GRB 090530
GCN Circular 9438
Subject
GRB 090530: Swift detection of a burst with an optical counterpart
Date
2009-05-30T03:30:01Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. K. Cannizzo (NASA/UMBC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (NASA/UMBC),
C. Gronwall (PSU), S. T. Holland (CRESST/USRA/GSFC),
V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
T. Sakamoto (NASA/UMBC), B. Sbarufatti (INAF-IASFPA),
M. H. Siegel (PSU), M. Stamatikos (NASA/ORAU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:
At 03:18:18 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090530 (trigger=353567). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 179.395, +26.584 which is
RA(J2000) = 11h 57m 35s
Dec(J2000) = +26d 35' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a single peak
with a duration of about 10 sec. The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 03:19:33.1 UT, 74.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 179.41927,
26.59282 which is equivalent to:
RA(J2000) = 11h 57m 40.62s
Dec(J2000) = +26d 35' 34.2"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 84 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.78e+20
cm^-2, Kalberla et al. 2005), with an excess column of 2.1
(+2.01/-1.71) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 6.42e-10 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 83 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 11:57:40.50 = 179.41876
DEC(J2000) = +26:35:38.6 = 26.59405
with a 90%-confidence error radius of about 0.75 arc sec. This position is 4.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.39 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02.
Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.nasa.gov).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN Circular 9440
Subject
GRB 090530: PAIRITEL NIR Detections
Date
2009-05-30T04:30:03Z (16 years ago)
From
Adam Morgan at U.C. Berkeley <qmorgan@gmail.com>
A. N. Morgan, D. A. Perley, J. S. Bloom, (UC Berkeley), and D.
Starr (UCB, LCOGT) report:
We observed the field of GRB 090530 (Cannizzo et al., GCN 9438) with
the 1.3-m PAIRITEL located at Mt Hopkins, Arizona. Observations began
at 2009-05-30 03:19:30 UT, 72 seconds after the Swift Trigger. We
detect the optical afterglow (Cannizzo et al., GCN 9438, Flewelling et
al., GCN 9439) in mosaics taken simultaneously in the J, H, and Ks
filters.
The preliminary photometry yields:
post_burst
t_mid (min) exp(s) filt mag merr
8.33 424 J 16.4 0.1
8.33 424 H 15.4 0.1
8.33 424 Ks 15.0 0.1
All magnitudes given in the Vega system, calibrated to 2MASS. No
correction for Galactic extinction has been made to the above reported
values. Observations are ongoing.
[GCN OPS NOTE(30may09); The typo in the Subject line was changed
from "090515" to "090530".]
GCN Circular 9441
Subject
GRB 090530: GRAS002 optical observations
Date
2009-05-30T09:13:47Z (16 years ago)
From
Veli-Pekka Hentunen at Taurus Hill Obs,A95 <veli-pekka.hentunen@kassiopeia.net>
Markku Nissinen (Taurus Hill Observatory) and Veli-Pekka Hentunen (Taurus
Hill Observatory) report:
We used Global-rent-a-scope GRAS002 Tak Mewlon 0.30m telescope with SBIG ST-8E
CCD at RAS Observatory Mayhill H06 (New Mexico, USA) for follow-up observations
of GRB090530 (J.K. Cannizzo et al., GCN 9438). The observations were started
on May 30, at 05:30 UTC (2.2 hours after the burst) and stopped on May 30,
at 06:16 UTC. Four unfiltered 600 seconds images were taken. We detected
very faint optical afterglow object at the position of RA 11h 57m 39s.8 and
Dec +26o 35' 47" (J2000) with possitional uncertainty of 10" with respect to
POSSII F/USNO-B1.0. This is in correlation with ROTSE-III optical counterpart
position (H. Flewelling et al., GCN 9439). Upper limit for the observations
is >20.2 mag (3UL). Quoted upper limit has been derived using POSSII F and
USNO-B1.0 field stars as reference.
