Papers by Vahram Chavushyan
Publications of the Astronomical Society of Japan, 2016
We report on a superoutburst of a WZ Sge-type dwarf nova (DN), ASASSN-15po. The light curve showe... more We report on a superoutburst of a WZ Sge-type dwarf nova (DN), ASASSN-15po. The light curve showed the main superoutburst and multiple rebrightenings. In this outburst, we observed early superhumps and growing (stage A) superhumps with periods of 0.050454(2) and 0.051809(13) d, respectively. We estimated that the mass ratio of secondary to primary (q) is 0.0699(8) by using P orb and a superhump period P SH of stage A. ASASSN-15po [P orb ∼ 72.6 min] is the first DN with an orbital period between 67-76 min. Although the theoretical predicted period minimum P min of hydrogen-rich cataclysmic variables (CVs) is about 65-70 min, the observational cutoff of the orbital period distribution at 80 min implies that the period minimum is about 82 min, and the value is widely accepted. We suggest the following four possibilities: the object is (1) a theoretical period minimum object, (2) a binary with a evolved secondary, (3) a binary with a metal-poor (Popullation II) seconday, or (4) a binary which was born with a brown-dwarf donor below the period minimum.
We develop a new avenue to creating the optical spectrometer for the Guillermo Haro astrophysical... more We develop a new avenue to creating the optical spectrometer for the Guillermo Haro astrophysical observatory (Mexico), which combines specifically progressed prism spectrometer with modern acousto-optical approach in the frame of a joint instrument. This schematic arrangement includes two principal novelties. First, we exploit recently developed acousto-optical nonlinearity of the two-phonon light scattering in crystals with linear acoustic losses, which admits an additional physical degree of freedom. This effect allows us to use nonlinear acousto-optical effect for linear processing of optical signals in parallel regime within all the visible range. Similar effect is based on the possibility for tuning the frequency of elastic waves and admits the nonlinear apodization improving the dynamic range. Secondly, we are using the cross-disperser technique with acousto-optical processing for the first time to our knowledge. Additionally, the acousto-optical spectrometers can provide alm...
The astronomer's telegram, 2015
Narrow-line Seyfert 1 galaxies (NLS1) are a class of active galactic nuclei that share many obser... more Narrow-line Seyfert 1 galaxies (NLS1) are a class of active galactic nuclei that share many observational properties with the much more powerful blazar classes. Despite their low black hole masses (typically 10^6-10^8 solar masses) and near- or super-Eddington accretion rates, a small minority are radio loud (RLNLS1s). A growing number of these have been detected in GeV gamma rays by the Fermi Large Area Telescope (LAT), indicating that a relativistic jet has formed in at least some of these sources. This presents a challenge to jet models, but may provide a link between jets found at the small scales of galactic binaries and the large scales of giant quasars. We are carrying out a multifrequency polarimetric radio monitoring campaign of a sample of 15 RLNLS1s using the Very Long Baseline Array (VLBA). Using data from this program, we will expand the currently limited knowledge of the parsec-scale properties and kinematics of this class of sources. We are complementing this campaign...
The Astrophysical Journal, 2018
On 2017 May 15, the FERMI/LAT gamma-ray telescope observed a transient source not present in any ... more On 2017 May 15, the FERMI/LAT gamma-ray telescope observed a transient source not present in any previous high-energy catalog: J1544-0649. It was visible for two consecutive weeks, with a flux peak on May 21. Subsequently observed by a Swift/XRT follow-up starting on May 26, the X-ray counterpart position was coincident with the optical transient ASASSN-17gs=AT2017egv, detected on May 25, with a potential host galaxy at z=0.171. We conducted a 4-month follow-up in radio (Effelsberg-100m) and optical (San Pedro Mártir, 2.1m) bands, in order to build the overall Spectral Energy Distribution (SED) of this object. The radio data from 5 to 15 GHz confirmed the flat spectrum of the source, favoring a line of sight close to the jet axis, not showing significant variability in the explored post-burst time window. The Rx ratio, a common indicator of radio loudness, gives a value at the border between the radio-loud and radio-quiet active galactic nuclei (AGNs) populations. The Ca II H&K break value (0.29 ± 0.05) is compatible with the range expected for the long-sought intermediate population between BL Lacs and FRI radio galaxies. An overall SED fitting from the radio to gammaray band shows properties typical of a low-power BL Lac. As a whole, these results suggest that this transient could be a new example of the recently discovered class of radio-weak BL Lac, showing for the first time a flare in the gamma/X-ray bands.
