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237 Nov 20, 2015

Multiwavelength evidence for quasi-periodic modulation in the gamma-ray blazar PG 1553+113

Italian scientists using about 7 years of data from NASA's Fermi Gamma-ray Large Area Telescope (LAT) have detected the first evidence of quasi-periodic changes in the gamma-ray flux emitted by the BL Lac object PG 1553+113. PG 1553+113 lies in the direction of the constellation Serpens Caput, with a redshift lying between 0.395 and 0.6. This optical/X-ray-selected blazar is intensively observed from Cherenkov telescopes at very-high energy gamma rays and may have associated PeV neutrino emission, potentially increasing the interest for this result.

If confirmed in the next years, the discovery would mark the first years-long cyclic gamma-ray and correlated multifrequency emission ever detected from any AGN, providing new insights into physical processes near the central supermassive black hole.

This research is led by S. Ciprini and S. Cutini two INFN researchers belonging the Fermi team at the ASI Science Data Center (ASDC) in strict cooperation with A. Stamerra, INAF Senior Scientist at ASDC. The work has seen also a synergetic international collaboration with scientists like S. Larsson (Royal Institute of Technology, Stockholm Sweden), R. Corbet (NASA Goddard Space Flight Center, USA), both periodical visitors and collaborators of the ASDC, D. Thompson (NASA Goddard Space Flight Center, USA and Deputy Project Scientist of the Fermi mission), W. Max-Moerbeck (National Radio Astronomy Observatory, Socorro, USA) and M. Perri (INAF Rome and 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 program in Finland, Lick Observatory, KAIT observatory in USA, and the Catalina Sky Survey near Tucson, Arizona, as well as optical and X-ray data from Swift XRT and UVOT instruments and radio, 15 GHz, data from the Owens Valley Radio Observatory, USA. Ciprini, Cutini, Stamerra and their collaborators published the findings in the Nov. 10 edition of The Astrophysical Journal Letters.

The indication of a possible 2-year periodic modulation was possible thanks to the continuous all-sky survey of Fermi; the increased capability of the new Fermi LAT Pass 8 data; and the long-term radio/optical monitoring of LAT gamma-ray blazars. If the gamma-ray cycle of PG 1553+113 is in fact real, the blazar 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. For example pulsational accretion flow instabilities, jet precession, rotation and/or helical structure, or mechanisms analogous to low-frequency QPO of high-mass binary stars. The most exciting scenario involves the presence of a second supermassive black hole closely orbiting at milliparsec scales 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.

In this rather less probable but exciting scenario very-low frequency gravitational wave emission would make PG 1553+113 an ideal multimessenger high-energy-photon/neutrino/gravitational-waves source, in this sense the blazars could represent the major "cost-free" accelerators in the nature and ideal multifrequency and multimessenger physics laboratories.

Fermi observations suggest possible years-long cyclic changes in gamma-ray emission from the blazar PG 1553+113.
The marginal significance of the 2.18+/-0.08 year period gamma-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes.
The first, top panel, shows Fermi Large Area Telescope data from August 2008 to July 2015 for gamma rays with energies above 100 million electron volts (MeV) with one possible explanation for the gamma-ray cycle, an oscillation of the jet produced by the gravitational pull of a second massive black hole, seen at top left in background in this artist's rendering [credits: NASA's Goddard Space Flight Center/CI Lab].
The panels following below the pictorial artist's rendering show all the data used in this research. From top to bottom the gamma-ray (E>100 MeV, and at E>1 GeV) flux light curves (the second, third and fourth panel), the X-ray (0.3-2.0 keV) integral flux by Swift XRT, the optical flux density (R filter) from Tuorla, Catalina CSS and KAIT monitoring programs and Swift UVOT, where the dotted line is the gamma-ray light curve scaled and superposed, and the 15 GHz flux density from the OVRO 40 m radio telescope and by VLBA (the fifth, sixth and seventh panel).

237 Oct 28, 2015

Swift catches its 1000th Gamma-ray Burst!

Swift 1000th gamma-ray burst (GRB), detected on October 27 2015, has triggered the usual flurry of mail announcements by optical and radio observers who hurried to their instruments to search for the afterglow of the high-energy event. The event is named GRB 151027B to reflect the date of the detection.

Gamma-ray bursts are the most energetic explosions in the universe.
The typically last about a minute and are located randomly across the sky. GRB 151027B had a duration of about 50 seconds. They are flashes of gamma rays produced when black holes are formed and are often referred to as the birth cries of black holes.

GRBs are classified according to the duration of the event: long ones (which account for roughly 90% of the detections) last for more than 2 seconds, short ones can be over in few milliseconds. More than half of the SWIFT GRBs have been seen at optical wavelengths and 60% of such detections yielded a redshift measurement making it possible to gauge precisely the distance of the events.

