Ehud Behar - Technion

Ehud Behar
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Name
Ehud Behar
Affiliation
Technion
City
Umm al-Fahm
Country
Israel

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High Energy Astrophysical Phenomena (24)
 
Astrophysics (15)
 
Cosmology and Nongalactic Astrophysics (13)
 
Astrophysics of Galaxies (12)
 
Solar and Stellar Astrophysics (6)
 
High Energy Physics - Phenomenology (1)
 
Instrumentation and Methods for Astrophysics (1)
 
Earth and Planetary Astrophysics (1)

Publications Authored By Ehud Behar

Black hole accretion disks appear to produce invariably plasma outflows that result in blue-shifted absorption features in their spectra. The X-ray absorption-line properties of these outflows are quite diverse, ranging in velocity from non-relativistic ($\sim 300$ km/sec) to sub-relativistic ($\sim 0.1c$ where $c$ is the speed of light) and a similarly broad range in the ionization states of the wind plasma. Read More

High resolution X-ray spectroscopy of the warm absorber in the nearby X-ray bright Seyfert 1 galaxy, Mrk 1040 is presented. The observations were carried out in the 2013-2014 timeframe using the Chandra High Energy Transmission Grating with a total exposure of 200 ks. A multitude of absorption lines from Ne, Mg and Si are detected from a wide variety of ionization states. Read More

Outflows in active galaxies (AGNs) are common, although their launching mechanism, location, and physical impact on the host galaxy remain controversial. We conducted a multiwavelength six-month campaign to observe the nearby Seyfert galaxy NGC 7469 with several observatories in order to better understand and quantify the outflow in this AGN. We report on the time-integrated line-resolved X-ray spectrum of NGC 7469 obtained with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. Read More

The 2175 \AA\ UV extinction feature was discovered in the mid-1960s, yet its physical origin remains poorly understood. One suggestion is absorption by Polycyclic Aromatic Hydrocarbons (PAH) molecules, which is supported by theoretical molecular structure computations and by laboratory experiments. PAHs are positively detected by their 3. Read More

High resolution soft X-ray spectroscopy of the prototype accretion disk wind quasar, PDS 456, is presented. Here, the XMM-Newton RGS spectra are analyzed from the large 2013-2014 XMM-Newton campaign, consisting of 5 observations of approximately 100 ks in length. During the last observation (hereafter OBS. Read More

2016Feb
Affiliations: 1, University of Southampton, UK, 2INAF-Osservatorio di Torino, Italy, 3Rochester Institute of Technology, USA, 4Technion, Haifa, Israel, 5Technion, Haifa, Israel

Several studies indicate that radio-loud (RL) Active Galactic Nuclei (AGN) are produced only by the most massive black holes (BH), $M_{\rm BH} \sim 10^8$-$10^{10} M_\odot$. This idea has been challenged by the discovery of RL Narrow Line Seyfert 1 (RL NLSy1), having estimated masses of $M_{\rm BH}$$\sim$$10^6$-$10^7$ M$_\odot$. However, these low $M_{\rm BH}$ estimates might be due to projection effects. Read More

We consider a sample of 107 Gamma Ray Bursts (GRBs) for which early UV emission was measured by Swift, and extrapolate the photon intensity to lower energies. Protons accelerated in the GRB jet may interact with such photons to produce charged pions and subsequently ultra high energy neutrinos $\varepsilon_\nu\geq 10^{16}$ eV. We use simple energy conversion efficiency arguments to predict the maximal neutrino flux expected from each GRB. Read More

The IceCube telescope has detected diffuse neutrino emission, 20 events of which were reported to be above 60~TeV. In this paper, we fit the diffuse neutrino spectrum using Poisson statistics, which are the most appropriate for the low counts per energy bin. We extend the fitted energy range and exploit the fact that no neutrinos were detected above 2~PeV, despite the high detector sensitivity around the Glashow resonance at 6. Read More

