We employ realistic constraints on astrophysical and instrumental selection effects to model the gamma-ray burst (GRB) redshift distribution using Swift triggered redshift samples acquired from ...optical afterglows and The Optically Unbiased GRB Host survey. Models for the Malmquist bias, redshift desert, and the fraction of afterglows missing because of host galaxy dust extinction are used to show how the 'true' GRB redshift distribution is distorted to its presently observed biased distribution. We also investigate another selection effect arising from a correlation between E
iso and L
opt. The analysis, which accounts for the missing fraction of redshifts in the two data subsets, shows that a combination of selection effects (both instrumental and astrophysical) can describe the observed GRB redshift distribution. Furthermore, the observed distribution is compatible with a GRB rate evolution that tracks the global star formation rate, although the rate at high z cannot be constrained with confidence. Taking optical selection effects into account, it may not be necessary to invoke high-energy GRB luminosity evolution with redshift to explain the observed GRB rate at high z.
ABSTRACT
Short gamma‐ray bursts (SGRBs) observed by Swift potentially reveal the first insight into cataclysmic compact object mergers. To ultimately acquire a fundamental understanding of these ...events requires pan‐spectral observations and knowledge of their spatial distribution to differentiate between proposed progenitor populations. Up to 2012 April, there are only some 30 per cent of SGRBs with reasonably firm redshifts, and this sample is highly biased by the limited sensitivity of Swift to detect SGRBs. We account for the dominant biases to calculate a realistic SGRB rate density out to z ≈ 0.5 using the Swift sample of peak fluxes, redshifts and those SGRBs with a beaming angle constraint from X‐ray/optical observations. We find an SGRB lower rate density of 8−3+5 Gpc −3 yr −1 (assuming isotropic emission) and a beaming corrected upper limit of 1100−470+700 Gpc −3 yr −1. Assuming a significant fraction of binary neutron star mergers produce SGRBs, we calculate lower and upper detection rate limits of (1–180) yr−1 by an Advanced LIGO (aLIGO) and Virgo coincidence search. Our detection rate is similar to the lower and realistic rates inferred from extrapolations using Galactic pulsar observations and population synthesis.
In this article we further constrain the phenomenology and progenitor properties of this peculiar GRB by performing a multiband temporal and spectral analysis of both the prompt and the afterglow ...emission. We use proprietary and publicly available data from Swift, Konus WIND, XMM-Newton, and TAROT, as well as from other ground-based optical and radio telescopes. We find some peculiar properties that are possibly connected to the exceptional nature of this burst, namely: (1) an unprecedented large optical delay of 410 + or - 50 s between the peak time in gamma-rays and the peak time in the optical of a marked multiwavelength flare; (2) multiwavelength prompt emission spectral modeling requires a certain amount of dust in the circumburst environment. (3) we detect the presence of a hard spectral extra power-law component at the end of the X-ray steep steep decay phase and before the start of the X-ray afterglow, which has never been revealed thus far in past GRBs.
We present optical, X-ray and gamma-ray observations of GRB 111209A, at a redshift of z = 0.677. We show that this event was active in its prompt phase for about 25000 seconds, making it the longest ...burst ever observed. This rare event could have been detected up to z ~ 1.4. Compared to other long GRBs, GRB 111209A is a clear outlier in the energy-fluence and duration plane. The high-energy prompt emission shows no sign of a strong black body component, as expected if the event was caused by a tidal disruption event or a supernova shock breakout. Given the extreme longevity of this event, and a lack of a supernova signature, we propose that GRB 111209A is a relatively rare stellar collapse of a low metallicity blue super giant star. Only this progenitor can supply mass to the central engine over a duration of thousands of seconds. Hence, GRB 111209A could have more in common with population III stellar explosions, rather than normal long gamma ray bursts.
