SIOUX project: a simultaneous multiband camera for exoplanet atmospheres studies

The exoplanet revolution is well underway. The last decade has seen order-of-magnitude increases in the number of known planets beyond the Solar system. Detailed characterization of exoplanetary atmospheres provide the best means for distinguishing the makeup of their outer layers, and the only hope for understanding the interplay between initial composition chemistry, temperature-pressure atmospheric profiles, dynamics and circulation. While pioneering work on the observational side has produced the first important detections of atmospheric molecules for the class of transiting exoplanets, important limitations are still present due to the lack of sys- tematic, repeated measurements with optimized instrumentation at both visible (VIS) and near-infrared (NIR) wavelengths. It is thus of fundamental importance to explore quantitatively possible avenues for improvements. In this paper we report initial results of a feasibility study for the prototype of a versatile multi-band imaging system for very high-precision differential photometry that exploits the choice of specifically selected narrow-band filters and novel ideas for the execution of simultaneous VIS and NIR measurements. Starting from the fundamental system requirements driven by the science case at hand, we describe a set of three opto-mechanical solutions for the instrument prototype: 1) a radial distribution of the optical flux using dichroic filters for the wavelength separation and narrow-band filters or liquid crystal filters for the observations; 2) a tree distribution of the optical flux (implying 2 separate foci), with the same technique used for the beam separation and filtering; 3) an exotic solution consisting of the study of a complete optical system (i.e. a brand new telescope) that exploits the chromatic errors of a reflecting surface for directing the different wavelengths at different foci

New Variable Stars Discovered by the APACHE Survey. II. Results After the Second Observing Season

Routinely operating since July 2012, the APACHE survey has celebrated its second birthday. While the main goal of the Project is the detection of transiting planets around a large sample of bright, nearby M dwarfs in the northern hemisphere, the APACHE large photometric database for hundreds of different fields represents a relevant resource to search for and provide a first characterization of new variable stars. We celebrate here the conclusion of the second year of observations by reporting the discovery of 14 new variables.Comment: 25 pages, accepted for publication on The Journal of the American Association of Variable Star Observers (JAVVSO

The whole earth blazar telescope campaign on the intermediate BL Lac object 3C 66A in 2007-2008

Prompted by a high optical state in 2007 September, the Whole Earth Blazar Telescope consortium organized an intensive optical, near-IR (JHK) and radio observing campaign on the intermediate BL Lac object 3C 66A throughout the fall and winter of 2007-2008. In this paper, we present data from 28 observatories in 12 countries, covering the observing season from late 2007 July through 2008 February. The source remained in a high optical state throughout the observing period and exhibited several bright flares on timescales of 10 days. This included an exceptional outburst around 2007 September 15-20, reaching a peak brightness at R 13.4. Our campaign revealed microvariability with flux changes up to |dR/dt| 0.02 mag hr-1. Our observations do not reveal evidence for systematic spectral variability in the overall high state covered by our campaign, in agreement with previous results. In particular, we do not find evidence for spectral hysteresis in 3C 66A for which hints were found in an earlier campaign in a somewhat lower flux state. We also did not find any evidence for spectral lags in the discrete correlation functions between different optical bands. We infer a value of the magnetic field in the emission region of B 19 e 2/7B τ-6/7h D 13/71 G, where eB is the magnetic field equipartition fraction, τh is the shortest observed variability timescale in units of hours, and D 1 is the Doppler factor in units of 10. From the lack of systematic spectral variability, we can derive an upper limit on the Doppler factor, D ≤ 28 τ-1/8h e 3/16B. This is in perfect agreement with superluminal motion measurements with the VLBI/VLBA of βapp ≤ 27 and argues against models with very high Lorentz factors of Γ ≳ 50, required for a one-zone synchrotron-self-Compton interpretation of some high-frequency-peaked BL Lac objects detected at TeV γ-ray energies. © 2009 The American Astronomical Society

The high activity of 3C 454.3 in autumn 2007: Monitoring by the WEBT during the AGILE detection

The quasar-type blazar 3C 454.3 underwent a phase of high activity in summer and autumn 2007, which was intensively monitored in the radio-to-optical bands by the Whole Earth Blazar Telescope (WEBT). The gamma-ray satellite AGILE detected this source first in late July, and then in November-December 2007. In this letter we present the multifrequency data collected by the WEBT and collaborators during the second AGILE observing period, complemented by a few contemporaneous data from UVOT onboard the Swift satellite. The aim is to trace in detail the behaviour of the synchrotron emission from the blazar jet, and to investigate the contribution from the thermal emission component. Optical data from about twenty telescopes have been homogeneously calibrated and carefully assembled to construct an R-band light curve containing about 1340 data points in 42 days. This extremely well-sampled optical light curve allows us to follow the dramatic flux variability of the source in detail. In addition, we show radio-to-UV spectral energy distributions (SEDs) at different epochs, which represent different brightness levels. In the considered period, the source varied by 2.6 mag in a couple of weeks in the R band. Many episodes of fast (i.e. intranight) variability were observed, most notably on December 12, when a flux increase of about 1.1 mag in 1.5 hours was detected, followed by a steep decrease of about 1.2 mag in 1 hour. The contribution by the thermal component is difficult to assess, due to the uncertainties in the Galactic, and possibly also intrinsic, extinction in the UV band. However, polynomial fitting of radio-to-UV SEDs reveals an increasing spectral bending going towards fainter states, suggesting a UV excess likely due to the thermal emission from the accretion disc

