A possible model for the long-term flares of Sgr A*

Author(s)

Okuda, Toru ; Singh, Chandra B. ; Das, Santabrata ; Aktar, Ramiz ; Nandi, Anuj ; de Gouveia Dal Pino, Elisabete M.

• Document type: Journal article
• Source: PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN; v. 71, n. 3, p. 15-pg., 2019-06-01.

Abstract

We examine the effects of magnetic field on low angular momentum flows with standing shock around black holes in two dimensions. The magnetic field brings change in behavior and location of the shock which results in regularly or chaotically oscillating phenomena of the flow. Adopting fiducial parameters like specific angular momentum, specific energy, and magnetic field strength for the flow around Sgr A*, we find that the shock moves back and forth in the range 60-170 R-g, irregularly recurring with a time-scale of similar to 5 d with an accompanying, more rapid, small modulation with a period of 25 hr without fading, where Rg is the Schwarzschild radius. The time-variability associated with the two different periods is attributed to the oscillating outer strong shock, together with another rapidly oscillating inner weak shock. As a consequence of the variable shock location, the luminosities vary roughly by more than a factor of 3. The time-dependent behaviors of the flow are well compatible with luminous flares with a frequency of similar to one per day and bright flares occurring every similar to 5-10 d in the latest observations by Chandra, Swift, and XMM-Newton monitoring of Sgr A*. (AU)

• FAPESP's process: 13/09065-8 - Origin and Collimation of Compact Source Jets and Acceleration Mechanisms
• Grantee: Chandra Bahadur Singh
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 13/10559-5 - Investigation of high energy and plasma astrophysics phenomena: theory, numerical simulations, observations, and instrument development for the Cherenkov Telescope Array (CTA)
• Grantee: Elisabete Maria de Gouveia Dal Pino
• Support Opportunities: Special Projects
• FAPESP's process: 09/54006-4 - A computer cluster for the Astronomy Department of the University of São Paulo Institute of Astronomy, Geophysics and Atmospheric Sciences and for the Cruzeiro do Sul University Astrophysics Center
• Grantee: Elisabete Maria de Gouveia Dal Pino
• Support Opportunities: Multi-user Equipment Program