Optical and Near-infrared Observations of the Afterglow of GRB 980329 from 15 Hours to 10 Days
ABSTRACT We report I-band observations of the GRB 980329 field made on 1998 March 29 with the 1.34 m Tautenberg Schmidt telescope, R-, J- and K-band observations made on 1998 April 1 with the APO 3.5 m telescope, R- and I-band observations made on 1998 April 3 with the Mayall 4 m telescope at KPNO, and J- and K-band observations made 1998 April 6-8 with the Keck-I 10 m telescope. We show that these and other reported measurements are consistent with a power-law fading of the optical/near-infrared source that is coincident with the variable radio source VLA J0702+3850. This firmly establishes that this source is the afterglow of GRB 980329.
- SourceAvailable from: David Bersier[Show abstract] [Hide abstract]
ABSTRACT: We present near-infrared (NIR) and optical observations of the afterglow of GRB 030115. Discovered in an infrared search at Kitt Peak 5 hr after the burst trigger, this afterglow is the faintest ever observed in the R band at such an early epoch and exhibits very red colors, with R - K ≈ 6. The optical magnitude of the afterglow of GRB 030115 is fainter than many upper limits for other bursts, suggesting that without early NIR observations it would have been classified as a "dark" burst. Both the color and optical magnitude of the afterglow are likely due to dust extinction at moderate redshift z > 2 and indicate that at least some optical afterglows are very faint due to dust along the line of sight. Multicolor Hubble Space Telescope observations were also taken of the host galaxy and the surrounding field. Photometric redshifts imply that the host and a substantial number of faint galaxies in the field are at z ~ 2.5. The overdensity of galaxies is sufficiently great that GRB 030115 may have occurred in a rich high-redshift cluster. The host galaxy shows extremely red colors (R - K = 5) and is the first GRB host to be classified as an extremely red object (ERO). Some of the galaxies surrounding the host also show very red colors, while the majority of the cluster are much bluer, indicating ongoing unobscured star formation. As it is thought that much of high-redshift star formation occurs in highly obscured environments, it may well be that GRB 030115 represents a transition object, between the relatively unobscured afterglows seen to date and a population of objects that are very heavily extinguished, even in the NIR.The Astrophysical Journal 12/2008; 647(1):471. · 6.28 Impact Factor
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ABSTRACT: We present V-, R-, and I-band observations made at the US Naval Observatory, Flagstaff Station, of the afterglow of GRB 980519 on UT 1998 May 20 and 22. These observations are combined with extensive data from the literature, and all are placed on a uniform magnitude system. The resultant R- and I-band light curves are fit by simple power laws with no breaks and indices of αR = 2.30 ± 0.12 and αI = 2.05 ± 0.07. This makes the afterglow of GRB 980519 one of the two steepest afterglows yet observed. The combined B-, V-, R-, and I-band observations are used to estimate the spectral power-law index, β = 1.4 ± 0.3, after correction for reddening. Unfortunately, GRB 980519 occurred at a relatively low Galactic latitude (b ≈ +15) where the Galactic reddening is poorly known and, hence, the actual value of β is poorly constrained. The observed α and range of likely β-values are, however, found to be consistent with simple relativistic blast-wave models. This afterglow and that of GRB 980326 displayed much steeper declines than the other seven well-observed afterglows, which cluster near α ≈ 1.2. GRB 980519 and GRB 980326 did not display burst characteristics in common that might distinguish them from the gamma-ray bursts with more typical light curves.The Astrophysical Journal 12/2008; 528(1):254. · 6.28 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: We present radio observations of the afterglow of the bright γ-ray burst GRB 980329 made between 1 month and several years after the burst, a reanalysis of previously published submillimeter data, and late-time optical and near-infrared (NIR) observations of the host galaxy. From the absence of a spectral break in the optical/NIR colors of the host galaxy, we exclude the earlier suggestion that GRB 980329 lies at a redshift of z 5. We combine our data with the numerous multiwavelength observations of the early afterglow, fit a comprehensive afterglow model to the entire broadband data set, and derive fundamental physical parameters of the blast wave and its host environment. Models for which the ejecta expand isotropically require both a high circumburst density and extreme radiative losses from the shock. No low-density model (n 10 cm-3) fits the data. A burst with a total energy of ~1051 ergs, with the ejecta narrowly collimated to an opening angle of a few degrees, driven into a surrounding medium with density of ~20 cm-3, provides a satisfactory fit to the light curves over a range of redshifts.The Astrophysical Journal 12/2008; 577(1):155. · 6.28 Impact Factor
