Tag Archives: #blazar

OU Astronomers Discover a ‘Changing-Look’ Blazar (Planetary Science)

A University of Oklahoma doctoral student, graduate and undergraduate research assistants, and an associate professor in the Homer L. Dodge Department of Physics and Astronomy in the University of Oklahoma College of Arts and Sciences are lead authors on a paper describing a “changing-look” blazar – a powerful active galactic nucleus powered by supermassive blackhole at the center of a galaxy. The paper is published in The Astrophysical Journal.

Hora D. Mishra, a Ph.D. student, and faculty member Xinyu Dai are lead authors of the paper, along with Christopher Kochanek and Kris Stanek at the Ohio State University and Ben Shappee at the University of Hawaii. The paper represents the findings of researchers from 12 different institutions who participated in a two-year collaborative project involving the collection of spectra or imaging data in different electromagnetic bands. The OU team led the effort in analyzing all the data collected from the collaboration and contributed primarily on the interpretation of the analysis results, assisted by OU graduate student Saloni Bhatiani and undergraduate students Cora DeFrancesco and John Cox who performed ancillary analyses to the project.

Blazars, explains Mishra, who also serves as president of Lunar Sooners, appear as parallel rays of light or particles, or jets, pointing to observers and radiating across all wavelengths of the electromagnetic spectrum. These jets span distances on the million light-year scales and are known to impact the evolution of the galaxy and galaxy cluster in which they reside via the radiation. These features make blazars ideal environments in which to study the physics of jets and their role in galaxy evolution. 

“Blazars are a unique kind of AGN with very powerful jets,” she said. “Jets are a radio mode of feedback and because of their scales, they penetrate the galaxy into their large-scale environment. The origin of these jets and processes driving the radiation are not well-known. Thus, studying blazars allows us to understand these jets better and how they are connected to other components of the AGN, like the accretion disk. These jets can heat up and displace gas in their environment affecting, for example, the star formation in the galaxy.”

The team’s paper highlights the results of a campaign to investigate the evolution of a blazar known as B2 1420+32. At the end of 2017, this blazar exhibited a huge optical flare, a phenomenon captured by the All Sky Automated Survey for SuperNovae telescope network.

“We followed this up by observing the evolution of its spectrum and light curve over the next two years and also retrieved archival data available for this object,” Mishra said. “The campaign, with data spanning over a decade, has yielded some most exciting results. We see dramatic variability in the spectrum and multiple transformations between the two blazar sub-classes for the first time for a blazar, thus giving it the name ‘changing-look’ blazar.”

The team concluded that this behavior is caused by the dramatic continuum flux changes, which confirm a long-proposed theory that separates blazars into two major categories.

“In addition, we see several very large multiband flares in the optical and gamma-ray bands on different timescales and new spectral features,” Mishra said. “Such extreme variability and the spectral features demand dedicated searches for more such blazars, which will allow us to utilize the dramatic spectral changes observed to reveal AGN/jet physics, including how dust particles around supermassive black holes are destructed by the tremendous radiation from the central engine and how energy from a relativistic jet is transferred into the dust clouds, providing a new channel linking the evolution of the supermassive black hole with its host galaxy.”

“We are very excited by the results of discovering a changing-look blazar that transforms itself not once, but three times, between its two sub-classes, from the dramatic changes in its continuum emission,” she added. “In addition, we see new spectral features and optical variability that is unprecedented. These results open the door to more such studies of highly variable blazars and their importance in understanding AGN physics.”

“It is really interesting to see the emergence of a forest of Iron emission lines, suggesting that nearby dust particles were evaporated by the strong radiation from the jet and released free Iron ions into the emitting clouds, a phenomenon predicted by theoretical models and confirmed in this blazar outburst,” Dai said.

