Narrow Field Instruments Research Articles

A Swift X-Ray View of the SMS4 Sample—X-Ray Properties of 31 Quasars and Radio Galaxies

We present Neil Gehrels Swift Observatory (hereafter Swift) observations of 31 sources from the SMS4 catalog, a sample of 137 bright radio sources originally designed to extend the well-studied 3CRR radio sample to the Southern Hemisphere. All these sources had no Chandra or XMM-Newton observations: 24 of these were observed with Swift through a dedicated proposal in 2015, and data for the remaining seven were retrieved from the Swift archive. The reduction and analysis of data collected by the Swift X-ray Telescope (XRT) led to 20 detections in the 0.3–10 keV band. We provide details of the X-ray emission in this band for these 20 detections, as well as upper limits for the remaining 11 SMS4 sources. When statistics allowed, we investigated the extent of the X-ray emission and the hardness ratio, and we carried out a spectral analysis. We matched the 20 X-ray-detected sources with infrared (AllWISE, CatWISE2020) and optical (GSC 2.3.2, DES DR2) catalogs to establish associations with infrared and optical sources and compared our results with previously published counterparts in these bands. Requiring a detection in both the infrared and optical bands to establish a candidate counterpart for our X-ray detections, we obtain reliable counterparts for 18 sources, while the remaining two sources need further investigation to establish firm identifications. In the infrared, we confirm 12 previously established counterparts and provide six new candidates. In the optical, we find agreement with 13 previously established counterparts, while we provide an alternative candidate for five SMS4 sources. We find that ∼35% of all the SMS4 sources lie below the lower limit of 10.9 Jy for the flux density at 178 MHz established for the 3CRR sample, at variance with the values extrapolated using measurements at higher frequencies. Therefore, for future studies where flux-density-limited samples are needed, we encourage the use of the more recent G4Jy sample. We present the list of 56 SMS4 sources that in 2022 March remain to be observed in the X-rays with narrow-field instruments, to highlight interesting sources and organize further observational campaigns to achieve complete X-ray coverage for the whole SMS4 in the forthcoming years.

Analytical simulations of the effect of satellite constellations on optical and near-infrared observations

Context. The number of satellites in low-Earth orbit is increasing rapidly and many tens of thousands of satellites are expected to be launched in the coming years. There is a strong concern among the astronomical community about the contamination of optical and near-infrared observations by satellite trails, what has led to several initial investigations of the impact of large satellite constellations. Aims. We expand the impact analysis of such constellations on ground-based optical and near-infrared astronomical observations in a more rigorous and quantitative way, using updated constellation information and considering imagers and spectrographs and their very different characteristics. Methods. We introduce an analytical method that allows us to rapidly and accurately evaluate the effect of a very large number of satellites, accounting for their magnitudes and the effect of trailing of the satellite image during the exposure. We use this to evaluate the impact on a series of representative instruments, including imagers (traditional narrow field instruments, wide-field survey cameras, and astro-photographic cameras) and spectrographs (long-slit and fibre-fed), taking their limiting magnitude into account. Results. Confirming earlier findings, the effect of satellite trails is more damaging for high-altitude satellites, on wide-field instruments, or essentially during the first and last hours of the night. Thanks to their brighter limiting magnitudes, low- and mid-resolution spectrographs will be less affected, but the contamination will be at about the same level as that of the science signal, introducing additional challenges. High-resolution spectrographs will essentially be immune. We propose a series of mitigating measures, including one that uses the described simulation method to optimise the scheduling of the observations. We conclude that no single mitigation measure will solve the problem of satellite trails for all instruments and all science cases.

Detection and characterization of circumstellar material with a WFIRST or EXO-C coronagraphic instrument: simulations and observational methods

The capabilities of a high (∼10−9 resel−1) contrast narrow-field coronagraphic instrument (CGI) on a space-based WFIRST-C or probe-class EXO-C/S mission are particularly and importantly germane to symbiotic studies of the systems of circumstellar material from which planets have emerged and interact with throughout their lifetimes. The small particle populations in “disks” of co-orbiting materials can trace the presence of planets through dynamical interactions that perturb the spatial distribution of light-scattering debris, which is detectable at visible wavelengths and resolvable with a WFIRST-C or EXO-S/C CGI. Herein, we (1) present the scientific case to study the formation, evolution, architectures, diversity, and properties of the material in the planet-hosting regions of nearby stars; (2) discuss how a CGI under current conception can uniquely inform and contribute to those investigations; (3) consider the applicability of CGI-anticipated performance for circumstellar debris system studies; (4) investigate, through WFIRST CGI image simulations, the anticipated interpretive fidelity and metrical results from specific representative zodiacal debris disk observations; (5) comment on specific observational modes and methods germane to and augmenting circumstellar debris system observations; and (6) present a case for augmenting future CGI instrumentation with the capability to obtain full linear-Stokes imaging polarimetery, which greatly benefits characterization of the material properties of circumstellar dust and exoplanet atmospheres (discussed in other studies).

