On the distance of GRO J1655-40

We challenge the accepted distance of 3.2 kpc of GRO J1655-40. We present VLT-UVES spectroscopic observations to estimate the absorption toward the source, and determine a maximum distance of GRO J1655-40. We show that the accepted value of 3.2 kpc is taken for granted by many authors. We retrieved in the ESO archive UVES spectra taken in April 2004 when GRO J1655-40 was in quiescence to determine the spectral type of the secondary star. For the first time we build a flux-calibrated mean (UVES) spectrum of GRO J1655-40 and compare its observed flux to that of five nearby stars of similar spectral types. We strengthen our results with the traditional pair method, using published photometric data of the comparison stars. We show that the distance of 3.2 kpc is questionable. We determine a spectral type F6IV for the secondary star. We demonstrate in details that the distance of GRO J1655-40 must be smaller than 1.7 kpc. The runaway black hole GRO J1655-40 could be associated with the open cluster NGC 6242 which is located at 1.0$\pm$0.1 kpc from the Sun. At $D \leq$ 1.7 kpc the jets are not a superluminal, and GRO J1655-40 becomes one of the closest known black holes to the Sun.Comment: 9 pages, 6 figures, accepted for publication in Astronomy & Astrophysics. Small correction of distance range values using the photometric method. (re-accepted by A&A

A Chandra observation of GRO J1744-28: the bursting pulsar in quiescence

We present a Chandra/ACIS-I observation of GRO J1744-28. We detected a source at a position of R.A = 17h 44m 33.09s and Dec. = -28degr 44' 27.0'' (J2000.0; with a 1sigma error of ~0.8 arcseconds), consistent with both ROSAT and interplanetary network localizations of GRO J1744-28 when it was in outburst. This makes it likely that we have detected the quiescent X-ray counterpart of GRO J1744-28. Our Chandra position demonstrates that the previously proposed infrared counterpart is not related to GRO J1744-28. The 0.5-10 keV luminosity of the source is 2 - 4 x 10^{33} erg/s (assuming the source is near the Galactic center at a distance of 8 kpc). We discuss our results in the context of the quiescent X-ray emission of pulsating and non-pulsating neutron star X-ray transients.Comment: Accepted for publication in ApJ Letters, 20 February 200

The gamma-ray observatory

An overview is given of the Gamma Ray Observatory (GRO) mission. Detection of gamma rays and gamma ray sources, operations using the Space Shuttle, and instruments aboard the GRO, including the Burst and Transient Source Experiment (BATSE), the Oriented Scintillation Spectrometer Experiment (OSSE), the Imaging Compton Telescope (COMPTEL), and the Energetic Gamma Ray Experiment Telescope (EGRET) are among the topics surveyed

Gamma-Ray Observations of GRO J1655-40

The bright transient X-ray source GRO J1655-40 = XN Sco 1994 was observed by the OSSE instrument on the Compton Gamma Ray Observatory (GRO). Preliminary results are reported here. The initial outburst from GRO J1655-40 was detected by BATSE on 27 Jul 1994. OSSE observations were made in five separate viewing periods starting between 4 Aug 1994 and 4 Apr 1995. The first, third, and fifth observations are near the peak luminosity. In the second observation, the source flux had dropped by several orders of magnitude and we can only set an upper limit. The fourth observation is a weak detection after the period of maximum outburst. In contrast with other X-ray novae such as GRO J0422+32, the spectrum determined by OSSE is consistent with a simple power law over the full range of detection, about 50 - 600 keV. The photon spectral index is in the range of -2.5 to 2.8 in all of the observations. We set an upper limit on fractional rms variation \u3c5% in the frequency range 0.01 – 60 Hz. No significant narrow or broad line features are observed at any energy

Nonthermal processes and neutrino emission from the black hole GRO J0422+32 in a bursting state

GRO J0422+32 is a member of the class of low-mass X-ray binaries (LMXBs). It was discovered during an outburst in 1992. During the entire episode a persistent power-law spectral component extending up to $\sim 1$ MeV was observed, which suggests that nonthermal processes should have occurred in the system. We study relativistic particle interactions and the neutrino production in the corona of GRO J0422+32, and explain the behavior of GRO J0422+32 during its recorded flaring phase. We have developed a magnetized corona model to fit the spectrum of GRO J0422+32 during the low-hard state. We also estimate neutrino emission and study the detectability of neutrinos with 1 km$^3$ detectors, such as IceCube. The short duration of the flares ($\sim$ hours) and an energy cutoff around a few TeV in the neutrino spectrum make neutrino detection difficult. There are, however, many factors that can enhance neutrino emission. The northern-sky coverage and full duty cycle of IceCube make it possible to detect neutrino bursts from objects of this kind through time-dependent analysis.Comment: 12 pages, 11 figures, accepted for publication in A&

COMPTEL observations of cosmic gamma‐ray bursts

The imaging γ‐ray telescope COMPTEL on board NASA’s Compton Gamma‐Ray Observatory (GRO) has observed many cosmic gamma‐ray bursts during the early mission phase of GRO. COMPTEL records time‐resolved burst spectra over 0.1 MeV to 10 MeV energies, and, for the first time, produces direct single‐telescope gamma‐ray images (0.8–30 MeV) of cosmic gamma‐ray bursts occurring in its 1 sr field of field