Filter Tmid(s) Exp(s) Mag (CR) USNO-B1.0
u 05:55:15 4x600 19.7
A jpeg preview of the observation showing the position of the afterglow is
at this URL: http://cutenews.kassiopeia.net/data/upimages/GRB090530A_new.jpg
GCN Circular 9442
Subject
GRB 090530: GRAS002 refined OA analysis
Date
2009-05-30T10:25:37Z (16 years ago)
From
Veli-Pekka Hentunen at Taurus Hill Obs,A95 <veli-pekka.hentunen@kassiopeia.net>
Markku Nissinen (Taurus Hill Observatory) and Veli-Pekka Hentunen (Taurus
Hill Observatory) report:
We used Global-rent-a-scope GRAS002 Tak Mewlon 0.30m telescope with SBIG ST-8E
CCD at RAS Observatory Mayhill H06 (New Mexico, USA) for follow-up observations
of GRB090530 (J.K. Cannizzo et al., GCN 9438). The observations were started
on May 30, at 05:30 UTC (2.2 hours after the burst) and stopped on May 30,
at 06:16 UTC. Four unfiltered 600 seconds images were taken. We detected
very faint optical afterglow object at the position of RA 11h 57m 40s.6 and
Dec +26o 35' 38".7 (J2000) with respect to POSSII F/USNO-B1.0 and this is in
good correlation with ROTSE-III optical counterpart position (H. Flewelling
et al., GCN 9439). Upper limit for the observations is >20.2 mag (3UL). Quoted
upper limit has been derived using POSSII F and USNO-B1.0 field stars as
reference.
Filter Tmid(s) Exp(s) Mag (CR) USNO-B1.0
u 05:55:15 4x600 19.2
A jpeg preview of the observation showing the position of the afterglow is
at this URL: http://cutenews.kassiopeia.net/data/upimages/GRB090530.jpg
GCN Circular 9443
Subject
GRB 090530: Swift-BAT refined analysis
Date
2009-05-30T12:34:07Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. K. Cannizzo (NASA/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090530 (trigger #353567)
(Cannizzo, et al., GCN Circ. 9438). The BAT ground-calculated position is
RA, Dec = 179.400, 26.590 deg, which is
RA(J2000) = 11h 57m 36.0s
Dec(J2000) = +26d 35' 23.0"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 41%.
The mask-weighted light curve shows a FRED-like peak starting at ~T-0.3 sec,
peaking at ~T+0.2 sec, and returning almost to background. Then a second and
much smaller peak starts at ~T+35 sec, peaks at ~T+45 sec, and ends
at ~T+50 sec. There is an ~3-sigma precursor peak at T-4sec. T90 (15-350 keV)
is 48 +- 36 sec (estimated error including systematics).
The time-averaged spectrum from T-12.2 to T+51.8 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.61 +- 0.17. The fluence in the 15-150 keV band is 1.1 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.0 sec in the 15-150 keV band
is 2.5 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/353567/BA/
GCN Circular 9445
Subject
GRB 090530: Enhanced Swift-XRT position
Date
2009-05-30T15:15:48Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 646 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 090530, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 179.41846, +26.59341 which is equivalent
to:
RA (J2000): 11h 57m 40.43s
Dec (J2000): +26d 35' 36.3"
with an uncertainty of 1.5 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, arXiv:0812.3662).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 9450
Subject
GRB090530: Swift/UVOT afterglow detection
Date
2009-05-30T17:08:39Z (16 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL-UCL) and J. K. Cannizzo (NASA/UMBC) report on behalf of
the Swift UVOT team:
The Swift/UVOT began settled observations of the field of GRB 090530 158s
after the BAT trigger (Cannizzo et al., GCN Circ. 9438) and a decaying
source is detected in all UVOT filters within the XRT error circle
(Beardmore et al., GCN Circ. 9445), putting an upper limit on the redshift
of z < 1.7. The source initially rises, and at around 100s after the BAT
trigger decays at a constant rate of 0.73+/-0.03 for the duration of
intial UVOT observations, out to ~20ks after the BAT trigger. The best
UVOT position determined from a co-added white band exposure is
RA (J2000) 11:57:40.50 = 179.41873 (deg)
Dec (J2000) +26:35:38.4 = +26.59400 (deg)
with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence,
statistical + systematic), consistent with the ROTSE-IIIb afterglow
position (Flewelling et al., GCN Circ. 9439).
The magnitudes for the observations currently available are as follows:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 83 233 147 17.43 +/- 0.03
v 624 644 19 17.69 +/- 0.29
b 550 570 19 18.60 +/- 0.27
u 295 545 246 17.46 +/- 0.05
uvw1 5735 5935 197 20.15 +/- 0.37
uvm2 5530 11687 1082 20.31 +/- 0.22
uvw2 5121 17468 1279 21.31 +/- 0.32
The values quoted above are not corrected for the Galactic extinction due
to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel
et al. 1998). The photometry is on the UVOT photometric system described
in Poole et al. (2008, MNRAS, 383, 627).
