V. Petrosian
A5055867902- Solar and Space Plasma Dynamics
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Ionosphere and magnetosphere dynamics
- Astro and Planetary Science
- Galaxies: Formation, Evolution, Phenomena
- Stellar, planetary, and galactic studies
- Dark Matter and Cosmic Phenomena
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Geophysics and Gravity Measurements
- Solar Radiation and Photovoltaics
- Pulsars and Gravitational Waves Research
- Cosmology and Gravitation Theories
- Astrophysics and Star Formation Studies
- Particle Accelerators and Free-Electron Lasers
- Scientific Research and Discoveries
- Statistical and numerical algorithms
- History and Developments in Astronomy
- Astronomical Observations and Instrumentation
- Earthquake Detection and Analysis
- Particle Detector Development and Performance
- Geomagnetism and Paleomagnetism Studies
- Particle accelerators and beam dynamics
Stanford University
2015-2024
Kavli Institute for Particle Astrophysics and Cosmology
2015-2024
SLAC National Accelerator Laboratory
2014-2024
University of Trieste
2021-2023
National Institute for Astrophysics
2023
Istituto Nazionale di Fisica Nucleare
2023
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
2021
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
2021
Max Planck Society
2018
University of Leicester
2018
It is well known that before the redshift-magnitude diagram of galaxies could be used for determination cosmological parameters one must know evolution galaxies. We propose use apparent surface brightness: which depends only on redshift and independent model inhomogeneities in universe: observational The needed observations are isophotal angular diameters magnitudes within this or any other reasonable diameter. application results q/sub 0/ discussed briefly. (AIP)
Recent detections of the starburst galaxies M82 and NGC 253 by gamma-ray telescopes suggest that rapidly forming massive stars are more luminous at energies compared to their quiescent relatives. Building upon those results, we examine a sample 69 dwarf, spiral, ultraluminous infrared photon 0.1–100 GeV using 3 years data collected Large Area Telescope (LAT) on Fermi Gamma-ray Space (Fermi). Measured fluxes from significantly detected sources flux upper limits for remaining used explore...
view Abstract Citations (406) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Energy Losses due to Neutrino Processes Beaudet, Gilles ; Petrosian, Vahé Salpeter, E. We consider the neutrino energy-loss rate pair process, photoneutrino and plasma in a hot plasma, including ntnbution from positrons present black-body radiation. derive some analytic expressions for include effects on rate. A discussion of approximations involved derivation is...
Abstract The Large Area Telescope (LAT) aboard the Fermi spacecraft routinely observes high-energy emission from gamma-ray bursts (GRBs). Here we present second catalog of LAT-detected GRBs, covering first 10 yr operations, 2008 to 2018 August 4. A total 186 GRBs are found; these, 91 show in range 30–100 MeV (17 which seen only this band) and 169 detected above 100 MeV. Most these sources were discovered by other instruments ( /GBM, Swift /BAT, AGILE, INTEGRAL ) or reported Interplanetary...
Some clusters of galaxies, in addition to thermal bremsstrahlung (TB), emit detectable diffuse radiation from the intracluster medium (ICM) at radio, EUV, and hard X-ray (HXR) ranges. The radio must be due synchrotron by relativistic electrons, inverse Compton scattering cosmic microwave background same electrons is most natural source for HXR perhaps EUV emissions. However, simple estimates give a weaker magnetic field than that suggested Faraday rotation measurements. Consequently,...
The Fermi Gamma-ray Space Telescope observed the bright and long GRB090902B, lying at a redshift of z = 1.822. Together Large Area (LAT) Burst Monitor (GBM) cover spectral range from 8 keV to >300 GeV. Here we show that prompt burst spectrum is consistent with emission jet photosphere combined nonthermal described by single power law photon index −1.9. gives rise strong quasi-blackbody which somewhat broader than Planck function has characteristic temperature ∼290 keV. We model photospheric...
view Abstract Citations (155) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Simple Test of Independence for Truncated Data with Applications to Redshift Surveys Efron, Bradley ; Petrosian, Vahe In analysis astronomical data, one is often faced determination bivariate distributions from truncated data. This leads the following statistical question: Is a sample observed points (X_i_, Y_i_) consistent hypothesis H_0_ that x and y are...
Petrosian magnitudes were designed to help with the difficult task of determining a galaxy's total light. Although these (taken here as flux within 2R_P, inverted index 1/eta(R_P)=0.2) can represent most an object's flux, they do course miss light outside aperture (2R_P). The size this deficit varies monotonically shape light-profile, i.e., its concentration. In case de Vaucouleurs R^{1/4} profile, is 0.20 mag; for R^{1/8} profile figure rises 0.50 mag. Here we provide simple method...
The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This was obtained using 80 months data re-processed with Pass 8, the newest event-level analysis, which significantly improves acceptance and angular resolution instrument. Most 2FHL at high Galactic latitude are blazars. Using detailed Monte Carlo simulations, we measure, for first time, source count distribution, dN/dS, extragalactic γ-ray E>50 find that it is...
