GRB 060502B
GCN Circular 5055
Subject
GRB 060502B: Swift detection of a short burst
Date
2006-05-02T18:08:11Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
E. Troja (INAF-IASFPA), S. D. Barthelmy (GSFC),
P. T. Boyd (NASA/GSFC), D. N. Burrows (PSU),
J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC),
S. T. Holland (GSFC/USRA), S. D. Hunsberger (PSU),
J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
V. La Parola (INAF-IASFPA), V. Mangano (INAF-IASFPA),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
T. Sakamoto (NASA/ORAU), G. Tagliaferri (INAF-OAB) and
D. E. Vanden Berk (PSU) report on behalf of the Swift Team:
At 17:24:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located the short GRB 060502B (trigger=208275). Swift slewed immediately
to the burst. The BAT on-board calculated location is
RA,Dec 278.936, +52.632 {18h 35m 45s, +52d 37' 56"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The TDRSS BAT light curve shows a single spike
with a FWHM of less than 128 msec. The peak count rate
was ~10000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began taking data at 17:25:51 UT, 70 seconds after the BAT
trigger. The XRT on-board centroid algorithm did not find a source in
the image, however analysis of downlinked data reveals a faint point
source at the following coordinates: RA(J2000) = 18h 35m 45.9s,
Dec(J2000) = 52d 37m 38.1s, with an estimated uncertainty of 10
arcseconds radius (90% containment). This position is 20 arcseconds
from BAT localization. We note that the XRT position lies 2.5
arcseconds from an possible galaxy with R=18.5 in the APM-North
catalogue (McMahon et al., 2000).
UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 74.2 seconds after the BAT trigger.
There is no detected new source in the rapidly available 2.7'x2.7'
sub-image, to a limiting White magnitude of about 19.1.
We are currently in the beginning of the Malindi downlink gap, so we
will not have the full data set until at least 01:00 03/May/06 UT.
GCN Circular 5056
Subject
GRB 060502B: MASTER optical observations
Date
2006-05-02T19:34:26Z (19 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <gcncirc@observ.inetcomm.ru>
V. Lipunov, V.Kornilov, N.Tyurina, A.Belinski, D.Kuvshinov, E.Gorbovskoy,
A.Krylov, G.Borisov, A.Sankovich, V.Vladimirov, P.Gritsyk, S.Korobkin
Sternberg Astronomical Institute, Moscow Union 'Optic'
MASTER robotic system (http://observ.pereplet.ru) responded
to GRB060502B (GRB_TIME is 2006-05-02 17:24:41.07, E. Troja et al.
GCN5055) by unfiltered, BVR-filtered, spectral and high time
resolution cameras.
The first image was at 2006-05-02 17:25:50.11 UT,
69 s after the GRB time on the bright evening sky.
The first images with more or less good limit was at 82 min after the GRB
time at high air mass.
The unfiltered image is calibrated relative to USNO A2.0 (0.8 R + 0.2 B).
The robot not find OT-candidate in error box brighter then 16.0 (s/n=5)
at Swift XRT position.
This work is supported by RFFI 04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru
GCN Circular 5057
Subject
GRB 060502B: Xinglong optical observation
Date
2006-05-02T20:40:39Z (19 years ago)
From
W.K. Zheng at NAOC <zwk@bao.ac.cn>
M.Zhai, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng(NAOC),X.F. Wang (THCA),
K.Y. Huang (NCU), Y. Urata (Saitama Univ.)
on behalf of EAFON report:
"We have imaged the field of GRB 060502B (Troja et al. GCN 5055) with
clear, R and I band using the 0.8m telescope at Xinglong Observatory.
First imaging was started from 305 s after the trigger. The limiting
magnitude is clear = ~ 20 (12 min after) and R=20.6 (60 min after)
derived from USNO-B1.0 r catalog. No new source was detected
brighter than the limits in the XRT error circle.
Further analysis is in progress."
This message may be cited.