GCN Circular 9451
Subject
GRB090530: Swift XRT refined analysis
Date
2009-05-30T21:09:24Z (16 years ago)
From
Vanessa Mangano at INAF-IASFPA <vanessa@ifc.inaf.it>
Mangano V., Sbarufatti B. (INAF-IASFPA), J. K. Cannizzo (NASA/UMBC)
report on behalf of the Swift XRT Team:
We have analyzed the first five orbits of Swift-XRT data of
GRB 090530 (trigger 353567; Cannizzo, et al., GCN Circ. 9438),
consisting of 22 s in Windowed Timing (WT) mode from T+81 to T+103 s and
9 ks in Photon Counting (PC) mode from T+105 s to T+24.4 ks.
The best position for the X-ray afterglow is the XRT UVOT-enhanced
position: RA, Dec = 179.41846, +26.59341 which is equivalent to:
RA (J2000): 11h 57m 40.43s
Dec (J2000): +26d 35' 36.3"
with an uncertainty of 1.5 arcsec (radius, 90% confidence), as given
by Beardmore, et al., GCN Circ 9445.
The 0.3-10 keV X-ray light curve is best fitted by a broken powerlaw
with early decay index of about -5.7, late decay index -0.60+/-0.04
and a break at about 140 s after the trigger. In the first orbit
a small amplitude flare is detected at T+300 s. Flaring activity
is also visible along the later decay.
If decaying at the present rate, the predicted rate after 24h from the
trigger is 2.0e-2 counts/s. However, we remark that a second break
followed by a steepening of the lightcurve is possibly expected.
The issue will be clarified with following Swift observations that
will resume on Sunday May 31st.
The average initial WT spectrum (covering the initial steep decay)
can be modeled as an absorbed power-law with index 2.3 (+0.5-0.4),
absorbing column NH < 11E20 cm-2 (three sigma upper limit) and
observed(unabsorbed) average flux in the 0.3-10 keV energy range of
2.9(3.6)E-10 ergs cm-2 s-1.
The average PC spectrum (roughly covering the flatter part of the
afterglow)
is best fitted by an absorbed power-law with index 2.00+/-0.15
The absorbing column is NH = (8.2 -2.9+3.6)E20 cm-2 in excess with
respect to the Galactic value of 1.78E+20 cm-2 (Kalberla et al. 2005).
The average observed(unabsorbed) flux is 4.0(4.9)E-12 ergs cm-2 s-1.
The count-rate to flux conversion factor is 5.4E-11.
All quoted errors are at 90% confidence level.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00353567.
This circular is an official product of the Swift-XRT team.
GCN Circular 9452
Subject
GRB 090530: NOT optical observations
Date
2009-05-30T23:26:56Z (16 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@astro.ku.dk>
D. Malesani, D. Xu, G. Leloudas, J.P.U. Fynbo (DARK/NBI), P. Jakobsson
(Univ. Iceland), M.E. Brown (Caltech), E.L. Schaller (Univ. Hawaii), and
T. Liimets (NOT & Tartu Obs.) report on behalf of a larger collaboration:
We observed the field of GRB 090530 (Cannizzo et al., GCN 9438) with the
NOT equipped with the MOSCA camera. Observations were carried out in the
R band, starting on 2009 May 30.879 UT (17.8 hr after the GRB).
The optical afterglow (Cannizzo et al., GCN 9438; Flewelling et al., GCN
9439; Morgan et al., GCN 9440) is clearly detected in a single 300s
exposure, with a magnitude R = 21.6 assuming R = 18.17 for the USNO star
at RA = 11:57:41.68, Dec = +26:35:43.3.
GCN Circular 9458
Subject
GRB 090530: break in light curve
Date
2009-05-31T12:36:48Z (16 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
A. Rossi (Tautenburg), F. Olivares, and J. Greiner (both MPE Garching)
report on behalf of the GROND team:
We observed the field of GRB 090530 (Swift trigger 353567, Cannizzo et al.,
GCN #9438) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m
MPI/ESO telescope at La Silla Observatory (Chile). Observations started on
31 May 2009 at 00:36 UT, 21.3 h after the burst.
We detect the optical/NIR afterglow (Cannizzo et al., GCN #9438;
Flewelling et al., GCN #9439; Morgan et al., GCN #9440; Nissinen & Hentunen,
GCN #9442) in stacked exposures of 20 min in JHK and 24 min in g'r'i'z'.