arXiv:astro-ph/9806082v2 8 Jan 1999
Accepted to The Astrophysical Journal
Optical and Near Infrared Observations of the Afterglow of GRB 980329 from
15 Hours to 10 Days1
Daniel E. Reichart2, Donald Q. Lamb2, Mark R. Metzger3, Jean M. Quashnock2,
David M. Cole2, Francisco J. Castander2, Sylvio Klose4, James E. Rhoads5,
Andrew S. Fruchter6, Asantha R. Cooray2, and Daniel E. Vanden Berk7
We report I-band observations of the GRB 980329 field made on March 29 with the
1.34-m Tautenberg Schmidt telescope, R-, J- and K-band observations made on April
1 with the APO 3.5-m telescope, R- and I-band observations made on April 3 with
the Mayall 4-m telescope at KPNO, and J- and K-band observations made between
April 6 - 8 with the Keck-I 10-m telescope. We show that these and other reported
measurements are consistent with a power-law fading of the optical/near infrared
source that is coincident with the variable radio source VLA J0702+3850. This firmly
establishes that this source is the afterglow of GRB 980329.
Subject headings: gamma-rays: bursts
On March 29.16, GRB 980329 triggered the BeppoSAX Gamma Ray Burst Monitor and was
detected simultaneously with the BeppoSAX Wide Field Cameras, which yielded an error circle
1Part of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific
partnership among the California Institute of Technology, the University of California and the National Aeronautics
and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck
2Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637
3Division of Physics, Mathematics, and Astronomy 105-24, Caltech, Pasadena, CA 91125
4Th¨ uringer Landessternwarte Tautenburg, Karl-Schwarzschild-Observatorium, D-07778 Tautenburg, Germany
5Kitt Peak National Observatory, National Optical Astronomy Observatories, 950 North Cherry Avenue, Tucson,
AZ 85719, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under
cooperative agreement with the National Science Foundation
6Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218
7McDonald Observatory, University of Texas, RLM 15.308, Austin, TX 78712
– 2 –
of 3 arcmin radius (Frontera et al. 1998). Seven hours later, this error circle was observed with
the BeppoSAX Narrow Field Instruments, which detected a fading medium-energy X-ray source,
1SAX J0702.6+3850, about 1 arcmin from the center of the error circle (in ’t Zand et al. 1998a).
On April 3, Taylor, Frail, & Kulkarni (1998) reported the detection of a variable radio
source, VLA J0702+3850, within the 1 arcmin radius error circle of 1SAX J0702.6+3850,
with measurements made between March 30 and April 2. On the same day, Djorgovski et
al. (1998) reported the detection of a faint (R = 25.7 ± 0.3 mag) optical source coincident with
VLA J0702+3850, with measurements made on April 2 with the Keck-II 10-m telescope; they
interpreted this source as the host galaxy of GRB 980329. Also on the same day, Klose (1998) (see
also Klose, Meusinger, & Lehmann 1998) reported an I-band measurement of this source, made
on March 30 with the Tautenburg Schmidt telescope, and Larkin et al. (1998a,b) reported K-band
measurements of this source, made on April 2 and April 3 with the Keck-I 10-m telescope.
On April 4, Mannucci et al. (1998) reported a J-band measurement of a source, made on
March 30 with the Gornergrat Infrared Telescope (TIRGO); however, the coincidence of their
source with VLA J0702+3850 cannot be established (Palazzi et al. 1998b). On April 5, Cole et
al. (1998a,b) reported a J-band upper limit at the position of VLA J0702+3850, made on April 1
with the APO 3.5-m telescope, that, when compared to the J-band measurement of Mannucci et
al. (1998), suggested that this source was fading.
Observations reported on April 6 by Palazzi et al. (1998a) (R-band, March 30), and on
April 8 by Pedersen et al. (1998) (R-band, March 31 + April 1 + April 2) provided evidence
that the source coincident with VLA J0702+3850 was fading. On April 7, Smith & Tilanus
(1998a,b) reported the detection of a fading submillimeter source coincident with this source,
with measurements made between April 5 and April 7 with SCUBA at the James Clerk Maxwell
Telescope. On April 12, Metzger (1998a,b) reported K-band measurements of the source, made
between April 6 and April 8 with the Keck-I 10-m telescope, which demonstrated that the source
continued to fade in the near infrared (NIR) as late as 10 days after the gamma-ray burst (GRB).