After more than 10 years of operations, 1000 GRBs and 6300 Target of Opportunity observations, Swift is expanding its grasp by providing coverage for gravitation wave alerts as well as for neutrino events.

Swift, launched in November 2004, is a NASA mission with international participation from the United States, the United Kingdom, and Italy. The Italian participation includes the provision of the Malindi ground station (ASI), the mirrors of the X-ray Telescope (INAF-OAB) and the ASI Science Data Center (ASDC) which hosts an official mirror of the Swift scientific data archive and has the responsibility of the development of the Data Reduction Software for the XRT instrument on board Swift (XRTDAS).

Positions of the first 1,000 Swift GRBs on an all-sky map of our galaxy, the Milky Way. Bursts are color coded by year, and the location of GRB 151027B is shown at lower right. An annual tally of the number of bursts Swift has detected appears below the label for each year. Background: An infrared view from the Two Micron All-Sky Survey.
[Credits: NASA's Goddard Space Flight Center and 2MASS/J. Carpenter, T. H. Jarrett, and R. Hurt]

237 Sep 17, 2015

NuSTAR 7th Data Release at ASDC

The NuSTAR 7th Data Release (DR7) is available from September 17, 2015 at ASDC. The NuSTAR DR7 constitutes the final primary mission data release and contains a total of 1750 data sets.

All the NuSTAR public data at ASDC are fully integrated in the ASDC Multi-Mission Interactive Archive (MMIA). Through the MMIA the user can perform on-line analysis of all NuSTAR public observations, without the need to download any software, including the extraction of high-level scientific products (cleaned event files, sky images, energy spectra, light-curves, ARFs and RMFs).

For more details on NuSTAR, see:

237 May 29, 2015

AGILE: 8 and counting

"AGILE: 8 and counting", this was the title of the 13th AGILE Workshop celebrating the eighth anniversary of the launch of the AGILE satellite.

Since its launch on 23 April 2007, AGILE has made several important scientific discoveries, such as the variability of the Crab Nebula in gamma-rays, and the existence of a high-energy component in terrestrial gamma-ray flashes (TGF) produced in the Earth atmosphere.

The 13th AGILE Workshop was held in the ASI Headquarters on May 25-26, 2015. The slides of all contributions are publicly available at the workshop website.

A special ASI-TV report by G. Pulcrano was dedicated to AGILE in this occasion. The video (in italian) can be viewed here.

CREDITS: ASI-TV report by Giuseppina Pulcrano, ASI-TV Chief Editor: Manuela Proietti, Video Editor: Daniele Quatrini.

237 May 12, 2015

Asymmetric explosion of SN1987A from 44Ti emission lines revealed with NuSTAR

The NASA's high-energy X-ray observatory Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the supernova 1987A (SN1987A) allowed to resolve the 67.87 and 78.32 kiloelectron volt emission lines from decay of 44Ti produced in the supernova explosion. NuSTAR data showed that these two lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, probing direct evidence of large-scale asymmetry in the explosion.

"Stars are spherical objects, but apparently the process by which they die causes their cores to be turbulent, boiling and sloshing around in the seconds before their demise," said Steve Boggs of the University of California, Berkeley, lead author of a new study on the findings, appearing in the May 8 issue of Science. "We are learning that this sloshing leads to asymmetrical explosions."

"Titanium is produced in the very heart of the explosion, so it traces the shape of the engine driving the disassembly of the star," said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology in Pasadena. "By looking at the shift of the energy of the X-rays coming from titanium, the NuSTAR data revealed that, surprisingly, most of the material is moving away from us."

Last year, NuSTAR created detailed 44Ti maps of another supernova remnant, called Cassiopeia A, also finding evidence of an asymmetrical explosion, though not to as great an extent as in 1987A. Together, these results suggest that lopsidedness is at the very root of core-collapse supernova.

NuSTAR brought a new tool to the study of supernovae. Thanks to the observatory's sharp high-energy X-ray vision, it has made the most precise measurements of 44Ti yet. This radioactive material is produced at the core of a supernova, so it provides astronomers with a direct probe into the mechanisms of a detonating star.

The Italian participation to NuSTAR includes the provision of the Malindi ground station (ASI), the ASI Science Data Center (ASDC), which contributes with the development of the NuSTARDAS software package and hosting an official mirror of the NuSTAR scientific public data archive, and a team of scientists of the Istituto Nazionale di Astrofisica (INAF) that actively collaborates on the primary scientific mission goals.

The NuSTAR team at ASDC is composed by M. Perri (INAF archive scientist), S. Puccetti (INAF archive scientist) and P. Giommi (ASDC Responsible).

