arXiv subjects

T. Cline

Publications and source records attributed to T. Cline.

At least 37 records · Page 2Linked to original sources

arXiv2005

HETE-2 Observation of two gamma-ray bursts at z > 3

GRB 020124 and GRB 030323 constitute half the sample of gamma-ray bursts with a measured redshift greater than 3. This paper presents the temporal and spectral properties of these two gamma-ray bursts detected and localized with HETE-2. While they have nearly identical redshifts (z=3.20 for GRB 020124, and z=3.37 for GRB 030323), these two GRBs span about an order of magnitude in fluence, thus sampling distinct regions of the GRB luminosity function. The properties of these two bursts are compared with those of the bulk of the GRB population detected by HETE-2. We also discuss the energetics of GRB 020124 and GRB 030323 and show that they are compatible with the Epeak - Eiso relation discovered by Amati et al. (2002). Finally, we compute the maximum redshifts at which these bursts could have been detected by HETE-2 and we address various issues connected with the detection and localization of high-z GRBs.

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arXiv2005

High Energy Observations of XRF 030723: Evidence for an Off-axis Gamma-Ray Burst?

We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-ray Monitor/French Gamma Telescope observations of XRF030723 along with observations of the XRF afterglow made using the 6.5m Magellan Clay telescope and the Chandra X-ray Observatory. The observed peak energy E_pk_obs of the nu F_nu burst spectrum is found to lie within (or below) the WXM 2-25 keV passband at 98.5% confidence, and no counts are detected above 30 keV. Our best fit value is E_pk_obs=8.4+3.5/-3.4 keV. The ratio of X-ray to Gamma-ray flux for the burst follows a correlation found for GRBs observed with HETE-2, and the duration of the burst is similar to that typical of long-duration GRBs. If we require that the burst isotropic equivalent energy E_iso and E_pk_rest satisfy the relation discovered by Amati et al. (2002), a redshift of z=0.38+0.36/-0.18 can be determined, in agreement with constraints determined from optical observations. We are able to fit the X-ray afterglow spectrum and to measure its temporal fade. Although the best-fit fade is shallower than the concurrent fade in the optical, the spectral similarity between the two bands indicates that the X-ray fade may actually trace the optical fade. If this is the case, the late time rebrightening observed in the optical cannot be due to a supernova bump. We interpret the prompt and afterglow X-ray emission as arising from a jetted GRB observed off-axis and possibly viewed through a complex circumburst medium due to a progenitor wind.

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arXiv2004

The Interplanetary Network Supplement to the BATSE Catalogs of Untriggered Cosmic Gamma Ray Bursts

We present Interplanetary Network (IPN) detection and localization information for 211 gamma-ray bursts (GRBs) observed as untriggered events by the Burst and Transient Source Experiment (BATSE), and published in catalogs by Kommers et al. (2001) and Stern et al. (2001). IPN confirmations have been obtained by analyzing the data from 11 experiments. For any given burst observed by BATSE and one other distant spacecraft, arrival time analysis (or ``triangulation'') results in an annulus of possible arrival directions whose half-width varies between 14 arcseconds and 5.6 degrees, depending on the intensity, time history, and arrival direction of the burst, as well as the distance between the spacecraft. This annulus generally intersects the BATSE error circle, resulting in a reduction of the area of up to a factor of ~650. When three widely separated spacecraft observed a burst, the result is an error box whose area is as much as 30000 times smaller than that of the BATSE error circle. Because the IPN instruments are considerably less sensitive than BATSE, they generally did not detect the weakest untriggered bursts, but did detect the more intense ones which failed to trigger BATSE when the trigger was disabled. In a few cases, we have been able to identify the probable origin of bursts as soft gamma repeaters. The vast majority of the IPN-detected events, however, are GRBs, and the confirmation of them validates many of the procedures utilized to detect BATSE untriggered bursts.

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arXiv2004

Global Characteristics of X-Ray Flashes and X-Ray-Rich GRBs Observed by HETE-2

We describe and discuss the global properties of 45 gamma-ray bursts (GRBs) observed by HETE-2 during the first three years of its mission, focusing on the properties of X-Ray Flashes (XRFs) and X-ray-rich GRBs (XRRs). We find that the numbers of XRFs, XRRs, and GRBs are comparable. We find that the durations and the sky distributions of XRFs and XRRs are similar to those of GRBs. We also find that the spectral properties of XRFs and XRRs are similar to those of GRBs, except that the values of the peak energy $E^{\rm obs}_{\rm peak}$ of the burst spectrum in $νF_ν$, the peak energy flux $\Fp$, and the energy fluence $S_E$ of XRFs are much smaller -- and those of XRRs are smaller -- than those of GRBs. Finally, we find that the distributions of all three kinds of bursts form a continuum in the [$S_E$(2-30 keV),$S_E$(30-400) keV]-plane, the [$S_E$(2-400 keV), $E_{\rm peak}$]-plane, and the [$F_{\rm peak}$(50-300 keV), $E_{\rm peak}$]-plane. These results provide strong evidence that all three kinds of bursts arise from the same phenomenon.