GCN Circular 5059
Subject
GRB060502B: correction to XRT position
Date
2006-05-02T21:25:00Z (19 years ago)
From
Vanessa Mangano at INAF-IASFPA <vanessa@ifc.inaf.it>
E. Troja (INAF-IASFPA), V. Mangano (INAF-IASFPA), J. Kennea (PSU),
A. Moretti (INAF-OAB) on behalf of the Swift XRT team:
A re-analysis of the XRT TDRSS data has led to a different position
from the one issued with GCN 5055. The new estimated position for
the candidate X-ray afterglow is:
RA (2000) = 18 35 45.6
Dec (2000) = +52 37 54.2
with an uncertainty of 7 arcsec (90% confinement).
We are still waiting for down-linked data for refined
coordinates of the source.
We apologize for the inconvenient.
GCN Circular 5062
Subject
Short GRB 060502B: Tautenburg Observation
Date
2006-05-03T00:28:27Z (19 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann, S. Klose & P. Ferrero (TLS Tautenburg) report:
We observed the location of the short burst GRB 060502B (Troja et al., GCN 5055)
with the Tautenburg 1.34m Schmidt telescope.
Observations were taken under bad observing conditions (airmass 1.95, twilight,
moonlight). The observation consisted of a single 900 sec exposure in the R band
taken at a mid-exposure time of 20060502.8356, 0.1101 days after the burst.
Due to the conditions, the image limit is shallow, with a 3 sigma limiting magnitude
of 20.2. The Galaxy mentioned in GCN 5055 is clearly detected at a magnitude of R
= 18.1 +/- 0.09 (measured vs. several surrounding USNO1.0B stars).
We detect a possible additional source to the southeast of the center of the galaxy
(but within the PSF in our image), at RA = 18:35:45.90, Dec.= +52:37:33.20 (errors
+/- 0.5"), which could possibly be a superposed faint afterglow, reminescent of
GRBs 050709 or 050724. But there seems to be a source here also in the DSS R
image, so this identification is very unsure.
Furthermore, we note that this galaxy is not included in the revised error circle
(Troja et al., GCN 5059) any more, which would rule it out as a host galaxy
altogether, unless it lies at low redshift and the progenitor has been ejected from the
galaxy. Spectroscopy is encouraged.
No source is detected at all within the revised error circle.
We are grateful to S. Melnikov for observing time.
This message may be cited.
GCN Circular 5063
Subject
GRB060502B: Swift XRT Team refined analysis
Date
2006-05-03T02:15:10Z (19 years ago)
From
Vanessa Mangano at INAF-IASFPA <vanessa@ifc.inaf.it>
E. Troja (INAF-IASFPA), V. Mangano (INAF-IASFPA),
V. La Parola (INAF-IASFPA), D. N. Burrows (PSU)
report on behalf of the Swift XRT Team:
We have analyzed the first 10 ks of PC data of GRB060502B
(Troja et al 2006, GCN 5055).
The refined position of the source is
RA (2000) = 18h 35m 45.65s
Dec (2000) = +52d 37' 51.97''
with an uncertainty of 5.4 arcsec (90% containement).
This position is only 2.2 arcsec from the corrected
XRT position (Troja et al 2006, GCN 5059).
The 0.2-10 keV X-ray light curve shows a decay behaviour
with slope of -1.2 +/ 0.2.
There are only 36 counts in the extraction region, that are not
enough for a detailed spectral analysis. The estimated source flux,
assuming a photon index of 2.0, is about 10^-13 ergs cm^-2 s^-1.
If decaying at the present rate the source will reach the
flux level of 1.5 x 10^-15 erg cm^-2 s^-1 (corresponding to
a count rate level of 2.9 x 10^-5 counts s^-1) after one day.
This Circular is an official product of the Swift XRT Team.
[GCN OPS NOTE(03may06): Per author's request, the "only 4 arcsec"
was changed to "only 2.2 arcsec".]
GCN Circular 5064
Subject
GRB 060502B: Refined analysis of the Swift-BAT short burst
Date
2006-05-03T04:31:23Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
G. Sato (ISAS), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/ORAU), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), M. Koss (UMD),
C. Markwardt (GSFC/UMD), J. Norris (GSFC), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), M. Stamatikos (GSFC/ORAU),
E. Troja (INAF-IASFPA), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
Using the data set from T-119 to T+183 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 060502B (trigger #208275)
(Troja, et al., GCN 5055). The BAT ground-calculated position is RA,Dec =
278.949, 52.642 deg {18h 35m 47.7s, 52d 38' 32.5"} (J2000) +- 1.8 arcmin,
(radius, sys+stat, 90% containment). The partial coding was 92%.
