No Sign of G2's Encounter Affecting Sgr A*'s X-Ray Flaring Rate from Chandra Observations

Abstract

An unusual object, G2, had its pericenter passage around Sgr A*, the 4 × 10 6 M supermassive black hole in the Galactic Centre, in Summer 2014. Several research teams have reported evidence that following G2's pericenter encounter the rate of Sgr A*'s bright X-ray flares increased significantly. Our analysis carefully treats varying flux contamination from a nearby magnetic neutron star and is free from complications induced by using data from multiple X-ray observatories with different spatial resolutions. We test the scenario of an increased bright X-ray flaring rate using a massive dataset from the Chandra X-ray Observatory, the only X-ray instrument that can spatially distinguish between Sgr A* and the nearby Galactic Centre magnetar throughout the full extended period encompassing G2's encounter with Sgr A*. We use X-ray data from the 3 Ms observations of the Chandra X-ray Visionary Program (XVP) in 2012 as well as an additional 1.5 Ms of observations up to 2018. We use detected flares to make distributions of flare properties. Using simulations of X-ray flares accounting for important factors such as the different Chandra instrument modes, we test the null hypothesis on Sgr A*'s bright (or any flare category) X-ray flaring rate around different potential change points. In contrast to previous studies, our results are consistent with the null hypothesis; the same model parameters produce distributions consistent with the observed ones around any plausible change point.

Constraining particle acceleration in Sgr A⋆with simultaneous GRAVITY,Spitzer,NuSTAR, andChandraobservations

“…of Sgr A have been detected so far by Chandra and XMM-Newton (Neilsen et al 2013;Ponti et al 2015;Mossoux et al 2016;Li et al 2017;Bouffard et al 2019). Figure 3 highlights the fluence and duration of the X-ray flare detected in this work and compared to previously detected flares.…”

“…In the X-ray band, Sgr A appears as a faint (L 2−10 keV ∼ 2 × 10 33 erg s −1 ) extended source with a size, ∼ 1 , comparable to the Bondi radius, emitting via bremsstrahlung emission from a hot plasma with T e ∼ 7 × 10 7 K and n e ∼ 100 cm −3 (Quataert 2002;Baganoff et al 2003;Xu et al 2006). In the X-ray band, Sgr A occasionally shows sudden rises (flares) of up to 1−2 orders of magnitudes, suggesting individual and distinct events, randomly punctuating an otherwise quiescent source (Baganoff et al 2001;Porquet et al 2003Porquet et al , 2008Neilsen et al 2013;Ponti et al 2015;Bouffard et al 2019). X-ray flares are associated with bright flux excursions in the near-infrared (NIR) band, which also led to the definition of the latter as flares (Genzel et al 2003;Ghez et al 2004).…”

Continuation of the X-ray monitoring of Sgr A*: the increase in bright flaring rate confirmed

“…As mentioned in Sect. 3, Bouffard et al (2019) considered Chandra flare 9 as two separated flares. We therefore also ap- Fig.…”

“…We therefore used the method of Degenaar et al (2013), but no flare was detected. Bouffard et al (2019) Compared to the Chandra flares detected by Bouffard et al (2019) after 2015, they detected the flares we labeled flares 4 to 8. The duration of these flares is slightly shorter that those we derived, but our mean count rate is consistent with the rates they computed after subtracting the quiescent level.…”

“…The most recent study of the flare energy distribution was performed by Bouffard et al (2019). These authors have analyzed the Chandra observations from 2012 to 2018 and detected 58 flares.…”