The GASP-WEBT monitoring of 3C 454.3 during the 2008 optical-to-radio and γ-ray outburst

Since 2001, the radio quasar 3C 454.3 has undergone a period of high optical activity, culminating in the brightest optical state ever observed, during the 2004-2005 outburst. The Whole Earth Blazar Telescope (WEBT) consortium has carried out several multifrequency campaigns to follow the source behaviour. The GLAST-AGILE Support Program (GASP) was born from the WEBT to provide long-term continuous optical-to-radio monitoring of a sample of gamma-loud blazars, during the operation of the AGILE and GLAST (now known as Fermi GST) gamma-ray satellites. The main aim is to shed light on the mechanisms producing the high-energy radiation, through correlation analysis with the low-energy emission. Thus, since 2008 the monitoring task on 3C 454.3 passed from the WEBT to the GASP, while both AGILE and Fermi detected strong gamma-ray emission from the source. We present the main results obtained by the GASP at optical, mm, and radio frequencies in the 2008-2009 season, and compare them with the WEBT results from previous years. An optical outburst was observed to peak in mid July 2008, when Fermi detected the brightest gamma-ray levels. A contemporaneous mm outburst maintained its brightness for a longer time, until the cm emission also reached the maximum levels. The behaviour compared in the three bands suggests that the variable relative brightness of the different-frequency outbursts may be due to the changing orientation of a curved inhomogeneous jet. The optical light curve is very well sampled during the entire season, which is also well covered by the various AGILE and Fermi observing periods. The relevant cross-correlation studies will be very important in constraining high-energy emission models

Multiwavelength observations of 3C 454.3. III. Eighteen months of agile monitoring of the "crazy diamond"

We report on 18 months of multiwavelength observations of the blazar 3C 454.3 (Crazy Diamond) carried out in the period 2007 July-2009 January. In particular, we show the results of the AGILE campaigns which took place on 2008 May-June, 2008 July-August, and 2008 October-2009 January. During the 2008 May-2009 January period, the source average flux was highly variable, with a clear fading trend toward the end of the period, from an average γ-ray flux F E>100 MeV ≳ 200 × 10-8photonscm -2s-1 in 2008 May-June, to F E>100 MeV 80 × 10-8photonscm-2s-1 in 2008 October-2009 January. The average γ-ray spectrum between 100 MeV and 1 GeV can be fit by a simple power law, showing a moderate softening (from ΓGRID ∼ 2.0 to ΓGRID ∼ 2.2) toward the end of the observing campaign. Only 3σ upper limits can be derived in the 20-60 keV energy band with Super-AGILE, because the source was considerably off-axis during the whole time period. In 2007 July-August and 2008 May-June, 3C 454.3 was monitored by Rossi X-ray Timing Explorer (RXTE). The RXTE/Proportional Counter Array (PCA) light curve in the 3-20 keV energy band shows variability correlated with the γ-ray one. The RXTE/PCA average flux during the two time periods is F 3-20 keV = 8.4 × 10-11ergcm-2s -1, and F 3-20 keV = 4.5 × 10 -11ergcm-2s-1, respectively, while the spectrum (a power law with photon index ΓPCA = 1.65 0.02) does not show any significant variability. Consistent results are obtained with the analysis of the RXTE/High-Energy X-Ray Timing Experiment quasi-simultaneous data. We also carried out simultaneous Swift observations during all AGILE campaigns. Swift/XRT detected 3C 454.3 with an observed flux in the 2-10 keV energy band in the range (0.9-7.5) × 10-11ergcm-2s-1 and a photon index in the range ΓXRT = 1.33-2.04. In the 15-150 keV energy band, when detected, the source has an average flux of about 5mCrab. GASP-WEBT monitored 3C 454.3 during the whole 2007-2008 period in the radio, millimeter, near-IR, and optical bands. The observations show an extremely variable behavior at all frequencies, with flux peaks almost simultaneous with those at higher energies. A correlation analysis between the optical and the γ-ray fluxes shows that the γ-optical correlation occurs with a time lag of τ = -0.4+0.6-0.8 days, consistent with previous findings for this source. An analysis of 15 GHz and 43 GHz VLBI core radio flux observations in the period 2007 July-2009 February shows an increasing trend of the core radio flux, anti-correlated with the higher frequency data, allowing us to derive the value of the source magnetic field. Finally, the modeling of the broadband spectral energy distributions for the still unpublished data, and the behavior of the long-term light curves in different energy bands, allow us to compare the jet properties during different emission states, and to study the geometrical properties of the jet on a time-span longer than one year. © 2010. The American Astronomical Society. All rights reserved

Insights into the high-energy γ-ray emission of Markarian 501 from extensive multifrequency observations in the Fermi era

We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size ≲0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (≃1044 erg s-1) constitutes only a small fraction (∼10-3) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude. © 2011. The American Astronomical Society