2015Sep
Affiliations: 1, Technion, Israel, 2, Technion, Israel, 3, Technion, Israel, 4Weizmann, Israel

We report short-cadence monitoring of a radio-quiet Active Galactic Nuclei (AGN), NGC7469, at 95 GHz (3 mm) over a period of 70 days with the CARMA telescope. The AGN varies significantly ($\pm3\sigma$ from the mean) by a factor of two within 4-5 days. The intrinsic 95 GHz variability amplitude in excess of the measurement noise (10%) and relative to the mean flux is comparable to that in the X-rays, and much higher than at 8. Read More

2015Apr
Affiliations: 1Technion, Israel, 2Technion, Israel, 3Technion, Israel, 4Weizmann, Israel, 5CSIRO, Australia, 6CSIRO, Australia

The physical origin of radio emission in Radio Quiet Active Galactic Nuclei (RQ AGN) remains unclear, whether it is a downscaled version of the relativistic jets typical of Radio Loud (RL) AGN, or whether it originates from the accretion disk. The correlation between 5 GHz and X-ray luminosities of RQ AGN, which follows $L_R = 10^{-5}L_X$ observed also in stellar coronae, suggests an association of both X-ray and radio sources with the accretion disk corona. Observing RQ AGN at higher (mm-wave) frequencies, where synchrotron self absorption is diminished, and smaller regions can be probed, is key to exploring this association. Read More

We present a study of X-ray ionization of magnetohydrodynamic (MHD) accretion-disk winds in an effort to constrain the physics underlying the highly-ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in various sub-classes of Seyfert active galactic nuclei (AGNs). Our primary focus is to show that magnetically-driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of the present X-ray spectroscopic observations. Employing a stratified MHD wind launched across the entire AGN accretion disk, we calculate its X-ray ionization and the ensuing X-ray absorption line spectra. Read More

Coronal elemental abundances are known to deviate from the photospheric values of their parent star, with the degree of deviation depending on the First Ionization Potential (FIP). This study focuses on the coronal composition of stars with super-solar photospheric abundances. We present the coronal abundances of six such stars: 11 LMi, $\iota$ Hor, HR 7291, $\tau$ Boo, and $\alpha$ Cen A and B. Read More

The radius and surface composition of an exploding massive star,as well as the explosion energy per unit mass, can be measured using early UV observations of core collapse supernovae (SNe). We present the first results from a simultaneous GALEX/PTF search for early UV emission from SNe. Six Type II SNe and one Type II superluminous SN (SLSN-II) are clearly detected in the GALEX NUV data. Read More

The winds of ionized gas driven by Active Galactic Nuclei (AGN) can be studied through absorption lines in their X-ray spectra. A recurring feature of these outflows is their broad ionization distribution, including essentially all ionization levels (e.g. Read More

The IceCube high-energy neutrino telescope has been collecting data since 2006. Conversely, hundreds of Gamma Ray Bursts (GRBs) have been detected by the GBM on board Fermi, since its launch in 2008. So far no neutrino event has been associated with a GRB, despite many models predicting the generation of high energy neutrinos through GRB photon interaction with PeV protons in the GRB jet. Read More

We explore the poloidal structure of two-dimensional (2D) MHD winds in relation to their potential association with the X-ray warm absorbers (WAs) and the highly-ionized ultra-fast outflows (UFOs) in AGN, in a single unifying approach. We present the density $n(r,\theta)$, ionization parameter $\xi(r,\theta)$, and velocity structure $v(r,\theta)$ of such ionized winds for typical values of their fluid-to-magnetic flux ratio, $F$, and specific angular momentum, $H$, for which wind solutions become super-\Alfvenic. We explore the geometrical shape of winds for different values of these parameters and delineate the values that produce the widest and narrowest opening angles of these winds, quantities necessary in the determination of the statistics of AGN obscuration. Read More