The lightcurve consists of two spikes. The main peak starts at ~T-0.060
and has a FWHM of ~40 msec. Its rise is faster than the decay.
There is also a possible second peak (a precurrsor) starting at
T-0.3 sec with a FWHM of ~100 msec and a significance of only ~4 sigma.
T90 (15-350 keV) is 90 +- 20 msec (estimated error including systematics).
The lag analysis shows this burst to be cleanly in the short hard burst class
(Norris and Bonnell, 2006, ApJ, accepted; see, Figure 3).
Specifically, the measured lags for the main peak are:
-4.0 ms +- 3.0 ms (15-25 keV vs. 50-100 keV)
-0.2 ms +- 2.8 ms (25-50 keV vs. 100-350 keV)
The time-averaged spectrum from T-0.05 to T+0.04 is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
0.92 +- 0.23. The fluence in the 15-150 keV band is
4 +- 0.5 x 10^-8 erg/cm2. The 1-sec peak photon flux measured
from T-0.43 sec in the 15-150 keV band is 4.4 +- 0.6 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.
GCN Circular 5065
Subject
GRB 060502B: AROMA optical observations
Date
2006-05-03T08:44:18Z (19 years ago)
From
Kazutaka Yamaoka at Aoyama Gakuin U <yamaoka@phys.aoyama.ac.jp>
I.Takahashi, T.Uehara, K.Yoshida, A.Kobayashi, K.Tanaka,
Y.E.Nakagawa, S.Sugita, K.Yamaoka, A.Yoshida (AGU) report:
The robot optical telescope, AROMA, at Aoyama Gakuin University (AGU)
responded to GRB 060502B (Troja et al. GCN 5055).
The observations started at 17:26:26 UT (105s after the GRB) by the
0.3m optical telescope with R-band filter located at the AGU campus
in Sagamihara, Japan.
No new source was found above the 3 sigma limiting magnitude of R~16
calibrated with USNO A2.0 by the preliminary routine analysis on the
first 20 frames of image with 5s exposure each. The mean time of the
data set corresponded to 319s after the burst.
Further analysis is underway.
GCN Circular 5066
Subject
GRB 060502B: MDM Optical Observation
Date
2006-05-03T09:38:13Z (19 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. P. Halpern (Columbia U.) and N. Mirabal (U. Michigan) report:
"We observed the location of Swift short GRB 060502B (Troja et al., GCN 5055)
in the R band on the MDM 1.3m telescope starting on May 03 08:22 UT,
15 hours after the trigger. A summed 45 minute exposure has a limiting
magnitude of R~23.5. To this limit, there is a single object in the refined
XRT error circle of Troja et al. (GCN 5063), at coordinates
(J2000) 18h 35m 45.89s +52d 37' 56.2" (+/- 1")
Its magnitude is R = 21.6 +/- 0.1, calibrated with Landolt standard stars,
and it appears unresolved in seeing of 1.7". Further optical observations
are encouraged.
This message may be cited."
GCN Circular 5069
Subject
GRB 060502B: Swift/UVOT upper limits
Date
2006-05-03T10:37:39Z (19 years ago)
From
Tracey Poole at MSSL <tsp@mssl.ucl.ac.uk>
T. S. Poole (UCL-MSSL), and E. Troja (INAF-IASFPA) on behalf of the
Swift/UVOT team.
The Swift/UVOT began observing the field of GRB060502b (BAT
Trigger=208275, E. Troja, et. al, GCN 5055) at 17:25:38 UT, 57s after
the BAT trigger (which includes the 10s V filter settling exposure). No
new source is detected at the XRT position (E. Troja, GCN 5063) in
coadded images with any of the filters. The following 5-sigma magnitude
upper limits are not corrected for Galactic extinction; E(B-V) = 0.044.
Filter T_range(s) T_exp(s) 5sigma(mag)
V 57-35329 3002 20.29
B 658-24560 1204 20.62
U 634-41112 3819 21.04
UVW1 610-40198 4038 21.29
UVM2 586-36126 3633 21.31
UVW2 686-34417 2259 21.29
WHITE 74-6845 619 20.49
Where T_range is time post-trigger, and T_exp is the exposure time of
the observation. A 6 arcsec radius was used for all filters.