Featured image: Sloan Digital Sky Survey archival image from March 2004 (left) and the image from the authors’ observation campaign of the blazar, B2 1420+32, taken in January 2020 using ASAS-SN (right). The blazar brightness increased by a factor of 100. © University of Oklahoma


Provided by University of Oklahoma

Introducing A Changing-look Blazar: B2 1420+32 (Planetary Science)

Hoda Mishra and colleagues presented multi-wavelength photometric and spectroscopic monitoring observations of the blazar, B2 1420+32, focusing on its outbursts in 2018-2020. They found that the object exhibits a large scale spectral variability and is the so-called “changing-look” blazar. Their study recently appeared on journal ArXiv.

Blazars are active galactic nuclei with their relativistic jets pointing toward the observer, with two major sub-classes, the flat spectrum radio quasars and BL Lac objects. 

AGNs are subdivided into several broad categories, including Type I (also called quasars, Seyfert I) that show a blue continuum from an accretion disk and broad emission lines created by photoionization and Type II (or Seyfert II), which show only narrow lines and no continuum variability. Some AGNs move from one class to another and therefore are dubbed “changing-look” sources. Studying changing look phenomena in blazars can provide useful insight into understanding the origin and particle acceleration processes of radio jets.

Now, Hora Mishra and colleagues reported the detection of a new changing-look blazar. Using mainly the Las Cumbres Observatory Global Telescope Network (LCOGT), they found that the blazar B2 1420+32, at a redshift of 0.682 and with a black hole mass of about 400 million solar masses, appears to shift back and forth between the optical spectrum of an FSRQ and that of a BL Lac several times, while also developing new spectral features.

They found that B2 1420+32 showcases large-scale spectral variability in both its continuum and line emission, together with dramatic gamma-ray and optical variability, on week to month timescales.

They also found that, between 2016–2019, the gamma-ray and optical fluxes increased by factors of 1500 (8 mags) and 40 (4 mags), respectively. The astronomers noted that observed optical variability amplitude is unprecedented, as the optical flux increases by a factor of 100 (5 mags) compared to the SDSS observations conducted in 1995.

For the first time, we detect components in the optical spectra consistent with single temperature blackbody emission, with 20% of the Eddington luminosity.

Wrote authors of the study.

This extreme variability we describe here has not been observed before. However, it may not be uncommon, because dedicated multi-band and spectroscopic monitoring of blazars are still rare. Dedicated searches for more changing-look blazars will extend the changing-look AGN studies to jetted AGNs and allow us to utilize the dramatic spectral changes to reveal AGN/jet physics.

— told Hora, lead author of the study.

Finally, researchers concluded that B2 1420+32 is a changing-look blazar transiting between FSRQ and BL Lac due to dramatic changes in the jet continuum flux diluting the line features. They emphasized that extreme variability, as in the case of B2 1420+32, has not been observed before in any blazar.

Featured image: Multi-band optical LCOGT, ASAS-SN, and Fermi light curves of B2 1420+32 © Mishra et al.


Reference: Hora D. Mishra, Xinyu Dai, Ping Chen, Jigui Cheng, T. Jayasinghe, Michael A. Tucker, Patrick J. Vallely, David Bersier, Subhash Bose, Aaron Do, Subo Dong, Thomas W. S. Holoien, Mark E. Huber, Christopher S. Kochanek, Enwei Liang, Anna V. Payne, Jose Prieto, Benjamin J. Shappee, K.Z. Stanek, Saloni Bhatiani, John Cox, Cora DeFrancesco, Zhiqiang Shen, Todd A. Thompson, Junfeng Wang, “The Changing Look Blazar B2 1420+32”, pp. 1-21, ArXiv, 2021. https://arxiv.org/abs/2103.08707


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Indian Astronomers Detect Huge Optical Flare In One Of The Oldest Astronomic Objects (Astronomy)

Indian Astronomers have reported one of the strongest flares from a feeding supermassive black hole or blazar called BL Lacertae. Analysis of the flare from this blazar, one of the oldest astronomical objects, can help trace the mass of the black hole and the source of this emission. Such analysis can provide a lead to probe into mysteries and trace events at different stages of evolution of the Universe.