The Chinese–French SVOM mission for gamma-ray burst studies

We present the SVOM (Space-based multi-band astronomical Variable Objects Monitor) mission that the Chinese National Space Agency and the French Space Agency have decided to jointly implement. SVOM has been designed to detect all known types of gamma-ray bursts (GRBs), to provide fast and reliable GRB positions, to measure the broadband spectral shape and temporal properties of the GRB prompt emission, and to quickly identify the optical/near-infrared afterglows of detected GRBs, including high-redshift ones. Scheduled to be in orbit in the second half of the present decade, the SVOM satellite will carry a very innovative scientific payload combining for the first time a wide field X- and gamma-ray coded mask imager for GRB real-time localizations to few arcmin, a non-imaging gamma-ray monitor, and two narrow-field instruments for the study of the GRB early afterglow emission in the X-ray and visible bands. The SVOM payload is complemented by ground-based instruments including a wide-field camera to catch the GRB prompt emission in the visible band and two robotic telescopes to measure the photometric properties of the early afterglow. A particular attention is paid to the GRB follow-up in facilitating the observation of the SVOM detected GRB by the largest ground based telescopes.

Monitoring Supergiant Fast X-Ray Transients with Swift . II. Rise to the Outburst in IGR J16479-4514

IGR J16479–4514 is a supergiant fast X-ray transient (SFXT), a new class of high-mass X-ray binaries, whose number is rapidly growing thanks to the INTEGRAL observations of the Galactic plane. It has been regularly monitored with Swift XRT since 2007 November to study the quiescent emission, the outburst properties, and their recurrence. A new bright outburst, reaching fluxes above 10−9 erg cm−2 s−1, was caught by the Swift BAT. Swift immediately repointed at the target with the narrow-field instruments so that, for the first time, an outburst from an SFXT where a periodicity in the outburst recurrence is unknown could be observed simultaneously in the 0.2-150 keV energy band. The X-ray emission is highly variable and spans almost 4 orders of magnitude in count rate during the Swift XRT observations covering a few days before and after the bright peak. The X-ray spectrum in outburst is hard and highly absorbed. The power-law fit resulted in a photon index of 0.98 ± 0.07, and in an absorbing column density of ~5 × 1022 cm−2. These observations demonstrate that in this source (similarly to what was observed during the 2007 outburst from the periodic SFXT IGR J11215–5952), the accretion phase lasts much longer than a few hours.

TheBeppoSAX WFC X-ray source catalogue

Aims. We present the catalogue of X-ray sources detected by the two Wide Field Cameras (WFCs) in complete observations on board BeppoSAX during its 6 years of operational lifetime, between April 1996 and April 2002. Methods. The BeppoSAX WFCs were coded mask instruments sensitive in the 2–28 keV energy band with a 40 × 40 square degree fields of view, pointing in opposite directions and perpendicularly to the BeppoSAX Narrow Field Instruments (NFI). The WFCs were usually operated simultaneously to NFI observations, each lasting up to several days. WFCs observed thus the entire sky several times with a typical sensitivity of 2 to 10 mCrab. A systematic analysis of all WFC observations in the BeppoSAX archive has been carried out using the latest post-mission release of the WFC analysis software and calibrations. Results. The catalogue includes 253 distinct sources, obtained from a total sample of 8283 WFC detections. We describe the basic statistical properties of the sample and present a six-year history of two celestial calibration X-ray sources.

GRB 050410 and GRB 050412: are they really dark gamma-ray bursts?