Recently, Fruchter (1998b) reported that the source, as well as an underlying or host galaxy, is
visible in a deep HST/NICMOS image, made approximately 200 days after the GRB. The faintness
of the underlying or host galaxy contradicts the previous claim of Djorgovski et al. (1998), unless
the galaxy is extremely blue and/or is at very high redshift.
Except for the X-ray measurements, which can be found in in ’t Zand et al. (1998b), the
submillimeter measurements, which can be found in Smith et al. (1998), the radio measurements,
which can be found in Taylor et al. (1998), and the NIR measurement of Fruchter (1998b), which
is not yet available, all of the above measurements and upper limits, as well as the measurements
and upper limits that we report in this paper, are listed in Table 1.
In this paper, we report Tautenburg, Apache Point Observatory (APO), Kitt Peak National
Observatory (KPNO), and Keck-I observations of the GRB 980329 field. In §2, we report KPNO
R- and I-band calibrations of the GRB 980329 field. We report the Tautenburg observations in
– 3 –
§3, the APO observations in §4, the KPNO observations in §5, and the Keck-I observations in
§6. In §7, we discuss some of the implications of these and the other reported observations. We
summarize our results in §8.
2.KPNO R- and I-band Calibrations of the GRB 980329 Field
On April 3, Rhoads, on behalf of the KPNO GRB followup team, observed the GRB 980329
field and the SA107 field of Landolt (1992) standard stars with the Mayall 4-m telescope at
KPNO using the Mosaic CCD Imager. Four 10-minute exposures were taken of the GRB 980329
field, two through the R-band filter and two through the I-band filter. Four brief exposures were
taken of the SA107 field, likewise, two through the R-band filter and two through the I-band
filter. Weather was photometric, though image quality was poor, ranging from 1.25 to 1.75 arcsec,
approximately. The GRB 980329 field was observed at an airmass of 1.1, and the SA107 field was
observed at an airmass of 1.4. All data reduction was done in IRAF, using the packages MSCRED
for basic data reduction, and APPHOT and PHOTCAL for the photometric measurements and
Reliable fluxes were measured for the Landolt standard stars SA107-212, 213, 357, 359, 351,
457, 456, 600, 599, 612, 626, and 627. Of these, the first five were measured twice in each filter,
and the remainder were measured only once in each filter. Fluxes were corrected to a 7 arcsec
radius aperture (the usual aperture size used by Landolt) using a curve of growth derived from
all of the cleanly observed standard stars in each filter. Unfortunately, these stars span a fairly
narrow range in color, roughly 0.35 mag < R − I < 0.50 mag; the only bluer standard star in the
field, SA107-215, has very large photometric errors in Landolt’s table, and consequently, it was
Photometry of the GRB 980329 field was done in a similar fashion: a curve of growth was
derived from multiaperture photometry and used to correct all magnitudes to an effective 7 arcsec
radius, using the IRAF task “mkapfile.” Photometric errors were also taken from “mkapfile”;
these include the uncertainties due to photon statistics, sky subtraction, and aperture corrections.
The magnitudes were then corrected for the difference in airmass between the GRB 980329 and
SA107 fields, and for color terms between our filters and the standard filters used by Landolt.
Since our standard stars were observed at only a single airmass, we adopted standard extinction
coefficients for Kitt Peak, and we conservatively assumed uncertainties in each coefficient equal to
that coefficient, giving 0.03 ± 0.03 mag/airmass for the I band and 0.08 ± 0.08 mag/airmass for
the R band. These values are IRAF defaults, and agree well with the values of 0.04 mag/airmass
(I band) and 0.10 mag/airmass (R band) measured during 1996 November at the WIYN telescope
on Kitt Peak (Smith 1997). We measured the color terms to be (+0.010 ± 0.07)(R − I − 0.42)
mag for the I band and (−0.049 ± 0.07)(R − I − 0.42) mag for the R band, where R − I = 0.42
mag is the approximate median color of the observed standard stars, and where the signs indicate
that blue objects appear brighter in the I band and fainter in the R band than they would for
– 4 –
the standard filters. If we fix the color and extinction terms and fit only for the photometric zero
point, we measure an uncertainty of ±0.004 mag for both filters; this corresponds to the statistical
uncertainty in the photometric calibration arising from uncertainties in the flux measurements of
the our standard stars.
