Time filter

Source Type

News Article | November 14, 2015
Site: phys.org

"Looking at many years of data from Fermi's Large Area Telescope (LAT), we picked up indications of a roughly two-year-long variation of gamma rays from a galaxy known as PG 1553+113," said Stefano Ciprini, who coordinates the Fermi team at the Italian Space Agency's Science Data Center (ASDC) in Rome. "This signal is subtle and has been seen over less than four cycles, so while this is tantalizing we need more observations." Supermassive black holes weighing millions of times the sun's mass lie at the hearts of most large galaxies, including our own Milky Way. In about 1 percent of these galaxies, the monster black hole radiates billions of times as much energy as the sun, emission that can vary unpredictably on timescales ranging from minutes to years. Astronomers refer to these as active galaxies. More than half of the gamma-ray sources seen by Fermi's LAT are active galaxies called blazars, like PG 1553+113. As matter falls toward its supermassive black hole, some subatomic particles escape at nearly the speed of light along a pair of jets pointed in opposite directions. What makes a blazar so bright is that one of these particle jets happens to be aimed almost directly toward us. "In essence, we are looking down the throat of the jet, so how it varies in brightness becomes our primary tool for understanding the structure of the jet and the environment near the black hole," said Sara Cutini, an astrophysicist at ASDC. Motivated by the possibility of regular gamma-ray changes, the researchers examined a decade of multiwavelength data. These included long-term optical observations from Tuorla Observatory in Finland, Lick Observatory in California, and the Catalina Sky Survey near Tucson, Arizona, as well as optical and X-ray data from NASA's Swift spacecraft. The team also studied observations from the Owens Valley Radio Observatory near Bishop, California, which has observed PG 1553+113 every few weeks since 2008 as part of an ongoing blazar monitoring program in support of the Fermi mission. "The cyclic variations in visible light and radio waves are similar to what we see in high-energy gamma-rays from Fermi," said Stefan Larsson, a researcher at the Royal Institute of Technology in Stockholm and a long-time collaborator with the ASDC team. "The fact that the pattern is so consistent across such a wide range of wavelengths is an indication that the periodicity is real and not just a fluctuation seen in the gamma-ray data." Ciprini, Cutini, Larsson and their colleagues published the findings in the Nov. 10 edition of The Astrophysical Journal Letters. If the gamma-ray cycle of PG 1553+113 is in fact real, they predict it will peak again in 2017 and 2019, well within Fermi's expected operational lifetime. The scientists identified several scenarios that could drive periodic emission, including different mechanisms that could produce a years-long wobble in the jet of high-energy particles emanating from the black hole. The most exciting scenario involves the presence of a second supermassive black hole closely orbiting the one producing the jet we observe. The gravitational pull of the neighboring black hole would periodically tilt the inner part of its companion's accretion disk, where gas falling toward the black hole accumulates and heats up. The result would be a slow oscillation of the jet much like that of a lawn sprinkler, which could produce the cyclic gamma-ray changes we observe. PG 1553+113 lies in the direction of the constellation Serpens, and its light takes about 5 billion years to reach Earth. More information: "Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-Ray Blazar PG 1553+113," M. Ackermann et al., 2015 November 10, Astrophysical Journal Letters iopscience.iop.org/article/10.1088/2041-8205/813/2/L41 , Arxiv: arxiv.org/abs/1509.02063


Koblik V.,Tuorla Observatory | Koblik V.,Umeå University | Polyakhova E.,Saint Petersburg State University | Sokolov L.,Saint Petersburg State University
Advances in Space Research | Year: 2011

Some modifications of solar sail radiation pressure forces on a plate and on a sphere for use in the numerical simulation of 'local-optimal' (or 'instantaneously optimal') trajectories of a spacecraft with a solar sail are suggested. The force model development is chronologically reviewed, including its connection with solar sail surface reflective and thermal properties. The sail surface is considered as partly absorbing, partly reflective (specular and diffuse), partly transparent. Thermal balance is specified because the spacecraft moves from circular Earth orbit to near-Sun regions and thermal limitations on the sail film are taken into account. A spherical sail-balloon can be used in near-Sun regions for scientific research beginning with the solar-synchronous orbit and moving outward from the Sun. The Sun is considered not only as a point-like source of radiation but also as an extended source of radiation which is assumed to be consequently as a point-like source of radiation, a uniformly bright flat solar disc and uniformly bright solar sphere. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.


