arXiv subjects

J. S. Bloom

Publications and source records attributed to J. S. Bloom.

At least 127 records · Page 7Linked to original sources

arXiv2004

Direct Detection of Dark Matter with Space-based Laser Interferometers

Dark matter pervades the Solar System, free-streaming at the halo's local Galactic orbital velocity and density. As these objects pass through the Solar system, they perturb gravitationally, and thus very weakly, all nearby inertial masses. Making use of this, we propose an approach to the direct detection of dark matter at previously inaccessible intermediate masses (1e14 -- 1e20 gm). Such mass scales are relevant for example for dark matter made of primordial black holes or clumped matter in a sequestered sector. If such dark matter exists it will be unambiguously detectable through its inelastic gravitational interaction with the proposed Laser Interferometer Space Antenna (LISA) experiment. We demonstrate the efficacy of this approach by studying the dark matter signal in numerical simulations of the LISA data stream. A more conservative approach -- to detect dark matter in the differential acceleration power spectrum -- significantly underestimates the expected rates for LISA. Interestingly, while the space-density of 1e15 gm DM objects would be comparable to the space-density of asteroids of similar masses, such ``light matter'' contaminants are readily detectable in reflected Solar light, allowing for the elimination of the major background.

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arXiv2004

Optical Bumps in Cosmological GRBs as Supernovae

From both photometric and broadband spectral monitoring of gamma-ray burst (GRB) lightcurve ``bumps,'' particularly in GRB 011121, a strong case grew for a supernova (SN) origin. The GRB-SN connection was finally solidified beyond a reasonable doubt with the discovery that the bump in GRB 030329 was spectroscopically similar to a bright Type Ic SN. In light of this result, I redress the previous SN bump claims and conclude that 1) the distribution of GRB-SN bump peak magnitudes is consistent with the local Type Ibc SNe peak distribution and suggest that 2) the late-time bumps in all long-duration GRBs are likely supernovae.

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arXiv2004

Discovery of a supernova associated with GRB 031203: SMARTS Optical-Infrared Lightcurves from 0.2 to 92 days

Optical and infrared monitoring of the afterglow site of gamma-ray burst (GRB) 031203 has revealed a brightening source embedded in the host galaxy, which we attribute to the presence of a supernova (SN) related to the GRB ("SN 031203"). We present details of the discovery and evolution of SN 031203 from 0.2 to 92 days after the GRB, derived from SMARTS consortium photometry in I and J bands. A template type Ic lightcurve, constructed from SN 1998bw photometry, is consistent with the peak brightness of SN 031203 although the lightcurves are not identical. Differential astrometry reveals that the SN, and hence the GRB, occurred less than 300 h_71^-1 pc (3-sigma) from the apparent galaxy center. The peak of the supernova is brighter than the optical afterglow suggesting that this source is intermediate between a strong GRB and a supernova.

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arXiv2004

Is the Redshift Clustering of Long-Duration Gamma-Ray Bursts Significant?

The 26 long-duration gamma-ray bursts (GRBs) with known redshifts form a distinct cosmological set, selected differently than other cosmological probes such as quasars and galaxies. Since the progenitors are now believed to be connected with active star-formation and since burst emission penetrates dust, one hope is that with a uniformly-selected sample, the large-scale redshift distribution of GRBs can help constrain the star-formation history of the Universe. However, we show that strong observational biases in ground-based redshift discovery hamper a clean determination of the large-scale GRB rate and hence the connection of GRBs to the star formation history. We then focus on the properties of the small-scale (clustering) distribution of GRB redshifts. When corrected for heliocentric motion relative to the local Hubble flow, the observed redshifts appear to show a propensity for clustering: 8 of 26 GRBs occurred within a recession velocity difference of 1000 km/s of another GRB. That is, 4 pairs of GRBs occurred within 30 h_65^-1 Myr in cosmic time, despite being causally separated on the sky. We investigate the significance of this clustering. Comparison of the numbers of close redshift pairs expected from the simulation with that observed shows no significant small-scale clustering excess in the present sample; however, the four close pairs occur only in about twenty percent of the simulated datasets (the precise significance of the clustering is dependent upon the modeled biases). We conclude with some impetuses and suggestions for future precise GRB redshift measurements.

