Abstract
The gamma-ray burst GRB000210 had the highest gamma-ray peak flux of any event localized by BeppoSAX as yet but it did not have a detected optical afterglow. It is therefore one of the events recently classified as dark GRBs or GHOST (GRB Hiding Optical Source Transient), whose origin is still unclear. Chandra observations allowed us to localize this GRB within ~1" and a radio transient was detected with the VLA. We identify the likely (P=0.01) host galaxy of this burst at z=0.846. The X-ray spectrum of the afterglow shows intrinsic absorption N_H=5x10**21 cm-2. The amount of dust needed to absorb the optical flux of this object is consistent with the above HI column density, given a dust-to-gas ratio similar to that of our Galaxy. We do not find evidence for a partially ionized absorber expected if the absorption takes place in a Giant Molecular Cloud. We therefore conclude that either the gas is local to the GRB, but is condensed in small-scale high-density (n>~10**9 cm-3) clouds, or that the GRB is located in a dusty, gas-rich region of the galaxy. Finally, if GRB000210 lies at z>5, its X-ray absorbing medium would have to be substantially different from that observed in GRBs with optical afterglows.
Highlights
It is observationally well-established that about half of accurately localized gamma-ray bursts (GRBs) do not produce a detectable optical afterglow (Frail et al 2000; Fynbo et al 2001), while most of them (≈ 90%) have an X-ray afterglow (Piro 2001)
Statistical studies have shown that the optical searches of these events, known variously as “dark GRBs”, “failed optical afterglows” (FOA), or “gamma-ray bursts hiding an optical source-transient” (GHOST), have been carried out to magnitude limits fainter on average than the known sample of optical afterglows (Lazzati et al (2002); Reichart & Yost (2001), but see Fynbo et al (2001))
Some of these GRBs could be intrinsically faint events, but this fraction cannot be very high, because the majority of dark GRBs shows the presence of an X-ray afterglow similar to that observed in GRBs with optical afterglows (Piro 2001; Lazzati et al 2002)
Summary
It is observationally well-established that about half of accurately localized gamma-ray bursts (GRBs) do not produce a detectable optical afterglow (Frail et al 2000; Fynbo et al 2001), while most of them (≈ 90%) have an X-ray afterglow (Piro 2001). Djorgovski et al (2001) recently showed how the detection of a short-lived radio transient for GRB 970828 allowed them to identify the probable host galaxy and to infer its properties (redshift, luminosity and morphology) They used estimates of the column density of absorbing gas from X-ray data, and lower limits on the rest frame extinction (AV > 3.8) to quantify the amount of obscuration towards the GRB. We note that the three redshifts determined or suggested so far for dark GRBs (z = 0.96, GRB970828, Djorgovski et al (2001);z = 1.3, GRB990506, Taylor et al (2000); Bloom et al (2002); z ≈ 0.47, GRB000214, Antonelli et al (2000)) are in the range of those measured for most bright optical afterglows, but whether this applies to the majority of these events is still to be assessed Interesting in this respect is the case of the so-called X-ray flashes or X-ray rich GRBs discovered by BeppoSAX(Heise et al 2001). GRB 000210 appears to be the newest member of a small but growing group of well-localized dark bursts (Frail et al 1999; Taylor et al 2000; Djorgovski et al 2001)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
