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GCN Circulars

GCN Circulars are rapid bulletins submitted by and distributed to the community. 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"
  1. GRB250329A: REM optical afterglow detection
  2. GRB 250329B: GWAC-F50A optical upper limit
  3. GRB 250329B: SVOM detection of a faint transient
  4. GRB 250329A: Swift-XRT afterglow detection
  5. GRB 250328A: SVOM/VT optical observation
  6. GRB 250329A: Fading optical counterpart detection by LCO.
  7. GRB 250328A: SVOM/C-GFT optical upper limit
  8. GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
  9. GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
  10. GRB 250329A: VLT/X-shooter redshift z = 2.921
  11. GRB 250329A: SVOM/VT optical counterpart confirmation
  12. GRB 250329A: SVOM detection of a burst
  13. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  14. GRB 250327B: J-band observations with WINTER
  15. GRB 250327B: MASTER detection of OT rebrightening
  16. GRB 250327B: LCO optical counterpart detection
  17. GRB 250328A: GWAC-F50A optical upper limit
  18. GRB 250328A: SVOM detection of a burst
  19. FRB 20250316A: FTW optical observations
  20. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  21. EP250302a: SPI-ACS/INTEGRAL Upper Limit
  22. GRB 250327B: CrAO and SAO RAS Optical Observations
  23. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  24. GRB 250327B: further optical observations by LCOGT
  25. EP250315a: Pan-STARRS r and i-band imaging and photometry
  26. GRB 250327b: Liverpool Telescope optical observations
  27. GRB 250322A: GRANDMA/TNOT optical upper limits
  28. LIGO/Virgo/KAGRA S250328ae: Updated Sky localization
  29. GRB 250327A: SVOM/VT upper limits on the XRT position
  30. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  31. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  32. GRB 250327B: Las Cumbres optical counterpart detection
  33. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  34. GRB 250327B: 1.6m Mephisto optical observations
  35. GRB 250327B: NOT spectroscopic redshift z = 3.035
  36. GRB 250327A: Swift-XRT refined Analysis
  37. GRB 250327B: GOTO optical counterpart detection
  38. GRB 250327B: SVOM/VT optically bright counterpart
  39. GRB 250327B: SAO RAS optical candidate
  40. GRB 250327B: SVOM detection of a burst
  41. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  42. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  43. GRB 250327A: J-band observations with WINTER
  44. GRB 250327A: SVOM/VT optical candidate
  45. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  46. GRB 250327A: Fermi GBM observation
  47. Fermi GRB 250327A: Global MASTER-Net observations report
  48. Swift GRB 250327A: Global MASTER-Net observations report
  49. GRB 250327A: DDOTI Optical Observations
  50. GRB 250327A: COLIBRÍ optical upper limit
  51. GRB 250327A: Swift detection of a burst
  52. GRB 250327A: Fermi GBM Final Real-time Localization
  53. Fermi trigger No 764700395: Global MASTER-Net observations report
  54. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  55. Konus-Wind detection of GRB 250322A (short)
  56. IPN triangulation of GRB 250322B
  57. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  58. EP250321a: Mondy AZT-33IK Continued Optical Observations
  59. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  60. GRB 250322A: third epoch of NOT optical observations
  61. GRB 250322A: Swift-BAT refined analysis
  62. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  63. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  64. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  65. GRB 250322A: further NOT optical observations
  66. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  67. GRB 250322A: Swift/UVOT Upper Limits
  68. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  69. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  70. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  71. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  72. GRB 250321B: Swift-XRT observations
  73. GRB 250322A: Swift-XRT refined Analysis
  74. EP250321a: TNOT Observation of Optical Counterpart
  75. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  76. GRB 250322A: Gemini-North redshift of candidate host galaxy
  77. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  78. SVOM/sb25032302: SVOM detection of a long X-ray transient
  79. GRB 250322A: AstroSat CZTI detection of a short burst
  80. GRB 250322B: AstroSat CZTI detection of a bright long burst
  81. GRB250322A: STEP/T80S optical limits
  82. GRB 250322A: Gemini-South optical observations
  83. GRB 250322A: VLT optical observations
  84. GRB 250322A: VLT near-infrared observations
  85. FRB 250316A: DDOTI Continued Optical Observations
  86. GRB 250322A: NOT optical upper limits
  87. GRB 250322A: Enhanced Swift-XRT position
  88. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  89. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  90. GRB 250322A: MASTER optical observation
  91. EP250321a: Liverpool Telescope optical follow-up
  92. EP250321a: Mondy AZT-33IK Optical Observations
  93. GRB 250322A: Swift detection of a short burst
  94. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  95. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  96. EP250321a: KAIT optical observations
  97. EP250321A: COLIBRÍ Continuing Optical Observations
  98. GRB 250225B: GECAM-A detection
  99. GRB 250312A: GECAM-A detection
  100. GRB 250321B: Swift ToO observations

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