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arXiv2004

Optical-Infrared ANDICAM Observations of the Transient Associated with GRB 030329

We present photometry of the transient associated with GRB 030329 obtained with the CTIO 1.3--meter telescope and the ANDICAM instrument, a dual optical/infrared imager with a dichroic centered at one micron. Without the need for light curve interpolation to produce snapshot broadband spectra, we show that the transient spectrum remained statistically achromatic from day 2.7 to day 5.6, during a re-brightening episode. Associating the light in these early epochs with the GRB afterglow, we infer a modest level of extinction due to the host galaxy in the line--of--sight toward the GRB: A_V(host) = 0.30 +/- 0.03 mag for beta = -0.5 and A_V(host) < 0.4 mag (3 sigma) for any physically plausible value of beta (with flux f_nu ~ lambda^-beta). We conclude that the spectral slope of the afterglow component was more than beta = -0.8 between day 2.7-5.6 after the GRB, excluding the possibility that the synchrotron cooling break passed through the optical/IR bandpass over that period. Taking extinction into account, a decomposition of the light curve into an afterglow and supernova component requires the presence of a supernova similar to that of SN 1998bw, an afterglow that shows some evidence for a second break around day 8-10, and a fifth re-brightening event around day 15. Assuming an SN 1988bw-like evolution and a contemporaneous GRB and SN event, the peak SN brightness was M_V = -19.8 +/- 0.4 - 5 log h_65 mag.

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arXiv2004

The detailed optical light curve of GRB 030329

(Abridged) We present densely sampled BVRI light curves of the optical transient associated with the gamma-ray burst GRB 030329, the result of a coordinated observing campaign conducted at five observatories. Augmented with published observations of this GRB, the compiled optical dataset contains 2687 photometric measurements, obtained between 78 minutes and 79 days after the burst. We show that the underlying supernova 2003dh evolved faster than, and was probably somewhat fainter than the type Ic SN 1998bw, associated with GRB 980425. We find that our data can be described by a broken power-law decay perturbed by a complex variable component. The early- and late-time decay slopes are determined to be ~1.1 and ~2, respectively. Assuming this single power-law model, we constrain the break to lie between ~3 and ~8 days after the burst. This simple, singly-broken power-law model, derived only from the analysis of our optical observations, may also account for available multi-band data, provided that the break happened ~8 days after the burst. The more complex double-jet model of Berger et al. provides a comparable fit to the optical, X-ray, mm and radio observations of this event. We detect a significant change in optical colors during the first day. Our color analysis is consistent with a cooling break frequency sweeping through the optical band during the first day. The light curves of GRB 030329 reveal a rich array of variations, superposed over the mean power-law decay. We find that the early variations are asymmetric, with a steep rise followed by a relatively slower (by a factor of about two) decline. The variations maintain a similar time scale during the first four days, and then get significantly longer.

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arXiv2004

Results of a search for new microquasars in the Galaxy

We present here the results of a search for new microquasars at low galactic latitudes, based on a cross-identification between the ROSAT all sky Bright Source Catalog (RBSC) and the NRAO VLA Sky Survey (NVSS) and follow-up observations. The results obtained up to now suggest that persistent/silent microquasars such as LS 5039 are rare objects in our Galaxy, and indicate that future deeper surveys, and harder than the RBSC in X-rays, will play a fundamental role in order to discover them.

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arXiv2004

Optical Limits on Precursor Emission from Gamma-Ray Bursts with Known Redshift

Making use of virtual observatory data, we present the first comprehensive sample of optical observations conducted before the explosion times of all gamma-ray bursts (GRBs) with known redshifts. In total, the fields of 11 such GRBs were observed by the Near-Earth Asteroid Tracking (NEAT) program from years to hours before the bursts. Though the typical limiting magnitudes from these observations are R~20 mag, we find no evidence for a significant detection of a precursor. The deepest non-detection of precursor emission is from GRB 030329, reaching down to an absolute B-band magnitude of M_B -18 mag from 6--1500 days (restframe) before the burst. This is of comparable brightness to supernovae, which, in some scenarios for GRB progenitors, are predicted to pre-date a GRB on similar timescales. Since sources cannot be localized to better than ~500 milliarcsecond (3 sigma) with current large-area surveys, unrelated supernovae or AGN activity in GRB hosts could be mistaken for genuine precursor emission. This possibility motivates the need for not only deep wide-field imaging, but imaging at high spatial resolution.

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arXiv2004

Optical spectroscopy of microquasar candidates at low galactic latitudes

We report optical spectroscopic observations of a sample of 6 low-galactic latitude microquasar candidates selected by cross-identification of X-ray and radio point source catalogs for |b|<5 degrees. Two objects resulted to be of clear extragalactic origin, as an obvious cosmologic redshift has been measured from their emission lines. For the rest, none exhibits a clear stellar-like spectrum as would be expected for genuine Galactic microquasars. Their featureless spectra are consistent with being extragalactic in origin although two of them could be also highly reddened stars. The apparent non-confirmation of our candidates suggests that the population of persistent microquasar systems in the Galaxy is more rare than previously believed. If none of them is galactic, the upper limit to the space density of new Cygnus X-3-like microquasars within 15 kpc would be 1.1\times10^{-12} per cubic pc. A similar upper limit for new LS 5039-like systems within 4 kpc is estimated to be 5.6\times10^{-11} per cubic pc.