Soft X-ray photoelectric absorption of high-z quasars has been known for two decades, but has no unambiguous astro-physical context. We construct the largest sample to date of 58 high redshift quasars (z > 0.45) selected from the XMM-Newton archive based on a high photon count criterion (> 1800). Read More

2013Jun
Authors: Kirpal Nandra1, Didier Barret2, Xavier Barcons3, Andy Fabian4, Jan-Willem den Herder5, Luigi Piro6, Mike Watson7, Christophe Adami8, James Aird9, Jose Manuel Afonso10, Dave Alexander11, Costanza Argiroffi12, Lorenzo Amati13, Monique Arnaud14, Jean-Luc Atteia15, Marc Audard16, Carles Badenes17, Jean Ballet18, Lucia Ballo19, Aya Bamba20, Anil Bhardwaj21, Elia Stefano Battistelli22, Werner Becker23, Michaël De Becker24, Ehud Behar25, Stefano Bianchi26, Veronica Biffi27, Laura Bîrzan28, Fabrizio Bocchino29, Slavko Bogdanov30, Laurence Boirin31, Thomas Boller32, Stefano Borgani33, Katharina Borm34, Nicolas Bouché35, Hervé Bourdin36, Richard Bower37, Valentina Braito38, Enzo Branchini39, Graziella Branduardi-Raymont40, Joel Bregman41, Laura Brenneman42, Murray Brightman43, Marcus Brüggen44, Johannes Buchner45, Esra Bulbul46, Marcella Brusa47, Michal Bursa48, Alessandro Caccianiga49, Ed Cackett50, Sergio Campana51, Nico Cappelluti52, Massimo Cappi53, Francisco Carrera54, Maite Ceballos55, Finn Christensen56, You-Hua Chu57, Eugene Churazov58, Nicolas Clerc59, Stephane Corbel60, Amalia Corral61, Andrea Comastri62, Elisa Costantini63, Judith Croston64, Mauro Dadina65, Antonino D'Ai66, Anne Decourchelle67, Roberto Della Ceca68, Konrad Dennerl69, Klaus Dolag70, Chris Done71, Michal Dovciak72, Jeremy Drake73, Dominique Eckert74, Alastair Edge75, Stefano Ettori76, Yuichiro Ezoe77, Eric Feigelson78, Rob Fender79, Chiara Feruglio80, Alexis Finoguenov81, Fabrizio Fiore82, Massimiliano Galeazzi83, Sarah Gallagher84, Poshak Gandhi85, Massimo Gaspari86, Fabio Gastaldello87, Antonis Georgakakis88, Ioannis Georgantopoulos89, Marat Gilfanov90, Myriam Gitti91, Randy Gladstone92, Rene Goosmann93, Eric Gosset94, Nicolas Grosso95, Manuel Guedel96, Martin Guerrero97, Frank Haberl98, Martin Hardcastle99, Sebastian Heinz100, Almudena Alonso Herrero101, Anthony Hervé102, Mats Holmstrom103, Kazushi Iwasawa104, Peter Jonker105, Jelle Kaastra106, Erin Kara107, Vladimir Karas108, Joel Kastner109, Andrew King110, Daria Kosenko111, Dimita Koutroumpa112, Ralph Kraft113, Ingo Kreykenbohm114, Rosine Lallement115, Giorgio Lanzuisi116, J. Lee117, Marianne Lemoine-Goumard118, Andrew Lobban119, Giuseppe Lodato120, Lorenzo Lovisari121, Simone Lotti122, Ian McCharthy123, Brian McNamara124, Antonio Maggio125, Roberto Maiolino126, Barbara De Marco127, Domitilla de Martino128, Silvia Mateos129, Giorgio Matt130, Ben Maughan131, Pasquale Mazzotta132, Mariano Mendez133, Andrea Merloni134, Giuseppina Micela135, Marco Miceli136, Robert Mignani137, Jon Miller138, Giovanni Miniutti139, Silvano Molendi140, Rodolfo Montez141, Alberto Moretti142, Christian Motch143, Yaël Nazé144, Jukka Nevalainen145, Fabrizio Nicastro146, Paul Nulsen147, Takaya Ohashi148, Paul O'Brien149, Julian Osborne150, Lida Oskinova151, Florian Pacaud152, Frederik Paerels153, Mat Page154, Iossif