Jose Antonio de Diego

TESTING TESTS ON ACTIVE GALACTIC NUCLEI MICROVARIABILITY

Literature on optical and infrared microvariability in Active Galactic Nuclei (AGNs) reflects a diversity of statistical tests and strategies to detect tiny variations in the lightcurves of these sources. Comparison between the results obtained using different methodologies is difficult, and the pros and cons of each statistical method are often badly understood or even ignored. Even worse, not properly tested methodologies are becoming more and more common, and biased results may be misleading to realize the origin of the AGN microvariability. This paper intends to point future research on AGN microvariability to the use of powerful and well tested statistical methodologies, providing a reference for choosing the best strategy to obtain unbiased results. Lightcurves monitoring have been simulated for quasars, reference and comparison stars. Changes for the quasar lightcurves include both Gaussian fluctuations and linear variations. Simulated lightcurves have been analyzed using chi-squaretests, F tests for variances, One-Way Analysis of Variances and C-statistics methodologies. Statistical Type I and Type II errors, which indicate the robustness and the power of the tests, have been obtained in each case. One-Way Analysis of Variances and chi-square show to be powerful and robust estimators for microvariations, while the C-statistics is not a reliable methodology and its use should be avoided.Literature on optical and infrared microvariability in active galactic nuclei (AGNs) reflects a diversity of statistical tests and strategies to detect tiny variations in the light curves of these sources. Comparison between the results obtained using different methodologies is difficult, and the pros and cons of each statistical method are often badly understood or even ignored. Even worse, improperly tested methodologies are becoming more and more common, and biased results may be misleading with regard to the origin of the AGN microvariability. This paper intends to point future research on AGN microvariability toward the use of powerful and well-tested statistical methodologies, providing a reference for choosing the best strategy to obtain unbiased results. Light curves monitoring has been simulated for quasars and for reference and comparison stars. Changes for the quasar light curves include both Gaussian fluctuations and linear variations. Simulated light curves have been analyzed using ?2 tests, F tests for variances, one-way analyses of variance and C-statistics. Statistical Type?I and Type?II errors, which indicate the robustness and the power of the tests, have been obtained in each case. One-way analyses of variance and ?2 prove to be powerful and robust estimators for microvariations, while the C-statistic is not a reliable methodology and its use should be avoided.

First Light with RATIR: An Automated 6-band Optical/NIR Imaging Camera

The Reionization and Transients InfraRed camera (RATIR) is a simultaneous optical/NIR multi-band imaging camera which is 100% time-dedicated to the followup of Gamma-ray Bursts. The camera is mounted on the 1.5-meter Johnson telescope of the Mexican Observatorio Astronomico Nacional on Sierra San Pedro Martir in Baja California. With rapid slew capability and autonomous interrupt capabilities, the system will image GRBs in 6 bands (i, r, Z, Y, J, and H) within minutes of receiving a satellite position, detecting optically faint afterglows in the NIR and quickly alerting the community to potential GRBs at high redshift (z>6-10). We report here on this Springs first light observing campaign with RATIR. We summarize the instrumental characteristics, capabilities, and observing modes.

NANODIAMOND DUST AND THE FAR-ULTRAVIOLET QUASAR BREAK

We explore the possibility that the steepening observed shortward of 1000 A in the energy distribution of quasars may result from absorption by dust, being either intrinsic to the quasar environment or intergalactic. We find that a dust extinction curve consisting of nanodiamonds, composed of terrestrial cubic diamonds or with surface impurities as found in carbonaceous chondrite meteorites, such as Allende, is successful in reproducing the sharp break observed. The intergalactic dust model is partially successful in explaining the shape of the composite energy distribution but must be discarded in the end, as the amount of crystalline dust required is unreasonable and would imply an improbable fine-tuning among the dust formation processes. The alternative intrinsic dust model requires a mixture of both cubic diamonds and Allende nanodiamonds and provides a better fit of the UV break. The gas column densities implied are of the order 1020 cm-2, assuming solar metallicity for carbon and full depletion of carbon into dust. The absorption only occurs in the ultraviolet and is totally negligible in the visible. The minimum dust mass required is of the order ~0.003r M☉, where rpc is the distance in parsecs between the dust screen and the continuum source. The intrinsic dust model reproduces the flux rise observed around 660 A in key quasar spectra quite well. We present indirect evidence of a shallow continuum break near 670 A (18.5 eV), which would be intrinsic to the quasar continuum.

Performance and Calibration of H2RG Detectors and SIDECAR ASICs for the RATIR Camera

The Reionization And Transients Infra-Red camera has been built for rapid Gamma-Ray Burst followup and will provide simultaneous optical and infrared photometric capabilities. The infrared portion of this camera incorporates two Teledyne HgCdTe HAWAII-2RG detectors, controlled by Teledyne’s SIDECAR ASICs. While other ground-based systems have used the SIDECAR before, this system also utilizes Teledyne’s JADE2 interface card and IDE development environment. Together, this setup comprises Teledyne’s Development Kit, which is a bundled solution that can be efficiently integrated into future ground-based systems. In this presentation, we characterize the system’s read noise, dark current, and conversion gain.

