GRB 070610: A Curious Galactic Transient

Abstract

GRB 070610 is a typical high-energy event with a duration of 5 s. Yet within the burst localization we detect a highly unusual X-ray and optical transient, Swift J195509.6+261406. We see high-amplitude X-ray and optical variability on very short timescales even at late times. Using near-infrared imaging assisted by a laser guide star and adaptive optics, we identified the counterpart of Swift J195509.6+261406. Late-time optical and near-infrared imaging constrain the spectral type of the counterpart to be fainter than a K-dwarf, assuming it is of Galactic origin. It is possible that GRB 070610 and Swift J195509.6+261406 are unrelated sources. However, the absence of a typical X-ray afterglow from GRB 070610 in conjunction with the spatial and temporal coincidence of the two motivate us to suggest that the sources are related. The closest (imperfect) analog to Swift J195509.6+261406 is V4641 Sgr, an unusual black hole binary. We suggest that Swift J195509.6+261406 along with V4641 Sgr define a subclass of stellar black hole binaries-the fast X-ray novae. We further suggest that fast X-ray novae are associated with bursts of gamma rays. If so, GRB 070610 defines a new class of celestial gamma-ray bursts and these bursts dominate the long-duration GRB demographics.

Faint Galactic X-ray Binaries

“…The deep limits on the near-infrared counterpart in quiescence of Swift J195509.6+261406 and the known interstellar extinction do exclude the possibility of a early type star as the counterpart to Swift J195509.6+261406 (see Kasliwal et al 2007). …”

“…However, the subsequent Swift/XRT and near-infrared monitoring (Kasliwal et al 2007) showed that the afterglow was unlike that of a GRB. Kasliwal et al (2007) propose the source to be a black hole X-ray transient.…”

“…However, the subsequent Swift/XRT and near-infrared monitoring (Kasliwal et al 2007) showed that the afterglow was unlike that of a GRB. Kasliwal et al (2007) propose the source to be a black hole X-ray transient. If indeed low-mass X-ray binaries are responsible for the two Swift events noted above they can by extension also be responsible for the other events listed in Table 1.…”

The unusual gamma-ray burst GRB 101225A explained as a minor body falling onto a neutron star

“…Tight upper limits were also derived in the optical and IR with H > 23, R > 26.0 and i > 24.5 (ref. 89,87). Given this observational framework Rea et al 80 questioned the magnetar interpretation, based on the too low quiescent X-ray flux.…”

Design of a CZT gamma-camera for GRB and fast transient follow-up: a wide-field-monitor for the EDGE mission

“…Other fast and strong events have been found in Black Hole (BH) systems, like rapid flux variability of V4641 SGR (e.g. Wijnands & Van der klis 2000) and possibly GRB 070610, likely to be associated to a stellar black hole (Kasliwal et al 2007). We also list giant outbursts of Cyg X-1 (Golenetskii et al 2003) and bright flares from XTE J1650-500 (Tomsick et al 2003).…”