Papadakis155, Giovanni Pareschi156, Robert Petre157, Pierre-Olivier Petrucci158, Enrico Piconcelli159, Ignazio Pillitteri160, C. Pinto161, Jelle de Plaa162, Etienne Pointecouteau163, Trevor Ponman164, Gabriele Ponti165, Delphine Porquet166, Ken Pounds167, Gabriel Pratt168, Peter Predehl169, Daniel Proga170, Dimitrios Psaltis171, David Rafferty172, Miriam Ramos-Ceja173, Piero Ranalli174, Elena Rasia175, Arne Rau176, Gregor Rauw177, Nanda Rea178, Andy Read179, James Reeves180, Thomas Reiprich181, Matthieu Renaud182, Chris Reynolds183, Guido Risaliti184, Jerome Rodriguez185, Paola Rodriguez Hidalgo186, Mauro Roncarelli187, David Rosario188, Mariachiara Rossetti189, Agata Rozanska190, Emmanouil Rovilos191, Ruben Salvaterra192, Mara Salvato193, Tiziana Di Salvo194, Jeremy Sanders195, Jorge Sanz-Forcada196, Kevin Schawinski197, Joop Schaye198, Axel Schwope199, Salvatore Sciortino200, Paola Severgnini201, Francesco Shankar202, Debora Sijacki203, Stuart Sim204, Christian Schmid205, Randall Smith206, Andrew Steiner207, Beate Stelzer208, Gordon Stewart209, Tod Strohmayer210, Lothar Strüder211, Ming Sun212, Yoh Takei213, V. Tatischeff214, Andreas Tiengo215, Francesco Tombesi216, Ginevra Trinchieri217, T. G. Tsuru218, Asif Ud-Doula219, Eugenio Ursino220, Lynne Valencic221, Eros Vanzella222, Simon Vaughan223, Cristian Vignali224, Jacco Vink225, Fabio Vito226, Marta Volonteri227, Daniel Wang228, Natalie Webb229, Richard Willingale230, Joern Wilms231, Michael Wise232, Diana Worrall233, Andrew Young234, Luca Zampieri235, Jean In't Zand236, Silvia Zane237, Andreas Zezas238, Yuying Zhang239, Irina Zhuravleva240
Affiliations: 1DE, 2FR, 3ES, 4UK, 5NL, 6IT, 7UK, 8FR, 9UK, 10PT, 11UK, 12IT, 13IT, 14FR, 15FR, 16CH, 17US, 18FR, 19IT, 20JP, 21IN, 22IT, 23DE, 24BE, 25IL, 26IT, 27IT, 28NL, 29IT, 30US, 31FR, 32DE, 33IT, 34DE, 35FR, 36IT, 37UK, 38IT, 39IT, 40UK, 41US, 42US, 43DE, 44DE, 45DE, 46US, 47IT, 48CZ, 49IT, 50US, 51IT, 52IT, 53IT, 54ES, 55ES, 56DK, 57US, 58DE, 59DE, 60FR, 61GR, 62IT, 63NL, 64UK, 65IT, 66IT, 67FR, 68IT, 69DE, 70DE, 71UK, 72CZ, 73US, 74CH, 75UK, 76IT, 77JP, 78US, 79UK, 80FR, 81FI, 82IT, 83IT, 84CA, 85UK, 86IT, 87IT, 88DE, 89GR, 90DE, 91IT, 92US, 93FR, 94BE, 95FR, 96AT, 97ES, 98DE, 99UK, 100US, 101ES, 102FR, 103SE, 104ES, 105NL, 106NL, 107UK, 108CZ, 109US, 110UK, 111FR, 112FR, 113US, 114D, 115FR, 116GR, 117US, 118FR, 119UK, 120IT, 121DE, 122IT, 123UK, 124CA, 125IT, 126UK, 127DE, 128IT, 129ES, 130IT, 131UK, 132IT, 133NL, 134DE, 135IT, 136IT, 137IT, 138US, 139ES, 140IT, 141ES, 142IT, 143FR, 144BE, 145FI, 146IT, 147US, 148JP, 149UK, 150UK, 151DE, 152DE, 153US, 154UK, 155GR, 156IT, 157US, 158FR, 159IT, 160IT, 161UK, 162NL, 163FR, 164UK, 165DE, 166FR, 167UK, 168FR, 169DE, 170US, 171US, 172NL, 173DE, 174IT, 175US, 176DE, 177BE, 178IT, 179UK, 180UK, 181DE, 182FR, 183US, 184IT, 185FR, 186CA, 187IT, 188DE, 189IT, 190PL, 191UK, 192IT, 193DE, 194IT, 195DE, 196ES, 197CH, 198NL, 199D, 200IT, 201IT, 202FR, 203UK, 204IE, 205DE, 206US, 207US, 208IT, 209UK, 210US, 211DE, 212US, 213JP, 214FR, 215IT, 216US, 217IT, 218JP, 219US, 220NL, 221US, 222IT, 223UK, 224IT, 225NL, 226IT, 227FR, 228US, 229FR, 230UK, 231DE, 232NL, 233UK, 234UK, 235IT, 236NL, 237UK, 238GR, 239DE, 240US

