"In this paper, we present a careful study on the impact of neutrino pair-production on core-collapse supernovae via spherically-symmetric, general-relativistic simulations of two different massive star progenitors with energy-dependent neutrino transport. We explore the impact and consequences of both the underlying microphysics and the implementation in the radiation transport algorithms on the supernova evolution, neutrino signal properties, and the explosion dynamics. We consider the two dominant neutrino pair-production processes found in supernovae, electron-positron annihilation as well as nucleon-nucleon bremsstrahlung in combination with both a simplified and a complete treatment of the processes in the radiation transport algorithms. We find that the use of the simplified prescription quantitatively impacts the neutrino signal at the 10% level and potentially the supernova dynamics, as we show for the case of a 9.6M$_odot$ progenitor. We also show that the choice of nucleon-nucleon bremsstrahlung interaction can also have a quantitative impact on the neutrino signal. A self-consistent treatment with state-of-the-art microphysics is suggested for precision simulations of core collapse, however the simplified treatment explored here is both computationally less demanding and results in a qualitatively similar evolution.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76614793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-10-01DOI: 10.1103/PHYSREVD.103.043006
E. Rrapaj, A. Patwardhan, Eve Armstrong, G. Fuller
The evolution of neutrino flavor in dense environments such as core-collapse supernovae and binary compact object mergers constitutes an important and unsolved problem. Its solution has potential implications for the dynamics and heavy-element nucleosynthesis in these environments. In this paper, we build upon recent work to explore inference-based techniques for estimation of model parameters and neutrino flavor evolution histories. We combine data assimilation, ordinary differential equation solvers, and neural networks to craft an inference approach tailored for non-linear dynamical systems. Using this architecture, and a simple two-neutrino, two-flavor model, we test various optimization algorithms with the help of four experimental setups. We find that employing this new architecture, together with evolutionary optimization algorithms, accurately captures flavor histories in the four experiments. This work provides more options for extending inference techniques to large numbers of neutrinos.
{"title":"Inference of neutrino flavor evolution through data assimilation and neural differential equations","authors":"E. Rrapaj, A. Patwardhan, Eve Armstrong, G. Fuller","doi":"10.1103/PHYSREVD.103.043006","DOIUrl":"https://doi.org/10.1103/PHYSREVD.103.043006","url":null,"abstract":"The evolution of neutrino flavor in dense environments such as core-collapse supernovae and binary compact object mergers constitutes an important and unsolved problem. Its solution has potential implications for the dynamics and heavy-element nucleosynthesis in these environments. In this paper, we build upon recent work to explore inference-based techniques for estimation of model parameters and neutrino flavor evolution histories. We combine data assimilation, ordinary differential equation solvers, and neural networks to craft an inference approach tailored for non-linear dynamical systems. Using this architecture, and a simple two-neutrino, two-flavor model, we test various optimization algorithms with the help of four experimental setups. We find that employing this new architecture, together with evolutionary optimization algorithms, accurately captures flavor histories in the four experiments. This work provides more options for extending inference techniques to large numbers of neutrinos.","PeriodicalId":8437,"journal":{"name":"arXiv: High Energy Astrophysical Phenomena","volume":"34 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73626619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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