1RXSJ062518.2+733433: A bright, soft intermediate polar

We present the results of 50 hours time-resolved R-band photometry of the ROSAT all-sky survey source 1RXSJ062518.2+733433. The source was identified by Wei et al. (1999) as a cataclysmic variable. Our photometry, performed in 10 nights between February 11, 2003, and March 21, 2003, reveals two stable periodicities at 19.7874 and 283.118 min, which are identified as probable spin and orbital periods of the binary. We therefore classify 1RXSJ062518.2+733433 as an intermediate polar. Analysis of the RASS X-ray observations reveal a variability of 100% in the X-ray flux and a likely soft X-ray excess. The new IP thus joins the rare group of soft IPs with only four members so far.Comment: submitted to A&A, 5 pages, 6 figures of reduced qualit

A tidal disruption flare in a massive galaxy? Implications for the fuelling mechanisms of nuclear black holes

We argue that the `changing look' AGN recently reported by LaMassa et al. could be a luminous flare produced by the tidal disruption of a super-solar mass star passing just a few gravitational radii outside the event horizon of a $\sim 10^8 M_{\odot}$ nuclear black hole. This flare occurred in a massive, star forming galaxy at redshift $z=0.312$, robustly characterized thanks to repeated late-time photometric and spectroscopic observations. By taking difference-photometry of the well sampled multi-year SDSS Stripe-82 light-curve, we are able to probe the evolution of the nuclear spectrum over the course of the outburst. The tidal disruption event (TDE) interpretation is consistent with the very rapid rise and the decay time of the flare, which displays an evolution consistent with the well-known $t^{-5/3}$ behaviour (with a clear superimposed re-brightening flare). Our analysis places constraints on the physical properties of the TDE, such as the putative disrupted star's mass and orbital parameters, as well as the size and temperature of the emitting material. The properties of the broad and narrow emission lines observed in two epochs of SDSS spectra provide further constraints on the circum-nuclear structure, and could be indicative that the system hosted a moderate-luminosity AGN as recently as a few $10^4$ years ago, and is likely undergoing residual accretion as late as ten years after peak, as seen from the broad H$\alpha$ emission line. We discuss the complex interplay between tidal disruption events and gas accretion episodes in galactic nuclei, highlighting the implications for future TDE searches and for estimates of their intrinsic rates.Comment: 20 pages, 9 figures, 3 tables. Accepted for publication in MNRA

V405 Peg (RBS 1955): A Nearby, Low-Luminosity Cataclysmic Binary

(Abridged). The cataclysmic binary V405 Peg, originally discovered as ROSAT Bright Source (RBS) 1955 (= 1RXS J230949.6+213523), shows a strong contribution from a late-type secondary star in its optical spectrum, which led Schwope et al. to suggest it to be among the nearest cataclysmic binaries. We present extensive optical observations of V405 Peg. Time-series spectroscopy shows the orbital period, Porb, to be 0.1776469(7) d (= 4.2635 hr), or 5.629 cycle/d. We classify the secondary as M3 - M4.5. Astrometry with the MDM 2.4m telescope gives a parallax 7.2 +- 1.1 milli-arcsec, and a relative proper motion of 58 mas/yr. Our best estimate of the distance yields d = 149 (+26, -20) pc. The secondary stars's radial velocity has K2 = 92 +- 3 km/s, indicating a fairly low orbital inclination if the masses are typical. Extensive I-band time-series observations in the show the system varying between a minimum brightness level of I = 14.14 and states of enhanced activity about 0.2 mag brighter. While the low-state shows an ellipsoidal modulation, an additional photometric modulation appears in the high state, with 0.1 mag amplitude and period 220-280 min. The frequency of this modulation appears to be stable for a month or so, but no single period was consistently detected from one observing season to the next. We estimate the system luminosity by combining optical measurements with the archival X-ray spectrum. The implied mass accretion rate is orders of magnitudes below the predictions for the standard angular momentum loss above the period gap. The system may possibly belong to a largely undiscovered population of hibernating CVs.Comment: 11 figures; 7 of these are .png or .jpg to save space. In press for Publications of the Astronomical Society of the Pacifi

Probing the AGN Unification Model at redshift z ∼\sim 3 with MUSE observations of giant Lyα\alpha nebulae