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Read More

Elemental abundance effects in active coronae have eluded our understanding for almost three decades, since the discovery of the First Ionization Potential (FIP) effect on the sun. The goal of this paper is to monitor the same coronal structures over a time interval of six days and resolve active regions on a stellar corona through rotational modulation. We report on four iso-phase X-ray spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried out approximately every two days, to match the rotation period of EI Eri. Read More

A major uncertainty in models for photoionised outflows in AGN is the distance of the gas to the central black hole. We present the results of a massive multiwavelength monitoring campaign on the bright Seyfert 1 galaxy Mrk 509 to constrain the location of the outflow components dominating the soft X-ray band. Mrk 509 was monitored by XMM-Newton, Integral, Chandra, HST/COS and Swift in 2009. Read More

2012Jun
Affiliations: 1NASA/GSFC, 2NASA/CRESST, 3Technion, Israel, 4Academy of Athens, Greece, 5NASA/USRA

We present a unified model for the structure and appearance of accretion powered sources across their entire luminosity range from galactic X-ray binaries to luminous quasars, with emphasis on AGN and their phenomenology. Central to this model is the notion of MHD winds launched from the accretion disks that power these objects. These winds provide the matter that manifests as blueshifted absorption features in the UV and X-ray spectra of a large fraction of these sources; furthermore, their density distribution in the poloidal plane determines the "appearance" (i. Read More

We present results of broad band photometric reverberation mapping (RM) to measure the radius of the broad line region, and subsequently the black hole mass (M$_{\rm BH}$), in the nearby, low luminosity active galactic nuclei (AGN) NGC 4395. Using the Wise Observatory's 1m telescope equipped with the SDSS g$'$, r$'$ and i$'$ broad band filters, we monitored NGC 4395 for 9 consecutive nights and obtained 3 light curves each with over 250 data points. The g$'$ and r$'$ bands include time variable contributions from H$\beta$ and H$\alpha$ (respectively) plus continuum. Read More

By analyzing the X-ray spectra of NGC 3516 from 2001 and 2006 obtained with the HETGS spectrometer on board the Chandra observatory, we find that the kinematic structure of the outflow can be well represented by four outflow components intrinsic to NGC 3516. The outflow velocities of the different components are 350 +-100 km s-1, 1500 +-150 km s-1, 2600 +-200 km s-1 and 4000 +-400 km s-1 for components 1, 2, 3 and 4, respectively. A local component at z = 0 could be confused with intrinsic component 3. Read More