Blazars or feeding supermassive black holes in the heart of distant galaxies receive a lot of attention from the astronomical community because of their complicated emission mechanism. They emitjets ofcharged particles traveling nearly at the speed of light and are one of the most luminous and energetic objects in the Universe.

BL Lacertae blazar is 10 million light-years away and is among the 50 most prominent blazars that can be observed with the help of a relatively small telescope. It was among the 3 to 4 blazars that was predicted to be experiencing flares by the Whole Earth Blazar Telescope (WEBT), an international consortium of astronomers.  

A team of astronomers led by Dr. Alok Chandra Gupta from Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous institute of the Department of Science & Technology, Government of India who had been following the blazar since October 2020 as part of an international observational campaign detected the exceptionally high flare on January 16, 2021, with the help of Sampurnanand Telescope (ST) and 1.3m Devasthal Fast Optical Telescopes located in Nainital.

The data collected from the flare observed will help calculation of the black hole mass, size of emission region, and mechanism of the emission from one of the oldest astronomical objects known, hence opening a door to the origin and evolution of the Universe.

The luminosity of BL Lac observed on 27 October 2020 (left panel of figure) was around 2.95 * 1012 Lʘ and after 80 days, i.e., 16 January 2021 (right panel of figure) was ~ 7.25 * 1012 Lʘ,i.e., ~ 250% increase in the luminosity which is equivalent to more than 4 trillion Lʘ  (here  Lʘ  = luminosity of the Sun). © Ministry of Science and Technology, India.

The link to Astronomical Telegram #14343 with the announcement of blazar BL Lacertae’s luminosity record: http://www.astronomerstelegram.org/?read=14343.

For more details, Dr. Alok Chandra Gupta (Scientist-F) (+91-7895966668, alok@aries.res.in ) can be contacted.


Provided by Press Information Bureau

IMAGE RELEASE: A Blazar In the Early Universe (Astronomy)

The supersharp radio “vision” of the National Science Foundation’s Very Long Baseline Array (VLBA) has revealed previously unseen details in a jet of material ejected at three-quarters the speed of light from the core of a galaxy some 12.8 billion light-years from Earth. The galaxy, dubbed PSO J0309+27, is a blazar, with its jet pointed toward Earth, and is the brightest radio-emitting blazar yet seen at such a distance. It also is the second-brightest X-ray emitting blazar at such a distance.

The VLBA image of the blazar PSO J0309+27 is composed of data from three observations made at different radio frequencies. Red is from an observation at 1.5 GHz; green from 5 GHz; and blue from 8.4 GHz. The lower-frequency, or longer wavelength, data show the large-scale structure of the object; the intermediate- and higher-frequency data reveal increasingly smaller structures invisible to the VLBA at the lower frequency. Credit: Spingola et al.; Bill Saxton, NRAO/AUI/NSF.

In this image, the brightest radio emission comes from the galaxy’s core, at bottom right. The jet is propelled by the gravitational energy of a supermassive black hole at the core, and moves outward, toward the upper left. The jet seen here extends some 1,600 light-years, and shows structure within it.

The blazar PSO J0309+27 is in the constellation Aries. Credit: Bill Saxton, NRAO/AUI/NSF

At this distance, PSO J0309+27 is seen as it was when the universe was less than a billion years old, or just over 7 percent of its current age.

An international team of astronomers led by Cristiana Spingola of the University of Bologna in Italy, observed the galaxy in April and May of 2020. Their analysis of the object’s properties provides support for some theoretical models for why blazars are rare in the early universe. The researchers reported their results in the journal Astronomy & Astrophysics.

