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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

16110 results found.

  1. Subject GRB 250903A: SVOM/MXT afterglow detection
  2. GRB 250903A: TRT optical counterpart detection
  3. GRB 250903A: SVOM detection of a burst
  4. EP250903a: TRT optical observations
  5. EP 250827B: Detection of supernova counterpart by LCO.
  6. EP/WXT01709201159: GOTO optical follow-up
  7. EP250827b / AT 2025wkm: TRT optical observations
  8. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  9. EP250827b: continued Liverpool Telescope observations
  10. GRB 250902B: SVOM/GRM observation
  11. GRB 250901A: Swift/UVOT Upper Limit
  12. GRB 250902A: SVOM/GRM observation
  13. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  14. GRB 250901A: EP-FXT follow-up observation
  15. GRB 250901A: NOT optical observations
  16. GRB 250901A: SVOM/VT optical afterglow with VHF data
  17. GRB 250901A: LCO optical upper limit
  18. EP250827b: Swift observations of AT 2025wkm
  19. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  20. EP250831a: NOT optical observations and tentative afterglow candidate
  21. EP250827b: FTW Observations of AT 2025wkm
  22. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  23. EP250901a: Mephisto optical upper limits
  24. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  25. EP250821a: SOAR observations
  26. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  27. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  28. EP250828a: Optical counterpart detection with Kinder observations
  29. EP250828a: Liverpool Telescope upper limits
  30. EP-WXT trigger 01709200800 : KAIT optical observations
  31. EP250828a: KAIT optical upper limit
  32. EP250827a: Swift/UVOT Detection
  33. EP250828a: NOT optical counterpart confirmation
  34. EP250828a: SVOM/VT optical candidate
  35. EP250828a: Seimei/TriCCS optical counterpart detection
  36. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  37. EP250828a: Optical upper limit with Kinder observations
  38. EP250827a: LCO observations show fading optical counterpart
  39. EP250827A: VLT/X-shooter redshift confirmation
  40. EP250827a: confirmation of optical rebrightening with LCO
  41. EP250827a: GOTO observation of the optical afterglow
  42. GRB 250826A: SVOM/GRM observation
  43. EP250827A: An optical rebrightening was detected by LCO.
  44. EP250827a: Swift-XRT counterpart detection
  45. EP250827a: TRT optical observations
  46. EP250827a: BOOTES-7 early optical dectection
  47. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  48. EP250827a: Gemini-South redshift z = 1.613
  49. EP250827a: Las Cumbres independent detection of the optical counterpart
  50. EP250827a: Gemini-South optical counterpart detection
  51. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  52. EP250821a: Gemini GMOS Redshift Confirmation
  53. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  54. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  55. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  56. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  57. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  58. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  59. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  60. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  61. GRB 250823A: COLIBRÍ optical observations
  62. GRB 250823A: SVOM/VT optical observation
  63. GRB 250823A: NOT optical observations
  64. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  65. GRB 250823A: Fermi GBM Observation
  66. GRB 250823A: LCOGT Optical Detection
  67. GRB 250823A: BOOTES6/DPRT early optical detection
  68. GRB 250823A: Liverpool Telescope optical detection
  69. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  70. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  71. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  72. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  73. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  74. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  75. GRB 250821A: Kilonova-Catcher optical upper limits
  76. EP250821a: Swift/XRT counterpart fading
  77. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  78. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  79. EP250821a: Swift/UVOT further observations.
  80. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  81. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  82. GRB 250821A: VLT/FORS2 Optical Observation
  83. GRB 250821B: SVOM/GRM observation
  84. EP250821a: SVOM/VT optical observation
  85. GRB 250821A: NOT z-band upper limit
  86. GRB 250821A: KAIT optical upper limit
  87. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  88. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  89. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  90. GRB 250821A: Swift/UVOT Upper Limits
  91. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  92. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  93. GRB 250821A: LCOGT Optical Upper Limits
  94. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  95. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  96. GRB 250818B: 10 GHz VLA detection
  97. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  98. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  99. GRB 250814A: Swift/UVOT Upper Limits
  100. GRB 250813B: Swift/UVOT Upper Limit

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