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arXiv2004

The bright optical afterglow of the long GRB 001007

We present optical follow up observations of the long GRB 001007 between 6.14 hours and ~468 days after the event. An unusually bright optical afterglow (OA) was seen to decline following a steep power law decay with index alpha = -2.03 +/- 0.11, possibly indicating a break in the light curve at t - to < 3.5 days, as found in other bursts. Upper limits imposed by the LOTIS alerting system 6.14 hours after the gamma ray event provide tentative (1.2 sigma) evidence for a break in the optical light curve. The spectral index beta of the OA yields -1.24 +/- 0.57. These values may be explained both by several fireball jet models and by the cannonball model. Fireball spherical expansion models are not favoured. Late epoch deep imaging revealed the presence of a complex host galaxy system, composed of at least two objects located 1.2" (1.7 sigma) and 1.9" (2.7 sigma) from the afterglow position.

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arXiv2004

The INTEGRAL view of the Soft Gamma-ray Repeater SGR 1806-20

We present the results obtained by INTEGRAL on the Soft-Gamma Ray Repeater SGR 1806-20. In particular we report on the temporal and spectral properties of the bursts detected during a moderately active period of the source in September and October 2003 and on the search for quiescent emission.

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arXiv2003

Scientific Highlights of the HETE-2 Mission

The HETE-2 mission has been highly productive. It has observed more than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has localized 43 GRBs to date. Twenty-one of these localizations have led to the detection of X-ray, optical, or radio afterglows, and as of now, 11 of the bursts with afterglows have known redshifts. HETE-2 has confirmed the connection between GRBs and Type Ic supernovae, a singular achievement and certainly one of the scientific highlights of the mission so far. It has provided evidence that the isotropic-equivalent energies and luminosities of GRBs are correlated with redshift, implying that GRBs and their progenitors evolve strongly with redshift. Both of these results have profound implications for the nature of GRB progenitors and for the use of GRBs as a probe of cosmology and the early universe. HETE-2 has placed severe constraints on any X-ray or optical afterglow of a short GRB. It is also solving the mystery of "optically dark' GRBs, and revealing the nature of X-ray flashes.

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arXiv2003

HETE-2 Observations of the Extremely Soft X-Ray Flash XRF 020903

We report HETE-2 WXM/FREGATE observations of the X-ray flash, XRF 020903. This event was extremely soft: the ratio log(S_X/S_gamma) = 0.7, where S_X and S_gamma are the fluences in the 2-30 and 30-400 keV energy bands, is the most extreme value observed so far by HETE-2. In addition, the spectrum has an observed peak energy E^{obs}_{peak} < 5.0 keV (99.7 % probability upper limit) and no photons were detected above ~10 keV. The burst is shorter at higher energies, which is similar to the behavior of long GRBs. We consider the possibility that the burst lies at very high redshift and that the low value of E^{obs}_{peak} is due to the cosmological redshift, and show that this is very unlikely. We find that the properties of XRF 020903 are consistent with the relation between the fluences S(7-30 keV) and S(30-400 keV) found by Barraud et al. for GRBs and X-ray-rich GRBs, and are consistent with the extension by a decade of the hardness-intensity correlation (Mallozzi et al. 1995) found by the same authors. Assuming that XRF 020903 lies at a redshift z = 0.25 as implied by the host galaxy of the candidate optical and radio afterglows of this burst, we find that the properties of XRF 020903 are consistent with an extension by a factor ~300 of the relation between the isotropic-equivalent energy E_iso and the peak E_peak of the nu F_nu spectrum (in the source frame of the burst) found by Amati et al. for GRBs. The results presented in this paper therefore provide evidence that XRFs, X-ray-rich GRBs, and GRBs form a continuum and are a single phenomenon. The results also impose strong constraints on models of XRFs and X-ray-rich GRBs.