The astronomer's telegram, 2015
Astronomy & Astrophysics, 2019
We investigate the relationship between the variable gamma-ray emission and jet properties in the... more We investigate the relationship between the variable gamma-ray emission and jet properties in the blazar 3C 279 by combining the Fermi-LAT data spanning a period of eight years and concurrent radio measurements made at multiple epochs with VLBA at 15 and 43 GHz within the MOJAVE and VLBA-BU monitoring programmes. The aim of this paper is to compare the flux variability of the different components found in the VLBA observations, to the variability in the gamma-rays. This analysis helps us to investigate whether any of the jet components can be associated with the gamma-ray variability. Through Spearman rank correlation we found that the gamma-ray variability is correlated with a particular region (feature B in the MOJAVE images) downstream from the observed base (core) of the jet. This jet component is therefore a likely location where an important fraction of the variable gamma-ray emission is produced. We also calculated the average proper motion of the component with respect to th...
The Astrophysical Journal Supplement Series, 1995
We present the data and initial results from a combined Hubble Space Telescope (HST)/IUE/ground-b... more We present the data and initial results from a combined Hubble Space Telescope (HST)/IUE/ground-based spectroscopic monitoring campaign on the Seyfert 1 galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-1989. IUE spectra were obtained once
We have studied the connection between black hole masses and jet parameters (Doppler and Lorentz ... more We have studied the connection between black hole masses and jet parameters (Doppler and Lorentz factors and viewing angle) in a sample of radio-bright flat spectrum radio quasars. Our preliminary results show a negative correlation between the black hole mass and the viewing angle, which could indicate a wind-like component in the broad line region of these sources. In contrast
Memorie della Società …, 2005
The Astrophysical Journal
The flat-spectrum radio quasar B2 1633+382 (4C 38.41) has been monitored for several years and ha... more The flat-spectrum radio quasar B2 1633+382 (4C 38.41) has been monitored for several years and has presented correlated variability in multiple wavelengths. In this article, we are performing different analyses for multiple frequencies, from gamma rays to radio, as well as the C iv λ1549 Å emission line and the λ1350 Å continuum. Using the nonthermal dominance parameter, we separated the C iv and the continuum light curves for when the dominant source of continuum is the accretion disk or the jet. We found a correlation at a delay consistent with zero between the line and the continuum dominated by disk emission indicating a very small broad-line region (BLR). From the resulting delay between the 15 GHz and gamma rays, we estimated the distance of the gamma-ray emission region from the jet apex to be ∼37 pc. The C iv flux decreases when the continuum and gamma rays increase at some of the high-activity periods. The C iv profile presents a larger variable component in its blue wing. ...
Frontiers in Astronomy and Space Sciences, 2017
arXiv: High Energy Astrophysical Phenomena, 2020
The flat-spectrum radio quasar 3C~454.3 throughout the years has presented very high activity pha... more The flat-spectrum radio quasar 3C~454.3 throughout the years has presented very high activity phases (flares) in which the different wavebands increase their flux dramatically. In this work, we perform multiwavelength analysis from radio to gamma-rays and study the Mg~II~$\lambda 2798$A emission line and the UV~Fe~II band from 2008-2018. We found that an increase in the 43 GHz flux density of the quasi-stationary component C, coincides with the estimated time at which a superluminal blob ejected from the radio core (which caused the brightest flare of 2010) collides with the quasi-stationary component (at a projected distance of $\sim4.6$ pc from the radio core). The spectral index different behavior in the first ($5000 < \text{JD}-2450000 < 5600$) and second ($6600 < \text{JD}-2450000 < 7900$) flaring periods suggest changes in the physical conditions. The complex nature of the second period can be a result of a superposition of multiple events at different locations. T...
Proceedings of An INTEGRAL view of the high-energy sky (the first 10 years) - 9th INTEGRAL Workshop and celebration of the 10th anniversary of the launch — PoS(INTEGRAL 2012)
Astronomical School’s Report
Proceedings of From Planets to Dark Energy: the Modern Radio Universe — PoS(MRU)
We aim to test the model proposed to explain the correlation between the flux density at 15 GHz o... more We aim to test the model proposed to explain the correlation between the flux density at 15 GHz of a stationary component in the parsec-scale jet and the optical continuum emission in the radio galaxy 3C 390.3. In the model, the double-peaked emission from 3C 390.3 is likely to be generated both near the disk and in a rotating subrelativistic outflow surrounding the jet, due to ionization of the outflow by the beamed continuum emission from the jet. This scenario is chosen since broad-emission lines are observed to vary following changes in the inner radio jet. For recent epochs we have imaged and modelled the radio emission of the inner jet of 3C 390.3, which was observed with very long baseline interferometry at 15 GHz, 22 GHz and 43 GHz, to image the inner part of the parsec-scale jet, locate the exact region where the bulk of the continuum luminosity is generated and search for the mechanism that drives the double-peaked profile emission. We present the preliminary results of testing the model using data from 11 years of active monitoring of 3C 390.3.
Uploads
Papers by Vahram Chavushyan