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arXiv2003

The First Two Host Galaxies of X-ray Flashes: XRF 011030 and XRF 020427

Given the paucity of empirical constraints, the nature of the newly-recognized phenomena called X-Ray Flashes (XRFs) has been an open question. However, with the recent detections of radio and X-ray afterglow it is finally possible to study the large- and small-scale environments of XRFs. We present Chandra, Hubble Space Telescope (HST), and Keck observations of the fields of XRFs 011030 and 020427. Astrometric comparisons of the X-ray transient positions and the HST images reveal the XRFs to be associated with faint blue galaxies. Photometric evidence of these putative hosts suggests that these two XRFs originated from redshifts less than z ~ 3.5, and thus cannot be due to GRBs at very high redshifts. In both host-burst offsets and host properties, these XRFs could have been drawn from distributions similar to those measured of gamma-ray bursts (GRBs). We conclude with a discussion of the implications of this XRF-GRB host connection for the possible progenitors of XRFs.

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arXiv2003

GRB Energetics and the GRB Hubble Diagram: Promises and Limitations

We present a complete sample of 29 GRBs for which it has been possible to determine temporal breaks (or limits) from their afterglow light curves. We interpret these breaks within the framework of the uniform conical jet model, incorporating realistic estimates of the ambient density and propagating error estimates on the measured quantities. In agreement with our previous analysis of a smaller sample, the derived jet opening angles of those 16 bursts with redshifts result in a narrow clustering of geometrically-corrected gamma-ray energies about E_gamma = 1.33e51 erg; the burst-to-burst variance about this value is a factor of 2.2. Despite this rather small scatter, we demonstrate in a series of GRB Hubble diagrams, that the current sample cannot place meaningful constraints upon the fundamental parameters of the Universe. Indeed for GRBs to ever be useful in cosmographic measurements we argue the necessity of two directions. First, GRB Hubble diagrams should be based upon fundamental physical quantities such as energy, rather than empirically-derived and physically ill-understood distance indicators. Second, a more homogeneous set should be constructed by culling sub-classes from the larger sample. These sub-classes, though now first recognizable by deviant energies, ultimately must be identifiable by properties other than those directly related to energy. We identify a new sub-class of GRBs (``f-GRBs'') which appear both underluminous by factors of at least 10 and exhibit a rapid fading at early times. About 10-20% of observed long-duration bursts appear to be f-GRBs.

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arXiv2003

The case for late-time optical bumps in GRB afterglows as a supernova signature

Observations of late-time optical bumps have been reported for several GRBs. The timescale for such bumps, and colors of such when available, find a natural explanation as due to associated supernovae. Ground-based and HST observations of the afterglow and bump of GRB 011121, in particular, place the strongest constraints yet on the physical nature of the supernova and any alternative explanations, such as supranovae or dust echoes. I summarize the search for underlying bumps in other GRBs and make the case for the supernova hypothesis in light of observed bumps and bump non-detections (e.g., GRB 010921).

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arXiv2003

Discovery of GRB 020405 and its Late Red Bump

We present the discovery of GRB 020405 made with the Inter-Planetary Network (IPN). With a duration of 60 s, the burst appears to be a typical long duration event. We observed the 75-square acrminute IPN error region with the Mount Stromlo Observatory's 50-inch robotic telescope and discovered a transient source which subsequently decayed and was also associated with a variable radio source. We identify this source as the afterglow of GRB 020405. Subsequent observations by other groups found varying polarized flux and established a redshift of 0.690 to the host galaxy. Motivated by the low redshift we triggered observations with WFPC2 on-board the Hubble Space Telescope (HST). Modeling the early ground-based data with a jet model, we find a clear red excess over the decaying optical lightcurves that is present between day 10 and day 141 (the last HST epoch). This `bump' has the spectral and temporal features expected of an underlying supernova (SN). In particular, the red color of the putative SN is similar to that of the SN associated with GRB 011121, at late time. Restricting the sample of GRBs to those with z<0.7, a total of five bursts, red bumps at late times are found in GRB 970228, GRB 011121, and GRB 020405. It is possible that the simplest idea, namely that all long duration GRBs have underlying SNe with a modest dispersion in their properties (especially peak luminosity), is sufficient to explain the non detections.

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arXiv2003

Cosmological Uses of Gamma-Ray Bursts

Studies of the cosmic gamma-ray bursts (GRBs) and their host galaxies are starting to provide interesting or even unique new insights in observational cosmology. GRBs represent a new way of identifying a population of star-forming galaxies at cosmological redshifts. GRB hosts are broadly similar to the normal field galaxy populations at comparable redshifts and magnitudes, and indicate at most a mild luminosity evolution out to z ~ 1.5 - 2. GRB optical afterglows seen in absorption provide a powerful new probe of the ISM in dense, central regions of their host galaxies, complementary to the traditional studies using QSO absorbers. Some GRB hosts are heavily obscured, and provide a new way to select a population of cosmological sub-mm sources, and a novel constraint on the total obscured fraction of star formation over the history of the universe. Finally, detection of GRB afterglows at z > 6 may provide a unique way to probe the primordial star formation, massive IMF, early IGM, and chemical enrichment at the end of the cosmic reionization era.

