Study of Cataclysmic Variables with the Satellites LOFT and Gaia

The goal of this paper is to discuss the capabilities of ESA satellite missions Gaia (already in space) and LOFT (considered for the ESA M4 slot) for investigation of cataclysmic variables (CVs). Both Gaia and LOFT can contribute to study of CVs and related objects. Spectrophotometry and low dispersion spectroscopy are the most important for CV analyses with the observations of Gaia. We present the possible strategies for investigation of CVs in the sampled photometric and spectroscopic data provided by Gaia. E.g. statistical properties of the long-term activity of various types of CVs can be determined from them. LOFT can be a promising satellite to provide a sensitive X-ray monitor which will enable to investigate the little studied long-term activity of various types of CVs (especially the magnetic ones) in the X-ray band

Activity of the Polar AM Her (RX J1816.2+4952): A Short Review

We show that AM Her displays the transitions between the high and low states with an intermittently existing dominant cycle with length between 400 and 800 days. Moreover, these transitions accumulate in clusters, which produces an additional long cycle after smoothing; a single isolated short episode of the low state does not suggest a break of this cycle. The seasons of existence of the cycle can be controlled by the lifetime of the active regions (e.g. prominences, spots) on the donor. In some high-state episodes, a higher luminosity of the bremsstrahlung emission is not accompanied by a higher optical (cyclotron+stream) emission. Part of the bremsstrahlung emission can be buried in some episodes. Changes of the structure of the accretion region(s) are necessary to explain the variations of the optical and X-ray activity in the high-state episodes of AM Her

GLORIA and Study of Cataclysmic Variables

We report here on the ongoing EU FP7 Project GLORIA (GLObal Robotic-telescopes Intelligent Array) with emphasis on possibility of investigation of cataclysmic variables by users. GLORIA will enable the first free and open-access network of robotic telescopes in the world. We show several examples of the not often used topics (but suitable for GLORIA) for the studies of activity of cataclysmic variables, e.g. search for outbursts in intermediate polars and the fluctuations of brightness in their quiescence, and investigation of the optical counterparts of supersoft X-ray sources

Analysis of the late phase of three optical afterglows of GRBs using color indices

We find that although the absolute magnitude of the optical afterglow (OA) of GRB011121 in the late phase (t − T0 > 10 days) is approximately consistent with that of the SN 1998bw-type supernova SN 2001ke, previously found by Garnavich P. M. et al. (ApJ, 582 (2003) 924), a good match of their colors occurs only for t − T0 = 13–23 days in the observer frame of GRB011121. We are able to constrain the possible SN in the OA of GRB010222 to be of the peculiar SN 1998bw or SN 2002ap type, but not of SNe classified as Type Ic in the database of Poznanski D. et al. (PASP, 114 (2002) 833). Neither colors nor absolute magnitude of the OA of GRB970508 in the late phase are consistent with those of any of the above-mentioned (sub)types of SN. These results imply that the bumps in the late phase of the OAs can be caused by several mechanisms. Color indices thus appear to be a powerful tool in the analysis of these phenomena, even for archival data of OAs

Perspectives of observing the color indices of optical afterglows of gamma-ray bursts with ESA Gaia

© 2017, Springer Science+Business Media B.V. We propose a strategy for detecting and analyzing optical afterglows (OAs) of long gamma-ray bursts (GRBs) without the need to obtain their light curves. This approach is useful for the Gaia satellite, which provides sampled optical ultra-low-dispersion spectroscopic observations of the sky. For this purpose, we show that most OAs of long GRBs display specific values of some of their color indices, representing synchrotron emission of the jet. They are stable in time during the event. These indices, which can be determined from the spectra, are very similar for the ensemble of OAs with redshift z < 3.5 and display a strong clustering in some color-color diagrams. These indices also enable to constrain the properties of the local interstellar medium of GRBs. The long-lasting mapping of the sky with the Gaia instruments also gives us a hope to search for the so-called orphan afterglows, which, according to some authors, can be considerably more numerous than OAs of the observed GRBs. We also show how to resolve OAs from other transients in the Gaia data. The color indices and the properties of the quiescent sources (host galaxies of OAs detectable later by the large ground-based telescopes at the co-ordinates of the OA determined by Gaia) would tell us which one, among transients detected by Gaia, is a GRB OA