VLBA image of the blazar PSO J0309+27, 12.8 billion light-years from Earth. Credit: Spingola et al.; Bill Saxton, NRAO/AUI/NSF.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Reference: https://www.aanda.org/articles/aa/pdf/2020/11/aa39458-20.pdf

Provided by NRAO

Astronomers Have Performed High-resolution Observations Of The Blazar PKS 1749+096 (Astronomy)

Using the Very Long Baseline Array (VLBA), astronomers have performed high-resolution observations of the blazar PKS 1749+096. Results of this observational campaign, provides essential information about the properties of the blazar’s inner jet.

©gettyimages

Blazars are very compact quasars associated with supermassive black holes at the centers of active, giant elliptical galaxies. Based on their optical emission properties, astronomers divide blazars into two classes: flat-spectrum radio quasars (FSRQs) that feature prominent and broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not.

In general, blazars belong to a larger group of active galaxies that host active galactic nuclei (AGN), and their characteristic features are relativistic jets pointed almost exactly toward the Earth. However, the detailed mechanisms of ejection and collimation of jets are still poorly understood, and more studies of this phenomenon are required to improve our knowledge on the subject.

At a redshift of 0.322, PKS 1749+096 is an ultra-luminous BL Lac object exhibiting strong variability from radio to X-rays. Previous observations have also identified unprecedented bright flaring activity in very high energy gamma-ray emission, together with X-ray and optical flares. Moreover, Very Long Baseline Interferometry (VLBI) studies of PKS 1749+096 have detected the existence of position angle swing exists in its jet.

BSMEM images of PKS 1749+096 in August 2011 and July 2014. For each image, contours start at 0.5 percent of the peak brightness in steps of two. Credit: Cui et al., 2020.

In order to shed more light on the innermost region of the PKS 1749+096’s jet and its possible variations, a team of astronomers led by Lang Cui of the Xinjiang Astronomical Observatory in Urumqi, China, has conducted a detailed VLBA imaging study of this blazar with unprecedented resolution.

“In order to investigate the jet kinematics, in particular, the orientation of the inner jet on the smallest accessible scales and the basic physical conditions of the core, in this work, we adopted a super-resolution technique, the bi-spectrum maximum entropy method (BSMEM), to reanalyze VLBI images based on the Very Long Baseline Array (VLBA) observations of PKS 1749+096 within the VLBA-BU-BLAZAR 7mm monitoring program,” the researchers explained.

The observational campaign lasted from 2009 to 2019. The astronomers found that the VLBA stacked image of the blazar’s inner jet has a limb-brightened structure with apparent opening angles of 50 and 42 degrees at the distance of about 2.93 and 4.56 light years from the core. This corresponds to an intrinsic jet opening angle of 5.2 and 4.3 degrees, respectively.

Furthermore, the images of the jet position angle in PKS 1749+096 show a clear swing phenomenon within the last 10 years, when it was observed by VLBA. It was noted that the swing weakly correlates with the peak brightness.

However, the study found no correlation between the inner jet position angle and gamma-ray flux. According to the authors of the paper, this indicates that the gamma-ray emission in PKS 1749+096 is not sensitive to orientation-dependent effects. Summing up the results, the scientists emphasize the importance of future observations with more gamma-ray flux measurements, which would allow further investigation of their possible connection to the inner jet orientation.

References: Lang Cui, Ru-Sen Lu, Wei Yu, Jun Liu, Víctor Patiño-Álvarez, Qi Yuan, “Resolving the inner jet of PKS 1749+096 with super-resolution VLBA images at 7 mm”, ArXiv, pp. 1-7, 2020. Doi: arxiv.org/abs/2010.12393 https://arxiv.org/abs/2010.12393

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The Grantecan Finds The Farthest Black Hole That Belongs To A Rare Family Of Galaxies (Astronomy)

An international team of astronomers has identified one of the rarest known classes of gamma-ray emitting galaxies, called BL Lacertae, within the first 2 billion years of the age of the Universe.

