Where is SGR1806-20?

We apply a statistical method to derive very precise locations for soft gamma repeaters using data from the interplanetary network. We demonstrate the validity of the method by deriving a 600 arcsec^2 error ellipse for SGR1900+14 whose center agrees well with the VLA source position. We then apply it to SGR1806-20, for which we obtain a 230 arcsec^2 error ellipse, the smallest burst error box to date. We find that the most likely position of the source has a small but significant displacement from that of the non-thermal core of the radio supernova remnant G10.0-0.3, which was previously thought to be the position of the repeater. We propose a different model to explain the changing supernova remnant morphology and the positions of the luminous blue variable and the bursting source.Comment: 12 pages and 2 color figures, accepted for publication in Astrophysical Journal Letter

Spectral Cross-calibration of the Konus-Wind, the Suzaku/WAM, and the Swift/BAT Data using Gamma-Ray Bursts

We report on the spectral cross-calibration results of the Konus-Wind, the Suzaku/WAM, and the Swift/BAT instruments using simultaneously observed gamma-ray bursts (GRBs). This is the first attempt to use simultaneously observed GRBs as a spectral calibration source to understand systematic problems among the instruments. Based on these joint spectral fits, we find that 1) although a constant factor (a normalization factor) agrees within 20% among the instruments, the BAT constant factor shows a systematically smaller value by 10-20% compared to that of Konus-Wind, 2) there is a systematic trend that the low-energy photon index becomes steeper by 0.1-0.2 and Epeak becomes systematically higher by 10-20% when including the BAT data in the joint fits, and 3) the high-energy photon index agrees within 0.2 among the instruments. Our results show that cross-calibration based on joint spectral analysis is an important step to understanding the instrumental effects which could be affecting the scientific results from the GRB prompt emission data.Comment: 82 pages, 88 figures, accepted for publication in PAS

Observations of giant outbursts from Cygnus X-1

We present interplanetary network localization, spectral, and time history information for 7 episodes of exceptionally intense gamma-ray emission from Cygnus X-1. The outbursts occurred between 1995 and 2003, with durations up to \~28000 seconds. The observed 15 - 300 keV peak fluxes and fluences reached 3E-7 erg /cm2 s, and 8E-4 erg / cm2 respectively. By combining the triangulations of these outbursts we derive an ~1700 square arcminute (3 sigma) error ellipse which contains Cygnus X-1 and no other known high energy sources. The outbursts reported here occurred both when Cyg X-1 was in the hard state as well as in the soft one, and at various orbital phases. The spectral data indicate that these outbursts display the same parameters as those of the underlying hard and soft states, suggesting that they represent another manifestation of these states.Comment: 27 pages, 9 figures. Revised version. Accepted for publication in the Astrophysical Journal, tentatively scheduled for October 20, 2003 Part

Interplanetary Network Localization of GRB991208 and the Discovery of its Afterglow

The extremely energetic (~10^-4 erg/cm^2) gamma-ray burst (GRB) of 1999 December 8 was triangulated to a ~14 sq. arcmin. error box ~1.8 d after its arrival at Earth with the 3rd interplanetary network (IPN), consisting of the Ulysses, Near Earth Asteroid Rendezvous (NEAR), and WIND spacecraft. Radio observations with the Very Large Array ~2.7 d after the burst revealed a bright fading counterpart whose position is consistent with that of an optical transient source whose redshift is z=0.707. We present the time history, peak flux, fluence, and refined 1.3 sq. arcmin. error box of this event, and discuss its energetics. This is the first time that a counterpart has been found for a GRB localized only by the IPN.Comment: Revised version, accepted for publication in the Astrophysical Journal Letter