Aims. We present a detailed analysis of the prompt and afterglow emission of GRB 050410 and GRB 050412 detected by Swift for which no optical counterpart was observed. Methods. We analysed data from the prompt emission detected by the Swift BAT and from the early phase of the afterglow obtained by the Swift narrow field instrument XRT. Results. The $15{-}150$ keV energy distribution of the GRB 050410 prompt emission shows a peak energy at 53$_{-21}^{+40}$ keV. The XRT light curve of this GRB decays as a power law with a slope of $\alpha=$ 1.06 ± 0.04. The spectrum is well reproduced by an absorbed power law with a spectral index $\Gamma_{\rm x}=2.4$ ± 0.4 and a low energy absorption N H = 4$^{+3}_{-2}$ $\times$ 10 21 cm -2 which is higher than the Galactic value. The $15{-}150$ keV prompt emission in GRB 050412 is modelled with a hard ( Γ = 0.7 ± 0.2) power law. The XRT light curve follows a broken power law with the first slope $\alpha_1$ = 0.7 ± 0.4, the break time T break = 254$_{-41}^{+79}$ s and the second slope $\alpha_2$ = 2.8$_{-0.8}^{+0.5}$. The spectrum is fitted by a power law with spectral index $\Gamma_{\rm x}=1.3$ ± 0.2 which is absorbed at low energies by the Galactic column. Conclusions. The GRB 050410 afterglow light curve reveals the expected characteristics of the third component of the canonical Swift light curve. Conversely, a complex phenomenology was detected in the GRB 050412 because of the presence of the very early break. The light curve in this case can be interpreted as being the last peak of the prompt emission. The two bursts present tight upper limits for the optical emission, however, neither of them can be clearly classified as dark. For GRB 050410, the suppression of the optical afterglow could be attributed to a low density interstellar medium surrounding the burst. For GRB 050412, the evaluation of the darkness is more difficult due to the ambiguity in the extrapolation of the X-ray afterglow light curve.

GRB 050713A: High‐Energy Observations of the Gamma‐Ray Burst Prompt and Afterglow Emission

Swift discovered GRB 050713A and slewed promptly to begin observing with its narrow field instruments 72.6 seconds after the burst onset, while the prompt gamma-ray emission was still detectable in the BAT. Simultaneous emission from two flares is detected in the BAT and XRT. This burst marks just the second time that the BAT and XRT have simultaneously detected emission from a burst and the first time that both instruments have produced a well sampled, simultaneous dataset covering multiple X-ray flares. The temporal rise and decay parameters of the flares are consistent with the internal shock mechanism. In addition to the Swift coverage of GRB 050713A, we report on the Konus-Wind (K-W) detection of the prompt emission in the energy range 18-1150 keV, an upper limiting GeV measurement of the prompt emission made by the MAGIC imaging atmospheric Cherenkov telescope and XMM-Newton observations of the afterglow. Simultaneous observation between Swift XRT and XMM-Newton produce consistent results, showing a break in the lightcurve at T+~15ks. Together, these four observatories provide unusually broad spectral coverage of the prompt emission and detailed X-ray follow-up of the afterglow for two weeks after the burst trigger. Simultaneous spectral fits of K-W with BAT and BAT with XRT data indicate that an absorbed broken powerlaw is often a better fit to GRB flares than a simple absorbed powerlaw. These spectral results together with the rapid temporal rise and decay of the flares suggest that flares are produced in internal shocks due to late time central engine activity.

SwiftXRT Observations of the Afterglow of XRF 050416A

Swift discovered XRF 050416A with the BAT and began observing it with its narrow field instruments only 64.5 s after the burst onset. Its very soft spectrum classifies this event as an X-ray flash. The afterglow X-ray emission was monitored up to 74 days after the burst. The X-ray light curve initially decays very fast, subsequently flattens and eventually steepens again, similar to many X-ray afterglows. The first and second phases end about 172 and 1450 s after the burst onset, respectively. We find evidence of spectral evolution from a softer emission with photon index Gamma ~ 3.0 during the initial steep decay, to a harder emission with Gamma ~ 2.0 during the following evolutionary phases. The spectra show intrinsic absorption in the host galaxy. The consistency of the initial photon index with the high energy BAT photon index suggests that the initial phase of the X-ray light curve may be the low-energy tail of the prompt emission. The lack of jet break signatures in the X-ray afterglow light curve is not consistent with empirical relations between the source rest-frame peak energy and the collimation-corrected energy of the burst. The standard uniform jet model can give a possible description of the XRF 050416A X-ray afterglow for an opening angle larger than a few tens of degrees, although numerical simulations show that the late time decay is slightly flatter than expected from on-axis viewing of a uniform jet. A structured Gaussian-type jet model with uniform Lorentz factor distribution and viewing angle outside the Gaussian core is another possibility, although a full agreement with data is not achieved with the numerical models explored.