Only a small fraction of the galaxies emits gamma rays, which is the most extreme form of light. Astronomers believe that these highly energetic photons originate from the vicinity of a supermassive black hole residing at the centers of these galaxies. When this happens, they are known as active galaxies. The black hole swallows matter from its surroundings and emits jets or, in other words, collimated streams of matter and radiation. Few of these active galaxies (less than 1%) have their jets pointing by chance toward Earth. Scientists call them blazars and are one of the most powerful sources of radiation in the universe.

Black-hole-powered galaxies called blazars are extremely rare. As matter falls toward the supermassive black hole at the galaxy’s center, some of it is accelerated outward at nearly the speed of light along jets pointed in opposite directions. When one of the jets happens to be aimed in the direction of Earth, as illustrated here, the galaxy appears especially bright and is classified as a blazar. ©M. Weiss/CfA

Blazars come in two flavors: BL Lacertae (BL Lac) and flat-spectrum radio-quasars (FSRQs). Our current understanding about these mysterious astronomical objects is that FSRQs are relatively young active galaxies, rich in dust and gas that surround the central black hole. As time passes, the amount of matter available to feed the black hole is consumed and the FSRQ evolves to become a BL Lac object. “In other words, BL Lacs may represent the elderly and evolved phase of a blazar’s life, while FSRQs resemble an adult,” explains Vaidehi Paliya, a DESY researcher who participated in this program.

“Since the speed of light is limited, the farther we look, the earlier in the age of the Universe we investigate,” says Alberto Domínguez of the Institute of Physics of Particles and the Cosmos (IPARCOS) at UCM and co-author of the study. Astronomers believe that the current age of the Universe is around 13.8 billion years. The most distant FSRQ was identified at a distance when the age of the universe was merely 1 billion years. For a comparison, the farthest BL Lac that is known was found when the age of the Universe was around 2.5 billion years. Therefore, the hypothesis of the evolution from FSRQ to BL Lacs appears to be valid.

Research Team On the left, Vaidehi S. Paliya. In the photo on the right: Cristina Cabello, Jesús Gallego, Alberto Domínguez, Armando Gil de Paz y Nicolás Cardiel.

Now, the team of international scientists has discovered a new BL Lac object, named 4FGL J1219.0+3653, much farther away than the previous record holder. “We have discovered a BL Lac existing even 800 million years earlier, this is when the Universe was less than 2 billion years old,” states Cristina Cabello, a graduate student at IPARCOS-UCM. “This finding challenges the current scenario that BL Lacs are actually an evolved phase of FSRQ,” adds Nicolás Cardiel, a professor at IPARCOS-UCM. Jesús Gallego, also a professor at the same institution and a co-author of the study concludes: “This discovery has challenged our knowledge of the cosmic evolution of blazars and active galaxies in general.”

The researchers have used the OSIRIS and EMIR instruments, designed and built by the Instituto de Astrofísica de Canarias (IAC) and mounted on GTC, also known as Grantecan. “These results are a clear example of how the combination of the large collecting area of ??GTC, the world’s largest optical-infrared telescope, together with the unique capabilities of complementary instruments installed in the telescope are providing breakthrough results to improve our understanding of the Universe,” underlines Romano Corradi, director of Grantecan.

References: Vaidehi S. Paliya, A. Domínguez, C. Cabello, et al. “The First Gamma-ray Emitting BL Lacertae Object at the Cosmic Dawn”, The Astrophysical Journal Letters, Oct. 2020 DOI: 10.3847/2041-8213/abbc06 arXiv:2010.12907

Provided by IAC

Astronomers Monitor Spectral Behavior Of Gamma-Ray Blazar S5 0716+714 (Astronomy)

Chinese astronomers reported the new results of spectroscopic observations of γ-ray blazar S5 0716+714 from 2019 September to 2020 March with the 2.4 m optical telescope at Lijiang Observatory of Yunnan Observatories. Their observations provided important insights into the spectral behavior of this source, finding that it is brightness-dependent.

