SWIFT DISCOVERY OF A NEW SOFT GAMMA REPEATER, SGR J1745–29, NEAR SAGITTARIUS A*

Abstract

Starting in 2013 February, Swift has been performing short daily monitoring observations of the G2 gas cloud near Sgr A* with the X-Ray Telescope to determine whether the cloud interaction leads to an increase in the flux from the Galactic center. On 2013 April 24 Swift detected an order of magnitude rise in the X-ray flux from the region near Sgr A*. Initially thought to be a flare from Sgr A*, detection of a short hard X-ray burst from the same region by the Burst Alert Telescope suggested that the flare was from an unresolved new Soft Gamma Repeater, SGR J1745−29. Here we present the discovery of SGR J1745−29 by Swift, including analysis of data before, during, and after the burst. We find that the spectrum in the 0.3-10 keV range is well fit by an absorbed blackbody model with kT BB ≃ 1 keV and absorption consistent with previously measured values from the quiescent emission from Sgr A*, strongly suggesting that this source is at a similar distance. Only one SGR burst has been detected so far from the new source, and the persistent light curve shows little evidence of decay in approximately 2 weeks of monitoring after outburst. We discuss this light curve trend and compare it with those of other well covered SGR outbursts. We suggest that SGR J1745−29 belongs to an emerging subclass of magnetars characterized by low burst rates and prolonged steady X-ray emission 1-2 weeks after outburst onset.

Neutron-Star Implosions as Heavy-Element Sources

“…This is consistent with observations [23] suggesting an underabundance of MSPs near the central Galactic black hole, Sgr A Ã . A recently discovered young, 4 × 10 4 -yr-old, magnetar J1745-2900 located just 0.1 pc from the GC [25,26] is also consistent with our results, since this magnetar's age is shorter than ht NS i. The unusual surface temperature [61] and x-ray luminosity of J1745-2900 warrants scrutiny, as this activity might be consistent with PBH destruction in progress.…”

“…DM-rich environments, such as the GC and dwarf spheroidal galaxies, are not known to host NSs. An exception is the young magnetar [25,26], whose age is small compared to the time scales of PBH capture. NSs are found in the disk and the halo, as well as in the globular clusters, where the darkmatter density [27,28] is too low to cause a substantial decrease in the pulsar population.…”

The Sleeping Monster: NuSTAR Observations of SGR 1806–20, 11 Years After the Giant Flare

“…The torque then returns to its nominal value on a timescale 1 year . On the other hand, SGR J1745−2900, the Galactic center magnetar that went into outburst in April 2013 (Kennea et al 2013;Mori et al 2013) has shown an increase ofν by a factor of 4.5, and no sign of decrease 3.5 years following the outburst Coti Zelati et al 2017). Last but not least, SGR 1900+14 has also shown strong timing noise following burst-active episodes, e.g., withν increasing by a factor of 5 following its late 1998 major bursting episode and GF (Woods et al 2002;Mereghetti et al 2006).…”

On the Existence of Pulsars in the Vicinity of the Massive Black Hole in the Galactic Center

“…It becomes especially encouraging that a magnetar, a highly magnetized pulsar, is recently discovered at a parsec (pc) distance from the central MBH. This magnetar has been used to reveal the magnetic field in the GC (see Rea et al 2013;Eatough et al 2013;Kennea et al 2013;Mori et al 2013). Magnetars are a rare type of pulsars, and the discovery of a magnetar in the GC suggests that many more normal pulsars exist there.…”