GROND coverage of the main peak of Gamma-Ray Burst 130925A

Prompt or early optical emission in gamma-ray bursts is notoriously difficult to measure, and observations of the dozen cases show a large variety of properties. Yet, such early emission promises to help us achieve a better understanding of the GRB emission process(es). We performed dedicated observations of the ultra-long duration (T90 about 7000 s) GRB 130925A in the optical/near-infrared with the 7-channel "Gamma-Ray Burst Optical and Near-infrared Detector" (GROND) at the 2.2m MPG/ESO telescope. We detect an optical/NIR flare with an amplitude of nearly 2 mag which is delayed with respect to the keV--MeV prompt emission by about 300--400 s. The decay time of this flare is shorter than the duration of the flare (500 s) or its delay. While we cannot offer a straightforward explanation, we discuss the implications of the flare properties and suggest ways toward understanding it.Comment: 9 pages, 9 figures, accepted for publ. in A&

Investigation of Primordial Black Hole Bursts using Interplanetary Network Gamma-ray Bursts

The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able to explain such events. The final bursts of evaporating Primordial Black Holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to gamma-ray bursts using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short duration GRBs detected by the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 10^13-10^18 cm (7-10^5 AU) range, consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Assuming these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.Comment: Accepted to the Astrophysical Journal (9 Figures, 3 Tables

Afterglow upper limits for four short duration, hard spectrum gamma-ray bursts

We present interplanetary network localization, spectral, and time history information for four short-duration, hard spectrum gamma-ray bursts, GRB000607, 001025B, 001204, and 010119. All of these events were followed up with sensitive radio and optical observations (the first and only such bursts to be followed up in the radio to date), but no detections were made, demonstrating that the short bursts do not have anomalously intense afterglows. We discuss the upper limits, and show that the lack of observable counterparts is consistent both with the hypothesis that the afterglow behavior of the short bursts is like that of the long duration bursts, many of which similarly have no detectable afterglows, as well as with the hypothesis that the short bursts have no detectable afterglows at all. Small number statistics do not allow a clear choice between these alternatives, but given the present detection rates of various missions, we show that progress can be expected in the near future.Comment: 19 pages, 4 figures; Revised version, accepted by the Astrophysical Journa

A giant, periodic flare from the soft gamma repeater SGR1900+14

Soft gamma repeaters are high-energy transient sources associated with neutron stars in young supernova remnants. They emit sporadic, short (~ 0.1 s) bursts with soft energy spectra during periods of intense activity. The event of March 5, 1979 was the most intense and the only clearly periodic one to date. Here we report on an even more intense burst on August 27, 1998, from a different soft gamma repeater, which displayed a hard energy spectrum at its peak, and was followed by a ~300 s long tail with a soft energy spectrum and a dramatic 5.16 s period. Its peak and time integrated energy fluxes at Earth are the largest yet observed from any cosmic source. This event was probably initiated by a massive disruption of the neutron star crust, followed by an outflow of energetic particles rotating with the period of the star. Comparison of these two bursts supports the idea that magnetic energy plays an important role, and that such giant flares, while rare, are not unique, and may occur at any time in the neutron star's activity cycle.Comment: Accepted for publication in Natur

Integrating the Fermi Gamma-Ray Burst Monitor into the 3rd Interplanetary Network

We are integrating the Fermi Gamma-Ray Burst Monitor (GBM) into the Interplanetary Network (IPN) of Gamma-Ray Burst (GRB) detectors. With the GBM, the IPN will comprise 9 experiments. This will 1) assist the Fermi team in understanding and reducing their systematic localization uncertainties, 2) reduce the sizes of the GBM and Large Area Telescope (LAT) error circles by 1 to 4 orders of magnitude, 3) facilitate the identification of GRB sources with objects found by ground- and space-based observatories at other wavelengths, from the radio to very high energy gamma-rays, 4) reduce the uncertainties in associating some LAT detections of high energy photons with GBM bursts, and 5) facilitate searches for non-electromagnetic GRB counterparts, particularly neutrinos and gravitational radiation. We present examples and demonstrate the synergy between Fermi and the IPN. This is a Fermi Cycle 2 Guest Investigator project.Comment: 5 pages, 11 figures. 2009 Fermi Symposium. eConf Proceedings C09112