We present data analysis and interpretation of an M1.4 class flare observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on 2002 April 30. This event, its footpoints occulted by solar limb, exhibits a rarely observed, but theoretically expected, double-source structure in corona. The two coronal sources, over 6-30 keV range, appear at different altitudes show energy-dependent structures higher energy emission being closer together. Spectral implies that energies...
Gamma rays reveal the Universe's history How many stars have formed in Universe, and when did they do so? These fundamental questions are difficult to answer because there systematic uncertainties converting light we observe into total mass of galaxies. The Fermi-LAT Collaboration addressed these by exploiting way that gamma from distant blazars propagate through intergalactic space, which depends on amount emitted all collaboration found star formation peaked about 3 billion years after Big...
Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We report analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA RHESSI. Bi-directional outflows forms plasmoid ejections contracting cusp-shaped loops originate between erupting flux rope underlying at speeds typically 200-300 km/s up 1050 km/s. These are associated with spatially separated double coronal X-ray sources centroid separation...
Gamma-ray bursts (GRBs), which have been observed up to redshifts z approx 9.5 can be good probes of the early universe and potential testing cosmological models. The analysis by Dainotti GRB Swift afterglow lightcurves with known definite X-ray plateau shows an anti-correlation between rest frame time when ends (the end time) calculated luminosity at that (or approximately duration luminosity). We present here update this correlation a larger data sample 101 GRBs lightcurves. Since some...
ABSTRACT We present results from γ -ray observations of the Coma cluster incorporating six years Fermi -LAT data and newly released “Pass 8” event-level analysis. Our analysis region reveals low-significance residual structures within virial radius that are too faint for a detailed investigation with current data. Using likelihood approach is free assumptions on spectral shape we derive upper limits flux expected energetic particle interactions in cluster. also consider benchmark spatial...
An incremental version of the fourth catalog active galactic nuclei (AGNs) detected by Fermi-Large Area Telescope is presented. This (4LAC-DR3) derives from third data release 4FGL based on 12 years E>50 MeV gamma-ray data, where spectral parameters, energy distributions (SEDs), yearly light curves, and associations have been updated for all sources. The new reported AGNs include 587 blazar candidates four radio galaxies. We describe properties sample outline changes affecting previously...
Abstract The bimodal distribution of the observed duration gamma-ray bursts (GRBs) has led to identification two distinct progenitors; compact star mergers, comprising either neutron stars (NSs) or an NS and a black hole, for short GRBs (SGRBs), so-called collapsars long (LGRBs). It is therefore expected that formation rate (FR) LGRBs should be similar cosmic (SFR), while SGRBs delayed relative SFR. localization some in around star-forming regions host galaxies away from such support this...
Abstract Truncated data play an important role in the statistical analysis of astronomical observations as well survival analysis. The motivating example for this article concerns a set measurements on quasars which there is double truncation. That is, are observed only if their luminosity occurs within certain finite interval, bounded at both ends, with interval varying different observations. Nonparametric methods testing and estimation doubly truncated developed. These extend some known...
Stochastic acceleration of electrons and protons by waves propagating parallel to the large scale magnetic fields magnetized plasmas is studied with emphasis on feasibility accelerating particles from a thermal background relativistic energies aim determining relative two species in one source. In general, stochastic these results distinct components particle distributions, quasi-thermal hard nonthermal, nonthermal being more prominent hotter and/or higher level turbulence. This can explain...
We investigate synchrotron emission models as the source of gamma-ray burst (GRB) spectra. show that including possibility for self-absorption, a "smooth cutoff" to electron energy distribution, and an anisotropic distribution pitch angles produces whole range low-energy spectral behavior. In addition, we procedure fitting GRB data over finite bandwidth can introduce spurious correlation between parameters—in particular, value peak νFν spectrum, Ep, photon index α (the lower Ep is, [softer]...
The discovery of hard X-ray sources near the top a flaring loop by Hard X-Ray Telescope on board Yohkoh satellite represents significant progress toward understanding basic processes driving solar flares. In this paper we extend previous study limb flares Masuda including all observations up through 1998 August. We report that from 1991 October to August, observed 20 X-ray-bright (where use same selection criteria as Masuda), which have sufficient data analyze 18 events, eight previously...
view Abstract Citations (120) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stochastic Acceleration of Electrons. I. Effects Collisions in Solar Flares Hamilton, Russell J. ; Petrosian, Vahe acceleration thermal electrons to nonrelativistic energies is studied under solar flare conditions. We show that, turbulent regions, electron-whistler wave interactions can result the times comparable or shorter than Coulomb collision time. The kinetic...
Here we investigate some aspects of stochastic acceleration ultrarelativistic electrons by magnetic turbulence. In particular, discuss the steady state energy spectra particles undergoing momentum diffusion due to resonant interactions with turbulent MHD modes, taking rigorously into account direct losses connected different radiative cooling processes. For turbulence assume a given power spectrum type W(k) ∝ k−q. contrast previous approaches, however, finite range wavevectors k, consider...
view Abstract Citations (127) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Impulsive phase of solar flares. I - Characteristics high energy electrons Leach, J. ; Petrosian, V. The models describing the operative physical processes occurring during impulsive a flare can be broadly classified as thermal or nonthermal models. current investigation is part series studies which analyze general characteristics 'nonthermal' results are presented...