We present the results of a reverberation mapping (RM) campaign on the black hole (BH) associated with the active galactic nucleus (AGN) in SDSS J114008.71+030711.4 (hereafter GH08). Read More

We present absorption line analysis of the outflow in the quasar IRAS F04250-5718. Far-ultraviolet data from the Cosmic Origins Spectrograph onboard the Hubble Space Telescope reveal intrinsic narrow absorption lines from high ionization ions (e.g. Read More

The angular power spectrum and polarization of the cosmic microwave background radiation (CMB), the relative abundances of primordial hydrogen, deuterium and helium isotopes, and the large-scale structure of the universe all indicate that 4.5% of the current mass density of the universe consists of baryons. However, only a small fraction of these baryons can be accounted for in stars and gas inside galaxies, galaxy groups and galaxy clusters, and in spectral-line absorbing gas in the intergalactic medium (IGM). Read More

Observations with the Swift satellite of X-ray afterglows of more than a hundred gamma ray bursts (GRBs) with known redshift reveal ubiquitous soft X-ray absorption. The directly measured optical depth \tau at a given observed energy is found to be constant on average at redshift z > 2, i.e. Read More

We extend our modeling of the ionization structure of magnetohydrodynamic (MHD) accretion-disk winds, previously applied to Seyfert galaxies, to a population of quasi-stellar-objects (QSOs) of much lower X-ray-to-UV flux ratios, i.e. smaller $\alpha_{\rm ox}$ index, motivated by UV/X-ray ionized absorbers with extremely high outflow velocities in UV-luminous QSOs. Read More

2010Apr
Affiliations: 1Technion, Israel, 2Technion, Israel, 3Technion, Israel, 4RIT, USA

We show that suprathermal particles, termed pick-up ions (PUIs), might reduce the postshock temperature of the fast wind and jets in some planetary nebulae (PNs) and in symbiotic systems. The goal is to explain the finding that the temperature of the hot bubble formed by the post-shock gas in some PNs and symbiotic nebulae is lower, sometimes by more than an order of magnitude, than the value expected from simple hydrodynamical calculations. Although various explanations have been proposed, there is as yet no prefered solution for this low tempeature problem. Read More

We report on the highest to date signal-to-noise-ratio X-ray spectrum of the luminous quasar PDS 456, as obtained during two XMM-Newton orbits in September 2007. The present spectrum is considerably different from several previous X-ray spectra recorded for PDS 456 since 1998. The ultra-high-velocity outflow seen as recently as February 2007 is not detected in absorption. Read More

We present the 2D ionization structure of self-similar MHD winds off accretion disks around irradiated by a central X-ray source. Based on earlier observational clues and theoretical arguments, we focus our attention on a subset of these winds, namely those with radial density dependence n(r)~1/r. We employ the photoionization code XSTAR to compute the ionic abundances of a large number of ions of different elements and then compile their line-of-sight (LOS) absorption columns. Read More

By analyzing the X-ray spectrum of MCG-6-30-15 obtained with the HETG spectrometer on board the Chandra Observatory, we identify three kinematically distinct absorption systems; two outflow components intrinsic to MCG-6-30-15, and one local at z = 0. The slow outflow at -100 +/- 50 km s^-1 has a large range of ionization manifested by absorption from 24 different charge states of Fe, which enables a detailed reconstruction of the absorption measure distribution (AMD). This AMD spans five orders of magnitude in ionization parameter: -1. Read More