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arXiv2003

Discovery of a New Transient Magnetar Candidate: XTE J1810-197

We report the discovery of a new X-ray pulsar, XTE J1810-197. The source was serendipitously discovered on 2003 July 15 by the Rossi X-ray Timing Explorer (RXTE) while observing the soft gamma repeater SGR 1806-20. The pulsar has a 5.54 s spin-period and a soft spectrum (photon index ~ 4). We detect the source in earlier RXTE observations back to 2003 January. These show that a transient outburst began between 2002 November 17 and 2003 January 23 and that the pulsar has been spinning down since then, with a high rate Pdot ~ 10^-11 s/s showing significant timing noise, but no evidence for Doppler shifts due to a binary companion. The rapid spin-down rate and slow spin-period imply a super-critical magnetic field B=3x10^14 G and a young characteristic age < 7600 yr. These properties are strikingly similar to those of anomalous X-ray pulsars and soft gamma repeaters, making the source a likely new magnetar. A follow-up Chandra observation provided a 2".5 radius error circle within which the 1.5 m Russian-Turkish Optical Telescope RTT150 found a limiting magnitude of R_c=21.5, in accord with other recently reported limits. The source is present in archival ASCA and ROSAT data as well, at a level 100 times fainter than the \~ 3 mCrab seen in 2003. This suggests that other X-ray sources that are currently in a state similar to the inactive phase of XTE J1810-197 may also be unidentified magnetars awaiting detection via a similar activity.

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arXiv2003

HETE-2 Localization and Observation of the Bright, X-Ray-Rich Gamma-Ray Burst GRB021211

A bright, x-ray-rich GRB was detected by HETE-2 at 11:18:34.03 UT on 11 Dec 2002. The WXM localization was to 14' and relayed to the GCN 22 s after the start of the burst. The ground SXC localization was within 2' of R.A. 08h 09m 00s, Dec 06d 44' 20" (J2000). GRB021211 consists of a single, FRED-like pulse with t90s of 2.3 s (85-400 keV) and 8.5 s (2-10 keV). The peak photon number and photon energy fluxes in the 2-400 keV band, are 34.0 +/- 1.8 ph cm^-2 s^-1 and 1.68 +/- 0.11 x 10^-6 erg cm^-2 s^-1, respectively. The energy fluences in the 2-30 keV and 30-400 kev energy bands are S_X = 1.36 +/- 0.05 x 10^-6 erg cm^-2 and S_gamma 2.17 +/- 0.15 x 10^-6 erg cm^-2, respectively. Thus GRB021211 is an X-ray-rich GRB (S_X/S_gamma = 0.63 > 0.32). The spectrum is well-fit by a Band function (alpha = -0.805, beta = -2.37, E_peak = 46.8 keV). The prompt localization allowed the detection of an optical afterglow for what would otherwise have been an ``optically dark'' GRB. GRB 021211 demonstrates that some fraction of burst afterglows are ``optically dark'' because their optical afterglows at times > 1 hr after the burst are very faint, and thus have often escaped detection. GRB 021211 shows that such ``optically dim'' bursts can have very bright afterglows at times < 20 min after the burst.

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arXiv2003

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.

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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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arXiv2002

HETE-2 Localization and Observations of the Short, Hard Gamma-Ray Burst GRB020531

The {\it HETE-2} (hereafter \HETE) French Gamma Telescope (FREGATE) and the Wide-field X-ray Monitor (WXM) instruments detected a short ($t_{50} = 360$ msec in the FREGATE 85-300 keV energy band), hard gamma-ray burst (GRB) that occurred at 1578.72 SOD (00:26:18.72 UT) on 31 May 2002. The WXM flight localization software produced a valid location in spacecraft (relative) coordinates. However, since no on-board real-time star camera aspect was available, an absolute localization could not be disseminated. A preliminary localization was reported as a GCN Position Notice at 01:54:22 UT, 88 min after the burst. Further ground analysis produced a refined localization, which can be expressed as a 90% confidence rectangle that is 67 arcminutes in RA and 43 arcminutes in Dec (90% confidence region), centered at RA = +15$^{\rm h}$ 14$^{\rm m}$ 45$^{\rm s}$, Dec = -19$^\circ$ 21\arcmin 35\arcsec (J2000). An IPN localization of the burst was disseminated 18 hours after the GRB (Hurley et al. 2002b). A refined IPN localization was disseminated $\approx$ 5 days after the burst. This hexagonal-shaped localization error region is centered on RA = 15$^{\rm h}$ 15$^{\rm m}$ 03.57$^{\rm s}$, -19$^\circ$ 24\arcmin 51.00\arcsec (J2000), and has an area of $\approx$ 22 square arcminutes (99.7% confidence region). The prompt localization of this short, hard GRB by \HETE and the anti-Sun pointing of the \HETE instruments, coupled with the refinement of the localization by the IPN, has made possible rapid follow-up observations of the burst at radio, optical, and X-ray wavelengths.

