Bursting behavior of the Galactic center faint X-ray transient GRS 1741.9–2853

Abstract

Aims. The neutron star low-mass X-ray binary GRS 1741.9-2853 is a known type-I burster at the Galactic center. It is transient, faint, and located in a very crowded region, only 10 from the supermassive black hole Sgr A . Therefore, its bursting behavior has been poorly studied so far. In particular, its persistent emission has rarely been detected between consecutive bursts, because of lack of sensitivity or confusion. This caused GRS 1741.9-2853 to be one of the nine "burst-only sources" identified by BeppoSAX a few years ago. The physical properties of GRS 1741.9-2853 bursts are of significant interest beacause we know little about the nuclear regimes of low accretion rate bursters. For the first time we analyze several bursts along with the persistent emission of the source, using INTEGRAL, XMM-Newton, and Swift observations. Methods. We investigate the source flux variability and bursting behavior during its 2005 and 2007 long outbursts. These events were monitored almost entirely by INTEGRAL, both in the soft (3-20 keV) and hard (20-100 keV) X-ray bands, and also partly by XMM-Newton and Swift (2-10 keV) in 2007.Results. In its last activity periods, 2005 and 2007, the persistent luminosity of GRS 1741.9-2853 varied between ∼1.7 and 10.5 × 10 36 erg s −1 , i.e., 0.9−5.3% of the Eddington luminosity. The shape of the spectrum as described by an absorbed power-law remained with a photon index Γ ≈ 2 and a column density N H ≈ 12 × 10 22 cm −2 throughout the outbursts. We discovered 11 type-I bursts with INTEGRAL, and inspected four additional bursts: two recorded by XMM-Newton and two by Swift. From the brightest burst, we derive an upper limit to the source distance of ∼7 kpc. The observed bursts characteristics and source accretion rate infer pure helium explosions igniting at column depths y ign ≈ 0.8 − 4.8 × 10 8 g cm −2 , for typical energy releases of ∼1.2 − 7.4 × 10 39 erg.

A four-year baselineSwiftstudy of enigmatic X-ray transients located near the Galactic center

“…3, are soft with powerlaw indices of Γ = 5.0 ± 2.5, 2.6 ± 0.1 and 3.0 ± 0.2 for the 2006, 2007 and 2009 activity, respectively. We note that our values for both N H and Γ are a bit higher than obtained from Chandra and XMM-Newton observations, albeit largely consistent within the errors (Muno et al 2003a;Wijnands et al 2006a;Trap et al 2009). The uncertainty on the spectral index of the short and weak 2006 outburst is very large, but comparing the 2007 and 2009 outburst data suggests that the X-ray spectrum is softer for the brightest of the two outbursts.…”

“…Since then, the system has been detected in outburst on multiple occasions with 2-10 keV luminosities of ∼10 36 erg s −1 (e.g., Sakano et al 2002;Muno et al 2003a;Wijnands et al 2006a;Trap et al 2009). In quiescence the source displays a luminosity of ∼10 32 erg s −1 (Muno et al 2003a).…”

“…The detection history in the past decade (see Trap et al 2009, for an overview), suggests a recurrence time of roughly ∼2 years. This implies a duty cycle of ∼10% and the average accretion rate during outburst appears to be typically a few times 10 −10 M yr −1 .…”

INTEGRAL,Swift, andRXTEobservations of the 518 Hz accreting transient pulsar Swift J1749.4−2807

“…We note that pure He runaways were also reported for the other burst-only source GRS 1741.9−2853 (Trap et al 2009). The detection of this kind of type-I X-ray bursts from the burstonly sources is particularly intriguing because it would argue against the idea that these sources are the prototypes of the (poorly observed) H-burning bursts with low accretion rates (see Sect.…”

“…Systems undergoing type-I X-ray bursts when subject to very low accretion rates allow us to test models of thermonuclear burning in a regime that is still poorly explored (see e.g., Cooper & Narayan 2007;Peng et al 2007). Moreover, the low persistent luminosity in quiescence and the spectral properties during the outbursts led to the suggestion that the burst-only sources could be linked to very faint transients and accreting millisecond X-ray pulsars (AMSPs, Wijnands et al 2006;Campana 2009;Trap et al 2009).…”