The overall uncertainty in the calibrated magnitude of each measured star in the GRB 980329
field was computed as the sum in quadrature of that star’s photometric uncertainty, the zero
point uncertainty (0.004 mag), the systematic uncertainty in the extinction term for a difference
in airmass of 0.3, and the systematic uncertainty in the color term. For the I band, this is the
quadratic sum of the photometric error, 0.004 mag, 0.010 mag, and 0.07(R − I − 0.42) mag;
for the R band, it is the quadratic sum of the photometric error, 0.004 mag, 0.024 mag, and
0.07(R − I − 0.42) mag. Since these errors include a substantial systematic component, the final
magnitude errors for different stars in the GRB 980329 field are not independent. We list the
calibrated magnitudes and their final errors for 11 stars in the GRB 980329 field in Table 2. A
finding chart is shown in Figure 1.
3. 1.34-m Tautenburg Schmidt Telescope Observations
On March 29, Klose observed the GRB 980329 field with the 1.34-m Tautenburg Schmidt
telescope, using a thinned, back-illuminated Tektronix 1024 × 1024 CCD. The pixel scale is 1.2
arcsec per pixel, which corresponds to a 20 arcmin field of view.
A series of 27 120-second exposures were taken between March 29.794 - 29.856 UT, nine
through the V -band filter, nine through the R-band filter, and nine through the I-band filter. A
second series of 36 120-second exposures were taken between March 29.863 - 29.947 UT, likewise,
twelve through each of the V -, R-, and I-band filters. To avoid problems with hot and warm
pixels, the telescope was dithered between exposures. The sky was nearly photometric at the
beginning of the observations; however, observing conditions worsened, and by March 29.95 UT,
cloud cover rendered further observations useless. During the observations, the airmass ranged
from 1.05 to 1.61.
The seven best I-band images of the first series and the ten best I-band images of the second
series were combined using standard IRAF tasks into two images: the equivalent of an 840 second
exposure of mean epoch March 29.827 UT, and the equivalent of a 1200 second exposure of mean
epoch March 29.907 UT. A source is clearly visible at the position of VLA J0702+3850 in both
of these images (Klose 1998; Klose, Meusinger, & Lehmann 1998). Using the KPNO I-band
calibration of Table 2, we find that the I-band magnitude of the source is 20.8 ± 0.3 in both the
March 29.827 UT image and the March 29.907 UT image. The combined March 29.827 + 29.907
UT, I-band image is shown in Figure 2.
Observations could not be made on the following night; however, I-band observations of
the GRB 980329 field were again made between March 31.8 - 31.9 UT. However, no source was
– 5 –
detected at the position of VLA J0702+3850 to a limiting magnitude of I ≈ 21. Likewise, no
source was detected at the position of VLA J0702+3850 in the V - and R-band images taken on
March 29 (Klose, Meusinger, & Lehmann 1998).
4. APO 3.5-m Telescope Observations
On April 1, the Astrophysical Research Consortium (ARC) GRB Afterglow Collaboration
observed the GRB 980329 field with the ARC’s 3.5-m telescope at APO. Both optical observations,
using the Seaver Prototype Imaging Camera (SPICam), and NIR observations, using the Near
Infrared Grism Spectrometer and Imager II (GRIM II), were made.
Six 10-minute exposures, centered on the position of VLA J0702+3850, were taken with the
SPICam between April 1.097 - 1.143 UT through the R-band filter. SPICam has a thinned SITe
2048 × 2048 CCD; we used a 2 × 2 binning, which corresponds to a pixel scale of 0.28 arcsec/pixel.
The effective seeing was 1.0 arcsec. The effective airmass was 1.042.