This message may be cited.
GCN Circular 5071
Subject
GRB 060502b: Gemini imaging and spectroscopy
Date
2006-05-03T17:52:27Z (19 years ago)
From
Edo Berger at Carnegie Obs <eberger@ociw.edu>
E. Berger (Carnegie Observatories), S. B. Cenko and A. Rau (Caltech)
report on behalf of a larger collaboration:
"We used the GMOS instrument on the Gemini North Telescope to image the
field of GRB 060502b (GCN 5064) and to obtain a spectrum of the object
detected within the XRT error circle (GCN 5063) by Halpern and Mirabal
(GCN 5066). We detect the latter object in a combined 1500 sec exposure
with an r-band magnitude of about 21.8, suggesting that the object has not
faded between the time of the MDM observation (15 hrs post burst) and our
observation (17 hrs post burst). Moreover, a spectrum of the object
reveals broad absorption bands centered on 5900, 6200, and 6700 A, which
are typical of cool giants (a comparison to stellar spectra indicates a
M2V - M4V classification).
In addition to this star, we also identify a fainter and marginally
extended object within the XRT error circle with r~24.7 mag located at
(J2000):
RA = 18:35:46.06
DEC= +52:37:51.46
with an uncertainty of about 0.3" in each coordinate.
An image of the region centered on the XRT error circle is available at:
http://www.ociw.edu/~eberger/grb060502b_gemini.gif
Source "S1" is the object found by Halpern and Mirabal (shown here to be a
star), and source "G1" is the faint galaxy discussed above."
GCN Circular 5072
Subject
GRB 060502B MDM Follow-up Observation
Date
2006-05-04T11:22:23Z (19 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. P. Halpern (Columbia U.) and N. Mirabal (U. Michigan) report:
"Following our initial report in GCN 5066, we continued observing the
XRT location of Swift short GRB 060502B (Troja et al., GCNs 5055,5063)
in the R band on the MDM 1.3m telescope on May 3 and 4 UT. In a summed
75 minute exposure centered at May 3 09:02 UT, we clearly detect the faint
galaxy candidate "G1" seen in the Gemini North image of Berger et al.
(GCN 5064) that was taken about 1.5 hours later. Observing on the
following night, a summed 105 minute exposure centered at May 4 08:56 UT
again shows "G1" at about the same magnitude. We measure R~23.9 for this
object, somewhat brighter than Berger et al. (GCN 5064). MDM images of
this field are posted at
http://www.astro.columbia.edu/~jules/grb/060502b/
This message may be cited."
GCN Circular 5073
Subject
GRB 060502B: AROMA refined photometric calibration
Date
2006-05-04T19:15:10Z (19 years ago)
From
Kazutaka Yamaoka at Aoyama Gakuin U <yamaoka@phys.aoyama.ac.jp>
I.Takahashi, T.Uehara, K.Yoshida, A.Kobayashi,
T.Koshiishi, K.Tanaka, Y.E.Nakagawa, S.Sugita, K.Yamaoka,
A.Yoshida (AGU) report:
After the previous report (GCN 5065), we carried out
further photometric calibrations for the observations
of the GRB 060502B field (Troja et al. GCN 5055, GCN 5059).
We have taken 100 frames of R band image with 20s exposure
each and photometric calibration was mede by every 20 frames
by comparing with USNO A2.0 stars in the same field.
The 3 sigma limiting magnitude of each combined image
is as below.
data set mean time time - burst[s] lim-mag R (3sigma)
======================================================
1st 17:30:00 UT 319 16.12 +/-0.16
2nd 17:37:35 UT 774 16.26 +/-0.19
3rd 17:45:13 UT 1232 16.00 +/-0.05
4th 17:52:44 UT 1683 16.00 +/-0.02
5th 18:00:13 UT 2132 16.30 +/-0.02
GCN Circular 5074
Subject
GRB 060502B: optical observations
Date
2006-05-05T09:03:29Z (19 years ago)
From
Daniele Malesani at SISSA-ISAS,Trieste,Italy <malesani@sissa.it>
E.J.A. Meurs, S.D. Vergani, C. O'Maoileidigh (Dunsink Observatory), D.
