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New grad student in the group: Lucas

Hello!

My name is Lucas Augusto L. Siconato and I’m a physics graduate at IFGW-UNICAMP. Right now, I’m beginning my master’s degree at IAG-USP under the supervision of professor Rodrigo Nemmen and being very honest: I’m very excited about this.

I believe that throughout my life I have been interested in astronomy, it is an incredible theme and we have a lot to learn about it yet. Because of that, since the beginning of my undergraduate studies, I tried to learn several subjects related to this topic and it couldn’t have been a better experience and I believe that this was what brought me here and helped me in the decision of being part of the Black Hole group.

Now, concerning the things that make up the universe, black holes are certainly among the most fascinating ones. They are breathtaking! I am sure that studying them will be both interesting and challenging, but I am extremely motivated to understand them a little better and get some insights about their physics considering the observations made by the Fermi Gamma-ray Space Telescope. I will be studying the low luminosity active galaxy nuclei and hope to learn some intriguing things about them!

Douglas joins the group

Hello!

My name is Douglas Ferreira Carlos and i’m a physics graduate at IF-USP. I’ll be starting my master’s degree in the Black Hole Group at IAG-USP under the supervision of Prof. Rodrigo Nemmen.

Since I was a kid I’ve always been interested in understanding the underlying principles of how the universe works and in questioning the claims that were previously taken as given, much to the annoyance of the less scientifically minded adults around me. Later I got the chance to answer some of these questions as an physics undergrad at the Universidade de São Paulo while raising many others, and now I’m humbled to have received the opportunity to keep asking and to keep discussing ways of expanding our collective knowledge!

That being said, there is no better way of advancing knowledge than by working on the frontier of what is known, and there are few things in the universe that are as mysterious to us today as black holes are. So I expect that by studying the observations made by the Fermi Gamma-ray Space Telescope we’re able to gain some insight into the physics that takes place close to these very extreme and curious objects.

Bolsa de doutorado direto FAPESP

Está disponível uma bolsa de doutorado direto FAPESP, para trabalhar no Grupo de Buracos Negros do Prof. Rodrigo Nemmen no IAG-USP, dentro do Projeto Jovem Pesquisador FAPESP “O Universo Extremo: Buracos Negros e o Telescópio Fermi“.

O projeto a ser desenvolvido é na área de astrofísica de altas energias, envolvendo observações em raios gama de buracos negros supermassivos com o Telescópio Espacial Fermi. O trabalho envolverá o estudante em colaborações internacionais do Prof. Nemmen.

A bolsa é livre de impostos e a FAPESP oferece apoio para os custos de mudança. O salário inicia em R$ 2043/mês, chegando a R$ 3726/mês no último ano de doutorado. A Reserva Técnica para participação em eventos, compra de material etc é de 30% do valor anual da bolsa (R$ 13414/ano).

Os candidatos interessados deverão entrar em contato por email com o Prof. Rodrigo Nemmen para entrevista, onde serão discutidos: • experiência em computação e pesquisa do candidato • motivação para fazer pós-graduação • redação • conhecimentos básicos em (astro)física. Os candidatos devem incluir no e-mail:

  • Histórico escolar de graduação (e de pós-graduação, se houver)
  • Link para o CV Lattes
  • Um ou dois contatos de referências

O candidato deverá passar primeiro o processo seletivo para o programa de Doutorado Direto em Astronomia do IAG-USP, com inscrições até 25 de Junho de 2020. Potenciais interessados também podem entrar em contato com o Prof. Nemmen para tirarem dúvidas, antes de se candidatarem ao programa de pós-graduação em Astronomia do IAG-USP.


One FAPESP PhD scholarship is available in the Black Hole Group of Prof. Rodrigo Nemmen at IAG-USP, within the Projeto Jovem Pesquisador FAPESP “The Extreme Universe: Black Holes And The Fermi Telescope”. The PhD project is in the field of high-energy astrophysics, involving the analysis of Fermi Large Area Telescope gamma-ray observations and associated physics. The work will involve the student in the scientific collaborations of Prof. Nemmen.

The salary is tax-free, and the funding agency provides relocation funding. The salary begins at R$ 2043/month, reaching R$ 3726/month in the last year of the graduate program. The scholarship includes funds for attending events in the amount of R$ 13414/year.

Candidates should contact Prof. Rodrigo Nemmen. If short-listed, they will be interviewed by the PI where they will be asked to discuss their: • research and computational experience • motivation for pursuing graduate school • writing skills • (astro)physics knowledge. The candidates should include in their e-mail:

  • Undergraduate transcripts (and graduate, if available)
  • Curriculum vitae
  • One or two reference contacts

The candidate must be accepted in the selection process for the programa de Doutorado Direto em Astronomia do IAG-USP (deadline: June 25, 2020). Candidates who are interested and have any questions should contact Prof. Nemmen.

