Ranjan Vasudevan

Ranjan Vasudevan
University of Cambridge | Cam · Institute of Astronomy

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18
Publications
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581
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Publications

Publications (18)
Article
The brightness of an active galactic nucleus is set by the gas falling onto it from the galaxy, and the gas infall rate is regulated by the brightness of the active galactic nucleus; this feedback loop is the process by which supermassive black holes in the centres of galaxies may moderate the growth of their hosts. Gas outflows (in the form of dis...
Article
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Active galactic nucleus (AGN) feedback is the process by which supermassive black holes in the centres of galaxies may moderate the growth of their hosts. Gas outflows from supermassive black holes release huge quantities of energy into the interstellar medium, clearing the surrounding gas. The most extreme of these, the ultra-fast outflows (UFOs),...
Article
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A multi-epoch, multi-instrument analysis of the Seyfert 1 galaxy HE 0436–4717 is conducted using optical to X-ray data from XMM–Newton and Swift (including the Burst Alert Telescope). Fitting of the UV-to-X-ray spectral energy distribution shows little evidence of extinction and the X-ray spectral analysis does not confirm previous reports of deep...
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We present results from a new optical/UV/X-ray monitoring campaign of the luminous Seyfert galaxy Fairall 9 using the Swift satellite. Using the UV-Optical Telescope (UVOT) on Swift, we find correlated optical/UV variability on all time scales ranging from the sampling time (4-days) to the length of the campaign (2.5 months). In one noteworthy even...
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The X-ray spectra of many active galactic nuclei (AGN) exhibit a `soft excess' below 1keV, whose physical origin remains unclear. Diverse models have been suggested to account for it, including ionised reflection of X-rays from the inner part of the accretion disc, ionised winds/absorbers, and Comptonisation. The ionised reflection model suggests a...
Article
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The X-ray background (XRB) is due to the aggregate of active galactic nuclei (AGN), which peak in activity at z~1 and is often modeled as the sum of different proportions of unabsorbed, moderately- and heavily-absorbed AGN. We present the summed spectrum of a complete sample of local AGN (the Northern Galactic Cap of the 58-month Swift/BAT catalog,...
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1ES 1927+654 is an active galactic nucleus (AGN) that appears to defy the unification model. It exhibits a type-2 optical spectrum, but possesses little X-ray obscuration. XMM–Newton and Suzaku observations obtained in 2011 are used to study the X-ray properties of 1ES 1927+654. The spectral energy distribution derived from simultaneous optical-to-...
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We present a detailed X-ray spectral analysis of the non-beamed, hard X-ray selected active galactic nuclei (AGNs) in the northern Galactic cap of the 58 month Swift Burst Alert Telescope (Swift/BAT) catalog, consisting of 100 AGNs with b > 50°. This sky area has excellent potential for further dedicated study due to a wide range of multi-wavelengt...
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We present a detailed X-ray spectral analysis of a complete sample of hard X-ray selected AGN in the Northern Galactic Cap of the 58-month Swift Burst Alert Telescope (Swift/BAT) catalog, consisting of 100 AGN with b>50deg. This region has excellent potential for further study due to the availability of a wide range of archival multi-wavelength dat...
Article
Accretion onto supermassive black holes in Active Galactic Nuclei (AGN) produces vast amounts of energy over optical, UV and X-ray wavelengths from an accretion disc and corona; this primary emission may then be reprocessed by a dusty torus surrounding the central engine, giving rise to infrared emission and a number of AGN also exhibit radio emiss...
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We study the fraction of dual active galactic nuclei (AGNs) in a sample of 167 nearby (z < 0.05), moderate-luminosity, ultra-hard X-ray-selected AGNs from the all-sky Swift Burst Alert Telescope (BAT) survey. Combining new Chandra and Gemini observations together with optical and X-ray observations, we find that the dual AGN frequency at scales <10...
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We study the fraction of dual AGN in a sample of 167 nearby (z<0.05), moderate luminosity, ultra hard X-ray selected AGN from the all-sky Swift BAT survey. Combining new Chandra and Gemini observations together with optical and X-ray observations, we find that the dual AGN frequency at scales <100 kpc is 10% (16/167). Of the 16 dual AGN, 3 (19%) we...
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We have discovered a binary active galactic nucleus (AGN) in the galaxy Mrk 739 using Chandra and Swift BAT. We find two luminous (L 2-10 keV = 1.1 × 1043 and 1.0 × 1042 erg s–1), unresolved nuclei with a projected separation of 3.4 kpc (58 ± 01) coincident with two bulge components in the optical image. The western X-ray source (Mrk 739W) is highl...
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We present an investigation of the ultraviolet and X-ray spectra of the Seyfert 1.5 galaxy Markarian 817. The ultraviolet analysis includes two recent observations taken with the Cosmic Origins Spectrograph (COS) in 2009 August and December, as well as archival spectra from the International Ultraviolet Explorer and the Hubble Space Telescope. Twel...
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We present early results from an analysis of variability in the optical–to–X-ray spectral index, α OX , in sample of 97 Seyfert 1–1.2 AGN. Simultaneous SEDs from XMM-Newton (PN and Opti-cal Monitor instruments) are used to determine α OX and related SED parameters, using accretion disc model fits and accounting for intrinsic dust extinction. Our wo...
Article
The hard X-ray all-sky survey with the Swift/BAT instrument has provided a detailed census of local AGN activity. The Swift/BAT AGN catalog from 9-months of operation has allowed the determination of the X-ray properties, SEDs, accretion rates and absorption properties of AGN in the local Universe. Here we present preliminary results from a complet...
Article
Feedback is an integral component of AGN and galaxy co-evolution. The outward radiation pressure balances the inward gravitational force on the dusty gas in the galaxy bulge at an effective Eddington limit, which is lower than the canonical Eddington limit. We have shown that absorption in AGN in The Swift/BAT 9-month survey is overwhelmingly locat...

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