We report the XMM-Newton/EPIC detection in 2008 March of a luminous (L_X ~ 10^32-33 erg/s), variable X-ray source in the vicinity (within ~6") of the enigmatic star V838 Mon, which underwent a spectacular outburst in early 2002. Spectral modeling of the XMM-Newton X-ray source indicates the presence of two plasma components with characteristic temperatures of TX ~ 2x10^6K and ~1.5x10^7K, attenuated by an absorbing column (N_H ~ 4 x 10^21cm^-2) that is consistent with the visual extinction measured toward V838 Mon (A_V ~ 2). Read More

For the past decade, ionized outflows of a few 100 km/s from nearby Seyfert galaxies have been studied in great detail using high resolution X-ray absorption spectra. A recurring feature of these outflows is their broad ionization distribution including essentially ions (e.g. Read More

2009Jan
Affiliations: 1Technion, Israel, 2Technion, Israel, 3Technion, Israel, 4Rochester Institute of Technology, NY, 5Rochester Institute of Technology, NY

X-rays from planetary nebulae (PNs) are believed to originate from a shock driven into the fast stellar wind (v ~ 1000 km/s) as it collides with an earlier circumstellar slow wind (v ~ 10 km/s). In theory, the shocked fast wind (hot bubble) and the ambient cold nebula can remain separated by magnetic fields along a surface referred to as the contact discontinuity (CD) that inhibits diffusion and heat conduction. The CD region is extremely difficult to probe directly owing to its small size and faint emission. Read More

The radio emission in radio loud quasars originates in a jet carrying relativistic electrons. In radio quiet quasars (RQQs) the relative radio emission is ~10^3 times weaker, and its origin is not established yet. We show here that there is a strong correlation between the radio luminosity (L_R) and X-ray luminosity (L_X) with L_R~10^-5L_X, for the radio quiet Palomar-Green (PG) quasar sample. Read More

2008Jun
Affiliations: 1Center for Imaging Science, Rochester Institute of Technology, 2Department of Physics, Technion, Israel, 3Center for Imaging Science, Rochester Institute of Technology, 4MIT Kavli Institute, 5Department of Physics, Technion, Israel, 6Department of Physics, Technion, Israel
Category: Astrophysics

We present the results of the first X-ray gratings spectroscopy observations of a planetary nebula (PN), the X-ray-bright, young BD+30 3639. We observed BD+30 3639 for a total of 300 ks with the Chandra X-ray Observatory's Low Energy Transmission Gratings in combination with its Advanced CCD Imaging Spectrometer(LETG/ACIS-S). The LETG/ACIS-S spectrum of BD+30 3639 is dominated by H-like resonance lines of O viii and C sc vi and the He-like triplet line complexes of Ne ix and O vii. Read More

2007Jul
Affiliations: 1Technion, Israel, 2Technion, Israel, 3Technion, Israel
Category: Astrophysics

We analyze velocity profiles of the X-ray spectral lines emitted by the Eta Carinae stellar binary at four epochs, just before the X-ray minimum (associated with periastron) and more than two years before the minimum (~apastron). The profiles are nicely resolved by the HETGS spectrometer on board Chandra. Far from periastron, we find symmetrical lines that are more or less centered at zero velocity. Read More

We analyze the Chandra X-ray spectrum obtained with the HETGS grating spectrometer of IRAS 13349+2438, which has one of the richest absorption spectra of a quasar outflow. Absorption from almost all charge states of Fe is detected. This allows for a detailed reconstruction of the absorption measure distribution (AMD), which we define as the continuous distribution of column density as a function of ionization parameter. Read More

We present the first reliable determination of chemical abundances in an AGN outflow. The abundances are extracted from the deep and simultaneous FUSE and HST/STIS observations of Mrk 279. This data set is exceptional for its high signal-to-noise, unblended doublet troughs and little Galactic absorption contamination. Read More

2006Oct
Affiliations: 1Technion, Israel, 2Technion, Israel, 3Technion, Israel, 4North Carolina State University
Category: Astrophysics