Malesani (SISSA), and R. Gualandi (Loiano Observatory), report:
We observed the field of the short GRB 060502B (Troja et al. 2006, GCN
5055) with the 152 Cassini telescope located in Loiano, Italy, equipped
with BFOSC. Observations were conducted under moderate weather
conditions (passing cirrus), securing three 20-min exposures. The mean
time was May 2.96198 UT (5.68 hr after the burst). The average seeing
was 1.8". No source was detected inside the revised XRT error circle
(Troja et al. 2006, GCN 5063) in the coadded frame. The limiting
magnitude is R = 20.6 (3 sigma) based on the USNO catalog.
This message can be cited.
GCN Circular 5077
Subject
GRB 060502b: Second epoch Gemini observations
Date
2006-05-06T02:43:27Z (19 years ago)
From
Paul Price at IfA,UH <price@ifa.hawaii.edu>
P.A. Price (IfA, Hawaii), E. Berger (OCIW), D.B. Fox (Penn State), S.B.
Cenko and A. Rau (Caltech) report on behalf of a larger collaboration:
We have obtained a second epoch of imaging with the Gemini North
telescope of the XRT localisation of the short/hard GRB 060502B (GCN
#5063). The observations commenced at 2006 May 4.43 UTC (1.7 days after
the GRB), and consisted of 5 x 300 sec exposures in r'. These
observations have better seeing and depth than our first epoch
observation (2006 May 3.43 UTC, 0.7 days after the GRB; GCN #5071).
Image subtraction does not reveal any variable sources within the XRT
error circle. In particular, the galaxy ("G1") and source ("S1")
identified in our previous observations have not appreciably changed in
brightness.
These observations place a limiting magnitude of any optical afterglow
in our first epoch observation of approximately R ~ 24.3 mag, based on
assuming R=17.5 mag for USNO-B1 star 426-035230 (RA,Dec =
278.92572,52.61611).
We identify in the second epoch image an additional faint source ("S2")
at R ~ 25.8 mag in the error circle at approximate coordinates:
18:35:45.86 +52:37:50.0 J2000
An image of the field is available at:
http://www.ifa.hawaii.edu/~price/grb060502b.gif
Note that the magnitude of the faint galaxy ("G1") in GCN #5071 is
measured to be R ~ 23.8 mag in our first epoch observation, using the
above calibration, consistent with the observation of Halpern & Mirabal
(GCN #5072). We apologise for any inconvenience this error may have
caused.
We thank the Gemini North observing team for obtaining these
observations.
GCN Circular 5093
Subject
GRB060502B: improvement in the XRT afterglow position
Date
2006-05-09T08:16:10Z (19 years ago)
From
Eleonora Troja at INAF-IASFPA <nora@ifc.inaf.it>
E. Troja (INAF-IASFPA), D. N. Burrows (PSU), and N. Gehrels (NASA/GSFC)
report on behalf of the Swift XRT Team:
We have improved the astrometry of the Swift XRT observation of the
short hard burst GRB 060502B (Troja et al. 2006, GCN Circs. 5055, 5059,
and 5063) using 28 serendipitous X-ray sources detected in the field
during our 30 ks observation.
We find 13 possible associations in the 2MASS or USNO 1.0B catalogs.
Four of these could be random matches, based on simulations with
28 sources placed randomly within the XRT field of view. From the 13
possible associations, we selected 7 guide sources with offsets <~ 3
arcsec from the X-ray sources, and used them to derive an astrometry
correction using the ccorr command in XIMAGE. We obtained shifts in the
coordinates of DeltaRA=1.3 arcsec, DeltaDec=-0.6 arcsec.
The final best position of the X-ray afterglow is:
RA(J2000) = 18h 35m 45.74s
Dec(J2000) = +52d 37' 52.47''
The uncertainty in the afterglow position on the detector is 2.0 arcsec.
The RMS scatter in the offsets between the corrected X-ray source
positions and the optical counterparts is 1.9 arcsec, giving us a 90%
confidence error radius of 4.4 arcsec.
This position is 1.0 arcsec from the previously reported XRT refined
position (GCN 5063) and 3.1 arcsec from the candidate galaxy G1 (Price
et al. 2006, GCN 5071).