Bonamente M.,University of Alabama in Huntsville | Bonamente M.,NASA | Nevalainen J.,Tartu Observatory | Tilton E.,University of Colorado at Boulder | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We have analysed Chandra low energy transmission grating and XMM-Newton Reflection Grating Spectrometer (RGS) spectra towards the z = 0.177 quasar PG 1116+215, a sightline that is rendered particularly interesting by the Hubble Space Telescope (HST) detection of several OVI and HI broad Lyman a absorption (BLA) lines that may be associated with the warm-hot intergalactic medium (WHIM). We performed a search for resonance Kα absorption lines from OVII and OVIII at the redshifts of the detected far-ultraviolet lines.We detected an absorption line in the Chandra spectra at the 5.2σ confidence level at wavelengths corresponding to OVIII Kα at z = 0.0911 ± 0.0004 ± 0.0005 (statistical followed by systematic error). This redshift is within 3σ of that of an HI broad Lyman a of b ≃ 130 km s-1 (corresponding to a temperature of log T(K) ≃ 6.1) at z = 0.092 79 ± 0.000 05. We have also analysed the available XMM-Newton RGS data towards PG 1116+215. Unfortunately, the XMM-Newton data are not suitable to investigate this line because of instrumental features at the wavelengths of interest. At the same redshift, the Chandra and XMM-Newton spectra have OVII Kα absorption-line features of significance 1.5σ and 1.8σ, respectively.We also analysed the available Sloan Digital Sky Survey (SDSS) spectroscopic galaxy survey data towards PG 1116+215 in the redshift range of interest. We found evidence for a galaxy filament that intersect the PG 1116+215 sightline and additional galaxy structures that may host WHIM. The HI BLA and the OVIII Kα absorbers are within a few Mpc of the filament (assuming that redshifts track Hubble flow distances) or consistent with gas accreting on to the filament from either direction relative to the sightline with velocities of a few × 100 km s-1. The combination of HST, Chandra, XMM-Newton and SDSS data indicates that we have likely detected a multi-temperature WHIM at z ≃ 0.091-0.093 towards PG 1116+215. The OVIII Ka absorption line indicates gas at high temperature, log T(K) = 6.4, with a total column density of the order of log NH(cm2) = 20 and a baryon overdensity ξb ~ 100-1000 for sightline lengths of L = 1-10 Mpc. This detection highlights the importance of BLA absorption lines as possible signposts of high-temperature WHIM filaments. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Colin P.,Max Planck Institute for Physics | Eisenacher D.,University of Würzburg | Hildebrand D.,ETH Zurich | Lombardi S.,National institute for astrophysics | And 17 more authors.
AIP Conference Proceedings | Year: 2012

The Perseus cluster of galaxies is a nearby cool-core cluster with an intra-clustermedium (ICM) characterized by very high central densities. The observation of the Perseus cluster with the MAGIC telescopes, during 85 h from 2009 to 2011, resulted in the discovery of 2 point-like sources at very high energy (>100 GeV, VHE) coinciding with the central radio galaxy NGC1275 and the radio galaxy IC310. The γ-ray properties of these 2 sources are presented, taking into account contemporaneous Fermi-LAT as well as multi-wavelength data. Flux variability and spectral energy distribution shapes indicate that the VHE γ-rays do not originate from large-scale interaction of the radio galaxies with ICM but more likely from the active nuclei of these two galaxies. They could be both misaligned version of BL Lac objects, the most common TeV AGN. Our results provide vital clues to understand emission mechanisms of such misaligned objects, and how they may be related to the beamed emission seen in BL Lacs. No evidence of large-scale VHE γ-ray emission from hadronic cosmic ray (CR) interactions with the ICM has been found. The flux upper limit above 1 TeV reaches the signal expected by some theoretical models, constraining the cluster CR physics. In the framework of the hadronicmodel of the radiomini-halos, this limit implies aminimal magnetic field ranging from 4-9μG for the central cluster region. © 2012 American Institute of Physics.