Each image was overscan-subtracted and flat-fielded with twilight flats, using standard IRAF
tasks. The images were then combined into a single, stacked image; a high-sigma threshold clipping
was applied to reject deviant pixels. The stacked image is equivalent to a 3600 second exposure of
mean epoch April 1.120 UT. A source is clearly visible at the position of VLA J0702+3850 (see
Figure 3). Using the KPNO R-band calibration of Table 2, we find that the R-band magnitude of
the source is 25.35+0.35
The GRIM II has a NICMOS array, with both J-band and Mauna Kea K′-band (bandpass 1.95
- 2.30 µm) filters. At the focal length of f/5, the pixel scale is 0.47 arcsec/pixel, which corresponds
to a 2 arcmin field of view. Between April 1.164 - 1.182 UT, we took randomly-dithered, 15-second
frames every 20 seconds of the VLA J0702+3850 field through the J-band filter. We combined
these frames into a single, stacked image with a total integration of 945 seconds and a mean epoch
of April 1.173 UT. Between April 1.183 - 1.207 UT, we took randomly-dithered, 20-second frames
every 25 seconds through the K′-band filter; the stacked image has a total integration of 1310
seconds and a mean epoch of April 1.195 UT. We returned to the VLA J0702+3850 field almost
two hours later, and again observed through the J-band filter: between April 1.267 - 1.281 UT,
we took randomly-dithered, 15-second frames every 20 seconds; the stacked image has a total
integration of 915 seconds and a mean epoch of April 1.274 UT. UKIRT faint standards 14 (B.
Zuckerman, private communication) and 33 (Turnshek et al. 1990) were observed throughout the
evening through both filters for both magnitude calibration and airmass correction.
Using a 3 arcsec diameter aperture, we find 1 σ detection limits of 20.8 mag for the first
J-band image, 19.7 mag for the K′-band image, and 20.7 mag for the second J-band image.
Combining the first and the second J-band images yields a 1 σ detection limit of 21.3 mag. We
list corresponding 3 σ detection limits in Table 1. No source was detected at the position of VLA
J0702+3850 in either the combined J-band image (Cole et al. 1998a,b), or in the K′-band image
– 6 –
to these limiting magnitudes.
5. KPNO Mayall 4-m Telescope Observations
Once combined, the four 10 minute exposures of the GRB 980329 field with the KPNO Mayall
4-m telescope (see §2) correspond to the equivalent of a 1200 second exposure of mean epoch April
3.147 through the R-band filter, and the equivalent of a 1200 second exposure of mean epoch
April 3.167 through the I-band filter. No source is detected at the position of VLA J0702+3850
in either of these images; however, we place upper limits. The I-band upper limit, in particular, is
constraining (see Figure 5).
For the R-band image, the most constraining upper limit is obtained with a 0.75 arcsec
radius aperture; in this case, the aperture-corrected flux (see §2) of a point source at the position
of VLA J0702+3850 is measured to be 0.40 ± 0.25 µJy. Photon statistics and sky subtraction
both contribute to this uncertainty. A larger aperture, in this case, of 1.25 arcsec radius, yields
a larger aperture-corrected flux: 0.80 ± 0.25 µJy. This discrepancy could be due to astrometric
error, in which case flux would be more accurately measured with the larger aperture; however,
this discrepancy is more likely due to some other source of error, perhaps flat fielding error
or uncertainty in the curve of growth with which the aperture corrections are made (see §2).
Accepting as conservative a 3 σ upper limit of 1.50 µJy gives R > 23.3 mag (Rhoads et al. 1998).
For the I band, the aperture-corrected fluxes measured in the 0.75 and 1.25 arcsec radius
apertures are 0.06 ± 0.51 µJy and −0.12 ± 0.44 µJy, respectively. Accepting as conservative a 3 σ
upper limit of 1.48 µJy gives I > 23.0 mag (Rhoads et al. 1998).
6. Keck-I 10-m Telescope Observations
On April 6 and April 8, Metzger observed the VLA J0702+3850 field with the Keck-I 10-m
telescope using the Near-Infrared Camera (NIRC, Matthews et al. 1993) through the J- and
K-band filters. The NIRC has 256 × 256 pixels that project to 0.15 arcsec/pixel on the sky, which
corresponds to a 38 arcsec field of view.
On April 6.27 UT and again on April 8.28 UT, 5-second frames were taken through the
K-band filter in a standard dither pattern. The frames were flattened and co-added with bad
pixel rejection to produce a single image for each night; each image has a total integration of
1080 seconds. On April 6.30, 10-second frames were taken through the J-band filter in a similar
fashion. Again, a single image with a total integration of 1080 seconds was produced. Several NIR
standards were observed on each night, both of which were clear, for magnitude calibration and
airmass correction for each band. Clipped mean stacks of the off-position dither frames were used
for the sky estimate in each case.