Calibrating the r' band data against the USNO star at RA = 11:57:41.7,
Dec = +26:35:43, we obtain R = (22.2 +-0.2) mag. Comparing this with
the white light magnitudes obtained by ROTSE (Flewelling et al., GCN #9439),
UVOT (Schady et al., GCN #9450) and GRAS002 (Nissinen & Hentunen,
GCN #9442) as well as the NOT R-band magnitude (Malesani et al., GCN #9452),
we find a break in the optical light at around 22 ksec post-burst (i.e.
before the NOT observation), with slopes of 0.5+-0.1 (pre-break) and
1.8+-0.4 (post-break). We note that a break at this time is also visible
in the Swift/XRT data (see repository; Evans et al. 2007).
GCN Circular 9459
Subject
GRB090530: R-band Observation
Date
2009-05-31T14:49:20Z (16 years ago)
From
Myungshin Im at Seoul Nat U <mim@astro.snu.ac.kr>
M. Im (CEOU/Seoul National Univ) and Y. Urata (NCU)
on behalf of EAFON team.
We observed GRB090530 (Cannizzo et al. GCN 9438) in R using
the 1.0m telescope at Mt. Lemmon (Arizona, US) operated by
the Korea Astronomy Space Science Institute.
The R-band imaging started at 2009 May 30, 04:18:02 UT
(~1 hr after the burst), with the mid-point at May 30,
04:45 UT.
In a stacked image of 9 frames (3 min exp. each),
the optical afterglow is clearly detected
at R=19.6 +- 0.15 mag.
The photometry was calibrated against R2mag of USNO-B1 stars
in the vicinity of GRB.
We thank the LOAO operator, J. Yoon for his assistance for this
observation.
GCN Circular 9466
Subject
GRB 090530: GRT Optical Observation
Date
2009-06-01T01:50:08Z (16 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori.sakamoto-1@nasa.gov>
T. Sakamoto (UMBC/GSFC), D. Donato (ORAU/GSFC), N. Gehrels (GSFC),
T. Okajima (JHU/GSFC), T. N. Ukwatta (GWU/GSFC), Y. Urata (NCU),
C. Wallace (FGCU)
We observed the field of GRB 090530 detected by Swift (trigger #353567;
Cannizzo et al., GCN #9438) with the 14-inch Goddard Robotic Telescope (GRT)
located at the Goddard Geophysical and Astronomical Observatory
(http://cddisa.gsfc.nasa.gov/ggao/).
100 set of 30 sec exposures were taken in the R filter starting
from May 30 03:33:00 (UT) about 15 min after the trigger and
stopped on May 30 04:29:30 (UT). We do not detect the optical
afterglow (Cannizzo et al., GCN #9438, Flewelling et al., GCN #9439,
Nissinen et al., GCN #9441, Malesani et al., GCN #9452, Im et al.,
GCN #9459) both in the individual images and the combined image.
The estimated three sigma upper limit of the combined image (total
exposure of 3000 sec) is ~18.1 mag using the USNO-B1 catalog.
GCN Circular 9478
Subject
GRB 090530: Early RAPTOR Optical Observations
Date
2009-06-02T00:37:08Z (16 years ago)
From
James Wren at LANL <jwren@nis.lanl.gov>
J. Wren, W.T. Vestrand, P.R. Wozniak, H. Davis, B. Norman
of Los Alamos National Laboratory report:
The RAPTOR telescope system responded to Swift trigger
353567 (Cannizzo et al., GCN 9438) under fair observing conditions.
Our narrow-field instruments began observing the location at
03:18:37.96 UTC, 19.6 s after the Swift trigger. We detect the
optical counterpart initially reported by Cannizzo et al. (GCN 9438)
and Flewelling et al. (GCN 9439). Our first image at T+22.1 seconds
shows the counterpart at R~17.1. It appears to brighten over the
next minute reaching a peak near R~16.3 and then begins fading in
the manner described by Schady et al. (GCN 9450) and Rossi et al.
(GCN 9458). Our unfiltered images were calibrated against the
USNO-B1 R-band. The following table gives selected observations,
not corrected for extinction, from this event.
t-mid(s) exp(s) mag mag-err
--------------------------------------------
22.08 5.0 17.13 0.25
57.90 5.0 16.30 0.10
84.50 5.0 16.60 0.13
133.21 10.0 16.87 0.11
414.65 30.0 17.31 0.09
GCN Circular 9487
Subject
GRB 090530: RTT150 Optical Observation
Date
2009-06-03T17:47:25Z (16 years ago)
From
Solen Balman at METU <solen@astroa.physics.metu.edu.tr>
S. Balman (METU), M. Parmaksizoglu (TUG)
Z. Eker (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.)
I. Bikmaev, N. Sakhibullin (KSU/AST)
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
report:
We observed the field of GRB 090530 (Swift trigger=353567,
Cannizzo et al.,2009 GCN Circ. 9438) with the Russian-Turkish 1.5-m telescope
(RTT150, Bakirlitepe, TUBITAK National Observatory, Turkey) on
30 May starting at 18:30:37.7 UT about 15.2 hours (0.633 d) after the burst
using the TFOSC CCD (burst detected at 03:18:18 UT with Swift Burst Alert
Telescope(BAT)).