Bolsa de mestrado FAPESP

Está disponível uma bolsa de mestrado FAPESP, para trabalhar no Grupo de Buracos Negros do Prof. Rodrigo Nemmen no IAG-USP, dentro do Projeto Jovem Pesquisador FAPESP “O Universo Extremo: Buracos Negros e o Telescópio Fermi“.

O projeto a ser desenvolvido envolve análise de observações em raios gama de buracos negros supermassivos com o Telescópio Espacial Fermi. O trabalho envolverá o estudante em colaborações internacionais do Prof. Nemmen.

A bolsa é livre de impostos e a FAPESP oferece apoio para os custos de mudança. O salário inicia em R$2043/mês. A Reserva Técnica para participação em eventos, compra de material etc é de 10% do valor anual da bolsa (R$2452/ano).

Os candidatos interessados deverão entrar em contato por email com o Prof. Rodrigo Nemmen para entrevista, onde serão discutidos: • experiência em computação e pesquisa do candidato • motivação para fazer pós-graduação • redação • conhecimentos básicos em (astro)física. Os candidatos devem incluir no e-mail:

  • Histórico escolar de graduação
  • Link para o CV Lattes
  • Um ou dois contatos de referências

O candidato deverá passar primeiro o processo seletivo para o programa de Mestrado em Astronomia do IAG-USP, com inscrições até 25 de Junho de 2020. Potenciais interessados podem entrar em contato com o Prof. Nemmen para tirarem dúvidas, antes de se candidatarem ao programa de pós-graduação em Astronomia do IAG-USP.

Paper: On the physical association of Fermi-LAT blazars with their low-energy counterparts

Associating γ-ray sources to their low-energy counterparts is one of the major challenges of modern γ-ray astronomy. In the context of the Fourth Fermi Large Area Telescope Source Catalog (4FGL), the associations rely mainly on parameters as apparent magnitude, integrated flux, and angular separation between the γ-ray source and its low-energy candidate counterpart. In this work we propose a new use of likelihood ratio (LR) and a complementary random forest (RF) technique to associate γ-ray blazars in 4FGL, based only on spectral parameters as γ-ray photon index, mid-infrared colors and radio-loudness.

The LR method

We modified the LR method used in 4FGL to estimate the association probability ρ of a counterpart for a given γ-ray  source. For each 4FGL source, we considered the γ-ray photon index interval ΔΓ= [Γ -σ, Γ + σ], where σ is the uncertainty on the photon index as listed in 4FGL. Then, given the known correlations between  Γ, the mid-infrared (MIR) colors c, and the MIR radio-loudness q for γ-ray blazars, we selected only those sources with parameters lying within the ΔΓ intervals, as in the figure below:

tris

For each MIR counterpart i of a γ-ray blazar source j we computed the LR and then the association probability ρ as a function of the LR, as shown in the figure below.

AP_500cats

The RF method

The RF is an ensemble classifier that uses decision trees as building blocks for classification. For classifying a new object, each tree in the forest chooses one class and, by aggregating the predictions of all decision trees, the RF makes a final prediction based on the choice made by the majority of the trees, thus improving the predictive capability and reducing the tendency of standard decision trees to overfit the training sample.

We trained the RF method with basically the same atributes used in the LR approach obtaining a modest final accuracy of ~80%. As this accuracy is not very high, we opted by using the RF approach as a complementary method to the LR.

Results

Compared with 4FGL, the association probabilities found by our methods tend to be higher than those listed in 4FGL (see figure below).

LR_comparison_zero.pngIn this work we were able to associate ~1000 blazars with both LR and RF methods, where ~300 of them are good targets for future optical spectroscopic campaigns. This was also the first work where spectral properties of blazars were used to associate γ-ray sources to their low-energy counterparts. Previous methods rely basically on parameters like apparent magnitude and angular separation between the γ-ray source center and the position of its candidate counterpart.

The original discussion of this work can be found in de Menezes et al. (2020).

This work was supported by FAPESP (Fundação de Ampara à Pesquisa do Estado de São Paulo) under grants 2016/25484-9, 2018/24801-6 (R. de Menezes) and 2017/01461-2 (R. Nemmen); and by many other institutions.

file

 

Paper: “Jet efficiencies and black hole spins in jetted quasars”

Black holes are fundamentally simple objects: only their mass and spin are enough to properly describe them. However, direct measurements of these two properties are not simple. Often, we look for observables which, upon being inserted in a physical model, may give us information about one of these fundamental properties of black holes. One such observable is luminosity. Our paper “Jet efficiencies and black hole spins in jetted quasars”, recently accepted by MNRAS (see preprint here), aims to relate jet properties with black hole spins.