– 7 –
A source is clearly visible at the position of VLA J0702+3850 on each night, and in each
band. The K-band magnitude of this source is 21.4 ± 0.2 on April 6.27 UT and 21.9 ± 0.2 on
April 8.28 UT (Metzger 1998a,b). The J-band magnitude of this source is 23.3 ±0.4 on April 6.30
UT. Fluxes were measured in a 1.5 arcsec diameter aperture and corrected to an effective 3 arcsec
diameter aperture using curves of growth from the brighter stars in the field; airmass corrections
were also applied. We show the combined April 6.27 + 8.28 UT K-band image in the right panel
of Figure 4; we show the J-band image in the left panel of Figure 4.
7.Some Implications of the Observations
In Figure 5, we plot the R-, I-, J-, and K-band light curves of the source that is coincident
with the variable radio source VLA J0702+3850, using the measurements that we have compiled
in Table 1. In this figure, we have corrected these measurements for Galactic extinction, using
the dust maps of Schlegel, Finkbeiner, & Davis (1998). These maps are reprocessed composites of
the COBE/DIRBE and IRAS/ISSA maps, with zodiacal foreground and confirmed point sources
removed. With DIRBE-quality calibration and IRAS resolution, these maps are more than twice
as accurate at extinction estimation than the H I maps of Burstein & Heiles (1982) (Schlegel,
Finkbeiner, & Davis 1998). Using the software that is publicly available at their web site8, we
find that at the position of VLA J0702+3850, E(B − V ) = 0.073 mag, which corresponds to
AV = 0.241 mag, AR= 0.194 mag, AI= 0.141 mag, AJ= 0.065 mag, and AK= 0.042 mag, for
RV = 3.1 (Schlegel, Finkbeiner, & Davis 1998). For purposes of comparison, we find that the
Burstein & Heiles (1982) maps give E(B − V ) = 0.124 mag, which corresponds to AV = 0.409
mag, for RV = 3.1. The 0.168 mag difference in the value of AV between these two estimates may
be due to systematic errors between the dust and H I extinction models of these authors, but it is
more likely due to the lower resolution of the Burstein & Heiles maps: there appears to be a large
dust lane a few arcminutes to the southeast of this position.
Visual inspection of Figure 5 suggests that the source is fading as a power law in these
optical and NIR bands. The light curves do not appear to level off, which suggests that these
measurements are not contaminated by an underlying or host galaxy (see §1); however, such a
scenario cannot be ruled out by these data alone. Assuming a power-law temporal fading, we
measure the temporal index, b, in each of these bands to be bR= −1.28+0.18
bJ∼> −1.39 (3 σ), and bK= −0.98+0.30
consistent with a single, frequency-independent temporal index of b = −1.21+0.13
ν = 10). A similar temporal index is found by in ’t Zand et al. (1998b) for the fading X-ray source
1SAX J0702.6+3850, within the error circle of which this optical/NIR source is located. This
combination of positional coincidence and temporal fading firmly establishes that the optical/NIR
source that is coincident with VLA J0702+3850 is the afterglow of GRB 980329.
−0.19, bI∼< −1.05 (3 σ),
−0.28. To within the measured uncertainties, these values are
– 8 –
Finally, we wish to briefly comment upon the form of the optical/NIR spectrum of this GRB
afterglow. As has been noted by Fruchter (1998a) and Reichart & Lamb (1998), this spectrum is
very flat between the K and the I bands, but is dramatically steeper between the I and the R
bands. Fruchter (1998a) proposes that this is the signature of the Lyman-α forest, which would
imply that GRB 980329 is at a redshift of z ∼ 5. A complete modeling of the radio through X-ray
afterglow of GRB 980329 in terms of the relativistic fireball model is presented in Reichart &
8. Summary of Results
We report R-, I-, J-, and K-band observations of the source that is coincident with the
variable radio source VLA J0702+3850, which lies in the error circle of the fading X-ray source
1SAX J0702.6+3850, as well as in the error circle of GRB 980329. These observations were taken
between 15 hours and 10 days after GRB 980329 with the 1.34-m Tautenburg Schmidt telescope,
the APO 3.5-m telescope, the KPNO Mayall 4-m telescope, and the Keck-I 10-m telescope. We
find that this optical/NIR source is fading as a power law with a temporal index of b = −1.21+0.13
This combination of positional coincidence and temporal fading firmly establishes that this source
is the afterglow of GRB 980329.