Flewelling et al. 2009 GCN Circ. 9439 found the afterglow at
16.0 mag at 03:18:42.7 UT. Calibrating the data against the USNO star at
RA = 11:57:41.7, Dec = +26:35:43, Rossi et al. 2009 GCN Circ. 9458
obtain R = (22.2 +-0.2) mag 21.3 hrs after burst. They also found a
break in the optical light at around 22 ksec post-burst (see also
GCN Circ.9440-9443, 9450-9452, 959, 9466, 9478 for white light
and UV photometry).
We obtained one 900 sec exposure using the R band filter (Bessell filter).
We used the Swift XRT position derived by Breadmore at al. (2009)
GCN Circ. 9445 to locate the afterglow candidate. We were able see the
source, but unable to calculate a magnitude using PSF photometry with
DAOPHOT within MIDAS software performed on the 13.3 by 13.3 arcmin field
around the candidate. We find a frame upper limit of R = 21.1+/-0.5 mag
at 3 sigma and 21.9+/-0.5 mag at 2 sigma confidence level
calculated using the same USNO star mentioned in the above paragraph.
This message can be cited.
GCN Circular 9488
Subject
GRB 090530: Further NOT optical observations
Date
2009-06-03T19:51:39Z (16 years ago)
From
Dong Xu at DARK,NBI <dong@astro.ku.dk>
D. Xu, G. Leloudas, D. Malesani, J. P. U. Fynbo, J. Hjorth (DARK/NBI),
P. Jakobsson (Univ. Iceland), and T. Liimets (NOT & Tartu Obs.) report
on behalf of a larger collaboration:
We continued to observe the field of GRB 090530 (Cannizzo et al., GCN
9438) with the Nordic Optical Telescope equipped with ALFOSC. We
obtained 3x600 s R-band frames staring on June 01, 22:04:19 UT, 66.7669
hr after the burst.
The optical afterglow (Cannizzo et al., GCN 9438) is still detected in
the stacked frame. The magnitude is R=22.6+/-0.2 against the same
reference star in Malesani et al. (GCN 9452).
Balman et al. (GCN 9487) found a 3sigma upper limit of R=21.1+/-0.5 mag
at 15.2 hr after the burst. Our first observation shows R=21.6 mag at
17.8 hr after the burst. Rossi et al. (GCN 9458) found R=22.2+/-0.2 mag
at 21.3 hr after the burst, and a break in the light curve at around 22
ksec post-burst with slopes of 0.5+-0.1 (pre-break) and 1.8+-0.4
(post-break), using previous obs (Flewelling et al., GCN 9439; Schady et
al., GCN 9450; Nissinen & Hentunen, GCN 9442). Our new observation
indicates that the optical decay is becoming much slower. The slower
optical decay may be due to the presence of a fairly bright host galaxy.
Further optical observations are encouraged.
GCN Circular 15571
Subject
GRB 090530: X-shooter redshift
Date
2013-12-03T18:31:28Z (12 years ago)
From
Paolo Goldoni at U.Paris/APC <goldoni@apc.univ-paris7.fr>
P. Goldoni (APC/Irfu - CEA), A. de Ugarte Postigo (IAA - CSIC and DARK/NBI) and J.P.U. Fynbo (DARK/NBI) report on behalf of the X-shooter GRB collaboration :
We reduced with the most recent pipeline the observations of the optical afterglow of GRB 090530 (Cannizzo et al., GCN 9438) made using the ESO VLT equipped with the X-shooter spectrograph. The observations were performed during commissioning with the instrument not fully calibrated. The observations started on 2009-05-30 at 23:56 UT (i.e., 20.63 hr after the burst). A total exposure of 1x900 s + 4x1200 s was obtained, covering the spectral range from ~3000 to ~24000 Ang.
The afterglow is detected in the UVB and VIS arms with a faint continuum. Superposed on the continuum we detected spectral features consistent with MgII, MgI, SiII, FeII and AlIII at a redshift ~1.266 fully consistent with the photometric redshift 1.28 (+0.16, -0.15) (Kruehler et al. 2011, A&A 526, 153).