A prediction of the classic active galactic nuclei (AGN) unification model is the presence of ionisation cones with different orientations depending on the AGN type. Confirmations of this model exist for present times, but it is less clear in the early Universe. Here, we use the morphology of giant Ly$\alpha$ nebulae around AGNs at redshift z$\sim$3 to probe AGN emission and therefore the validity of the AGN unification model at this redshift. We compare the spatial morphology of 19 nebulae previously found around type I AGNs with a new sample of 4 Ly$\alpha$ nebulae detected around type II AGNs. Using two independent techniques, we find that nebulae around type II AGNs are more asymmetric than around type I, at least at radial distances $r>30$~physical kpc (pkpc) from the ionizing source. We conclude that the type I and type II AGNs in our sample show evidence of different surrounding ionising geometries. This suggests that the classical AGN unification model is also valid for high-redshift sources. Finally, we discuss how the lack of asymmetry in the inner parts (r$\lesssim$30 pkpc) and the associated high values of the HeII to Ly$\alpha$ ratios in these regions could indicate additional sources of (hard) ionizing radiation originating within or in proximity of the AGN host galaxies. This work demonstrates that the morphologies of giant Ly$\alpha$ nebulae can be used to understand and study the geometry of high redshift AGNs on circum-nuclear scales and it lays the foundation for future studies using much larger statistical samples.Comment: 15 pages, 13 figures, accepted for publication in MNRA

Chandra survey in the AKARI North Ecliptic Pole Deep Field. I. X-ray data, point-like source catalog, sensitivity maps, and number counts

We present data products from the 300 ks Chandra survey in the AKARI North Ecliptic Pole (NEP) deep field. This field has a unique set of 9-band infrared photometry covering 2-24 micron from the AKARI Infrared Camera, including mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the deepest ever achieved at ~15 micron, and is by far the widest among those with similar depths in the MIR. This makes this field unique for the MIR-selection of AGN at z~1. We design a source detection procedure, which performs joint Maximum Likelihood PSF fits on all of our 15 mosaicked Chandra pointings covering an area of 0.34 square degree. The procedure has been highly optimized and tested by simulations. We provide a point source catalog with photometry and Bayesian-based 90 per cent confidence upper limits in the 0.5-7, 0.5-2, 2-7, 2-4, and 4-7 keV bands. The catalog contains 457 X-ray sources and the spurious fraction is estimated to be ~1.7 per cent. Sensitivity and 90 per cent confidence upper flux limits maps in all bands are provided as well. We search for optical MIR counterparts in the central 0.25 square degree, where deep Subaru Suprime-Cam multiband images exist. Among the 377 X-ray sources detected there, ~80 per cent have optical counterparts and ~60 per cent also have AKARI mid-IR counterparts. We cross-match our X-ray sources with MIR-selected AGN from Hanami et al. (2012). Around 30 per cent of all AGN that have MID-IR SEDs purely explainable by AGN activity are strong Compton-thick AGN candidates.Comment: 23 pages, 20 figures; catalogs, sensitivity maps, and upper limit flux maps are available from the VizieR Servic

Trinucleotide cassettes increase diversity of T7 phage-displayed peptide library

<p>Abstract</p> <p>Background</p> <p>Amino acid sequence diversity is introduced into a phage-displayed peptide library by randomizing library oligonucleotide DNA. We recently evaluated the diversity of peptide libraries displayed on T7 lytic phage and M13 filamentous phage and showed that T7 phage can display a more diverse amino acid sequence repertoire due to differing processes of viral morphogenesis.</p> <p>Methods</p> <p>In this study, we evaluated and compared the diversity of a 12-mer T7 phage-displayed peptide library randomized using codon-corrected trinucleotide cassettes with a T7 and an M13 12-mer phage-displayed peptide library constructed using the degenerate codon randomization method.</p> <p>Results</p> <p>We herein demonstrate that the combination of trinucleotide cassette amino acid codon randomization and T7 phage display construction methods resulted in a significant enhancement to the functional diversity of a 12-mer peptide library. This novel library exhibited superior amino acid uniformity and order-of-magnitude increases in amino acid sequence diversity as compared to degenerate codon randomized peptide libraries. Comparative analyses of the biophysical characteristics of the 12-mer peptide libraries revealed the trinucleotide cassette-randomized library to be a unique resource.</p> <p>Conclusion</p> <p>The combination of T7 phage display and trinucleotide cassette randomization resulted in a novel resource for the potential isolation of binding peptides for new and previously studied molecular targets.</p