Lobster eye optics for nano-satellite x-ray monitor

The Lobster eye design for a grazing incidence X-ray optics provides wide field of view of the order of many degrees, for this reason it would be a convenient approach for the construction of space X-ray monitors. In this paper, we compare previously reported measurements of prototype lobster eye X-ray optics called P-25 with computer simulations and discuss differences between the theoretical end experimentally obtained results. Usability of this prototype lobster eye and manufacturing technology for the nano-satellite mission is assessed. The specific scientific goals are proposed

Complicated variations of early optical afterglow of GRB 090726

We report on a detection of an early rising phase of optical afterglow (OA) of a long GRB 090726. We resolve a complicated profile of the optical light curve. We also investigate the relation of the optical and X-ray emission of this event. We make use of the optical photometry of this OA obtained by the 0.5 m telescope of AI AS CR, supplemented by the data obtained by other observers, and the X-ray Swift/XRT data. The optical emission peaked at ~ 17.5 mag (R) at t-T0 ~ 500 s. We find a complex profile of the light curve during the early phase of this OA: an approximately power-law rise, a rapid transition to a plateau, a weak flare superimposed on the center of this plateau, and a slowly steepening early decline followed by a power-law decay. We discuss several possibilities to explain the short flare on the flat top of the optical light curve at t-T0 ~ 500 s; activity of the central engine is favored although reverse shock cannot be ruled out. We show that power-law outflow with Theta_obs/Theta_c > 2.5 is the best case for OA of GRB 090726. The initial Lorentz factor is Gamma_0 ~ 230-530 in case of propagation of the blast wave in a homogeneous medium, while propagation of this wave in a wind environment gives Gamma_0 ~ 80-300. The value of Gamma_0 in GRB 090726 thus falls into the lower half of the range observed in GRBs and it may even lie on the lower end. We also show that both the optical and X-ray emission decayed simultaneously and that the spectral profile from X-ray to the optical band did not vary. This OA belongs to the least luminous ones in the phase of its power-law decay corresponding to that observed for the ensemble of OAs of long GRBs.Comment: 5 pages, 5 figures, accepted to A&

Colors and luminosities of the optical afterglows of the gamma-ray bursts

Results of the study of the color indices and luminosities of 17 optical afterglows (OAs) of GRBs are presented. We show that the color variations during the decline of OAs (except for GRB000131) are relatively small during t-T_0 < 10 days and allow a comparison among them, even for the less densely sampled OAs. The colors in the observer frame, corrected for the Galactic reddening, concentrate at (V-R)_0 = 0.40 +- 0.13, (R-I)_0 = 0.46 +- 0.18, (B-V)_0 = 0.47 +- 0.17. The color evolution of the OAs is negligible although their brightness declines by several magnitudes during the considered time interval. Such a strong concentration of the color indices also suggests that the intrinsic reddening (inside their host galaxies) must be quite similar and relatively small for all these events. The absolute brightness of OAs in the observer frame, corrected for the host galaxy, lies within M_(R_0) = -26.5 to -22.2 for (t-T_0)_rest = 0.25 days. This spread of M_(R_0) is not significantly influenced by the shifts of lambda, caused by the different redshift z of the respective OAs. The general decline rate of the OA sample considered here seems to be independent of the absolute optical brightness of the OA, measured at some t-T_0 identical for all OAs, and the light curves of all events are almost parallel, when corrected for the redshift-induced time dilation.Comment: 11 pages, 2 tables, 7 figures; to be published on Astronomy & Astrophysic