From Jagiellonian University – Cracow (PL) [Uniwersytet Jagielloński] via “” : “Research examines X-ray intraday variability of blazar Markarian 421”

From Jagiellonian University- Cracow (PL) [Uniwersytet Jagielloński]



June 13, 2022
Tomasz Nowakowski

Sloan Digital Sky Survey image of Mrk 421. Credit: Sloan Digital Sky Survey.

Apache Point Observatory
SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft).

Apache Point Observatory near Sunspot, New Mexico Altitude 2,788 meters (9,147 ft).


By analyzing the data from ESA’s XMM-Newton satellite, astronomers from the Astronomical Observatory of the Jagiellonian University in Kraków, Poland, and elsewhere, have investigated X-ray intraday variability of a nearby blazar known as Markarian 421.

Results of the study, published June 5 for The Astrophysical Journal Supplement Series, could help us better understand the nature of high-energy X-ray sources.

Blazars are very compact quasars associated with supermassive black holes (SMBHs) at the centers of active giant elliptical galaxies. They belong to a larger group of active galaxies that host active galactic nuclei (AGN), and are the most numerous extragalactic gamma-ray sources. 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.

At a distance of some 134 million light years, Markarian 421 (or Mrk 421 for short) is one of the nearest blazars to Earth. Previous observations of Mrk 421 classified it as a BL Lac due to its featureless optical spectrum, compact radio emission, strongly polarized and variable fluxes in optical and radio bands. The blazar hosts a central SMBH with a mass estimated to be between 200 and 900 million solar masses.

Mrk 421 is also classified as a high-energy peaked blazar (HBL) given that its synchrotron peak in the spectral energy distribution (SED) was found in X-ray energies higher than 0.1 keV. This, together with its featureless non-thermal spectrum, make Mrk 421 a good candidate to study intraday flux and spectral variations over time. So a team of astronomers led by Angel Priyana Noel analyzed its X-ray observations spanning 17 years.

“We utilize public archive data of 25 pointed observations of Mrk 421 with an EPIC-pn instrument on board of XMM-Newton carried out within a period of 17 years (2000–2017) for analysis of flux and spectral variations on IDV [intraday variability] timescales and to study the X-ray emission tentatively expected to be generated in the jet close to the central black hole of the blazar,” the researchers explained.

In general, the available EPIC-pn data allowed the team to carry analysis of flux variability, spectral variability, and cross correlated studies of soft and hard X-ray bands of Mrk 421 on IDV timescales. For all the pointed X-ray observations, they inspected light curves in soft (0.3–2.0 keV), hard (2.0–10.0 keV), and total (0.3–10.0 keV) energy bands.

The study found that the fractional variability displays clear evidence of large amplitude IDV in 23 out of 25 pointed observations in all considered X-ray bands. The IDV duty cycle was estimated to be 96%, however some level of variability was also identified in all data.

Furthermore, the results suggest that the fractional variability amplitude depends on the studied X-ray energy range and is always higher in the hard band than in the soft band. The total energy weighted minimum variability timescales for all pointed observations occur in the range from 1,030 to 1,059 seconds.

The researchers also identified time lags between soft and hard energy bands, but they do not reveal any constant pattern. They added that the occurrence of the big lags in soft or hard photons is moderately related to the degree of flux variability.

See the full article here.


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Two hundred years of the Cracow Observatory

Among the three oldest Polish astronomical observatories belonging to the universities in Vilna, Cracow and Warsaw, the Cracow University Observatory was fortunately able to act continuously since the year of its foundation (1791-1792) until present.

Also in Cracow the longest in Poland, unbroken series of meteorological observations has been recorded and preserved. However, the beginning of the institution was rather difficult. The idea of setting up the astronomical observatory in Cracow did not find there, in the first half of 18th century, a favorable atmosphere. The excellent astronomical traditions of the Cracow Academy, dating back to the 15th century (cf. H. Schedel, Liber Chronicarum, Nürnberg, 1493), were then forgotten. Moreover, the further progress in astronomy was not followed there. At the Cracow University the heliocentric theory of Copernicus, its most prominent student, was not accepted and the syllabus including the lectures on astronomy according to Ptolemy and Peuerbach was obligatory till 1750 CE and later on.

The Jagiellonian University [Uniwersytet Jagielloński] also known as the University of Craków) is a research university in Craków (PL).

Founded in 1364 by Casimir III the Great, the Jagiellonian University is the oldest university in Poland, the second oldest university in Central Europe, and one of the oldest surviving universities in the world. Notable alumni include astronomer Nicolaus Copernicus, poet Jan Kochanowski, Polish King John III Sobieski, constitutional reformer Hugo Kołłątaj, chemist Karol Olszewski, anthropologist Bronisław Malinowski, writer Stanisław Lem, and President of Poland Andrzej Duda. Students at the University who did not earn diplomas included Nobel laureates Ivo Andrić and Wisława Szymborska. Pope John Paul II enrolled in the Jagiellonian University of Krakow in 1938 to study Polish Studies at the JU Faculty of Philosophy, but shortly after enrollment, his studies were interrupted by Sonderaktion Krakau. In 1953, Father Wojtyła presented a dissertation at the Jagiellonian University of Krakow on the possibility of grounding a Christian ethic on the ethical system developed by Max Scheler.

The campus of the Jagiellonian University is centrally located within the city of Kraków. The university consists of fifteen faculties, including the humanities, law, the natural and social sciences, and medicine. The university employs roughly 4,000 academics, and has more than 40,000 students who study in some 80 disciplines. More than half of the student body are women. The language of instruction is usually Polish, although several degrees are offered in either German or English. The university library is one of Poland’s largest, and houses several medieval manuscripts, including Copernicus’ De Revolutionibus.

Due to its history, the Jagiellonian University is traditionally considered Poland’s most reputable institution of higher learning, this standing equally being reflected in international rankings. The Jagiellonian University is a member of the Coimbra Group and Europaeum.

In 2019, the Academic Ranking of World Universities placed the university within the 301–400 band globally.