The XMM-Newton Wide Angle Survey (XWAS): the X-ray spectrum of type-1 AGN

We discuss the broad band X-ray properties of one of the largest samples of X-ray selected type-1 AGN to date (487 objects in total), drawn from the XMM-Newton Wide Angle Survey. The objects cover 2-10 keV luminosities from ~10^{42}-10^{45} erg s^{-1} and are detected up to redshift ~4. We constrain the overall properties of the broad band continuum, soft excess and X-ray absorption, along with their dependence on the X-ray luminosity and redshift and we discuss the implications for models of AGN emission. We constrained the mean spectral index of the broad band X-ray continuum to =1.96+-0.02 with intrinsic dispersion sigma=0.27_{-0.02}^{+0.01}. The continuum becomes harder at faint fluxes and at higher redshifts and luminosities. The dependence of Gamma with flux is likely due to undetected absorption rather than to spectral variation. We found a strong dependence of the detection efficiency of objects on the spectral shape which can have a strong impact on the measured mean continuum shapes of sources at different redshifts and luminosities. We detected excess absorption in ~3% of our objects, with column densities ~a few x10^{22} cm^{-2}. The apparent mismatch between the optical classification and X-ray properties of these objects is a challenge for the standard AGN unification model. We found that the fraction of objects with detected soft excess is ~36%. Using a thermal model, we constrained the soft excess mean temperature and intrinsic dispersion to ~100 eV and sigma~34 eV. The origin of the soft excess as thermal emission from the accretion disk or Compton scattered disk emission is ruled out on the basis of the temperatures detected and the lack of correlation of the measured temperature with the X-ray luminosity (abridged).Comment: 13 pages, 24 figures, Accepted for publication in Astronomy and Astrophysic

The changing accretion states of the intermediate polar MU Camelopardalis

We study the timing and spectral properties of the intermediate polar MU Camelopardalis (1RXS J062518.2+733433) to determine the accretion modes and the accretion geometry from multi-wavelength, multi-epoch observational data. Light curves in different observed energy ranges (optical, UV, X-ray) are extracted. The timescales of variability in these light curves are determined using Analysis of Variance. Phase-resolved X-ray spectra are created with respect to the most prominent detected periodicities and each fitted with an identical model, to quantify the differences in the fitted components. The published tentative value for the spin period is unambiguously identified with the rotation period of the white dwarf. We detect a distinct soft X-ray component that can be reproduced well by a black body. The analysis of data obtained at different epochs demonstrates that the system is changing its accretion geometry from disk-dominated to a combination of disk- plus stream-dominated, accompanied with a significant change in brightness at optical wavelengths.Comment: Accepted for publication in Astron. Astrophys., 13 pages, 10 figure

RBS1423 - a new QSO with relativistic reflection from an ionised disk

We present the analysis and results of a 20 ks XMM-Newton observation of RBS1423. X-ray spectral analysis is used to establish a significantly broadened relativistic iron K-alpha line from a highly ionised disk. A QSO at z=2.262 was considered to be the optical counterpart of this ROSAT Bright Survey X-ray source. Based on the improved XMM-Newton source position we identified a z=0.208 QSO as optical counterpart to RBS1423. The 0.2-12 keV X-ray luminosity of this radio-quiet QSO is 6x10^{44} erg/s. The XMM-EPIC spectra are well described by a power law with a significantly broadened iron K-alpha line. Disk line models for both Schwarzschild and Kerr black holes require hydrogen-like iron ions to fit the measured line profile. Significant ionisation of the reflection disk is confirmed by model fits with ionised disk models, resulting in an ionisation parameter xi~2000.Comment: 7 pages, 8 figures, accepted for publication in A&A (2 April 2007

Discovery of the lensed quasar eRASS1 J050129.5-073309 with SRG/\textit{SRG}/eROSITA and Gaia{\it Gaia}

We report the discovery and spectroscopic identification of the bright doubly lensed quasar eRASS1 J050129.5-073309 at redshift $z=2.47$, selected from the first all-sky survey of the ${\it Spectrum\; Roentgen\; Gamma\; (SRG)}$ eROSITA telescope and the ${\it Gaia}$ EDR3 catalog. We systematically search for extragalactic sources with eROSITA X-ray positions having multiple ${\it Gaia}$ counterparts and have started spectroscopic follow-up of the most promising candidates using long-slit spectroscopy with NTT/EFOSC2 to confirm the lens nature. The two images are separated by $2.7''$ and their average ${\it Gaia}$ ${\it g}$-band magnitudes are 16.95 and 17.33. Legacy Survey DR10 imaging and image modeling reveal both the lensing galaxy and tentatively the lensed image of the quasar host galaxy. Archival optical light curves show evidence of a variability time delay with the fainter component lagging the brighter by about 100 days. The fainter image has also decreased its brightness by about 1 magnitude since 2019. This dimming was still obvious at the time of the spectroscopic observations and is probably caused by microlensing. The optical spectroscopic follow-up obtained from NTT/EFOSC2 and the evidence provided by the imaging and timing analysis allow us to confirm the lensed nature of eRASS1 J050129.5-073309.Comment: Accepted for publication in A&