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

¹ Service d'Astrophysique (SAp) / IRFU / DSM / CEA Saclay, Bât. 709, 91191 Gif-sur-Yvette Cedex, France e-mail: trap@apc.univ-paris7.fr
² AstroParticule & Cosmologie (APC) / Université Paris VII / CNRS / CEA / Observatoire de Paris, Bât. Condorcet, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
³ International Space Science Institute (ISSI), Hallerstrasse 6, 3012 Bern, Switzerland
⁴ Istituto Nazionale Di Astrofisica (INAF) / Osservatorio Astronomico di Roma, via Frascati 33, Monte Porzio Catone, 00044 Rome, Italy
⁵ INTEGRAL Science Data Center (ISDC) / Science data center for Astrophysics, Ch. d'Ecogia 16, 1290 Versoix (Ge), Switzerland
⁶ Observatoire astronomique de Strasbourg / Université de Strasbourg / CNRS / INSU, 11 rue de l'Université, 67000 Strasbourg, France
⁷ Department of Physics and Astronomy / University of Leicestern, LE1 7RH Leicester, UK

Received: 3 February 2009
Accepted: 11 June 2009

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 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  erg s^-1, i.e., % of the Eddington luminosity. The shape of the spectrum as described by an absorbed power-law remained with a photon index and a column density  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  g cm^-2, for typical energy releases of ~ erg.