Colin P.,Max Planck Institute for Physics | Gonzalez J.B.,Institute of Astrophysics of Canarias | Lindfors E.,Tuorla Observatory | Lombardi S.,University of Padua | Sitarek J.,University of Lodz
Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011 | Year: 2011

The two BL Lac objects 1ES 1215+303 and 1ES 1218+304, separated by 0.8°, were observed with the MAGIC telescopes in 2010 and 2011. The 20 hours of data registered in January 2011 resulted in the first detection at Very High Energy (>100 GeV) of 1ES 1215+303 (also known as ON-325). This observation was triggered by a high optical state of the source reported by the Tuorla blazar monitoring program. Comparison with the 25 hours of data carried out from January to May 2010 suggests that 1ES 1215+303 was flaring also in VHE gamma-rays in 2011. In addition, the Swift ToO observations in X-rays showed that the flux was almost doubled respect to previous observations (December 2009). Instead, 1ES 1218+304 is a well known VHE gamma-ray emitter lying in the same field of view, which was then simultaneously observed with the MAGIC telescopes. The overall observation time of nearly 45 hours has permitted to measure the spectrum of this source with a much higher precision than previously reported by MAGIC. Here, we present the results of the MAGIC and the multi-wavelength observations of these two VHE gamma-ray emitting AGNs.


Nevalainen J.,Tartu Observatory | Tempel E.,Tartu Observatory | Liivamagi L.J.,Tartu Observatory | Branchini E.,Third University of Rome | And 10 more authors.
Astronomy and Astrophysics | Year: 2015

We propose a new approach to the problem of the missing baryons. Building on the common assumption that the missing baryons are in the form of the warm hot intergalactic medium (WHIM), we also assume here that the galaxy luminosity density can be used as a tracer of the WHIM. This last assumption is supported by our discovery of a significant correlation between the WHIM density and the galaxy luminosity density in recent hydrodynamical simulations. We also found that the percentage of the gas mass in the WHIM phase is substantially higher (by a factor of ~1.6) within large-scale galactic filaments, i.e. ~70%, compared to the average in the full simulation volume of ~0.1 Gpc3. The relation between the WHIM overdensity and the galaxy luminosity overdensity within the galactic filaments is consistent with a linear one: δwhim = 0.7 ± 0.1 × δLD 0.9±0.2. We then applied our procedure to the line of sight towards the blazar H2356-309 and found evidence of WHIM that corresponds to the Sculptor Wall (SW) (z ~ 0.03 and log NH = 19.9+ 0.1 -0.3) and Pisces-Cetus (PC) superclusters (z ~ 0.06 and log NH = 19.7+ 0.2 -0.3), in agreement with the redshifts and column densities of the X-ray absorbers identified recently. This agreement indicates that the galaxy luminosity density and galactic filaments are reliable signposts for the WHIM and that our method is robust for estimating WHIM density. The signal that we detected cannot originate in the halos of nearby galaxies because they cannot account for the high WHIM column densities that our method and X-ray analysis consistently find in the SW and PC superclusters. © 2015 ESO.


Vaisanen P.,SAAO | Reunanen J.,Tuorla Observatory | Kotilainen J.,FINCA | Mattila S.,Tuorla Observatory
Proceedings of the International Astronomical Union | Year: 2012

We present SINFONI observations of IRAS 19115-2124, dubbed the Bird, an intriguing triple galaxy encounter. NIR line strengths and line ratios are used to study the sequence of events in this complex system. The most massive and obscured component shows LINER-like activity, while the least massive irregular component is the source of 3/4 of the current total SF. This most recent compact starburst lies 3 kpc away from the dynamically dominant components. Cool and warm gas inflows and outflows are detected at the locations of the progenitor nuclei. © 2013 International Astronomical Union.