Strategy of the Suzaku gamma-ray burst observations

Suzaku launched in July 2005 is equipped with the wideband instruments covering 0.3–700 keV. In addition to these main instruments, active shield counters of the hard X-ray detector are designed to be a wideband all-sky monitor (WAM). The WAM is a powerful gamma-ray burst monitor with a wide energy range of 50–5000 keV and with a large effective area of 400 cm 2 even around 1 MeV. The paper describes the strategy for the prompt GRB observation with the WAM, and the follow-up observation of X-ray afterglows with the narrow field instruments. So far, the WAM has detected 53 GRBs and half of them were detected simultaneously with other satellites. In addition to that, from at least 8 GRBs, including a bright and hard GRB 051008, it is succeeded to observe significant gamma-ray emission up to 1 MeV. The X-ray afterglow observations were carried out on January 5 and on September 4, 2006. Their results are reported in separate paper.

Swift observations of GRB 050904: the most distant cosmic explosion ever observed

Swift discovered the high redshift (z=6.29) GRB050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This gamma-ray burst is the most distant cosmic explosion ever observed. Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (0.2-150 keV; 1.4-1090 keV in the source rest frame) at a very early source-frame time (22 s). GRB050904 was a long, multi-peaked, bright GRB with strong variability during its entire evolution. The light curve observed by the XRT is characterized by the presence of a long flaring activity lasting up to 1-2 hours after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs. However, the BAT tail extrapolated to the XRT band joins the XRT early light curve and the overall behavior resembles that of a very long GRB prompt. The spectral energy distribution softens with time, with the photon index decreasing from -1.2 during the BAT observation to -1.9 at the end of the XRT observation. The dips of the late X-ray flares may be consistent with an underlying X-ray emission arising from the forward shock and with the properties of the optical afterglow reported by Tagliaferri et al. (2005b). We interpret the BAT and XRT data as a single continuous observation of the prompt emission from a very long GRB. The peculiarities observed in GRB050904 could be due to its origin within one of the first star-forming regions in the Universe; very low metallicities of the progenitor at these epochs may provide an explanation.

Panchromatic study of GRB 060124: from precursor to afterglow

We present observations of GRB 060124, the first event for which both the prompt and the afterglow emission could be observed simultaneously and in their entirety by the three Swift instruments. Indeed, Swift-BAT triggered on a precursor ~570s before the main burst peak, and this allowed Swift to repoint the narrow field instruments to the burst position ~350s before the main burst occurred. GRB 060124 also triggered Konus-Wind, which observed the prompt emission in a harder gamma-ray band (up to 2MeV). Thanks to these exceptional circumstances, the temporal and spectral properties of the prompt emission can be studied in the optical, X-ray and gamma-ray ranges. While the X-ray emission (0.2-10keV) clearly tracks the gamma-ray burst, the optical component follows a different pattern, likely indicating a different origin, possibly the onset of external shocks. The prompt GRB spectrum shows significant spectral evolution, with both the peak energy and the spectral index varying. As observed in several long GRBs, significant lags are measured between the hard- and low-energy components, showing that this behaviour extends over 3 decades in energy. The GRB peaks are also much broader at soft energies. This is related to the temporal evolution of the spectrum, and can be accounted for by assuming that the electron spectral index softened with time. The burst energy (E_iso~5x10^{53} erg) and average peak energy (E_p~300keV) make GRB 060124 consistent with the Amati relation. The X-ray afterglow is characterized by a decay which presents a break at t_b~10^5s.

The Early X‐Ray Emission from GRBs

We present observations of the early X-ray emission for a sample of 40 gamma-ray bursts (GRBs) obtained using the Swift satellite, for which the narrow-field instruments were pointed at the burst within 10 minutes of the trigger. Using data from the Burst Alert Telescope and the X-Ray Telescope, we show that the X-ray light curve can be well described by an exponential that relaxes into a power law, often with flares superimposed. The transition time between the exponential and the power law provides a physically defined timescale for the burst duration. In most bursts, the power law breaks to a shallower decay within the first hour, and a late emission "hump" is observed, which can last for many hours. In other GRBs the hump is weak or absent. The observed variety in the shape of the early X-ray light curve can be explained as a combination of three components: prompt emission from the central engine, afterglow, and the late hump. In this scenario, afterglow emission begins during or soon after the burst, and the observed shape of the X-ray light curve depends on the relative strengths of the emission due to the central engine and that of the afterglow. There is a strong correlation such that those GRBs with stronger afterglow components have brighter early optical emission. The late emission hump can have a total fluence equivalent to that of the prompt phase. GRBs with the strongest late humps have weak or no X-ray flares.

