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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').
Advanced Search

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.

Advanced Search Examples (click to copy):

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

20967 results found.

  1. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  2. IceCube Alert 250831.75: Global MASTER-Net observations report
  3. EP250831a: Global MASTER-Net observations report
  4. EP250831a: EP-WXT detection of a fast X-ray transient
  5. GRB 250831A: Swift-XRT counterpart detection
  6. GRB 250830B: Swift-XRT observations
  7. EP250830a: Global MASTER-Net observations report
  8. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  9. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  10. GRB 250830B: Swift ToO observations
  11. EP250821a: SOAR observations
  12. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  13. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  14. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  15. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  16. EP250828a: Optical counterpart detection with Kinder observations
  17. Swift GRB 250828B: Global MASTER-Net observations report
  18. EP250828a: Global MASTER-Net observations report
  19. EP-WXT trigger 01709200800 : KAIT optical observations
  20. EP250827a: Swift/UVOT Detection
  21. EP250828a: NOT optical counterpart confirmation
  22. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  23. EP250828a: Optical upper limit with Kinder observations
  24. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  25. EP250827a: LCO observations show fading optical counterpart
  26. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  27. EP250827A: VLT/X-shooter redshift confirmation
  28. Fermi GRB 250827A: Global MASTER-Net observations report
  29. EP250827a: confirmation of optical rebrightening with LCO
  30. EP250827a: GOTO observation of the optical afterglow
  31. EP250827A: An optical rebrightening was detected by LCO.
  32. EP250827a: Swift-XRT counterpart detection
  33. EP250827a: TRT optical observations
  34. EP250827a: Gemini-South redshift z = 1.613
  35. EP250827a: Global MASTER-Net observations report
  36. EP250827a: Gemini-South optical counterpart detection
  37. Fermi GRB 250826A: Global MASTER-Net observations report
  38. EP250821a: Gemini GMOS Redshift Confirmation
  39. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  40. Fermi trigger No 777883624: Global MASTER-Net observations report
  41. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  42. Fermi GRB 250824B: Global MASTER-Net observations report
  43. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  44. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  45. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  46. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  47. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  48. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  49. EP250821a: MeerKAT radio counterpart
  50. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  51. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  52. GRB 250823A: COLIBRÍ optical observations
  53. GRB 250823A: Swift/UVOT Detection
  54. GRB 250823A: NOT optical observations
  55. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  56. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  57. GRB 250818B: MeerKAT Detection
  58. GRB 250823A: Liverpool Telescope optical detection
  59. GRB 250823A: Swift detection of a burst
  60. Swift GRB250823.84: Global MASTER-Net observations report
  61. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  62. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  63. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  64. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  65. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  66. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  67. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  68. GRB 250806A: Gemini observations of host galaxy candidate
  69. GRB 250821A: Kilonova-Catcher optical upper limits
  70. EP250821a: Swift/XRT counterpart fading
  71. GRB 250812A: SVOM/ECLAIRs refined analysis
  72. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  73. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  74. EP250821a: Swift/UVOT further observations.
  75. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  76. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  77. GRB 250821A: VLT/FORS2 Optical Observation
  78. Fermi GRB 250821B: Global MASTER-Net observations report
  79. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  80. Swift GRB 250821A: Global MASTER-Net observations report
  81. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  82. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  83. GRB 250821A: Swift/UVOT Upper Limits
  84. EP250821a: Swift XRT and UVOT counterpart detection
  85. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  86. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  87. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  88. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  89. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  90. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  91. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  92. GRB 250818B: 10 GHz VLA detection
  93. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  94. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  95. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  96. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  97. GRB 250814A: Swift/UVOT Upper Limits
  98. GRB 250813B: Swift/UVOT Upper Limit
  99. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  100. GRB 250818B: Kilonova-Catcher optical afterglow detection

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