News Article | October 26, 2016
Site: www.newscientist.com

Ladies and gentlemen, your challenger. Meet a black hole new to the neighbourhood, weighing 140 million suns. That’s nothing to sneeze at: this plucky upstart is 35 times more massive than the black hole that holds court at the centre of our Milky Way. And now, make way for the current champion: a black hole with a mass of 18 billion suns. For front-row seats to this cosmic boxing match, you’ll want to (cautiously) approach OJ 287, the core region of a galaxy 3.5 billion light years away. Here, the smaller black hole orbits its larger rival. With every trip around, it falls closer, on track to be swallowed up in about 10,000 years. But in the meantime, it’s putting up an admirable fight. Even though the system is so far away, OJ 287 releases enough energy to appear about as bright in the sky as Pluto. We’ve been capturing it on photographic plates since the 1880s, but it first caught the eye of Mauri Valtonen at Finland’s Tuorla Observatory in Turku almost a century later. His team noticed that unlike other galactic centres, which brighten and dim sporadically, this one seemed to keep to a tight schedule. Every 12 years, it has an outburst. Well, not exactly every 12 years. Not only do the outbursts look different each time, but the gap between them seems to grow shorter by about 20 days each cycle. In the decades since we noticed the pattern, we’ve gone a long way towards figuring out why. OJ 287’s situation is a window into what must have happened in galaxies all over the universe. Galaxies grow by eating their own kind, and almost all of them come with a supermassive black hole at the centre. Once two galaxies merge, their black holes – now forced to live in one new mega-galaxy – will either banish their rival with a gravitational kick that flings their opponent out of the galaxy, or eventually merge into an even bigger black hole. In OJ 287, the smaller black hole is en route to becoming a snack for the larger one. The larger one is also growing from a surrounding disc of gas and dust, the material from which slowly swirls down the drain. Each time the smaller black hole completes an orbit, it comes crashing through this disc at supersonic speeds. That violent impact blows bubbles of hot gas that expand, thin out, and then unleash a flood of ultraviolet radiation – releasing as much energy as 20,000 supernova explosions in the same spot. You could stand 36 light years away and tan faster than you would from the sun on Earth. Even with all this thrashing, the smaller black hole has no chance of escape.  Energy leaches away from the binary orbit, bringing the pair closer together and making each cycle around the behemoth a little shorter than the last. Although the outbursts may be impressive, the black holes’ orbital dance emits tens of thousands of times more energy as undulations in space time called gravitational waves. Last year, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US offered a preview of the endgame of OJ 287 in miniature. Twice in 2015, LIGO heard gravitational waves from the final orbits of black-hole pairs in which each black hole was a few dozen times the size of the sun, and then the reverberations of the single one left behind. Because its black holes are so massive, the ultimate collision at the heart of OJ 287 will be too low-frequency for LIGO to hear. But the outcome will be much the same. Where once two black holes from two separate galaxies tussled, one black hole will remain, smug and secure at the centre.


Shi J.C.,Chinese Academy of Sciences | Ma Y.H.,Chinese Academy of Sciences | Zheng J.Q.,Tuorla Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2014

We presentphotometric investigations of three distant active comets, 228P/LINEAR, C/2006 S3 Lowell Observatory Near-Earth-Object Search (LONEOS) and 29P/Schwassmann-Wachmann 1. The data were obtained with the 1-m optical telescope at Lulin Observatory in Taiwan on 2011 February 5 and 6. These comets were observed at heliocentric distances larger than 3 au, all of them appeared to be active. By cometary morphological and photometric studies, the upper limits of the nuclei radii were derived. Also, the surface brightness profiles, Afρ parameters, mass production rates and the coma colours were measured. Finally, we discussed possible driver of activity in comets. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Yuan-Yuan C.,Chinese Academy of Sciences | Yuehua M.,Chinese Academy of Sciences | Jiaqing Z.,Tuorla Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2016

We explore planetary migration scenarios for the formation of high-inclination Neptunian Trojans (NTs) and how they are affected by the planetary migration of Neptune and Uranus. If Neptune's and Uranus's eccentricity and inclination were damped during planetary migration, then their eccentricities and inclinations were higher prior and during the migration than their current values. Using test particle integrations, we study the stability of primordial NTs, objects that were initially Trojans with Neptune prior to migration. We also study trans-Neptunian objects captured into resonance with Neptune and becoming NTs during planet migration. We find that most primordial NTs were unstable and lost if eccentricity and inclination damping took place during planetary migration. With damping, secular resonances with Neptune can increase a low eccentricity and inclination population of trans-Neptunian objects increasing the probability that they are captured into 1: 1 resonance with Neptune, becoming high-inclination NTs. We suggest that the resonant trapping scenario is a promising and more effective mechanism to explain the origin of NTs, which is particularly effective if Uranus and Neptune experienced eccentricity and inclination damping during planetary migration. © 2016 The Authors.

Loading Tuorla Observatory collaborators
Loading Tuorla Observatory collaborators