Andrea Martocchia

The Lack of Broad-Line Regions in Low Accretion Rate Active Galactic Nuclei as Evidence of Their Origin in the Accretion Disk

In this Letter, we present evidence suggesting that the absence or presence of hidden broad-line regions (HBLRs) in Seyfert 2 galaxies is regulated by the rate at which matter accretes onto a central supermassive black hole, in units of the Eddington rate. Evidence is based on data from a subsample of type 2 active galactic nuclei extracted from the Tran spectropolarimetric sample and made up of all those sources that also have good-quality X-ray spectra available and for which a bulge luminosity can be estimated. We use the intrinsic (i.e., unabsorbed) X-ray luminosities of these sources and their black hole masses (estimated by using the well-known relationship between nuclear mass and bulge luminosity in galaxies) to derive the nuclear accretion rate in Eddington units. We find that virtually all HBLR sources have accretion rates larger than a threshold value of thres 10-3 (in Eddington units), while non-HBLR sources lie at thres. These data nicely fit predictions from a model proposed by Nicastro in which the broad-line regions (BLRs) are formed by accretion disk instabilities occurring in proximity of the critical radius at which the disk changes from gas pressure dominated to radiation pressure dominated. This radius diminishes with decreasing ; for low enough accretion rates (and therefore luminosities), the critical radius becomes smaller than the innermost stable orbit and BLRs cannot form.

Evidence for a relativistic iron line in GRS 1915+105

We report on the discovery of a relativistic iron K fluorescent emission line in the BeppoSAX spectrum of the microquasar GRS 1915+105, taken on April 19, 1998, when the line was unusually intense. The feature is broad and skewed, clearly indicating emission from the innermost regions of the accretion disc. The inner emitting orbit is larger than the innermost stable orbit, even in Schwarzschild metric: thus, a non-zero BH spin is not required by these data.

On the origin of the broad, relativistic iron line of MCG–6-30-15 observed by XMM-Newton

The relativistic iron line prole recently observed by XMM-Newton in the spectrum of the Seyfert 1 galaxy MCG{6-30-15 (Wilms et al. 2001) is discussed in the framework of the lamp-post model. It is shown that the steep disc emissivity, the large line equivalent width and the amount of Compton reflection can be self-consistently reproduced in this scenario.

The low X-ray state of LS 5039/RX j1826.2-1450

Recent XMM-Newton and Chandra observations of the high mass X-ray binary LS 5039 / RX J1826.2-1450 caught the source in a faint X-ray state. In contrast with previous RXTE observations, we fail to detect any evidence of iron line emission. We also fail to detect X-ray pulsations. The X-ray spectrum can be well fitted by a simple powerlaw, slightly harder than in previous observations, and does not require the presence of any additional disk or blackbody component. XMM-Newton data imply an X-ray photoelectric absorption (

The complex X-ray spectrum of NGC 4507

N_{\rm H} \sim 7 \times 10^{21}

Variable Line Profiles Due to Non-Axisymmetric Patterns in an Accretion Disc around a Rotating Black Hole

 cm -2 ) consistent with optical reddening, indicating that no strong local absorption occurs at the time of these observations. We discuss possible source emission mechanisms and hypotheses on the nature of the compact object, giving particular emphasis to the young pulsar scenario.

Iron line diagnostics for the GRS 1915+105 black hole

XMM-Newton and Chandra/HETG spectra of the Compton-thin (NH ∼ 4 × 10 23 cm −2 ) Seyfert 2 galaxy, NGC 4507, are analyzed and discussed. The main results are: a) the soft X-ray emission is rich in emission lines; an (at least) two-zone photoionization region is required to explain the large range of ionization states; b) the 6.4 keV iron line is likely emitted from Compton-thick matter, implying the presence of two circumnuclear cold regions, one Compton-thick (the emitter), one Compton-thin (the cold absorber); c) evidence of an Fe  absorption line is found in the Chandra/HETG spectrum. The column density of the ionized absorber is estimated to be a few ×10 22 cm −2 .

Supernovae astrophysics from Middle Age documents

We have explored spectral line profiles due to spiral patterns in accretion discs around black holes. A parametrization was employed for the shape and emissivity of spiral waves, which can be produced by non-axisymmetric perturbations affecting the disc density and ionization structure. The effects of the light-travel time, energy shift, and gravitational focusing near to a rotating black hole were taken into account. A high-resolution ray-tracing code was used to follow the time variations of the synthetic line profile. A variety of expected spectral features were examined and the scheme applied to a broad iron line observed in MCG-6-30-15.

The XMM‐Newton view of GRS 1915+105 during a “plateau”

Abstract The properties of the broad Fe line detected in two BeppoSAX observations of the microquasar GRS 1915+105 are summarized.

LS 5039 / RX J1826.2‐1450: A Young Pulsar?

The supernova explosion of 1054 AD, which originated the Crab Nebula and Pulsar, is probably the astronomical event which has been most deeply studied by means of historical sources. However, many mysteries and inconsistencies, both among the different sources and between what is deduced by the historical records and the present day astronomical data, are demanding extraordinary efforts by theoretical astrophysicists in order to put all the data in a meaningful framework. An accurate analysis of the historical sources, like the one we are presenting here, may contribute to solve some of these problems.