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arXiv2002

GRB 011121: A Massive Star Progenitor

Of the cosmological gamma-ray bursts, GRB 011121 has the lowest redshift, z=0.36. More importantly, the multi-color excess in the afterglow detected in the Hubble Space Telescope (HST) light curves is compelling observational evidence for an underlying supernova. Here we present near-infrared and radio observations of the afterglow. We undertake a comprehensive modeling of these observations and those reported in the literature and find good evidence favoring a wind-fed circumburst medium. In detail, we infer the progenitor had a mass loss rate of Mdot ~ 10^-7 / v_w3 Mo/yr where v_w3 is the speed of the wind from the progenitor in units of 10^3 km/s. This mass loss rate is similar to that inferred for the progenitor of SN 1998bw which has been associated with GRB 980425. Our data, taken in conjunction with the HST results of Bloom et al. (2002), provide a consistent picture: the long duration GRB 011121 had a massive star progenitor which exploded as a supernova at about the same time as the GRB event.

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arXiv2002

GRB010921: Localization and Observations by the HETE Satellite

On September 21 at 18950.56 SOD (05:15:50.56) UT the FREGATE gamma-ray instrument on the High Energy Transient Explorer (HETE) detected a bright gamma-ray burst (GRB). The burst was also seen by the X-detector on the WXM X-ray instrument and was therefore well-localized in the X direction; however, the burst was outside the fully-coded field-of-view of the WXM Y-detector, and therefore information on the Y direction of the burst was limited. Cross-correlation of the HETE and Ulysses time histories yielded an Interplanetary Network (IPN) annulus that crosses the HETE error strip at a ~45 degree angle. The intersection of the HETE error strip and the IPN annulus produces a diamond-shaped error region for the location of the burst having an area of 310 square arcminutes. Based on the FREGATE and WXM light curves, the duration of the burst is characterized by a t90 = 18.4 s in the WXM 4 - 25 keV energy range, and 23.8 s and 21.8 s in the FREGATE 6 - 40 and 32 - 400 keV energy ranges, respectively. The fluence of the burst in these same energy ranges is 4.8 10^{-6}, 5.5 10^{-6}, and 11.4 10^{-6} erg cm^{-2}, respectively. Subsequent optical and radio observations by ground-based observers have identified the afterglow of GRB010921 and determined an apparent redshift of z = 0.450.

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arXiv2002

The Current Performance of the Third Interplanetary Network

The 3rd Interplanetary Network (IPN) has been operating since April 2001 with two distant spacecraft, Ulysses and Mars Odyssey, and numerous near-Earth spacecraft, such as BeppoSAX, Wind, and HETE-II. Mars Odyssey is presently in orbit about Mars, and the network has detected approximately 30 cosmic, SGR, and solar bursts. We discuss the results obtained to date and use them to predict the future performance of the network.

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arXiv2002

HETE-II and the Interplanetary Network

The FREGATE experiment aboard HETE-II has been successfully integrated into the Third Interplanetary Network (IPN) of gamma-ray burst detectors. We show how HETE's timing has been verified in flight, and discuss what HETE can do for the IPN and vice-versa.

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arXiv2001

LOTIS, Super-LOTIS, SDSS and Tautenburg Observations of GRB 010921

We present multi-instrument optical observations of the High Energy Transient Explorer (HETE-2)/Interplanetary Network (IPN) error box of GRB 010921. This event was the first gamma ray burst (GRB) localized by HETE-2 which has resulted in the detection of an optical afterglow. In this paper we report the earliest known observations of the GRB010921 field, taken with the 0.11-m Livermore Optical Transient Imaging System (LOTIS) telescope, and the earliest known detection of the GRB010921 optical afterglow, using the 0.5-m Sloan Digital Sky Survey Photometric Telescope (SDSS PT). Observations with the LOTIS telescope began during a routine sky patrol 52 minutes after the burst. Observations were made with the SDSS PT, the 0.6-m Super-LOTIS telescope, and the 1.34-m Tautenburg Schmidt telescope at 21.3, 21.8, and 37.5 hours after the GRB, respectively. In addition, the host galaxy was observed with the USNOFS 1.0-m telescope 56 days after the burst. We find that at later times (t > 1 day after the burst), the optical afterglow exhibited a power-law decline with a slope of $α= 1.75 \pm 0.28$. However, our earliest observations show that this power-law decline can not have extended to early times (t < 0.035 day).

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