PIONEER ANOMALY? GRAVITATIONAL PULL DUE TO THE KUIPER BELT

In this work, we study the gravitational influence of the material extending from Uranus orbit to the Kuiper belt and beyond on objects moving within these regions. We conclude that a density distribution given by generates a constant acceleration towards the Sun on those objects, which, with the proper amount of mass, accounts for the blue shift detected on the Pioneers space crafts. We also discuss the effect of this gravitational pull on Neptune, and comment on the possible origin of such a matter distribution.

ON THE RELIABILITY OF MICROVARIABILITY TESTS IN QUASARS

Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to detect. Variance-based probes such as the C and F tests, or a combination of both, are popular methods to compare the light curves of the quasar and a comparison star. Recently, detection claims in some studies have depended on the agreement of the results of the C and F tests, or of two instances of the F-test, for rejecting the non-variation null hypothesis. However, the C-test is a non-reliable statistical procedure, the F-test is not robust, and the combination of tests with concurrent results is anything but a straightforward methodology. A priori power analysis calculations and post hoc analysis of Monte Carlo simulations show excellent agreement for the analysis of variance test to detect microvariations as well as the limitations of the F-test. Additionally, the combined tests yield correlated probabilities that make the assessment of statistical significance unworkable. However, it is possible to include data from several field stars to enhance the power in a single F-test, increasing the reliability of the statistical analysis. This would be the preferred methodology when several comparison stars are available. An example using two stars and the enhanced F-test is presented. These results show the importance of using adequate methodologies and avoiding inappropriate procedures that can jeopardize microvariability detections. Power analysis and Monte Carlo simulations are useful tools for research planning, as they can demonstrate the robustness and reliability of different research approaches.

TESTING MICROVARIABILITY IN QUASAR DIFFERENTIAL LIGHT CURVES USING SEVERAL FIELD STARS

Microvariability consists in small time scale variations of low amplitude in the photometric light curves of quasars, and represents an important tool to investigate their inner core. Detection of quasar microvariations is challenging for their non-periodicity, as well as the need for high monitoring frequency and high signal-to-noise ratio. Statistical tests developed for the analysis of quasar differential light curves usually show either low power or low reliability, or both. In this paper we compare two statistical procedures that include several stars to perform tests with enhanced power and high reliability. We perform light curve simulations of variable quasars and non-variable stars, and analyze them with statistical procedures developed from the F-test and the analysis of variance. The results show a large improvement in the power of both statistical probes, and a larger reliability, when several stars are included in the analysis. The results from the simulations agree with those obtained from observations of real quasars. The high power and high reliability of the tests discussed in this paper improve the results that can be obtained from short and long time scale variability studies. These techniques are not limited to quasar variability; on the contrary, they can be easily implemented to other sources such as variable stars. Their applications to future research and to the analysis of large field photometric monitoring archives can reveal new variable sources.

DDOTI: the deca-degree optical transient imager

DDOTI will be a wide-field robotic imager consisting of six 28-cm telescopes with prime focus CCDs mounted on a common equatorial mount. Each telescope will have a field of view of 12 deg2, will have 2 arcsec pixels, and will reach a 10σ limiting magnitude in 60 seconds of r ≈ 18:7 in dark time and r ≈ 18:0 in bright time. The set of six will provide an instantaneous field of view of about 72 deg2. DDOTI uses commercial components almost entirely. The first DDOTI will be installed at the Observatorio Astronómico Nacional in Sierra San Pedro Martír, Baja California, México in early 2017. The main science goals of DDOTI are the localization of the optical transients associated with GRBs detected by the GBM instrument on the Fermi satellite and with gravitational-wave transients. DDOTI will also be used for studies of AGN and YSO variability and to determine the occurrence of hot Jupiters. The principal advantage of DDOTI compared to other similar projects is cost: a single DDOTI installation costs only about US

ALMA and RATIR observations of GRB 131030A

500,000. This makes it possible to contemplate a global network of DDOTI installations. Such geographic diversity would give earlier access and a higher localization rate. We are actively exploring this option.

High redshift galaxies through gravitational lensing

We report on the first open-use based Atacama Large Millimeter/submm Array (ALMA) 345GHz observation for the late afterglow phase of GRB131030A. The ALMA observation constrained a deep limit at 17.1 d for the afterglow and host galaxy. We also identified a faint submillimeter source (ALMAJ2300-0522) near the GRB131030A position. The deep limit at 345 GHz and multifrequency observations obtained using Swift and RATIR yielded forward shock modeling with a two-dimensional relativistic hydrodynamic jet simulation and described X-ray excess in the afterglow. The excess was inconsistent with the synchrotron self-inverse Compton radiation from the forward shock. The host galaxy of GRB131030A and optical counterpart of ALMAJ2300-0522 were also identified in the SUBARU image. Based on the deep ALMA limit for the host galaxy, the 3-σ upper limits of IR luminosity and the star formation rate (SFR) is estimated as LIR < 1.11×10L t and SFR< 18.7 (M t yr), respectively. Although the separation angle from the burst location (3.5) was rather large, ALMAJ2300-0522 may be one component of the GRB131030A host galaxy, according to previous host galaxy cases.