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arXiv2003

The Broadband Afterglow of GRB980703

We present radio observations of the afterglow of the bright gamma-ray burst GRB980703 made between one day and one year after the burst. These data are combined with published late-time radio measurements and existing optical, near-infrared (NIR) and X-ray observations to create a comprehensive broadband dataset for modeling the physical parameters of the outflow. While a wind-stratified medium cannot be ruled out statistically, it requires a high fraction of the shock energy in the electrons, and so is not favored on theoretical grounds. Instead, the data are consistent with a fireball model in which the ejecta are collimated and expanding into a constant density medium. The radio data cannot be fit with an isotropic shock but instead require a jet break at ~ 3.5 days, not seen at optical wavelengths due to the presence of a a bright host galaxy. The addition of the full radio dataset constrains the self-absorption frequency, giving an estimate of the circumburst density of n ~ 30 cm^-3, a value which differs substantially from previous estimates. This result is consistent with the growing number of GRB afterglows for which broadband modeling yields n ~= 0.1-100 cm^-3, with a typical value ~ 10 cm^-3.

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arXiv2003

The Cosmic Gamma-Ray Bursts and Their Host Galaxies in a Cosmological Context

Studies of the cosmic gamma-ray bursts (GRBs) and their host galaxies are now starting to provide interesting or even unique new insights in observational cosmology. Observed GRB host galaxies have a median magnitude R ~ 25 mag, and show a range of luminosities, morphologies, and star formation rates, with a median redshift z ~ 1. They represent a new way of identifying a population of star-forming galaxies at cosmological redshifts, which is mostly independent of the traditional selection methods. They seem to be broadly similar to the normal field galaxy populations at comparable redshifts and magnitudes, and indicate at most a mild luminosity evolution over the redshift range they probe. Studies of GRB optical afterglows seen in absorption provide a powerful new probe of the ISM in dense, central regions of their host galaxies, which is complementary to the traditional studies using QSO absorption line systems. Some GRB hosts are heavily obscured, and provide a new way to select a population of cosmological sub-mm sources. A census of detected optical tranistents may provide an important new way to constrain the total obscured fraction of star formation over the history of the universe. Finally, detection of GRB afterglows at high redshifts (z > 6) may provide a unique way to probe the primordial star formation, massive IMF, early IGM, and chemical enrichment at the end of the cosmic reionization era.

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arXiv2003

Hubble Space Telescope and Ground-Based Optical and Ultraviolet Observations of GRB010222

We report on Hubble Space Telescope WFPC2 optical and STIS near ultraviolet MAMA observations, and ground-based optical observations of GRB010222, spanning 15 hrs to 71 days. The observations are well-described by a relativistic blast-wave model with a hard electron-energy distribution, p = 1.57, and a jet transition at t_j=0.93 days. These values are slightly larger than previously found as a result of a correction for the contribution from the host galaxy to the late-time ground-based observations and the larger temporal baseline provided by the Hubble Space Telescope observations. The host galaxy is found to contain a very compact core (size <0.25 arcsec) which coincides with the position of the optical transient. The STIS near ultraviolet MAMA observations allow for an investigation of the extinction properties along the line of sight to GRB010222. We find that the far ultraviolet curvature component (c_4) is rather large. In combination with the low optical extinction A_V =0.11 mag, when compared to the Hydrogen column inferred from X-ray observations, we suggest that this is evidence for dust destruction.

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arXiv2002

Optical Spectropolarimetry of the GRB 020813 Afterglow

The optical afterglow of gamma-ray burst 020813 was observed for 3 hours with the LRIS spectropolarimeter at the Keck-I telescope, beginning 4.7 hours after the burst was detected by HETE-2. The spectrum reveals numerous metal absorption lines that we identify with two systems at z=1.223 and z=1.255. We also detect an O II 3727 emission line at z=1.255 and we identify this galaxy as the likely host of the GRB. After a correction for Galactic interstellar polarization, the optical afterglow has a linear polarization of 1.8-2.4% during 4.7-7.9 hours after the burst. A measurement of p = 0.80% +/- 0.16% on the following night by Covino et al. demonstrates significant polarization variability over the next 14 hours. The lack of strong variability in the position angle of linear polarization indicates that the magnetic field in the jet is likely to be globally ordered rather than composed of a number of randomly oriented cells. Within the framework of afterglow models with collimated flows, the relatively low observed polarization suggests that the magnetic field components perpendicular and parallel to the shock front are only different by about 20%.

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