Second Scale Submillimeter Variability of Sagittarius A* during flaring activity of 2019: On the Origin of Bright Near Infrared Flares

Abstract

In 2019, Sgr A* -the supermassive black hole in the Galactic Center -underwent unprecedented flaring activity, brightening by up to a factor of 100 compared to quiescent values. Here we report ALMA observations of Sgr A*'s continuum variability at 1.3 mm (230 GHz) -a tracer of the accretion rate -conducted one month after the brightest detected near infrared (NIR) and in the middle of the flaring activity of 2019. We develop an innovative light curve extraction technique which (together with ALMA's excellent sensitivity) allows us to obtain the light curves which are simultaneously of high time resolution (2 seconds) and high signal-to-noise ratio (∼ 500). We construct an accurate intrinsic structure function of the Sgr A* submm variability, improving on previous studies by about two orders of magnitude in timescale and one order of magnitude in sensitivity. We compare the June 2019 variability behavior with that of 2001-2017, and suggest that the most likely cause of the bright NIR flares is magnetic reconnection.

Black hole flares: ejection of accreted magnetic flux through 3D plasmoid-mediated reconnection

“…Sgr A * shows daily near-infrared and X-ray flares from the inner 10r g , on average every 6 and 12 hours, lasting for 30-80 minutes, respectively (Baganoff et al 2001;Eckart et al 2006;Gravity Collaboration et al 2018;Witzel et al 2021;Murchikova & Witzel 2021). The flare periods in our simulation last for ∼ 100r g /c ∼ 30 minutes, and the subsequent quiescent period for ∼ 2000r g /c ∼ 10 hours for Sgr A * .…”

Remarkable correspondence of Sagittarius A* submillimeter variability with a stellar-wind-fed accretion flow model

“…We use observational data sets from Murchikova & Witzel (2021), Witzel et al (2021), andDexter et al (2014). The data were obtained at the frequency of about 230 GHz with the Atacama Large Millimeter/submillimeter Array (ALMA), the Submillimeter Array (SMA), and Combined Array for Research in Millimeter-wave Astronomy (CARMA) between 2009 and 2019.…”

“…Detailed descriptions of the observations and the data reduction can be found in the corresponding papers. We reanalyze the ALMA data from project 2018.1.01124.S (PI Murchikova) described in Murchikova & Witzel (2021). We update the light curve extraction procedure, which allows us to obtain the timestamps with decimal second accuracy.…”

“…In this work we analyze the submm variability of Sgr A* on scales between about 10 seconds to about 200 minutes. We compare observational results (Murchikova & Witzel 2021;Witzel et al 2021;Dexter et al 2014) with simulations (White et al 2020;, and identify an accretion flow model that describes Sgr A* variability nearly perfectly. This model traces accretion from stellar winds at parsec scales down to the event horizon.…”

“…As a measure of Sgr A* variability we use the intrinsic structure function (SF) defined in Murchikova & Witzel (2021) as an extension of the standard structure function definition to the case where observational uncertainties are present:…”