GCN Circular 5184
Subject
GRB060502b: optical observations
Date
2006-05-29T10:02:37Z (19 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
V.Rumyantsev (CrAO), R. Karimov (MAO), R. Salyamov (MAO), E. Pavlenko
(CrAO), Yu. Efimov (CrAO), A. Pozanenko (IKI), M. Ibrahimov (MAO) on behalf
of larger GRB follow up collaboration report:
We observed the location of Swift short GRB060502B (Troja et al., GCNs 5055,
5059, 5063, 5093) in the R band with 1.5m telescope of Maidanak Astronomical
Observatory (MAO) starting on May 02 22:43 (UT) (5.3 hours after the
trigger) and Shajn 2.6m telescope of CrAO between May 03 (UT) 01:27 - 02:41
(8.6 hours after the trigger). Totally we obtained 6 images of 180 sec
exposure with mean seeing ~0.95" in Maidanak 1.5m and 39 images of 60 sec
exposure in CrAO observatory (seeing ~3"). In combined images we detect G1
galaxy mentioned by Berger et al. (GCN 5071) and Halpern et al. (GCN 5072)
and do not detect S2 source (Price et al. GCN 5077). A photometry of G1 and
S1 sources is based on USNO B1.0 star R=17.5 mag (USNO-B1 426-035230 RA,
Dec = 278.92572,52.61611):
Mid time Telescope Exp. G1 S1 Limiting (UT)
sec mag mag mag
May 02.954 MAO 1.5m 6�180 ~24.2 21.40 +/-0.10 23.6
May 03.086 CrAO 2.6m 39x60 23.7 +/-0.3 21.65 +/-0.05 24.1
Our brightness estimation of G1 is consistent with brightness estimations
obtained in MDM 1.3 (T0+15 h) R~23.9 (Halpern et al. GCN5072) and in
Gemini North (T0+17 h) R~23.8 (Price et al. GCN5077).
The combined images can be found in http://grb.rssi.ru/GRB060502b
This message may be cited.
GCN Circular 5238
Subject
GRB 060502B: A Bright Early-type Galaxy as Putative Host of the Short Burst
Date
2006-06-07T10:36:49Z (19 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
GRB 060502B: A Bright Early-type Galaxy as Putative Host of the Short
Burst
J. S. Bloom, D. Perley, D. Kocevski, N. Butler (UC Berkeley), J. X.
Prochaska (UCO/Lick), and H.-W. Chen report:
On 31 May 2006 UT, using Keck I (+LRIS), we obtained spectra of a
bright red extended source ("G*"; RA, DEC J2000 = 18:35:45.7,
+52:37:37) that is 11.2 arcsec South of the southern edge of the
revised XRT error circle (Troja et al. GCN 5093). Strong absorption
features, which we identify as Ca II H+K, indicate a redshift for
this early type galaxy of z=0.287. Weak [OII] emission can be seen
indicating some low level of active star formation.
We advance the hypothesis that this galaxy is the host of short burst
GRB 060502B (Troja et al. GCN 5055) based on several points:
1. The galaxy is a massive early-type similar to the putative
hosts of 050509B [1] and 050724 [2].
2. The redshift inferred of the hosts of 050509b (z=0.225) and
050724 (z=0.258) are remarkably similar to that of G* indicating
comparable energetics of the respective bursts.
3. At the redshift of z=0.287, the burst location would be
between 47 - 67 kpc in projection from the center of the putative
host, similar to the offset (39 +/- 13 kpc) inferred for 050509b.
There are viable progenitors scenarios (e.g. degenerate binary
mergers) where bursts occur at such distances from their birthsite.
4. Weak X-ray afterglow and no detected optical afterglow would
seem to indicate a low density circumburst environment, as would be
expected if the GRB originated far from the progenitor birthsite.
We recognize the difficulty of now confirming this hypothesis but
note that in the striking similarity of the host, redshift,
afterglow, and offset configuration to GRB 050509b, these
observations and inferences have a priori precedent."
A false color image will be posted at:
http://astro.berkeley.edu/~jbloom/grb060502B_color_keck1.gif
This message may be cited.
[1] Bloom et al. 2006ApJ...638..354B (astro-ph/0505480); Gehrels et
al. 2005Natur.437..851G (astro-ph/0505630)
[2] Berger et al. Nature 438 (2005) 988-990 (astro-ph/0508115)