SwiftObservations of GRB 050603: An Afterglow with a Steep Late‐Time Decay Slope

We report the results of Swift observations of the Gamma Ray Burst GRB 050603. With a V magnitude V=18.2 about 10 hours after the burst the optical afterglow was the brightest so far detected by Swift and one of the brightest optical afterglows ever seen. The Burst Alert Telescope (BAT) light curves show three fast-rise-exponential-decay spikes with $T_{90}$=12s and a fluence of 7.6$\times 10^{-6}$ ergs cm$^{-2}$ in the 15-150 keV band. With an $E_{\rm \gamma, iso} = 1.26 \times 10^{54}$ ergs it was also one of the most energetic bursts of all times. The Swift spacecraft began observing of the afterglow with the narrow-field instruments about 10 hours after the detection of the burst. The burst was bright enough to be detected by the Swift UV/Optical telescope (UVOT) for almost 3 days and by the X-ray Telescope (XRT) for a week after the burst. The X-ray light curve shows a rapidly fading afterglow with a decay index $\alpha$=1.76$^{+0.15}_{-0.07}$. The X-ray energy spectral index was $\beta_{\rm X}$=0.71\plm0.10 with the column density in agreement with the Galactic value. The spectral analysis does not show an obvious change in the X-ray spectral slope over time. The optical UVOT light curve decays with a slope of $\alpha$=1.8\plm0.2. The steepness and the similarity of the optical and X-ray decay rates suggest that the afterglow was observed after the jet break. We estimate a jet opening angle of about 1-2$^{\circ}$

SwiftXRT Observations of the Afterglow of GRB 050319

Swift discovered the high-redshift GRB 050319 with the Burst Alert Telescope (BAT) and began observing with its narrow-field instruments only 225 s after the burst onset. The afterglow X-ray emission was monitored by the XRT up to 28 days after the burst. The light curve shows a decay with three different phases, each characterized by a distinct slope: an initial steep decay with a power-law index of ~5.5, a second phase characterized by a flat decay slope of ~0.54, and a third phase with a decay slope of ~1.14. During the first phase the spectral energy distribution is softer than in the following two phases, and the photon index is consistent with the GRB prompt spectrum. The extrapolation of the BAT light curve to the XRT band suggests that the initial fast-decaying phase of the XRT afterglow might be the low-energy tail of the prompt emission. The second break in the afterglow light curve occurs about 27,000 s after the burst. The spectral energy distribution before and after the second break does not change, and it can be tentatively interpreted as a jet break or the end of a delayed or continuous energy injection phase.

The puzzling case of GRB 990123: prompt emission and broad-band afterglow modeling

We report on BeppoSAX simultaneous X- andγ-ray observations of the bright γ-ray burst (GRB) 990123. We present the broad-band spectrum of the prompt emission, including optical, X- andγ-rays, confirming the suggestion that the emission mechanisms at low and high frequencies must have different physical origins. In the framework of the standard fire ball model, we discuss the X-ray afterglow observed by the Narrow Field Instruments (NFIs) on board BeppoSAX and its hard X- ray emission up to 60 keV several hours after the burst, detected for about 20 ks by the Phoswich Detection System (PDS). Considering the 2− 10 keV and optical light curves, the 0.1− 60 keV spectrum during the 20 ks in which the PDS signal was present and the 8.46 GHz upper limits, we find that the multi-wavelength observ ations cannot be readily accommodated by basic afterglow models. While the temporal and spectral behavior of the optical afterglow is possibly explained by a synchrotron cooling frequency between the optical and the X-ray energy band during the NFIs observations, in X-rays this assumption only accounts for the slope of the 2− 10 keV light curve, but not for the flatness of the 0.1− 60 keV spectrum. Including the contribution of Inverse Compton (IC) scattering, we solve the problem of the flat X-ray spectrum and justify the hard X-ra y emission; we also suggest that the lack of a significant detec tion of 15− 60 keV emission in the following 75 ks and last 70 ks spectra, should be related to poorer statistics rather than to an important suppression of IC contribution. However, considering also the radio band data, we find the 8.46 GHz upper limits violated. On the other hand, leaving unchanged the emission mechanism requires modifying the hydrodynamics by invoking an ambient medium whose density rises rapidly with radius and by having the shock losing energy. Thus we are left with an open puzzle which requires further inspection.