Fig. The left panel is spectral indices (top) and light curves (bottom). The right panel is interpolation cross-correlation functions

Blazars are very compact quasars associated with supermassive black holes at the centers of active, giant elliptical galaxies, and can exhibit variability on a wide range of timescales. They belong to a larger group of active galaxies that host active galactic nuclei (AGN), and their characteristic features are relativistic jets pointed almost exactly toward the Earth.

Based on their optical emission properties, astronomers divide blazars into two classes: flat-spectrum radio quasars (FSRQs) that feature prominent and broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not.

S5 0716+714 is a typical BL Lac exhibiting extreme variability and a prominent relativistic jet. Previous observations of this object have suggested that it showcases the so-called bluer-when-brighter (BWB) chromatic trend. The BWB chromatism, perceived as an evidence of physical processes in jets, is one of the most common phenomena in BL Lacs. In the case of S5 0716+714, its BWB trends may depend on the brightness, for instance, the correlations at the bright state are weaker than those at the faint state.

In order to further investigate the BWB trends in this blazar, a group of astronomers led by Hai-Cheng Feng of Yunnan Observatories, China, conducted spectroscopic observations of the source with Lijiang Observatory’s 2.4-m optical telescope.

Feng’s team monitored S5 0716+714 during two observation periods (Epoch1 and Epoch2) between 2018 and 2020. In general, the source was observed to show a strong BWB trend, and the correlation between brightness and spectral index was found to become weaker toward the blazar’s brighter state.

According to the study, the data reveal an extremely bright state of S5 0716+714 at Epoch2, and it seems that the BWB trend becomes saturated at the highest state during this observation period. It was noted that the BWB trend of Epoch2 differs significantly from that of the Epoch1.

Trying to explain the spectral behavior of S5 0716+714, the astronomers assume that it may be a result of magnetic field amplification due to the turbulence generated in the post-shock region. They added that the BWB trend in this blazar is seemingly dominated by the relative position changes of the synchrotron peak frequency with respect to the observational frequency range, and effectively may be controlled by the variations of electron average energy and magnetic field in the emitting region.


References: Hai-Cheng Feng, Sen. Yang, Zi-Xu. Yang, H. T. Liu, J. M. Bai, Sha-Sha. Li, X. H. Zhao, Jin. Zhang, Y. B. Li, M. Xiao, Y. X. Xin, L. F. Xing, K. X. Lu, L. Xu, J. G. Wang, C. J. Wang, X. L. Zhang, J. J. Zhang, B. L. Lun, S. S. He, “Spectroscopic Monitoring of Blazar S5 0716+714: Brightness-Dependent Spectral Behavior”, pp. 1-16, 2020. arXiv:2008.11341 [astro-ph.HE] arxiv.org/abs/2008.11341 link: https://arxiv.org/abs/2008.11341

Introducing The Universe’s Most Epic Object: Blazar (Astronomy)

What’s the most powerful thing in the universe? A star? A supernova? A black hole? None of those compare to the epic awesomeness that is a blazar.

A blazar is the turducken of awesome space objects: it’s a supermassive black hole inside a radioactive accretion disk inside an active galaxy. Oh, and it shoots jets of radiation from either end at close to the speed of light, right in our direction. Let us explain.

Blazar

Most large galaxies contain supermassive black holes at their centers (even our own Milky Way). Black holes suck the gas, dust, and other debris around them so fast that not everything can keep up. This forms a sort of traffic jam around the black hole known as an accretion disk. The gravitational pressure exerted by the black hole on this disk is enough to heat it up to millions of degrees, making it emit a massive amount of radiation. The black hole, meanwhile, is spinning rapidly, which forms a magnetic field strong enough to turn the radioactive material into powerful jets that blast out of each end at close to the speed of light for hundreds of thousands of light years.

Technically, we just described three objects. How’s that? A black hole that shoots a radioactive jet perpendicular to our vantage point is called a radio galaxy. If that jet is at an angle, it’s called a quasar. If the jet is pointed right at us—making it bright enough to be detectable by Earth-based instruments as far as 9 billion light-years away—it’s a blazar.