Alexei Baskin - Technion, Israel

Alexei Baskin
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Alexei Baskin
Technion, Israel

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Cosmology and Nongalactic Astrophysics (6)
Astrophysics (5)
Astrophysics of Galaxies (3)
High Energy Astrophysical Phenomena (2)

Publications Authored By Alexei Baskin

UV and optically selected candidates for stellar tidal disruption events (TDE) often exhibit broad spectral features (HeII emission, H$\alpha$ emission, or absorption lines) on a blackbody-like continuum (1e4KRead More

There is a large diversity in the C IV broad absorption line (BAL) profile among BAL quasars (BALQs). We quantify this diversity by exploring the distribution of the C IV BAL properties, FWHM, maximum depth of absorption and its velocity shift ($v_{\rm md}$), using the SDSS DR7 quasar catalogue. We find the following: (i) Although the median C IV BAL profile in the quasar rest-frame becomes broader and shallower as the UV continuum slope ($\alpha_{\rm UV}$ at 1700-3000 A) gets bluer, the median individual profile in the absorber rest-frame remains identical, and is narrow (FWHM = 3500 km/s) and deep. 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

A fraction of quasars present broad absorption lines, produced by outflowing gas with typical velocities of 3000 - 10,000 km/s. If the outflowing gas fills a significant fraction of the volume where it resides, then it will be highly ionized by the quasar due to its low density, and will not produce the observed UV absorption. The suggestion that the outflow is shielded from the ionizing radiation was excluded by recent observations. Read More

We analyze the hydrostatic effect of AGN radiation pressure on optically thick gas in the host galaxy. We show that in luminous AGN, the radiation pressure likely confines the ionized layer of the illuminated gas. Radiation pressure confinement (RPC) has two main implications. Read More

Active galactic nuclei (AGN) are characterized by similar broad emission lines properties at all luminosities ($10^{39}$-$10^{47}$ erg s$^{-1}$). What produces this similarity over a vast range of $10^8$ in luminosity? Photoionization is inevitably associated with momentum transfer to the photoionized gas. Yet, most of the photoionized gas in the Broad Line Region (BLR) follows Keplerian orbits, which suggests that the BLR originates from gas with a large enough column for gravity to dominate. Read More

Broad absorption line quasars (BALQs) present a large diversity in their broad absorption line (BAL) profiles. To investigate what physical parameters underlie this diversity, we construct a sample of BALQs which covers lambda_rest ~ 800-3000 {\AA}, based on the Sloan Digital Sky Survey DR7 quasar catalogue. The average BAL properties are evaluated by taking the ratios of average BALQ spectra to the average spectra of matched samples of non-BALQs, where the matching is based on various emission properties. Read More

Outflows from active galactic nuclei may be produced by absorption of continuum radiation by UV resonance lines of abundant metal ions, as observed in broad absorption line quasars (BALQs). The radiation pressure exerted on the metal ions is coupled to the rest of the gas through Coulomb collisions of the metal ions. We calculate the photon density and gas density which allow decoupling of the metal ions from the rest of the gas. Read More

We report the detection of variable UV absorption lines in NGC 4395, based on UV observations with the HST STIS carried out in April and July, 2004, as part of a reverberation-mapping campaign. Low-ionization lines of O I, N I, Si II, C II, and Fe II, are present in the low-state spectra (April 2004) at a velocity v_shift=-250 km/s (system A_l), and additional high-ionization lines of C IV and N V appear in the high-state spectra (July 2004) at v_shift=-250 km/s (system A_h) and at v_shift=-840 km/s (system B). The absence of absorption from the low metastable levels of Si II implies a density <~10^3 cm^(-3) for system A_l, indicating a location outside the narrow line region (NLR). Read More

Affiliations: 1Technion, Israel, 2Technion, Israel
Category: Astrophysics

AGN display an extreme range in the narrow emission line equivalent widths. Specifically, in the PG quasar sample the equivalent width of the narrow [O III] 5007 line has a range of >300, while the broad Hb line, for example, has a range of 10 only. The strength of [O III] 5007 is modulated by the covering factor, CF, of the narrow line region (NLR) gas, its density n_e, and ionization parameter U. Read More

Affiliations: 1Technion, Israel, 2Technion, Israel
Category: Astrophysics

The high ionization lines in active galactic nuclei (AGN), such as C IV, tend to be blueshifted with respect to the lower ionization lines, such as H beta, and often show a strong blue excess asymmetry not seen in the low ionization lines. There is accumulating evidence that the H beta profile is dominated by gravity, and thus provides a useful estimate of the black hole mass in AGN. The shift and asymmetry commonly seen in C IV suggest that non gravitational effects, such as obscuration and radiation pressure, may affect the line profile. Read More

Affiliations: 1Technion, Israel, 2Technion, Israel
Category: Astrophysics

The origin of the luminosity dependence of the equivalent width (EW) of broad emission lines in AGN (the Baldwin effect) is not firmly established yet. We explore this question for the broad C IV \lambda 1549 line using the Boroson & Green sample of the 87 z < 0.5 Bright Quasar Survey (BQS) quasars. Read More

Affiliations: 1Technion, Israel, 2Technion, Israel
Category: Astrophysics

The origin of the luminosity dependence of the strength of broad and narrow emission lines in AGN (i.e. the Baldwin effect) is not firmly established yet. Read More