Swift Observations of GRB 050128: The Early X-Ray Afterglow

Swift discovered GRB050128 with the Burst Alert Telescope and promptly pointed its narrow field instruments to monitor the afterglow. X-ray observations started 108 s after the trigger time. The early decay of the afterglow is relatively flat with a temporal decay modeled with a power law with index ~ -0.3. A steepening occurs at later times (~ 1500 s) with a power law index of ~ -1.3. During this transition, the observed X-ray spectrum does not change. We interpret this behaviour as either an early jet break or evidence for a transition from the fast cooling regime to the slow cooling regime in a wind environment.

Prompt and afterglow X-ray emission from the X-Ray Flash of 2002 April 27

We report on the X-ray observations of the X-ray flash (XRF) which occurred on 2002 April 27, three days before BeppoSAX was switched off. The event was detected with the BeppoSAX Wide Field Cameras but not with the Gamma ray Burst Monitor. A follow-up observation with the BeppoSAX Narrow Field Instruments was soon performed and a candidate afterglow source was discovered. We present the results obtained. We also include the results obtained from the observations of the XRF field with the Chandra X-ray satellite. The spectral analysis of the prompt emission shows that the peak energy of the EF(E) spectrum is lower than 5.5 keV, with negligible spectral evolution. The X-ray afterglow spectrum is consistent with a power law model with photon index of about 2, while the 2-10 keV flux fades as a power law with a decay index -1.33. Both these indices are typical of GRBs. A very marginal excess around 4.5-5 keV is found in the afterglow spectrum measured by BeppoSAX . As for many GRBs, the extrapolation of the 2-10 keV fading law back to the time of the prompt emission is consistent with the X-ray flux measured during the second part of the event. We estimate a possible range of values of the redshift and discuss our results in the light of current models of XRFs.

A Decreasing Column Density during the Prompt Emission from GRB 000528 Observed withBeppoSAX

We report observation results of the prompt X- and gamma-ray emission from GRB 000528. This event was detected with the Gamma-Ray Burst Monitor and one of the two Wide Field Cameras aboard the BeppoSAX satellite. The gamma-ray burst (GRB) was promptly followed on with the BeppoSAX narrow field instruments and with ground optical and radio telescopes. The X-ray afterglow source was identified, but no optical or radio counterpart found. We report here results from the prompt and afterglow emission analysis. The main feature derived from spectral evolution of the prompt emission is a high hydrogen equivalent column density with evidence of its decrease with time. We model this behavior in terms of a time-dependent photoionization of the local circumburst medium, finding that a compact and dense environment is required by the data. We also find a fading of the late part of the 2‐10 keV prompt emission, which is consistent with afterglow emission. We discuss this result in the light of the external shock model scenario. Subject headingg gamma rays: bursts — gamma rays: observations — X-rays: bursts

On the constraining observations of the dark GRB 001109 and the properties of az= 0.398 radio selected starburst galaxy contained in its error box

We present optical and NIR (near infrared) follow up observations of the GRB 001109 from 1 to 300 days after the burst. No transient emission was found at these wavelengths within this GRB's (Gamma Ray Burst) 50" radius BeppoSAX error box. Strong limits (3 sigma) are set with: R >~ 21, 10.2 hr after the GRB; I >~ 23, 11.4 hr after the GRB; H >~ 20.7, 9.9 hr after the GRB; and Ks >~ 20, 9.6 hours after the GRB. We discuss whether the radio source found in the GRB's error box (Taylor et al. 2000) might be related to the afterglow. We also present a multiwavelength study of a reddened starburst galaxy, found coincident with the potential radio and the X ray afterglow. We show that our strong I band upper limit makes of the GRB 001109 the darkest one localised by the BeppoSAX's NFI (Narrow Field Instrument), and it is one of the most constraining upper limits on GRB afterglows to date. Further to it, the implications of these observations in the context of dark GRBs are considered.