With a sample of 154 flat-spectrum radio quasars (FSRQs), a subclass of blazars, whose masses had been previously estimated, we set out to find their gamma-ray luminosities in the Fermi 4FGL catalog, which comprises 8 years of observations performed with the Fermi Large Area Telescope (Fermi-LAT). Our first result is a correlation between jet luminosity and black hole mass, suggesting that more luminous jets are powered by more massive black holes.

mass_lg

We also estimated the jet power of these blazars. For this, we used a relation found in Nemmen et al. 2012. This, along with the assumption that these black holes are accreting at around 10 per cent of the Eddington rate — such high accretion rates are necessary for the thin discs believed to feed FSRQs — allowed us to estimate the jet efficiencies in these objects.

eta_hist

Having estimated the jet efficiencies, we used a simulation-based model to estimate the black hole spins. We found that, overall, these black holes are rotating very fast: the average spin was 0.84. This result is consistent with scenarios for the cosmological evolution of SMBHs which support rapidly rotating black holes as their host galaxies — and the black holes themselves — merge.

The preprint of the accepted version, with a full discussion, can be found here.

Artur defends his MsC dissertation

The black hole group has a new master: Artur Vemado defended his MsC dissertation, entitled “radiative cooling and state transitions in stellar mass black holes”. The defense was very successful.

Here, Artur reported his numerical simulations of black hole accretion flows where he incorporated radiative cooling (with some approximations otherwise the problem is essentially intractable!). We observe the self-consistent emergence of a hot corona enveloping a cold thin accretion disk. Artur quantified the inner radius of the thin disk, the size of the corona, and how these properties respond to varying the mass accretion rate onto the black hole. The resulting simulated black holes are similar to observations of stellar mass black holes in binary systems.

We are looking forward to reporting these exciting results on the emergence of the corona (not the covid-19!) and truncated disk in an upcoming publication.

Many thanks to FAPESP funding through grant 2017/25710-1.

Dr. Gustavo R. R. Soares, PhD in Astrophysics

Congratulations to the now Dr. Gustavo R. R. Soares, for a successful PhD thesis defense! 🎉🍾

The thesis is entitled “Accretion discs, jets, and black hole spins: a study of blazars” and was done under my supervision. The whole defense was entirely online, following the social distancing recommendations of the World Health Organization and the São Paulo State government, in order to ensure the safety of all involved with respect to COVID-19.

The defense lasted for almost five hours (!!), with the thesis committee members in two countries—Brasil and US—and in three states in Brasil: Pernambuco, Rio de Janeiro and São Paulo.

Gustavo presenting his thesis work

Thanks to Dr. Soares’s work, we now we know a bit more about the role of black holes in the universe, and how the supermassive ones power relativistic jets.

Gustavo will begin a postdoc at Oregon State University in the Fall. We are all wishing Gustavo a huge success for his future career!

Our thanks to the Brazilian science funding agencies CAPES, CNPq and FAPESP. Without them, this work would not have been possible.

Group at IAU GALFEED Symposium

On the week of March 2nd to 6th, the Black Hole Group attended the IAU Symposium 359: Galaxy Evolution and Feedback Across Different Environments, or simply the GALFEED symposium. The event occurred at the beautiful setting of Bento Gonçalves in the south of Brasil. This is the wine region of the country, which specializes in the merlot variety.

This was an incredible event which led to many fruitful interactions between the group members and the galaxy evolution community. Beginning on March 2nd, Fabio and Raniere gave poster flash talks where they had the daunting challenge of summarizing their posters in only one minute. Not so easy, but they did a great job!

On Tuesday, it was Ivan and Gustavo’s turn to face the one-minute-present-all-your-research challenge. And again, it went fantastic!

On Wednesday, we surprised Fabio with a surprise birthday party: it was his 40th birthday! There was cake and presents!

Fabio’s birthday. From left to right: Raniere, Gustavo, Fabio, Ivan, Rodrigo and Roderik

On Thursday, it was Rodrigo’s turn. He surprised the audience by beginning hist talk about spin estimates for M87*…

Rodrigo begins his talk on the spin of M87*. Certainly not the best of pictures…

… and then switching gears to talk about the first AI simulation of a black hole—the work of graduate student Roberta Pereira.

The first quarter of 2020 was very bright and productive for the group, despite the worrying news with COVID-19 all over the world.

Thanks to the IAU and FAPESP for funding our group’s attendance to this meeting.