This research was supported in part by NASA grant NAG5-2868 and NASA contract
NASW-4690. M.R.M.’s research was supported in part by Caltech.
– 9 –
Table 1. Optical and Near Infrared Observations of the Afterglow of GRB 980329
Mar 30.93 + 31.87
Mar 29.83 + 29.91
Apr 1.17 + 1.27
23.6 ± 0.2 mag
25.0 ± 0.5 mag
25.7 ± 0.3 mag
> 23.3 magc
20.8 ± 0.3 mag
> 23.0 magc
> 19.6 magc
> 19.4 magc
23.3 ± 0.4 mag
> 17.8 magc
20.7 ± 0.2 mag
20.9 ± 0.2 mag
21.4 ± 0.2 mag
21.9 ± 0.4 mag
−0.25mag APO 3.5 m
Keck-II 10 m
KPNO Mayall 4 m
KPNO Mayall 4 m
APO 3.5 m
Keck-I 10 m
APO 3.5 m
Keck-I 10 m
Keck-I 10 m
Keck-I 10 m
Keck-I 10 m
4, 6, 7, 8
4, 10, 11
4, 10, 11
4, 14, 15
4, 14, 15
a1998 March 29.85 - April 8.28, UT in decimal days.
b1. Palazzi et al. 1998a; 2. Palazzi et al. 1998b; 3. Pedersen et al. 1998; 4. this paper;
5. Djorgovski et al. 1998; 6. Rhoads et al. 1998; 7. Klose 1998; 8. Klose, Meusinger, &
Lehmann 1998; 9. Mannucci et al. 1998; 10. Cole et al. 1998a; 11. Cole et al. 1998b;
12. Larkin et al. 1998a; 13. Larkin et al. 1998b; 14. Metzger 1998a; 15. Metzger 1998b.
c3 σ, 1-sided confidence interval.
– 10 –
Table 2.KPNO R- and I-Band Calibrations of the GRB 980329 Field
15.7 ± 1.0d
15.8 ± 1.0d
16.3 ± 0.3d
16.966 ± 0.031e
18.443 ± 0.028
20.655 ± 0.065
20.386 ± 0.054
20.514 ± 0.046
21.288 ± 0.069
17.659 ± 0.046
17.966 ± 0.026
15.3 ± 0.2d
15.45 ± 0.12d
15.988 ± 0.036e
16.647 ± 0.0155
18.093 ± 0.0175
19.473 ± 0.0623
19.331 ± 0.0478
19.625 ± 0.0459
20.026 ± 0.0711
16.668 ± 0.0399
17.539 ± 0.0161
aSee Figure 1 for a finding chart.
c1 σ errors are not independent; extinction and color terms introduce systematic
errors (see §2).
dEstimate due to saturation.
ePossibly marginally saturated.
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This preprint was prepared with the AAS LATEX macros v4.0.
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Fig. 1.— KPNO Mayall 4-m telescope I-band image of the GRB 980329 field (April 3.17 UT).
The image is 90 arcsec square; north is up and east is left. The optical transient is not detected.
Calibrated stars of Table 2 are labeled.
Fig. 2.— 1.34-m Tautenburg Schmidt telescope stacked (March 29.83 + 29.91 UT) I-band image
of the GRB 980329 field. The optical transient is detected (arrow).
Fig. 3.— APO 3.5-m telescope R-band image of the GRB 980329 field (April 1.12 UT). The optical
transient is detected (arrow).
Fig. 4.— Keck-1 10-m telescope images of the VLA J0702+3850 field: J-band (April 6.30 UT,
left) and stacked (April 6.27 + 8.28 UT) K-band (right). The NIR transient (circled) is detected
in both bands, and on both nights (in the K-band).
measurements of Table 1, corrected for Galactic extinction (see §7), and the best power law fit
to these data. Circles denote the R band, pentagons denote the I band, squares denote the J band,
and triangles denote the K band. Upper limits are 1, 2, and 3 σ.
5.— The R-, I-, J-, and K-band light curves of the optical/NIR transient from the
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