Assuming neutron star (NS) or NS/stellar-mass black hole (BH) mergers as progenitors of the short gamma-ray bursts, we derive and demonstrate a simple analysis tool for modelling the efficiency of ...recovering on-axis optical afterglows triggered by a candidate gravitational wave event detected by the Advanced LIGO and Virgo network. The coincident detection efficiency has been evaluated for different classes of operating telescopes using observations of gamma-ray bursts. We show how the efficiency depends on the luminosity distribution of the optical afterglows, the telescope features, and the sky localization of gravitational wave triggers. We estimate a plausible optical afterglow and gravitational wave coincidence rate of 1 yr−1 (0.1 yr−1) for NS–NS (NS–BH), and how this rate is scaled down in detection efficiency by the time it takes to image the gravitational wave sky localization and the limiting magnitude of the telescopes. For NS–NS (NS–BH), we find maximum detection efficiencies of >80 per cent when the total imaging time is less than 200 min (80 min) and the limiting magnitude fainter than 20 (21). We show that relatively small telescopes (m < 18) can achieve similar detection efficiencies to metre class facilities (m < 20) with similar fields of view, only if the less sensitive instruments can respond to the trigger and image the field within 10–15 min. The inclusion of LIGO India into the gravitational wave observatory network will significantly reduce imaging time for telescopes with limiting magnitudes ∼20 but with modest fields of view. An optimal coincidence search requires a global network of sensitive and fast response wide-field instruments that could effectively image relatively large gravitational-wave sky localizations and produce transient candidates for further photometric and spectroscopic follow-up.
We show that the redshift and peak flux distributions of gamma-ray bursts (GRBs) have an observation time dependence that can be used to discriminate between different burst populations. We ...demonstrate how observation time relations can be derived from the standard integral distributions and that they can differentiate between GRB populations detected by both the Burst and Transient Source Experiment (BATSE) and Swift satellites. Using Swift data, we show that a redshift-observation time relation (log Z-log T) is consistent with both a peak flux-observation time relation (log P-log T) and a standard log N-log P brightness distribution. As the method depends only on rarer small-z events, it is invariant to high-z selection effects. We use the log Z-log T relation to show that subluminous GRBs are a distinct population occurring at a higher rate of the order of 150+ 180
− 90 Gpc− 3 yr− 1. Our analysis suggests that GRB 060505 - a relatively nearby GRB observed without any associated supernova - is consistent with a subluminous population of bursts. Finally, we show that our relations can be used as a consistency test for some of the proposed GRB spectral energy correlations.
Caveolin-1 has a complex role in prostate cancer and has been suggested to be a potential biomarker and therapeutic target. As mature caveolin-1 resides in caveolae, invaginated lipid raft domains at ...the plasma membrane, caveolae have been suggested as a tumor-promoting signaling platform in prostate cancer. However, caveola formation requires both caveolin-1 and cavin-1 (also known as PTRF; polymerase I and transcript release factor). Here, we examined the expression of cavin-1 in prostate epithelia and stroma using tissue microarray including normal, non-malignant and malignant prostate tissues. We found that caveolin-1 was induced without the presence of cavin-1 in advanced prostate carcinoma, an expression pattern mirrored in the PC-3 cell line. In contrast, normal prostate epithelia expressed neither caveolin-1 nor cavin-1, while prostate stroma highly expressed both caveolin-1 and cavin-1. Utilizing PC-3 cells as a suitable model for caveolin-1-positive advanced prostate cancer, we found that cavin-1 expression in PC-3 cells inhibits anchorage-independent growth, and reduces in vivo tumor growth and metastasis in an orthotopic prostate cancer xenograft mouse model. The expression of α-smooth muscle actin in stroma along with interleukin-6 (IL-6) in cancer cells was also decreased in tumors of mice bearing PC-3-cavin-1 tumor cells. To determine whether cavin-1 acts by neutralizing caveolin-1, we expressed cavin-1 in caveolin-1-negative prostate cancer LNCaP and 22Rv1 cells. Caveolin-1 but not cavin-1 expression increased anchorage-independent growth in LNCaP and 22Rv1 cells. Cavin-1 co-expression reversed caveolin-1 effects in caveolin-1-positive LNCaP cells. Taken together, these results suggest that caveolin-1 in advanced prostate cancer is present outside of caveolae, because of the lack of cavin-1 expression. Cavin-1 expression attenuates the effects of non-caveolar caveolin-1 microdomains partly via reduced IL-6 microenvironmental function. With circulating caveolin-1 as a potential biomarker for advanced prostate cancer, identification of the molecular pathways affected by cavin-1 could provide novel therapeutic targets.