For more details on NuSTAR, see:

Right: 59-80 keV NuSTAR spectrum of SN1987A with detected 44Ti emission lines. The observations indicate that supernovae belonging to a class called Type II or core-collapse blast apart in a lopsided fashion, with the core of the star hurtling in one direction, and the ejected material mostly expanding the other way (see model diagram at left).
[Credit: NASA/JPL-Caltech/UC Berkeley]

237 Apr 15, 2015

April 15-17: AMS Days at CERN

New results from AMS-02 are presented at CERN at the tree days event organized by the collaboration.
The event has been organized to understand the interrelation between AMS results and those of other major cosmic rays experiments and current theories.

Link to the original press release:

The "AMS Days" can be followed live:

The program of the event:

237 Mar 31, 2015

NuSTAR 6th Data Release at ASDC

The NuSTAR 6th Data Release is available from March 31, 2015 at ASDC. This new release contains 679 new data sets observed up to July 31, 2014.

All the NuSTAR public data at ASDC are fully integrated in the ASDC Multi-Mission Interactive Archive (MMIA). Through the MMIA the user can perform on-line analysis of all NuSTAR public observations, without the need to download any software, including the extraction of high-level scientific products (cleaned event files, sky images, energy spectra, light-curves, ARFs and RMFs).

For more details on NuSTAR, see:

237 Feb 06, 2015

Planck 2015 release of data products and scientific papers: cosmic reionisation and first stars

Map of the Cosmic Microwave Background polarisation at large angular scales. Colours represent temperature anisotropies, while textures indicate polarisation direction. [Credit: ESA/Planck Collaboration]

On February 5, 2015, the Planck Collaboration released a new set of data products and scientific papers. New results are based on all the data collected throughout the mission, between 2009 and 2013. In addition to the intensity maps at all nine frequency bands observed by Planck, polarisation maps at four frequencies (30, 44, 70, and 353 GHz) are being released.

Planck polarisation data not only provides an independent confirmation of the basic cosmological picture drawn using CMB intensity from both 2013 and 2015 maps. In fact, studying the properties of CMB polarisation at large angular scales, Planck scientists concluded that the reionisation of the Universe due to first stars happened 550 million years after the Big Bang, more than 100 million years later than previously thought. So, the Dark Ages of the Universe ended later. This is of fundamental importance because that 100 million years difference is significantly reducing the tension between CMB results and current knowledge of first stars and early galaxies.

Polarisation doesn't mean only reionisation. Indeed, by analysing polarised maps at different frequencies, Planck scientists obtained new insights on the properties of the Galactic magnetic field. Planck's new findings include also neutrino physics and dark matter annihilation.

The whole list of Planck scientific results is much longer, as described in the papers that are available on ESA website. Planck public data products can be accessed through the Planck Legacy Archive. Additional results and products will be released in the forthcoming weeks.

For more information, see:
The ASDC team working on Planck-LFI consortium includes G. Polenta (archive scientist) and P. Natoli (senior scientist). Planck ERCSC and PCCS source catalogues are available on the ASDC website.

237 Feb 03, 2015

Results from Planck and BICEP2/Keck Array joint study: no conclusive evidence for primordial gravitational waves

On March 2014, the BICEP2 team announced for the first time a significant detection of a B-mode polarisation signal, and this was interpreted as the tiny imprints in the CMB field of the primordial gravitational waves produced during the inflationary epoch 10-34 s after the Big Bang.

However, some concerns about the cosmological origin of the detected signal were raised by the scientific community, as the instrument was observing at only one frequency band thus preventing to separate contributions from the Early and the local Universe. Doubts strengthened even more in September 2014, when the Planck Collaboration published the results from a study of the polarised emission of the interstellar dust at high galactic latitudes, including also the region of the sky observed by the BICEP2 telescope. Scientists therefore decided to join forces to take advantage of both the outstanding sensitivity of BICEP2/Keck Array and the wide frequency coverage of the Planck satellite.

On January 30, 2015, the results from the joint analysis of data from Planck, BICEP2, and Keck Array experiments were published, showing no evidence for a significant detection of primordial gravitational waves. In fact, when accounting for the contribution of polarised emission produced by the interstellar dust in the Milky Way, there is no statistical evidence for the presence of primordial gravitational waves signatures in the BICEP2 and Keck Array data.

However, inflation is not ruled out by the new results as gravitational waves might still be hiding deeper into the data: the quest for CMB B-mode polarisation is not over.

For more information, see:
The ASDC team working on Planck-LFI consortium includes G. Polenta (archive scientist) and P. Natoli (senior scientist). Planck ERCSC and PCCS source catalogues are available on the ASDC website.

Planck view of the submillimiter sky in the BICEP2 region. The colour scale represents the interstellar dust emission, while textures indicates the orientation of the Galactic magnetic field as derived from interstellar dust polarisation. The highlighted area shows the region observed by BICEP2 and the Keck Array.
[Image - Credit: ESA/Planck Collaboration]