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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"

21800 results found.

  1. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  2. EP250827A: VLT/X-shooter redshift confirmation
  3. Fermi GRB 250827A: Global MASTER-Net observations report
  4. EP250827a: confirmation of optical rebrightening with LCO
  5. EP250827a: GOTO observation of the optical afterglow
  6. EP250827A: An optical rebrightening was detected by LCO.
  7. EP250827a: Swift-XRT counterpart detection
  8. EP250827a: TRT optical observations
  9. EP250827a: Gemini-South redshift z = 1.613
  10. EP250827a: Global MASTER-Net observations report
  11. EP250827a: Gemini-South optical counterpart detection
  12. Fermi GRB 250826A: Global MASTER-Net observations report
  13. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  14. EP250821a: Gemini GMOS Redshift Confirmation
  15. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  16. Fermi trigger No 777883624: Global MASTER-Net observations report
  17. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  18. Fermi GRB 250824B: Global MASTER-Net observations report
  19. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  20. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  21. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  22. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  23. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  24. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  25. EP250821a: MeerKAT radio counterpart
  26. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  27. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  28. GRB 250823A: COLIBRÍ optical observations
  29. GRB 250823A: Swift/UVOT Detection
  30. GRB 250823A: NOT optical observations
  31. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  32. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  33. GRB 250818B: MeerKAT Detection
  34. GRB 250823A: Liverpool Telescope optical detection
  35. GRB 250823A: Swift detection of a burst
  36. Swift GRB250823.84: Global MASTER-Net observations report
  37. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  38. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  39. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  40. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  41. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  42. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  43. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  44. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  45. GRB 250806A: Gemini observations of host galaxy candidate
  46. GRB 250821A: Kilonova-Catcher optical upper limits
  47. EP250821a: Swift/XRT counterpart fading
  48. GRB 250812A: SVOM/ECLAIRs refined analysis
  49. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  50. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  51. EP250821a: Swift/UVOT further observations.
  52. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  53. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  54. GRB 250821A: VLT/FORS2 Optical Observation
  55. Fermi GRB 250821B: Global MASTER-Net observations report
  56. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  57. Swift GRB 250821A: Global MASTER-Net observations report
  58. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  59. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  60. GRB 250821A: Swift/UVOT Upper Limits
  61. EP250821a: Swift XRT and UVOT counterpart detection
  62. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  63. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  64. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  65. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  66. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  67. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  68. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  69. GRB 250818B: 10 GHz VLA detection
  70. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  71. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  72. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  73. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  74. GRB 250814A: Swift/UVOT Upper Limits
  75. GRB 250813B: Swift/UVOT Upper Limit
  76. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  77. GRB 250818B: Kilonova-Catcher optical afterglow detection
  78. GRB 250818B: Liverpool Telescope optical detections
  79. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  80. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  81. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  82. GRB 250818B: Swift/UVOT Detection
  83. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  84. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  85. GRB 250818B: TRT Optical Observation
  86. Fermi GRB 250816A: Global MASTER-Net observations report
  87. GRB 250818B: SAO RAS optical observations
  88. Swift GRB 250818A: Global MASTER-Net observations report
  89. GRB 250818B: NOT optical observations
  90. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  91. Fermi trigger No 776849714: Global MASTER-Net observations report
  92. GRB 250818B: KAIT optical observations
  93. GRB 250818A: Swift/UVOT Upper Limits
  94. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  95. GRB 250813B: SVOM/ECLAIRs refined analysis
  96. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  97. GRB 250818B: SVOM/VT optical observation
  98. GRB 250814A: Further GRAWITA TNG NIR observations
  99. GRB 250818B: Swift-XRT afterglow detection
  100. GRB 250818B: GOTO optical counterpart candidate

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