We calculate the X-ray emission from both constant and time evolving shocked fast winds blown by the central stars of planetary nebulae (PNs) and compare with observations. Using spherically symmetric numerical simulations with radiative cooling, we calculate the flow structure, and the X-ray temperature and luminosity of the hot bubble formed by the shocked fast wind. We find that a constant fast wind gives results that are very close to those obtained from the self-similar solution. Read More

2006Jul
Affiliations: 1Center for Imaging Science, Rochester Institute of Technology, 2Center for Imaging Science, Rochester Institute of Technology, 3MIT Kavli Institute, 4Department of Physics, Technion, Israel, 5Department of Physics, Technion, Israel, 6Department of Physics, Technion, Israel
Category: Astrophysics

We present preliminary results from the first X-ray gratings spectrometer observations of a planetary nebula (PN). We have used the Chandra X-ray Observatory Low Energy Transmission Gratings Spectrometer (LETGS) to observe the bright, diffuse X-ray source within the well-studied BD +30 3639. The LETGS spectrum of BD +30 3639 displays prominent and well-resolved emission lines of H-like C, O, and Ne and He-like O and Ne. Read More

2006Jun
Affiliations: 1Technion, 2Technion, 3Technion, 4Technion
Category: Astrophysics

eta Carinae is a stellar binary system with a period of 5.54 years. It harbors one of the brightest and most massive stars in our galaxy. Read More

We continue to explore the accretion model of the massive binary system eta Carinae by studying the anomalously high He II 4686 line. The line appears just before periastron and disappears immediately thereafter. Based on the He II 4686 line emission from O-stars and their modeling in the literature, we postulate that the He II 4686 line comes from the acceleration zone of the secondary stellar wind. Read More

We provide improved atomic calculation of wavelengths, oscillator strengths, and autoionization rates relevant to the $2\to 3$ inner-shell transitions of Fe~VI--XVI, the so-called Fe~M-shell unresolved transition array (UTA). A second order many-body perturbation theory is employed to obtain accurate transition wavelengths, which are systematically larger than previous theoretical results by 15--45~m{\AA}. For a few transitions of Fe~XVI and Fe~XV where laboratory measurements exist, our new wavelengths are accurate to within a few m{\AA}. Read More

We present and discuss high-resolution grating spectra of the quasar PG1211+143 obtained over three years. Based on an early observation from 2001, we find an outflow component of about 3000 km/s in contrast with the much higher velocity of about 24000 km/s reported earlier for this source, and based on the same data set. Subsequent grating spectra obtained for PG1211+143 are consistent with the first observation in the broad-band sense, but not all narrow features used to identify the outflow are reproduced. Read More

We analyze the X-ray spectrum of the quasar PG1211+143 observed with the CCD and grating spectrometers on board XMM-Newton. Using an ion by ion fitting model we find an outflow component of about 3000 km/s that includes absorption lines of K-shell and L-shell ions of the astrophysically abundant elements. We also identify and include in our model broad (FWHM = 6000 km/s) emission lines from H-like ions of C, N, O, and Ne, and He-like ions of O, Ne, and Mg. Read More

2005Sep

We calculate the X-ray luminosity and light curve for the stellar binary system Eta Carinae for the entire orbital period of 5.54 years. By using a new approach we find, as suggested before, that the collision of the winds blown by the two stars can explain the X-ray emission and temporal behavior. Read More

2005Aug
Affiliations: 1Dept. of Physics, Technion, 2Dept. of Physics, Technion, 3Dept. of Physics, Technion
Category: Astrophysics

We calculate the X-ray emission from the shocked fast wind blown by the central stars of planetary nebulae (PNs) and compare with observations. Using spherically symmetric self similar solutions, we calculate the flow structure and X-ray temperature for a fast wind slamming into a previously ejected slow wind. We find that the observed X-ray emission of six PNs can be accounted for by shocked wind segments that were expelled during the early PN phase, if the fast wind speed is moderate, v_2~400-600 km/sec, and the mass loss rate is a few times 10^{-7} Mo/year. Read More