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Intense flares that occur at late times relative to the prompt phase have been observed by the Swift satellite in the X-ray afterglows of gamma-ray bursts (GRBs). Here, we present a detailed analysis ...on the fall back accretion process to explain the intense flare phase in the very early X-ray afterglow light curves. To reproduce the afterglow at late times, we resort to the external shock by engaging energy injections. By applying our model to GRBs 080810, 081028 and 091029, we show that their X-ray afterglow light curves can be reproduced well. We then apply our model to the ultralong Swift GRB 111209A, which is the longest burst ever observed. The very early X-ray afterglow of GRB 111209A showed many interesting features, such as a significant bump observed at around 2000 s after the Swift/BAT trigger. We assume two constant energy injection processes in our model. These can explain the observed plateau at X-ray wavelength in the relatively early stage (8.0 x 10 super( 3) s) and a second X-ray plateau and optical rebrightening at about 10 super( 5) s. Our analysis supports the scenario that a significant amount of material may fall back towards the central engine after the prompt phase, causing an enhanced and long-lived mass accretion rate powering a Poynting-flux-dominated outflow.
We compute the intrinsic isotropic peak luminosity function (LF) and formation rate of long gamma-ray bursts (LGRBs) using a novel approach. We complement a standard log N-log P brightness ...distribution and V
max estimations with two observation–time relations: a redshift–observation-time relation (log z-log T) and a new luminosity–observation-time relation (log L-log T). We show that this approach reduces degeneracies that exist between the rate and LF of a brightness distribution. To account for the complex triggering algorithm employed by Swift, we use recent results of Lien et al. (2014) to produce a suite of efficiency functions. Using these functions with the above methods, we show that a log L-log T method can provide good constraints on the form of the LF, particularly the high end. Using a sample of 175 peak luminosities determined from redshifts with well-defined selection criteria, our results suggest that LGRBs occur at a local rate (without beaming corrections) of 0.7 < ρ0 < 0.8 Gpc−3 yr−1. Within this range, assuming a broken power-law LF, we find best estimates for the low- and high-energy indices of −0.95 ± 0.09 and −2.59 ± 0.93, respectively, separated by a break luminosity 0.80 ± 0.43 × 1052 erg s−1.
Abstract
We present coordinated observations of GRB 170202A carried out by the Zadko and the Virgin Island Robotic Telescopes. The observations started 59 s after the event trigger, and provided ...nearly continuous coverage for two days, due to the unique locations of these telescopes. We clearly detected an early rise in optical emission, followed by late optical flares. By complementing these data with archival observations, we show that GRB 170202A is well described by the standard fireball model if multiple reverse shocks are taken into account. Its fireball is evidenced as expanding within a constant-density interstellar medium, with most burst parameters being consistent with the usual ranges found in the literature. The electron and magnetic energy parameters (
ϵ
e
,
ϵ
B
) are orders of magnitude smaller than the commonly assumed values. We argue that the global fit of the fireball model achieved by our study should be possible for any burst, pending the availability of a sufficiently comprehensive data set. This conclusion emphasizes the crucial importance of coordinated observation campaigns of gamma-ray bursts, such as the one central to this work, to answer outstanding questions about the underlying physics driving these phenomena.
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